April 2006


Chess Adams DVM, DACVR
University of Wisconsin

Radiography and Radiographic Interpretation of the Thorax and Abdomen

  1. Before Radiography

    1. Measure consistently.

      1. Have everyone measure in the same place. Measure across the level of the 11th or 12th ribs for lateral. For DV or VD measure in the same place, but the other direction.
      2. Try to close the calipers the same amount each time.
        Don't "squash" the patients!

    2. Assess the patient's body condition.
      Is a technique change called for? Take into account the patient's physical exam findings and results from any referral or previous radiographs. Determine if a change in technique is needed for optimal results.

      1. Increase the technique if there is fluid of any kind in the thorax (ie: chylothorax, hemothorax, pleural effusion, etc.).
      2. Increase technique for patients in heart failure.
      3. Increase for obese patients.
      4. The amount of increase depends on the degree of obesity or severity of disease. A kVp increase of 10-15% or double the mAs may be needed.
      5. Decrease the technique for patients with pneumothorax.
      6. Decrease for emaciated, very thin patients.
      7. Decreases of 10-15% less kVp or half the mAs should be made as anticipated by the severity of the condition.

      Assessing body type for thorax patients

      View of patients from the front:

      Optimal Thorax kVp Guidelines
      Tabletop cats & tiny dogs50-65 kVp
      Small dogs and large cats <15cm70-80 kVp*
      Medium dogs 15-23 cm75-90 kVp*
      Large dogs >23 cm90-125 kVp*

      *With grid to control scattered radiation

    3. Technique

      1. Proper kVp ranges
      2. mAs is typically low .8-2.5 mAs

    4. Required views

      1. VD or Dave

        1. The VD position offers a better inspiratory thorax radiograph, is easier to learn how to position, and is needed to see the cardiac silhouette on patients with fluid in the thorax.
        2. DV is better for cardiac evaluation (less magnification of the heart), is less scary than VD for many patients, is less work than rolling large patients on their backs, but cannot be tolerated by some patients with lumbar or hip issues.

      2. Both right and left lateral recumbent views are required for a complete study. Because the weight of the patient compresses the lungs on the recumbent side, the lungs on the "up" side are the most air filled and visualized the best.

    5. Positioning for the lateral view

      1. Pull front legs forward.
      2. Center beam on the caudal border of the scapula.
      3. Check to make sure the sternum is in the primary beam.
      4. Is patient in "true" lateral?
        The spine and sternum should both be at the same level.

    6. Positioning for VD

      1. Patient lies in dorsal recumbency.
      2. The thorax should be straight, not rolled to the right or left.
      3. The patient's head should not be crooked or turned. Hold it either in between the forelegs or just resting straight.
      4. Center on the heart. Locate the xiphoid and center cranial to it or mid-sternum.

    7. Positioning for DV

      1. Patient lies in sternal recumbency.
      2. The hind feet should be under each hip and visible on each side.
      3. The front legs should be extended slightly and one on each side of the patient's neck.
      4. When possible the head should be resting on the tabletop and the head and neck should be straight.
      5. Palpate the dorsal spinous processes of the lumbar spine to check for straightness. If they are tilted to one side, slightly abduct and adjust the hind foot on that side.
      6. Center on the caudal border of the scapulae.

    8. Make the exposure on full inspiration.

      1. The lungs should be as air filled as possible.
      2. Avoid motion by stopping the patient from panting if possible.

        1. Lightly blow on the patient's nose when you make the exposure.
        2. Hold the patient's mouth closed during the exposure.

      3. Take an additional lateral on expiration when looking for tracheal collapse.

  2. Film Assessment

    1. Technique

      1. Overexposure can easily happen due to the inherent high contrast of air filled lungs.

        1. Can result in overlooking small, subtle lung lesions or changes such as metastases, blasto, and asthma.
        2. Can the caudal vena cava be seen?
        3. Correct by decreasing the kVp by 10-15% or decreasing the mAs by 30-50%.

      2. Underexposure can make visualizing large, extensive disease processes difficult.

        1. Can the dorsal spinous processes be seen on the lateral view?
        2. Can the spine be visualized through the heart on the VD or DV?
        3. Correct by increasing the kVp by 10-15% or increasing the mAs by 30-100%. Increasing mAs should be the second choice since increasing the exposure time could cause motion artifacts.

      3. In very thin deep-chested breeds such as greyhounds, dobermans, and borzois two different techniques may be needed to evaluate the heart and the lung structures adequately.

    2. Positioning

      1. Was the patient in "true" lateral? Look for superimposition of the ribs where they join the spine.
      2. Assess VD or DV views for rotation. Dorsal spinous processes and the sternum should be superimposed exactly in the middle of the thorax. Ribs should look symmetrical.
      3. Is all of the thorax anatomy visible?
      4. Is there any undesired anatomy overlying any thoracic structures?

What's Up With the Lungs??
Chess Adams, DVM, Dipl. ACVR (Radiology, Radiation Oncology)


Overexposure! Due to inherent high contrast of air-filled lungs, overexposure is common, which results in overlooking small lung lesions (ie. metastases).

Ask yourself - can I easily see the caudal vena cava?

Solution: Technique chart for thorax using an mAs range limited to 1-2 mAs - varying only the kVp for patient thickness. (This will also minimize motion artifacts)

New Solution: As above (high kVp, low mAs), then post process your digital images as needed.

Other Technical shortcomings
  1. Under exposure = thoracic spinous processes beneath the scapulae are not seen. Accurate patient measuring and Technique Chart. Better to over-expose if you have digital imaging.

  2. Incomplete study = < 3 views. With digital imaging, no good excuse to stop at 2 views!

  3. Poor restraint = poor positioning and/or motion. Sedation!. but not anesthesia
    Digital imaging is NO help for this.

False negative interpretation

Incorrect exposure, inadequate views, patient motion, lesion location and lesion size all contribute. The solution = Rigorously scrutinizing good quality films from a complete study.

False positive interpretation
  • Dorsal / Right deviation of the thoracic trachea: this normal variation when the neck is flexed during radiography may mimic a cranial mediastinal mass.

  • Mammary nipples / skin tags mimic metastasis: smear barium on the nipple to prove.

  • Pulmonary osteomas (heterotopic bone) may mimic metastasis - osteomas are 2-3 mm, bright and often irregular.

  • End-on vessels may mimic mets: look for vessel connecting to "nodule".

  • End - on view of the right main pulmonary artery on some lateral views may be confused with hilar lymphadenopathy: lymphadenopathy typically occurs dorsal or caudal to the carina - the artery is ventral.
    Scalloping of lung margins may be fat rather than pleural effusion in obese animals: look for a discernable heart margin to aid in differentiation.

Thoracic Radiographs and Cancer

Patients suspected of having a malignancy, should have thoracic films performed early in the patient evaluation process:
  1. Pulmonary metastases seldom produce clinical signs.

  2. Metastases seldom cause auscultable abnormality on physical exam.

  3. Dyspnea is most frequently noted, if pulmonary signs of metastasis occur.
    (Coughing and hemoptysis are uncommon/rare signs of metastasis.)


Trachea bifurcates at the carina into the left and right mainstem bronchi.


four bronchial divisions (4 lobes)
right cranial
right middle
right caudal
accessory (off right caudal)


two bronchial divisions (2 lobes; cranial lobe subdivided)
left cranial (divides into cranial and caudal subsegment)
left caudal

Pulmonary arteries -
dorsal in lateral view; lateral in DV view.

Pulmonary veins -
ventral or central to the arteries.
Pulmonary arteries and veins should be approximately the same size and should taper gradually.
Caudal vena cava should be less than 1.5 times the diameter of the aorta.

Normal Variation

Obese animals have a relatively more opaque lung with a wider cranial mediastinum. Poor inspiration will result in a relatively more opaque thorax and relatively larger heart. Chondro-dystrophic breeds may have a relatively more opaque thorax wider mediastinum and a relatively larger heart. Deep narrow chested breeds vertical narrow heart on lateral, round on DV. Shallow wide chested breeds - heart appears more rounded and larger. Older animals have increased opacity to the lung interstitium.


Radiologic Signs

1. The Silhouette Sign

The air in the lung provides radiolucent contrast enabling pulmonary vessels, lesions, borders of thoracic structures to be seen in a correctly exposed film. Absence of aerated lung in contact with the borders obliterates the border, e.g., pleural effusion displacing lung from diaphragm. If lung tissue adjacent to the border of an organ becomes opaque enough due to disease causing loss of air, the borders of the lesion and the organ become joined. Only a silhouette is seen of the two. This sign indicates that a pulmonary lesion is contiguous with that organ, usually the heart or diaphragm.

2. Air Bronchogram Sign

If air in the alveoli is replaced by fluid or cellular material, and/or the alveoli are collapsed and airless (atelectasis), the larger bronchi usually stand out in radiolucent contrast to the soft tissue opacity of the lung. This is the air bronchogram sign. Its presence enables localization of thoracic opacity to the lung (vs pleural cavity or mediastinum) and is a sign of the alveolar pattern of lung infiltration. Sometimes, the radiolucent stripe or "branching tree" of the air bronchogram is more obvious than the pulmonary infiltrate itself (e.g., right middle lobe pneumonia over heart, in left lateral view). Do not mistake the radiolucent space between an artery and vein for an air bronchogram. If an air bronchogram is present, by definition, air contrast is excluded from around the vessels, and they are not visible.

3. Tracheoesophageal Stripe Sign

This is a narrow radiopaque band of tissue running from the thoracic inlet to the heart base. It is a sign of esophageal dilation with gas (air). Normally, there is practically no air in the esophagus. If the esophagus is distended with air, its ventral wall against the dorsal tracheal wall creates the appearance of a narrow stripe of tissue dorsal to the trachea. Often the trachea is depressed ventrally.

The terminology and classifications used in radiology of the lungs are listed in the following tables.

  1. Type of lesion - solitary, multiple, consolidating

  2. Extent of lesion - confined, disseminated, diffuse

  3. Anatomical location - hilar, apical, peripheral, subpleural

  4. Radiographic pattern - alveolar, interstitial, bronchial, vascular, mixed

  5. Delineation - well-defined, ill-defined, coalescing

  6. Shape - nodular, irregular

  7. Degree of opacity - homogenous vs. inhomogeneous soft tissue opacity, air opacity, mineral or metallic opacities

  8. Potentially associated lesions of other organs - heart, thoracic wall, liver mediastinum, diaphragm

  1. Increased radiopacity
    1. Circumscribed nodules or masses
      • Multiple or solitary
    2. Ill-defined nodules
      • Multiple or solitary
    3. Lobar consolidations
      • Homogenous or inhomogeneous
    4. Linear patterns
      • bronchi and vessels
    5. Ill-defined pulmonary radiopacity
      • Alveolar pattern
      • Unstructured interstitial pattern
      • Mixed pattern (more than one pattern)
  2. Diminished radiopacity or hyperlucency
    1. Diffuse hyperlucency (emphysema)
    2. Focal hyperlucency (cavitary lesions)
Normal radiopacity with superimposed nonpulmonary disease
  1. Pleural effusion/pneumothorax
  2. Mediastinal enlargement
Artifactual variations in pulmonary opacity
  • phase of respiration
  • obesity/cachexia
  • technical artifacts/exposure level

Solitary pulmonary lesions are not common. Underlined conditions are the most common within this group.
  1. Neoplasm
    1. Primary lung tumors - (bronchogenic carcinoma)
    2. Solitary metastatic tumors
    3. Benign tumors (extremely rare)

  2. Granulomas
    1. Fungal granulomas - coccidioidomycosis, histoplasmosis, blastomycosis, (in endemic areas) cryptococcosis
    2. Bacterial granulomas, tuberculosis
    3. Foreign body granulomas (grass seed)
    4. Eosinophilic granulomas - dirofilariasis, unknown causes

  3. Abscesses (not drained)
    Foreign bodies, pyogenic infections, fungal infections

  4. Infarcts
    Dirofilariasis, neoplasm, thromboembolism

  5. Hematomas

  6. Solitary consolidation (rarely tumor)
    1. localized pneumonia
    2. focal atelectasis
    3. edema or hemorrhage

  7. Cavitary lesions (thin smooth wall)
    1. Parenchymal bullae or blebs
    2. Congenital bronchial cysts

  8. Cavitary lesions (thick irregular wall)
    1. Cavitating tumors
    2. Abscesses, cavitating granulomas
    3. Paragonimus kellicotti (in endemic areas)


Characteristics are
  1. Increased pulmonary opacity
  2. Ill defined margin
    Because of the open cell sponge-like nature of canine and feline lung tissue, alveolar lung diseases have a poorly defined "front" or margin with normal lung, except when the lesion reaches a pleural margin. The ill defined margin gives a fluffy or blotchy appearance.
  3. Air bronchograms (previously described)
  4. Air alveolograms
    This is a mottled, granular, or finely stippled pattern formed when some groups of alveoli are flooded and others are not. It occurs at the edge of an alveolar lesion, or when it is mild or early or regressing alveolar disease.
  5. Lability
    Because the opacity is caused by fluid filled or collapsed alveoli (in most cases) it may regress rapidly (even completely), despite its opacity.
    Lability assessment is very important in ambiguous cases. Repeat films after diuretic treatment for suspected pulmonary edema can confirm or refute the tentative diagnosis. Clearing of alveolar infiltrates by therapy may reveal underlying (nonlabile) focal lesions.

Acute Chronic
  • Pulmonary edema: left ventricular failure
  • Lobar pneumonia
  • Bronchopneumonia
  • Pulmonary
  • Pulmonary edema of noncardiogenic origin
  • Inhalation pneumonia
  • Pneumonia of unusual etiology
  • Hypersensitivity pneumonia (PIE syndrome)
  • Granulomatous diseases especially in cats: toxoplasmosis, mineral oil aspiration, infectious feline vasculitis (IFP)
  • Bronchial and alveolar cell carcinoma
  • Disseminated metastases
  • Alveolar microlithiasis




Perihilar; Symmetrical or mostly right caudal lobe Confluent, multifocal or ill-defined nodules Accentuated (veins) Uninvolved except sometimes in canine dilated cardiomypathy Enlarged left heart (uninvolved in non-cardiogenic edema
Cranioventral, peripheral, peribronchial Focal (blotchy or lobar) Accentuated Often accentuated, indistinct Uninvolved
Hemorrhage No preference No preference, often patchy Uninvolved or small asymmetric Uninvolved Uninvolved or small



Infarcts Peripheral, caudal lobes Focal, triangular Accentuated (arteries in dirofilariasis) Uninvolved Uninvolved or right heart enlarged
Neoplasia Primary Caudal lobes Hilar Uninvolved Uninvolved Uninvolved
Neoplasia Metastases No preference No preference Uninvolved Uninvolved Uninvolved
Hematogenous pneumonias (thrombo-embolic) No preferred location often peripheral and caudal lobe Focal (blotchy) Accentuated Uninvolved Uninvolved
Neurogenic edema Caudal lobes Focal Uninvolved Uninvolved Uninvolved

Italicized conditions are common
  1. Lobar involvement. Suggests lobar pneumonia, acute bronchial obstruction (foreign body or torsion).
  2. Peribronchial distribution indicates bronchopneumonia.
  3. Bilaterally symmetrical, predominantly dorsal distribution suggests pulmonary edema.
  4. Irregular, patchy distribution: acute pulmonary edema, unusual pneumonia (hematogenous, fungal), infarct, trauma (contusion and hemorrhage), neoplasia (particularly bleeding hemangiosarcoma, alveolar cell carcinoma)
Because of its opacity, an alveolar pattern may mask other underlying lesions. If they are suspected, treat and reradiograph.


Cardiogenic (left sided) failure
  1. Mitral valve degeneration (common)
  2. Cardiomyopathy: dilated in large breed dogs, hypertrophic in cats
  3. Congenital heart disease
Bacterial endocarditis

Noncardiogenic causes

  1. Allergy
  2. Neurogenic: electric cord bite, brain trauma, epilepsy, hypoglycemia
  3. Toxins: ANTU, snake venom, smoke, 100% oxygen, endotoxin
  4. Disseminated intravascular coagulation
  5. Pulmonary infarction
  6. Hypoxia

Vessels and bronchial walls, are visible in all but severe cases. Increased opacity caused by interstitial disease may be edema, acute or chronic cellular deposition (RBCs, PMNs, eosinophils, neoplastic cells), or connective tissue (pulmonary fibrosis).

Types of interstitial pattern

  1. Unstructured: Hazy, ground-glass -like. Difficult to separate from background variations in lung opacity caused by respiration phase, obesity, or technique. May resemble alveolar pattern in distribution.
  2. Structured: nodules or net-like (reticulation).
Italicized conditions are common
  1. Unstructured pattern
    Interstitial pneumonia
    Mild edema (allergy, early or resolving congestive heart failure)
    Mild hemorrhage
    Neoplasia (rare)
    Fibrosis (old age)

  2. Structured pattern (nodules, lines, reticulation)
    Neoplasia (secondary, primary)
    Granuloma (fungal - in endemic areas)
    Miliary infiltrates (fungal, bacterial, neoplastic)
    Fibrosis (old age, dusty environment)

  3. Differential diagnosis, artifacts
    Underexposed radiographs
    Thick thoracic wall, obesity
    Underinflation of lungs, expiratory radiographs

Interstitial edema With cardiomegaly, indicates left heart disease; without cardiomegaly, allergy, toxemia, fluid overload, contusion, shock lung
Interstitial pneumonia Pneumonias in the early and healing phases, uremic pneumonitis, inhalation of irritants
Interstitial hemorrhage Trauma, coagulopathies (DIC)
Granulomatous diseases Early and late phases of fungal diseases
Pulmonary fibrosis Normal aging process, healing phase of a large number of diseases
Lymphosarcoma Usually associated with enlarged lymph nodes

Italicized conditions are common
Acute Fungal diseases Coccidioidomycosis, histoplasmosis, blastomycosis (depending on geographic region)
Subacute Aelurostrongylosis (cat) Tuberculosis   
Chronic Metastatic neoplasm Particularly adenocarcinoma: occasionally lymphosarcoma

Italicized conditions are common
Metastatic lung tumors Most common pattern of secondary neoplasia in dogs
Primary lung tumors Occasional finding
Fungal diseases Uncommon except in endemic areas of histoplasmosis and blastomycosis

Pulmonary metastases   
Pulmonary fibrosis Remnants of prior disease, normal in old dogs and cats (Fib. 4.A)
Acute pulmonary edema (air alveologram pattern) Acute left ventricular failure
Granulomatous disease Fungal diseases
Primary disseminated lung tumors, bronchiolar-alveolar carcinoma   


Caused by thickened bronchial wall and/or peribronchial connective tissue sheath becoming infiltrated (peribronchial "cuffing") with inflammatory material or edema.

Radiographic Signs
  1. Thin parallel or gradually converging lines ("railroad tracks")
  2. Thin round shadows with fuzzy external margins, ("rings" or "donuts")
    Normal bronchi are visible in the hilar zone of large dogs. Many old dogs have calcified bronchi which are prominent. This can be a problem in diagnosis of coughing old dogs.
  3. Thin walled saccular dilations indicate bronchiectasis (uncommon).
Conditions causing prominent bronchial markings
  • Benign calcification of the bronchi in older and/or chondrodystrophic dogs
  • Tracheobronchitis (disease may be present with normal films)
  • Chronic bronchitis (disease may be present with normal films)
  • Bronchopneumonia (peribronchial infiltrates)
  • Acute pulmonary edema (peribronchial "cuffing")
  • Asthma (allergic bronchitis)
  • Bronchiectasis (usually saccular dilations forming cavities)
Many cases of bronchitis and tracheobronchitis have no radiographic signs. Some coughing dogs (small breeds) cough due to a collapsing trachea.


Changes in diameter of vessels and opacity of lung reflect abnormalities of blood pressure and flow. Size of vessels is assessed very subjectively and takes experience. Artery is usually slightly wider than corresponding vein (artery dorsal, vein ventral; artery lateral, vein medial). Examine the cranial lobar vessels in the lateral view for comparison of artery and vein:
  1. Hypervascular pattern (overcirculation). Arteries and veins are widened into the peripheral zone, plus increased interstitial opacity.
  2. Hypovascular pattern. Arteries and veins are thin, lung are hyperlucent. Seen in shock (e.g., trauma), congenital R-L shunt (Tetralogy of Fallot), severe dehydration, acute Addison's disease (adrenocortical insufficiency). Associated signs are: small heart, thin caudal vena cava, overinflated lungs). Physiologic (deep breath while struggling on the table), and iatrogenic (overinflation while on gas anesthesia) overinflation decreases venous return and causes the same appearance.
  3. Enlarged arteries. Arteries also become tortuous. Causes: heartworms, Eisenmenger's syndrome (hypertension due to VSD or PDA)
  4. Enlarged veins. Pulmonary venous hypertension (mitral regurgitation).

Causes of hypervascular pattern

Left-to-right shunting in congenital heart diseases; patent ductus arteriosus, ventricular septal defect or arteriovenous fistulas

Severe long-standing anemia

Causes of hypovascular pattern

Hypovolemic shock
Severe dehydration
Severe overinflation (under anesthesia usually)

Right heart failure
Addison's disease (acute adrenocortical insufficiency)
Right-to-left shunting in congenital heart diseases such as tetralogy of Fallot and Eisenmenger complex


Many diseases include more than one pattern, e.g., in severe dirofilariasis, severe interstitial inflammatory reaction or alveolar pattern from a post treatment infarct may obscure the dilated tortuous arteries. Neoplasia may cause secondary obstructive pneumonia causing alveolar pattern. Overcirculation has interstitial as well as vascular components.

Focal or Well-Defined Lung Lesions

Nodular shadows greater than 2 mm can be distinguished from a structured interstitial pattern, except when the nodules are small and extremely numerous. Look in the thin parts of the lung for less superimposition of shadows. Neoplastic nodules vary more in size than inflammatory nodules.

Lines and bands
Branching lines and bands are usually pulmonary vessels or bronchi.
Nonbranching bands or lines may be pleural fissures thickened by fluid or scarring, skin folds, mediastinal structures (particularly in pneumomediastinum) or artifacts.

Cavitary lesions

A. Bronchial structures seen end-on
  1. Old age
  2. Bronchitis, with severe peribronchial reaction (look for a linear lung field and normal-sized bronchi)
  3. Bronchiectasis (adjacent to multiple, tubular structures -- abnormally large bronchi, honeycomb pattern and fibrosis, atelectasis, and emphysema)
B. Cysts and cyst-like structures (thin-walled,smooth ring shadows)
  1. Developmental cysts (congenital bronchiogenic)
  2. Paragonimiasis
  3. Thin-walled abscess (cavitating fungal granuloma)
  4. Pneumatocele (pneumonia)
  5. Traumatic pulmonary cysts with hemorrhage

*Tables from Suter, P.F.: Thoracic Radiography of the Dog and Cat, Peter F. Suter, Wettswil, Switzerland, 1984.

The Rest of the Thorax
Lisa J. Forrest, VMD, DACVR (Radiology, Radiation Oncology)


Cardiac radiography is useful
  • As a screening tool for cardiac abnormalities
  • To assess pulmonary circulation
  • To determine if cardiac decompensation (heart failure) has occurred
However for accurate assessment of cardiac chamber size and function, echocardiography is the procedure of choice.

Cardiac enlargement
  • Barrel-chested dogs have a heart that looks artifactually big. Misdiagnoses of cardiomegaly in chondrodystrophoid dogs and athletic dogs is common
  • Vertebral heart scale - cardiac measurement system that takes into account the inherent breed variation in cardiac size. In the lateral view the lengths of the long and short axes of the heart are measured and scaled against the length of thoracic vertebrae, starting at T4. Normal scale ranges from 8.7-10.7.

Left atrium. In the lateral view, enlargement of the left atrium results in dorsal deviation of the left main stem bronchus and straightening of the caudodorsal border of the heart. In the ventrodorsal or dorsoventral view there is abaxially deviation of the main stem bronchi (bowlegged cowboy sign).
  • Mitral insufficiency
  • Cardiomyopathy
  • PDA, mitral dysplasia

Left ventricle. With left ventricular hypertrophy the heart may elongate, causing dorsal displacement of the thoracic trachea. The trachea will run parallel to the long axis of the spine, rather than diverging away from the spine.
  • PDA, VSD, aortic stenosis
  • Mitral insufficiency
  • Cardiomyopathy

Right atrium. Dilation of the right atrium results in a bulge in the cardiac silhouette in the 9:30 to 11:30 position in the ventrodorsal or dorsoventral view. In the lateral view, a dilated right atrium results in a bulge of the cranial cardiac silhouette just below the trachea.
  • Tricuspid dysplasia
  • Pulmonic stenosis

Right ventricle. Hypertrophy of the right ventricle results in increased sternal contact and lifting of the apex on the lateral view and a reverse D sign on the ventrodorsal or dorsoventral view.
  • Pulmonic stenosis
  • Heartworm disease

Generalized cardiomegaly. Heart is globoid in shape.
  • Cardiomyopathy
  • Pericardial effusion

Pulmonary Vessels
  • Under circulation (dehydration, shock). Pulmonary artery and vein are smaller than proximal 4th rib on lateral view.
  • Over circulation (fluid overload, congenital shunts - PDA, VSD). Pulmonary artery and vein are enlarged.
  • Left heart failure. Pulmonary vein is larger than corresponding artery and there is evidence of left sided heart enlargement. Increased pulmonary opacity (edema) in caudodorsal lung.
  • Pulmonary hypertension. Pulmonary artery is larger than corresponding vein. Most common cause is heartworm disease.

The Mediastinum
The mediastinum extends from the thoracic inlet to the diaphragm. It can be subdivided into a cranial portion cranial to the heart, a middle portion at the level of and containing the heart, and a caudal portion caudal to the heart.

What lives in the mediastinum, lots of stuff.

Cranial mediastinum
  • Cranial vena cava
  • Thymus
  • Sternal lymph nodes
  • Aortic arch
  • Brachiocephalic artery
  • Left subclavian
  • Mediastinal lymph nodes
  • Trachea
  • Vagosympathetic trunk
  • Intercostals arteries and veins
  • Internal thoracic arteries and veins
  • Esophagus
  • Thoracic duct
  • Sympathetic trunks
  • Phrenic nerves

Middle mediastinum
  • Trachea
  • Vagosympathetic trunk
  • Intercostal arteries and veins
  • Internal thoracic arteries and veins
  • Esophagus
  • Thoracic duct
  • Sympathetic trunks
  • Phrenic nerves
  • Descending aorta
  • Bronchoesophageal arteries and veins
  • Azygous vein
  • Heart
  • Tracheobronchial lymph nodes
  • Main pulmonary artery
  • Main pulmonary veins
  • Principal bronchi

Caudal mediastinum
  • Intercostal arteries and veins
  • Internal thoracic arteries and veins
  • Esophagus
  • Thoracic duct
  • Sympathetic trunks
  • Phrenic nerves
  • Descending aorta
  • Bronchoesophageal arteries and veins
  • Azygous vein
  • Caudal vena cava
  • Vagus nerves

Mediastinal Abnormalities - general classifications
  1. Mediastinal shift
  2. Mediastinal masses
  3. Mediastinal fluid
  4. Pneumomediastinum

Mediastinal Shift
This is best determined from a well-positioned ventrodorsal or dorsoventral radiographic view. Mediastinal shift will occur with the following:
  • Unilateral decrease in lung volume (ipsilateral shift). Unilateral lung atelectasis will result in a mediastinal shift to that side.
  • Unilateral increase in lung volume (contralateral shift). A unilateral tension pneumothorax will result in a mediastinal shift to the opposite side.
  • Presence of an intrathoracic mass (contralateral shift).

Mediastinal Masses
Mediastinal lymphadenopathy is one of the most common causes of a mediastinal mass. The cranial mediastinal lymph nodes drain the head and neck region. These lymph nodes can be involved in lymphosarcoma, lymphomatoid granulomatosis, and malignant histiocytosis. These neoplastic processes can also involve the sternal and tracheobronchial lymph nodes. Enlargement of the tracheobronchial (hilar) lymph nodes will result in abaxial deviation of the main stem bronchi on the ventrodorsal or dorsoventral radiographic view, mimicking left atrial enlargement. However, on the lateral view the lymphadenopathy appears as a soft tissue opaque mass dorsal to the carina and there is no straightening of the caudodorsal border of the heart. The sternal lymph nodes drain the abdomen and thoracic wall, not the lungs. Aggressive abdominal tumors can metastasize to the sternal node. The tracheobronchial lymph nodes drain the pulmonary parenchyma.

Causes of mediastinal mass

Mediastinal lymphadenopathy
Sternal lymphadenopathy
Hilar lymphadenopathy
Neurogenic/paraspinal tumor
Generalized megaesophagus
Spirocerca lupi
Ectopic thyroid
Heart-base tumor

Cranioventral, ventral to trachea
Cranioventral, dorsal to sternum
Cranioventral, perihilar
Craniodorsal, perihilar

Mediastinal Fluid
Because mediastinal fluid is soft tissue in opacity it will appear radiographically as a mass or as cardiomegaly, if it collects around the heart. The more common causes of mediastinal fluid include FIP, trauma, coagulopathy, and esophageal perforation.


Free gas in the mediastinum provides excellent radiographic contrast resulting in visualization of mediastinal organs not normally seen.

Causes of penumomediastinum (in descending order of likelihood)
  • Air escaping into the lung interstitium from alveolar rupture diffuses along bronchi and vessels into the mediastinum. This occurs after trauma and after iatrogenic pulmonary hyperinflation during anesthesia or resuscitation. Pneumothorax is not present unless the pulmonary pleura is torn or there is perforation of the mediastinal pleura.
  • Caudal extension of gas in neck fascial planes into the mediastinum. This is a common sequel to neck or oral cavity trauma and may result from esophageal or tracheal rupture.
  • A hole in the wall of the trachea may occur as a result of trauma. Erosion of the trachea secondary to neoplasia or inflammation can also occur, but this is uncommon. Over distention of the endotracheal tube cuff in anesthetized cats can lead to tracheal rupture and pneumomediastinum. These animals often have concomitant subcutaneous emphysema.
  • Esophageal trauma, neoplasia or inflammation leading to perforation.
  • Extension of retroperitoneal gas into the mediastinum.
  • Gas-producing organism in the mediastinum (unlikely).

The Thoracic Wall

Thoracic wall trauma

Thoracic wall trauma often results in fractured ribs. Healing rib fractures are difficult to distinguish from tumor or infection. In these cases a rib aspirate, biopsy or radiographs in 2-3 weeks is recommended.

Rib tumors and infection

A thoracic wall mass (trauma, infection or neoplasia) may result in an extrapleural sign. This is a medial extension of a mass from the thoracic wall, causing an intrathoracic mass effect with a broad base. This pleural displacement will also displace the lung. The extrapleural sign is best seen when the x-ray beam strikes the lesion tangentially.

Rib infection is uncommon in dogs and cats. Primary and metastatic rib tumors are more common. Most primary rib tumors are either chondrosarcoma or osteosarcoma. Pleural effusion often accompanies primary rib tumors. The rib is a common site for solitary tumor metastasis. Mammary and prostatic adenocarcinomas will metastasize to the ribs.

Abdominal Radiography Technical Tips
By Amy S. Lang, B.A., R.T.R.

  1. Before Radiography
    1. Measure consistently.
      1. Measure abdomen in the same place as thorax at the level of the 11th -12th ribs. The measurement should be taken through the area of the liver, not back by the pelvis.
      2. Have everyone measure in the same place.
      3. Try to close the calipers the same amount each time. Please don't "squash" the patients!
    2. Radiography vs. ultrasonography. Is there ascites or fluid in the abdomen that would compromise the abdomen study? If so, ultrasonography may be a better use of your time and materials and the client's money.
    3. Technique
      1. Proper kVp ranges

        Abdomen kVp Guidelines
        Tabletop cats and tiny dogs 50-65 kVp
        Small dogs & large cats <15cm 60-70 kVp*
        Medium dogs 15-23 cm 70-80 kVp*
        Large dogs >24 cm 75-90 kVp*

        *A grid must be used to control scatter radiation

      2. mAs amount will depend on the screen/film speed and can vary from 5-30 mAs.
      3. Increase mAs for pregnancy/fetal count by 50-100%.
    4. Required views
      1. Right or left lateral and VD for routine abdomens.
      2. Additional view of caudal abdomen with hindlegs forward for the male dog urinary tract when indicated.
      3. Both laterals and VD to look for GI obstruction, intussusception, or foreign bodies.
    5. Positioning for the lateral view

      1. Pull front legs forward and hind legs back.
      2. The cranial edge of the primary beam should extend 1 1/2" cranial to the xiphoid.
      3. The caudal extent of the primary beam should include as far back as the acetabulum for female patients.
      4. On male patients with urinary problems the entire caudal end of the patient should be included.
      5. Is patient in "true" lateral. The spine and sternum should both be at the same level.
    6. For male dogs with urinary issues
      1. Flex hind legs forward.
      2. Center on distal urethra.
      3. Use the same lateral technique as routine lateral view.

    7. Positioning for the VD view

      1. The patient should be in dorsal recumbency.
      2. The patient should be straight. The sternum and pelvis should not be rolled to the right or the left.
      3. The primary beam should extend 1 1/2" cranial to the xiphoid.
    8. Make the exposure on full expiration.
      1. Having the diaphragm as far cranial as possible allows the abdominal organs to spread out and makes it easier to visualize them.
      2. Expiration allows more time to fit the exposure in before the next breath. Avoid motion by stopping the patient from panting if possible.
  2. Film Assessment
    1. Technique
      1. Overexposure
        1. Decrease kVp by 10% or halve the mAs to make the film half the density of the overexposed film.
      2. Underexposure
        1. Increase kVp by 10% or increase mAs by 30-100%.
        2. Increasing the kVp will make the radiograph more dense but will decrease the contrast you would have had on the film at the same kVp but with more mAs.
        3. Increasing the mAs will increase the film density but may cause motion artifacts if the exposure time was increased.
      3. Decreased contrast (gray films)
        1. Was a grid used to control scatter radiation? In general any part over 10cm. should be radiographed using a grid.
        2. What kVp was used? Using kVps over the ranges previously discussed may produce abdomen films that are lacking in contrast.
    2. Positioning
      1. Was the patient in "true" lateral? Look for superimposition of the ilia of the pelvis and of the ribs where they join the spine.
      2. Assess the VD view for rotation. Ribs on each side and the pelvis should look symmetrical. The spine should not look rotated.
      3. Is all of the desired abdominal anatomy visible?
      4. Is there any undesired anatomy overlying abdominal structures that are being evaluated?

Can You Read This Abdomen?
Chess Adams, DVM, Dipl. ACVR (Radiology, Radiation Oncology)


Verify diagnosis - did he really swallow that toy? RADS MAY BE QUICKER / EASIER

Surgical disease or not - is there clear evidence of obstruction? RADS OR US (US best for intussusception)

Prognosis - is there evidence of bowel rupture? (Consider US guided aspirate)

Follow up - are the bowel loops enlarging? RADS very useful

VSPF: "Very Simple Plan (to) Follow"


Swallowing problem: Pharynx; usually acquired - adult
  • foreign body: direct visualization or survey film
  • neuromuscular: dynamic contrast study
Regurgitation: Esophagus; congenital or acquired; immature or adult
  1. survey films = esophageal enlargement or foreign body
  2. pneumonia
  3. presence of a mass
  4. stomach location
  5. esophagram if surveys negative, or to define
  6. degree of dysfunction
  7. specific cause
Vomiting: Stomach or beyond; many causes; any age
  • survey films = lumen enlargement, foreign body or mass
  • loss of detail
  • displacement of organs
  • hepatic or urinary causes
  • upper GI contrast if surveys negative, or to define
  • degree of dysfunction
  • specific cause
Diarrhea: Small or large bowel; many causes; any age
  • survey films = increased diameter and fluid filled
  • length of affected bowel
  • often unrewarding (normal appearing) - upper GI contrast vs. US
  • to determine bowel wall thickening
Straining to defecate: Constipation vs obstipation
  • survey films = may localize disease
  • Pneumocolonogram vs. US vs. colonoscopy = may define lesion site
  • Ba enema - rarely done anymore, in favor of above exams
Note: Restraint drugs affect alimentary tract motility. Do not use general anesthetics or narcotics when motility is to be evaluated. Recommended for dogs: low dose of ace promazine; for cats: ketamine.


Ba suspension
  • diluted to 20% for large volume complete upper GI
    12 ml/kg, followed by 3 ml/kg air
  • full strength (60%) for esophagram or double contrast gastrogram
    3 ml/kg for esophagram
    6 ml/kg followed by 6 ml/kg air for gastrogram
  • paste; for esophagrams
    2 - 3 ml/kg
    1 - 2 ml/kg mixed with canned or kibble food
Iodinated solutions (when suspect perforation):
  • organic, ionic (gastrografin; oral hypaque)
  • 2 - 3 ml/kg full strength - will dilute by attracting fluid intraluminally
  • organic, nonionic (iohexol; iopamidol)
  • 12 ml/kg diluted 1:2 - avoids possibility of dehydrating patient, but more expensive
Barium-impregnated polyethylene spheres (BIPS)
  • for evaluation of gastric and small bowel transit/obstruction
  • 10 5-mm and 30 1.5 mm spheres (follow manufacturers directions)
  • easily administered - but remember; no mucosal information
  • study time may be protracted (up to 10 hours for normal transit)


  • May replace radiographic study; especially thin or fluid filled abdomen
  • May complement radiographic study; eg. internal evaluation of solid organs
  • May provide definitive assessment; eg. intussusception, guided Bx or aspirate
  • Highly operator dependent
  • Excessive gas or ingesta compromises evaluation
  • Obesity or large size may compromise evaluation

  1. Distinguish between idiopathic megaesophagus, vascular ring anomaly and esophageal foreign body.
  2. Recognize normal variations in appearance of the esophagus, stomach, and colon in the dog and cat.
  3. Differentiate between gastric dilatation and gastric volvulus.
  4. Recognize the plain film and contrast film signs indicative of a gastric or an intestinal obstruction.
  5. Recognize the appearance of a linear foreign body.
  6. Differentiate functional ileus from mechanical ileus.


    Cranial esophageal (Cricopharyngeal) sphincter, caudal esophageal (cardiac) sphincter.

    Diameter similar to small bowel (2 cm in 35 lb dog).


    1. Megaesophagus - look for tracheoesophageal stripe sign or tubular soft tissue opacity.
      Entire esophagus dilated:

      1. Idiopathic
      2. Metabolic disorder (e.g. myasthenia gravis, Addison's)

      Part of esophagus dilated:
      1. Obstruction (intrinsic or extrinsic)
      2. Vascular ring anomaly
      3. Esophagitis

    1. If suspect entire esophagus functioning poorly - use a thin suspension.
    2. If mucosal abnormalities are suspected - use barium paste.
    3. If 1 or 2 fail to demonstrate dysfunction - mix barium with food.
    Cardia, Fundus, Body, Pylorus

    Varies With Positioning

    1. Normal location
      1. Lateral projection
        1. Parallel 10th-11th intercostal space
        2. Dorsal - cardia, fundus
        3. Ventral - body, pylorus

      2. Ventrodorsal projection
        1. 10th to 12th intercostal space
        2. Fundus is left of midline
        3. Pylorus is right of midline
        4. Pylorus of cat is on midline

    2. Abnormal location
      1. Caudal displacement
        1. Liver enlargement
        2. Ingesta filled

      2. Cranial displacement
        1. Small liver
        2. Diaphragmatic hernia
        3. Large mass caudal to and compressing stomach

    3. Enlargement
      1. after large meal (ingesta pattern)
      2. Gastric dilation (usually gas)
      3. Gastric volvulus (gas or gas and ingesta)
      4. Pyloric outflow obstruction (fluid or fluid and ingesta)

    4. Appearance of gastric walls and lumen
      1. Gastric wall and rugae
        1. Gastric rugae should be parallel and equal size
        2. Thickened gastric walls or rugae may be associated with gastritis

      2. Gastric lumen
        1. Stomach should be empty 6-8 hours after eating
        2. Foreign body may be difficult to see if radiolucent - double contrast study may be required.

    5. Gastric diseases
      1. Gastric volvulus - rotation of the stomach along its longitudinal axis.
        1. Radiographic signs
          1. large or very large stomach
          2. Compartmentalization - esp. on DV view (margins of fundus and pyloric antrum distinct)
          3. Displacement of the pylorus dorsally and fundus ventrally - right lateral view
          4. May see generalized small intestinal ileus
          5. Enlargement and ventral displacement of the spleen
          6. May see evidence of stomach rupture - free abdominal gas
      2. Gastric dilation - distended stomach without volvulus
        1. Radiographic signs
          1. Gross distention of stomach without compartmentalization
      3. Pyloric canal obstruction
        1. Causes
          1. Pyloric spasm, hypertrophy
          2. Pyloric neoplasia, foreign body
        2. Radiographic signs
          1. Survey radiographs
            1. Enlarged stomach; normal shape and location
            2. Contains food and/or fluid
          2. Positive contrast gastrogram
            1. Delayed gastric emptying (> 3-4 hours)
            2. Pyloric canal may be consistently narrowed and/or irregular on repeated films or fluoroscopy
      4. Gastric tumors
        1. Radiographic signs
          1. Survey radiographs and/or US
            1. Frequently involve the lesser curvature of the stomach
            2. Thickening of wall or luminal filling defect
            3. May not be seen on survey radiographs / may be obscured by gas on
          2. Contrast study - double contrast gastrogram
            1. Filling defect in contrast pool
            2. Thickening of gastric wall
            3. Repeatable rigidity - repeat films during the first hour, till convinced not an artifact of peristalsis.

    1. Visualized by gas and fluid within lumen and omental/mesenteric fat surrounding them.

    2. Evaluate for:
      1. Location
        1. Normally they are evenly spaced.
        2. Displacement by abdominal masses.
        3. Displacement due to diaphragmatic or peritoneal hernia.
        4. May be gathered together due to linear foreign body, chronic adhesions, or peritonitis.

      2. Normal intraluminal appearance
        1. Gas or homogeneous fluid in small bowel.
        2. Gas or heterogeneous (granular) ingesta in stomach and colon.
        3. Determination of intestinal wall thickness from survey radiographs is likely to be inaccurate - use US or contrast study
        4. Radiopaque foreign bodies - occasionally clinically significant (obstructive, perforating or toxic).

      3. Normal external bowel diameter
        1. Duodenum - up to 1.5 x diameter of L2 or L5 vertebral body endplate (VBE) on lateral view.
        2. Jejunum/ileum - up to 1.0 x diameter of L2 or L5 VBE.
        3. Colon - up to 2.5 x diameter of L2 or L5 VBE.

    3. Ileus
      Radiographic definition: localized or generalized increased bowel diameter (due to obstruction of intestine outflow or excessive intestinal secretions).
      1. Localized (mechanical) ileus:
        1. Partial or complete obstruction of bowel lumen with accumulation of gas, ingesta, and mucosal secretions proximal to the obstruction.
        2. Caused by:
          1. Foreign body
          2. Tumor
          3. Adhesion
          4. Intussusception
          5. bowel infarction (rare)
        3. Radiographic signs
          1. Gas or fluid distention of a localized segment of bowel beyond normal diameter (i.e., two populations of small or large bowel).
          2. Retention of foreign material/foreign body within distended bowel.
          3. "Hairpin turning" and "layering" of distended bowel loops.

      2. Generalized (functional) ileus
        1. Abnormal collection of gas and/or fluid involving the entire small bowel.
        2. Caused by:
          1. Generalized enteritis
          2. Dysfunction of the intestinal wall musculature

      3. Localized functional ileus: Focal irritation, often associated with abdominal pain due to:
        1. Peritonitis (e.g., pancreatitis)
        2. Trauma (e.g., local vascular compromise)
        3. Linear foreign body (radiographic signs include small crescent shaped intraluminal gas collections, bowel gathering and local loss of detail).

    An U.G.I. is the special procedure used to evaluate the stomach and small intestines for position, motility, thickness of bowel wall, size and contents of the lumen, and contour of the mucosal surface following the administration of a positive contrast agent.

    1. Indications
      1. Recurrent or nonresponsive vomiting
      2. Hematemesis
      3. Chronic diarrhea associated with weight loss
      4. Melena
      5. Suspicion of radiolucent foreign body or neoplasia
      6. Verify hernia

    2. Contraindications
      1. Obvious ileus
      2. Following administration of anticholinergic drugs
      3. Barium sulfate when there is suspected perforation
      4. Ionic organic iodine solutions in dehydrated or debilitated patients

    3. Patient preparation
      1. Well prepared abdomen is optimal but not always feasible
        1. Colon free of feces
        2. Empty urinary bladder
        3. Clean hair coat
      2. 24 hour fast - no food, water OK
      3. Cleansing water or saline enema (8 tsp. table salt per gallon of tap water) 2-4 hours prior to the study and allow to evacuate
      4. Commercial enema kits are unsatisfactory
      5. Survey films
        1. Right and left lateral recumbent abdominal radiographs
        2. Ventrodorsal abdominal radiograph
        3. Rationale:
          1. Check positioning and technique
          2. Check preparation
          3. Reference films for comparison
          4. May make or further confirm suspected diagnosis - U.G.I. may not be needed

    4. Normal Study
      1. Transit time
        1. Dogs (ace promazine sedation to facilitate stomach tube placement)
          1. Barium sulfate; 2 - 3 hours to reach colon
          2. Organic iodine solution; 30 - 60 minutes to reach colon
          3. Within 2-3 hours stomach essentially emptied
          4. Within 6-8 hours most is in the colon (2 -3 hours for organic iodine)
        2. Cats (ketamine to facilitate stomach tube placement)
          1. Barium sulfate; 30 - 60 minutes to reach colon
          2. Organic iodine solution; 15 - 30 minutes to reach colon
          3. Stomach emptied within 1 to 2 hours
          4. Within 3-4 hours most is in the colon (1 - 2 hours for organic iodine)
        3. Frightened animals may have prolonged transit times (sedation helps)
      2. Normal variables
        1. "Pseudoulcers" in dogs
        2. "String of Pearls" in cats

    5. Complications
      1. Aspiration of contrast - verify tube placement before dosing
      2. Leakage of barium sulfate into the peritoneal cavity through a perforated bowel
      3. Ionic organic iodine solutions may cause dehydration and if aspirated can cause pulmonary edema


    1. Enteritis
      1. Hypermotility
      2. Rapid transit time
      3. Mucosal irregularity - very subjective

    2. Linear foreign body
      1. Small bowel loops gathered
      2. Accordion-like pleating of the small bowel
      3. Prolonged transit time

    3. Infiltrative bowel disease - lymphosarcoma, histoplasmosis, eosinophilic enteritis, and lymphangiectasis
      1. Rapid transit time
      2. Circumferential compromise of the bowel lumen by thickened walls
      3. May see irregular filling defects in the mucosa

    4. Intestinal tumors
      1. Thickened bowel wall (lymphosarcoma)
      2. Bowel lumen stricture with proximal loop ileus (2 populations of small bowel)
      3. Smooth or irregular mucosal borders at site of thickening (depending on mucosal involvement of tumor)

    1. Cecum - at the ileocolic junction
      1. Dog - semicircular to spiral (C - shaped) structure lying on the right of midline at level of L3
      2. Cat - not seen (quite small)

    2. Ascending colon - right of midline

    3. Transverse colon

    4. Descending colon left of midline

    5. Location of all portions easily displaced by other organomegaly


    1. Indications
      When endoscopic or US examinations are not feasible

    2. Procedure
      1. Withhold food 24 hours
      2. Warm water/saline enema 6 hours prior to the study
      3. Survey radiographs to verify the colon is empty
      4. Anesthetize the animal and place in right lateral recumbency

    3. Radiographic appearance
      1. Normal mucosal surface should appear regular and smooth
      2. Large bowel disease
        1. Irregular mucosal surface; colitis
        2. Stricture of the lumen; neoplasia, adhesions
        3. Intraluminal filling defects; neoplasia, intussusception
        4. Diverticulum of the colon


    1. Megacolon - abnormally enlarged colon
      1. Mechanical blockage
        1. Narrowed pelvic canal from trauma
        2. Neoplasia - filling defect or displacement
        3. Adhesions - stricture
      2. Neurogenic
        1. Primary neurologic disorder - no specific signs
        2. Spinal cord disorders - observe lumbar vertebrae
      3. Psychogenic - no specific signs

    2. Intussusception - invagination of one segment of the intestines into another segment of the intestines.
      1. Occurs most frequently at ileocolic junction
      2. Most frequently seen in puppies
      3. Radiographic sign
        1. Survey films
          1. Small bowel localized or generalized ileus (depending on location and duration)
          2. May see tubular soft tissue mass in area of cecum
        2. Contrast study
          1. Barium enema is preferred contrast study
          2. Filling defect seen in contrast study
        3. Ultrasound can be diagnostic - our study of choice

Abdomen - What Else is in There
Lisa J. Forrest, VMD, Dipl. ACVR (Radiology, Radiation Oncology)

Abdominal organs visible on survey radiographs in a normal dog and cat include:
  • Liver
  • Spleen
  • Kidneys
  • Urinary bladder
  • GIT

Abdominal Masses

Abdominal masses are often difficult to visualize on survey radiographs because a silhouette sign will occur with the organ of origin and adjacent soft tissue structures. Recognizing displacement of normal organs will help identify which organ is involved.


Alterations in liver size can be diffuse or focal.
  • Diffuse hepatomegaly results in displacement of the pylorus caudally, dorsally and to the left. Liver margins are rounded. Diffuse hepatomegaly may be caused by inflammatory disease or neoplasia. Liver enlargement is commonly seen with lymphosarcoma, venous congestion (right heart failure), fat infiltration, steroid hepatopathy, acute cirrhosis, or storage diseases.
  • Microhepatica is a diffuse change and results in cranial displacement of the stomach and a decrease distance between the diaphragm and stomach. Causes of a small liver include chronic liver disease and cirrhosis or a congenital portal systemic shunt.
  • Focal liver masses represent primary or metastatic neoplasia, granulomas or abscesses. Different organs will be displaced depending on which liver lobe is affected.
    • Right lateral or medial lobes: dorsomedial displacement of the pylorus, proximal descending duodenum and ascending colon. Small intestines are displaced caudodorsally.
    • Left lateral or medial lobes: dorsomedial displacement of the head of the spleen, adjacent small intestine, and gastric fundus.
    • Central lobes: caudodorsal displacement of the body of the stomach.
Alterations in splenic size can be diffuse or focal.
  • Assessing spleen size on radiographs is subjective. If the spleen has rounded margins and obviously displaces adjacent viscera, it should be considered enlarged. Diffuse splenomegaly can be secondary to non-pathologic variation is size, such as a physiologic response to medications (phenothiazines and barbiturates). Diseases affecting the reticuloendothelial system (mastocytosis, lymphosarcoma, histoplasmosis) will cause diffuse splenomegaly. Diffuse enlargement is seen with splenic torsion.
  • Primary or metastatic neoplasms, and subcapsular hematomas cause focal splenic masses.
    • Masses in the head of the spleen: caudodorsal displacement of adjacent small intestines in the lateral view and caudomedial displacement of intestines in the ventrodorsal view.
    • Masses in the body or tail of the spleen: ventral mid-abdominal mass on lateral view.

Pancreatic Masses and Pancreatitis

Enlargement of the pancreas either secondary to a mass or edema will result in viscera displacement depending on the location within the pancreas.
  • Right limb: lateral displacement of the descending duodenum on the ventrodorsal view and ventral displacement of the duodenum on the lateral view. In cases of pancreatitis there is often a localized peritonitis, resulting in a focal loss of visceral detail.
  • Left limb: increased soft tissue opacity medial to the head of the spleen on ventrodorsal view. There is usually no extrinsic distortion of the gastric wall.
  • Body: may displace the transverse colon caudally.

Renal Masses

The kidneys and adrenal glands are retroperitoneal structures. Because of this renal masses remain dorsal in the abdomen. Adrenal gland enlargement or adrenal masses are difficult to see unless there is dystrophic mineralization.
  • Right kidney: enlargement will produce medial and ventral displacement of the descending duodenum and ascending colon. There is often left and ventral displacement of the adjacent small intestine.
  • Left kidney: ventral and medial displacement of the descending colon and adjacent small intestine.
  • Unilateral renal enlargement/mass:
    • Compensatory hypertrophy - contralateral kidney often small
    • Primary or secondary neoplasm - irregular margin, either focal or multifocal
    • Renal cyst - irregular margin
    • Hydronephrosis - smooth margin
    • Renal abscess or renal hematoma - irregular margin
  • Bilateral renal enlargement/masses:
    • Acute nephritis - smooth margins
    • Polycystic kidneys - irregular margins
    • Lymphoma - smooth or irregular margins
    • F.I.P. - smooth or irregular margins
    • Hydronephrosis - smooth margins
    • Pyelonephritis - smooth or irregular margins
  • Small kidneys:
    • End-stage renal disease - irregular margins
    • Congenital hypoplasia - smooth margins

Uterine enlargement cannot be detected until the uterus exceeds the diameter of adjacent bowel. A detectable enlarged uterine body and horns causes craniodorsal displacement of the small bowel in the lateral view. The uterus lies between the colon and bladder, resulting in a mass effect on the lateral view when enlarged. In the ventrodorsal view there is cranial and midline displacement of small intestine.

Prostate Gland

The normal prostate gland is intrapelvic. The prostate is considered enlarged when it extends cranial to the pelvic brim on the lateral view.

Causes of prostatic enlargement include:
  • Benign prostatic hypertrophy (symmetric, smooth margins)
  • Prostatitis (symmetric, +/- irregular margins)
  • Neoplasia (asymmetric, irregular margins, +/- mineralization)
  • Cysts (asymmetric, smooth margins)
  • Paraprostatic cyst (asymmetric, smooth margins) - Contrast radiography is often needed to differentiate the urinary bladder from paraprostatic cyst.
  • Abscess (asymmetric, variable margins)
When you can't see anything - What does it mean?

If your technique is adequate and it is difficult to see abdominal organs, then there is loss of visceral detail. Causes of this loss of detail include:
  • Emaciation - there is no intra-abdominal fat to provide contrast
  • Puppies & Kittens - young patients have brown fat, which has a high water content and is the same opacity as the soft tissue organs
  • Peritoneal effusion
  • Peritonitis
  • Gross organomegaly - other organs are compressed
  • Carcinomatosis
Abdominal ultrasound is indicated in most instances of poor radiographic abdominal detail, when an abdominal disorder is suspected. US guided abdominocentesis is indicated for diagnosis in cases where effusion is suspected.

© 2006 - Chess Adams DVM, DACVR - All rights reserved