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Surgery/Interventional Radiology Chick Weisse, VMD, DACVS Allyson C. Berent, DVM, DACVIM Animal Medical Center of New York Veterinary Interventional Radiology Chick Weisse, Diplomate ACVS Following the description of percutaneous arterial catheterization by Sven Ivar Seldinger in 1953, angiography developed into a widely-utilized and essential medical diagnostic tool (for humans). Technological advances have since helped transform this diagnostic modality into a sub-specialization with enormous therapeutic potential. Interventional radiology (IR) involves the use of contemporary imaging techniques such as fluoroscopy and ultrasonography to selectively access vessels and other structures in order to deliver different materials for therapeutic reasons. ADVANTAGES AND DISADVANTAGES The use of IR techniques in veterinary patients offers a number of advantages compared to more traditional therapies. These procedures are minimally invasive and can therefore lead to reduced peri-operative morbidity and mortality, shorter anesthesia times and shorter hospital stays. Some less equipment-intensive procedures can result in reduced costs as well. In addition, some techniques such as chemoembolization of tumors or palliative stenting for malignant obstructions offer alternative treatment options for patients with various conditions that may not be amenable to standard therapies. The primary disadvantages of IR include the required technical expertise, the specialized equipment necessary (fluoroscopy with or without digital subtraction capabilities), and the large initial capital investment necessary to provide a suitable inventory of catheters, guidewires, balloons, stents and coils. EQUIPMENT AND TECHNIQUE As most of these procedures are minimally-invasive (performed through catheters or small holes in the skin), traditional sterile operating rooms are not required, but recommended. Most of these procedures are performed in clean angiography suites. The entry sites receive a traditional sterile scrub, and operators wear full lead gowns, lead thyroid shields, caps, gowns, and masks. The radiation exposure during conventional or C-arm fluoroscopy can be substantial. The operator should review radiation safety guidelines, minimize exposure time and beam size, and maximize shielding and distance from the beam. For many of the more commonly performed IR procedures, a traditional fluoroscopy unit is sufficient. A C-arm fluoroscopy unit has the advantage of mobility of the image intensifier, permitting multiple tangential views without moving the patient. Occasionally, ultrasonography is useful for percutaneous needle access into vessels or other structures. Digital subtraction angiography (DSA) and "road-mapping" allow high resolution images to be obtained with minimal use of contrast agent which is often a concern in our relatively small veterinary patients. DSA is required for super-selective angiograms of small caliber vessels and those vessels in the head (or where there is substantial bone which makes angiogram visualization difficult). Tracheal Collapse Tracheal collapse is a progressive, degenerative disease of the cartilage rings in which hypocellularity and decreased glycosaminoglycan and calcium content leads to dynamic tracheal collapse during respiration. Many of these animals are palliated with medications including anti-inflammatories, cough suppressants, sedatives/tranquilizers, and bronchodilators. Candidates for surgical therapy are those that have failed initial conservative medical management. Various surgical techniques have been described, however the currently recommended surgical therapy for patients with extrathoracic tracheal collapse is extraluminal polyprolpylene ring (or spiral) prostheses. This procedure is not without complications however.1 This study reported that 5% of animals died peri-operatively, 11% developed laryngeal paralysis from the surgery, 19% required permanent tracheostomies (half within 24 hours), and ~23% die of respiratory problems with a median survival of 25 months. The current therapy in humans is intra-luminal stenting with one of a number of FDA-approved tracheobronchial stents. A number of stents have been evaluated in the canine trachea, including both balloon-expandable (Palmaz), and self-expanding (Stainless steel, Laser-cut nitinol, Knitted nitinol) stents.2-4 Clinical improvement rates in 75%-90% of animals treated with self-expanding, intra-luminal stainless steel stents have been reported.3,4 Immediate complications were mostly minor although there was a peri-operative mortality rate of approximately 10%. Late complications included stent shortening, excessive granulation tissue, progressive tracheal collapse, and stent fracture. Congenital Intrahepatic Portosystemic Shunts Portosystemic shunts (PSSs) are anomalous vascular communications between the portal venous and systemic circulations that result in a clinical syndrome with various neurological, biochemical, and hematological consequences. Numerous techniques have been described for intrahepatic PSS attenuation, ranging from careful liver dissection around the shunting vessel to more technically demanding and complicated procedures involving temporary vascular hepatic inflow occlusion for intravascular repair (References available from the author). A review of six major veterinary reports on canine intrahepatic PSSs reveals mortality rates following surgical treatment ranging from 10% to 66%.5-10 Interestingly, the majority of mortalities occurred peri-operatively with fewer than 20% occurring later than one week post-operatively. The goal of IR techniques for intrahepatic PSSs is to reduce the unacceptably high, peri-operative mortality rates associated with traditional open surgical techniques and hopefully improve the outcome for these cases. We have performed over 60 percutaneous transvenous coil embolizations (PTCE) with a vena caval stent and thrombogenic coils placed within the shunt.11 Peri-operative complications were minor and peri-operative mortalities were comparatively low. Percutaneous Transarterial Embolization (TAE) and Chemoembolization (TACE) Bland arterial embolization entails selective, catheter-directed delivery of particulate material in order to control hemorrhage, occlude vascular malformations, or reduce tumor growth. Some current indications in human medicine include embolization of arterio-venous malformations, intractable epistaxis or gastrointestinal bleeding, and uterine artery embolization for symptomatic uterine fibroids in women. In addition, embolization with or without chemotherapy of metastatic bone lesions in humans has been shown to aid in decreasing pain associated with the malignancy. In some cases, subsequent surgical resection was possible following the embolization-induced tumor shrinkage. Regional Tumor Therapies Chemoembolization involves selective intra-arterial chemotherapy delivery in conjunction with subsequent particle embolization. Intra-arterial chemoembolization has been shown to result in a 10- to 50-fold increase in intra-tumoral drug concentrations when compared to systemic intravenous chemotherapy administration.12 Various tumors may respond to chemoembolization as well. We have performed this procedure in dogs with unresectable invasive sinus carcinomas with some encouraging results. A "post-embolization syndrome" comprised of general malaise, fever, and pain has been described in people to last several days. Patients routinely respond to supportive care consisting of intravenous fluids, anti-emetics, gastro-protectants, and analgesics. We have not encountered a similar syndrome in animals, however we treat all patients prophylactically with similar medications. Palliative Stenting for Malignant Obstructions Veterinary patients can present with advanced stages of malignancy in which traditional therapies such as surgery, chemotherapy, or radiation therapy are either associated with excessive morbidity, cost, or poor outcome. Presenting clinical signs may be associated with the tumor location and subsequent local effects rather than the systemic effects of the tumor burden. For example, malignant obstructions of the urinary tract are usually due to transitional cell carcinomas or prostatic tumors and affected animals can present with life-threatening signs associated with urinary tract obstruction. IR techniques involving the placement of intra-luminal stents to palliate similar malignant obstructions in humans have been described. The author has performed a number of palliative stenting procedures in the urinary tract, and upper and lower gastrointestinal tracts to relieve luminal obstructions due to neoplasia in animals as small as a ferret. These IR techniques were rapid, safe, and effective, and complications were minor and uncommon.14 REFERENCES
General Surgical Oncology Chick Weisse, Diplomate ACVS Surgery plays a major role in managing the veterinary oncology patient through cancer prevention, diagnosis, cure and palliation. Even in light of the major advances that have recently occurred in other areas of human and veterinary oncology, surgery remains the best chance for a cure in most patients. However, a careful understanding of tumor biology combined with complete patient evaluation (including tumor stage and grade) and owner expectations are critical in order to guarantee surgery is only pursued in the patient's best interest. All too commonly, basic principles of surgical oncology are violated resulting in additional surgical procedures or even a missed opportunity for a surgical cure. Close communication between the general practitioner, veterinary oncologist and veterinary surgeon will ensure the optimal strategy is pursued. Cancer Prevention A number of tumors encountered in veterinary medicine have been demonstrated to be hormonally influenced, enabling surgical intervention in order to reduce the future risk of tumor development. The most notable preventative surgical procedures are ovariohysterectomy and castration. Not only do these procedures remove the possibility of ovarian and uterine neoplasia and testicular neoplasia, respectively, but the incidence of certain hormonally-induced tumors are reduced as well. Surgical Diagnosis and Biopsy The importance of accurate diagnosis, tumor grade, and tumor stage cannot be overemphasized if appropriate therapy is to be initiated. While many techniques are currently available for obtaining samples for evaluation (including endoscopy, trans-tracheal wash, etc.), sample collection via fine-needle aspiration (FNA) versus various methods of biopsy sample collection will be briefly described below. When possible, cytology is a useful, inexpensive and non-invasive means of obtaining a diagnosis without requiring surgery. Round cell tumors (lymphoma, mast cell tumor, histiocytoma, plasma cell tumor, transmissible venereal tumor, and some include malignant melanoma) exfoliate easily, often permitting a definitive diagnosis. FNA of severely vascular tumors, those with concurrent infections, or tumors with cells that do not exfoliate easily tend to be less diagnostic. However, FNA can often differentiate between benign and malignant processes in some of these cases and thereby provide valuable information. Whenever possible, a tissue sample is preferred to a needle aspirate as the former can typically provide a definitive diagnosis as well as tumor grade and other criteria of malignancy that can aid with treatment planning. A cutting needle biopsy (e.g. Tru-Cut biopsy needle) will typically provide a small but sufficient amount of tissue necessary to obtain a definitive diagnosis. Laparoscopy and thoracoscopy have recently been gaining increased use in veterinary medicine to obtain small biopsy samples from the abdominal and thoracic cavities with minimal invasiveness and morbidity. When one of these previous techniques has failed, or more tissue is required, the surgeon must decide between performing an incisional versus excisional biopsy. Both of these techniques are more invasive than those previously described. Decisions are made on an individual case basis, however incisional biopsies are typically performed when the biopsy results will drastically alter the subsequent treatment plan. Excisional biopsies are typically performed when a mass can be removed easily with wide margins and minimal morbidity, or when other techniques would be impractical (such as a lung lobectomy instead of an incisional biopsy of a lung tumor). Excisional biopsies can also be performed when the surgical margins would be the same regardless of the biopsy results. While biopsies are critical for appropriate treatment of our cancer patients, it is important to warn owners of the associated risks and potential complications. Examination of the regional draining lymph nodes is also critical during the staging process. It is typically recommended to obtain FNA or biopsy of the regional lymph node when it is readily accessible, particularly for carcinomas and other tumors known to spread readily to the lymph nodes (e.g. mast cell tumors). More recently, advanced imaging modalities have become available to veterinarians. Nuclear scintigraphy has been useful for pre-operative screening to document subclinical skeletal metasteses. CT scans are particularly useful for boney lesions or cases in which concern exists regarding soft tissue tumor invasion into bone. CT is also the diagnostic modality of choice for evaluating the presence of pulmonary metastatic disease. MRI is most useful for evaluating the extent of soft tissue tumors. Surgical Principles Once the tumor type, grade, and stage have been determined, a treatment plan can formulated. For localized disease, a surgical cure may be possible. For systemic disease, surgery may play a role in palliation. All available treatment modalities should be considered and often a variety of treatment options are presented. The patient's quality of life is always the primary concern and communication with the caregiver is critical to understand their expectations and limitations. The first surgery is the best chance for a cure. Careful planning is imperative to ensure complete tumor excision is performed initially. Follow-up surgeries for incomplete tumor resections present significant obstacles to achieving a complete resection. The previous surgical incision must be treated as tumor, thereby necessitating a larger resection for each subsequent procedure. In addition, normal anatomical architecture is often obscured by scar tissue and landmarks may be difficult to identify. The delay between surgeries and the comparatively active replication of microscopic disease previously located at the tumor margins facilitate metastatic spread and rapid tumor regrowth. Surgical margins will be based upon tumor type, grade, location and treatment plan. Knowledge of the tumor type and grade will provide information about the tumor biology. Although not all tumors are graded histopathologically, careful interpretation of the pathology report will reveal different criteria of malignancy and suggest the aggressiveness of the particular tumor. Various margin classifications have been described.
Exact, measured guidelines for "wide" tumor margins have not been determined. In general, 1cm margins for carcinomas and sarcomas have been recommended while up to 3cm margins have been suggested for mast cell tumors. Ideally, the surgeon should evaluate each case on an individual basis. Whenever dissection is limited, removal of one fascial plane deep is a recommend depth of dissection as this tissue is relatively resistant to tumor penetration. When the pathology report describes a particularly aggressive tumor, the surgeon may choose to attempt larger margins than for a similarly sized tumor described with lower grade characteristics. To the author's knowledge, there has been no scientific correlation between the size of a tumor and the required surgical margins. Biopsy submission and evaluation As a general rule, any mass worth excising is worth submitting for biopsy. The tissues are fixed in 10% neutral buffered formalin in a 1:10 ratio of tumor tissue to formalin in order to achieve adequate tissue penetration and preservation. In order to maximize biopsy margin evaluation, marking of the specimen margins is recommended. To the author's knowledge, there are no clear guidelines established to describe a "complete margin" in terms of adequate "distance" between tumor cell extension and an excised margin. In addition, it is not feasible to evaluate the entire surface of a biopsy specimen. For this reason, pathology reports stating "clean margins" should be interpreted with caution. If margins are reportedly incomplete, or if there is concern by the surgeon that tumor tissue remains, a surgical re-resection or adjuvant therapies must be considered. Adjuvant Therapies When surgical resection is incomplete or when the probability of local tumor recurrence is high, additional surgery or adjuvant therapy is recommended. As discussed previously, subsequent surgeries are routinely more difficult and alternative local treatments should be considered if additional surgery is not indicated. Chemotherapy and radiation therapy are both routinely used in the adjuvant or neo-adjuvant (before the primary treatment) setting. Both modalities can be used to treat local disease while chemotherapy also treats systemic disease. Both are most effective for rapidly dividing cells and therefore tend to work optimally for microscopic disease in which a higher proportion of cells are in the replicating phase of the cell cycle. For this reason, these modalities are most often used post-operatively, following the removal of macroscopic disease. Non-Resectable Tumors Traditional treatment modalities still remain an important part of managing patients with metastatic or non-resectable cancers. Systemic chemotherapy typically demonstrates poor response rates for most bulky tumors or metastatic disease, however can occasionally "down-stage", or shrink, excessively large tumors enabling subsequent resection. Radiation therapy is routinely used for palliation of pain associated with bony tumors and can slow tumor growth. Surgery can still play a major role in animals with advanced malignancies, even when tumor excision is not possible. Tracheal Collapse - Extraluminal Rings and Tracheal Stents Chick Weisse, Diplomate ACVS OVERVIEW Tracheal collapse, or tracheal chondromalacia, is a progressive, degenerative condition of the hyaline cartilage rings that support the tracheal lumen. Weakening of the trachealis muscle contributes to the loss of tracheal lumen during different phases of respiration. The resulting clinical syndrome typically manifests as a "goose honk" cough with varying degrees of dyspnea and is most commonly identified in toy breed dogs. Conservative management techniques and medical management (Table 1) can be useful to palliate clinical signs for years, however more aggressive treatment is often required for those animals that eventually fail these more conventional treatments. 
Aggressive medical therapy is ALWAYS performed before any more invasive techniques are pursued as these treatments are basically salvage procedures associated with considerable risk. In addition, other concurrent conditions such as underlying pulmonary, cardiac, laryngeal/upper airway, and endocrine diseases should be appropriately addressed before invasive tracheal procedures are considered. If conservative therapy fails to provide a reasonable quality of life for the patient, surgical rings and tracheal stents are the more invasive treatments currently available. There is a tendency to compare these two treatment options, however both play an important role in the management of this frustrating disease process. DIAGNOSIS Accurate diagnosis of the LOCATION of the collapse is important before choosing which technique to perform or recommend. Routine radiography can be useful for the diagnosis of concurrent conditions and the presence of tracheal collapse, but more DYNAMIC studies are necessary to fully appreciate the extent of the collapse. During inspiration, the sub-atmospheric airway pressures generated in the cervical trachea lead to collapse in that location, whereas during exhalation, the increased intra-thoracic pressures lead to collapse of the intra-thoracic trachea. Individual STATIC radiographs may fail to document the fully extent of the collapse as demonstrated in FIGURE 1 which is the same dog during two different phases of respiration (cervical tracheal collapse during inspiration and intra-thoracic tracheal collapse during expiration). 
RINGS OR STENT ? The placement of tracheal rings (Figure 2A) or a tracheal stent (Figure 2B) remains one of the most difficult and controversial decisions regarding the treatment of this disease. 
Ultimately, decisions are made on an individual basis however some basic guidelines can be used (Table 2). In general, the immediate post-operative period is most dangerous following tracheal ring surgery. Patients typically recover well following tracheal stent placement, however the potential risk of stent fatigue and fracture persists in these patients over the long term. Regardless of treatment used, considerable discussion with the client is important to ensure outcome expectations are clear. Tracheal collapse is progressive disease and all current treatments are purely palliative in nature. The majority of patients will require lifelong medical treatment following surgery or stenting. In addition, concurrent bronchial collapse appears to carry a worse long-term prognosis, however this does mean the patient may not benefit from one of these treatments. 
TRACHEAL RING SURGERY The patient is placed in dorsal recumbency and a standard ventral midline cervical incision is made from the larynx to the thoracic inlet. The subcutaneous muscles and paired sternohyoid muscles are separated using sharp and blunt dissection to expose the trachea. Extreme care is taken to avoid stretching or damaging the recurrent laryngeal nerves (Figure 3A) coursing dorsolaterally along the trachea which could result in laryngeal paralysis. Curved or right-angled hemostats facilitate the gentle creation of narrow fenestrations around the trachea (Figure 3B) in order to pass the tracheal rings which are made from polypropylene syringes or purchased pre-fabricated (New Generation Devices, Franklin Lakes, NJ). Four or five polydiaxanone sutures (3-0 or 4-0) are passed around the ring and tracheal cartilage. The rings are spaced approximately 5mm apart and the endotracheal tube is moved between placement of rings to make certain it was not engaged by a suture (Figure 4). Post-operative care typically involves environmental oxygen enhancement as needed, injectable analgesia, intravenous fluids, and supportive care. Anti-tussives, anti-inflammatories, and antibiotics are used on an individual case basis. 
TRACHEAL STENTING The patient is placed in lateral recumbency and a hydrophilic guidewire and marker catheter combination are advanced down the esophagus under fluoroscopic guidance. Under positive pressure ventilation of 20cm H2O, a radiograph is taken and maximal tracheal diameter measurements are extrapolated using the known measurements from the esophageal marker catheter (Figure 5A). The delivery system and constrained stent are advanced down the trachea (Figure 5B) and the delivery sheath is withdrawn under fluoroscopic guidance to observe accurate placement of the stent. Following complete stent deployment, the delivery system is removed and a radiograph is obtained to confirm appropriate stent placement and restored tracheal lumen (Figure 5C). Post-operative care typically involves environmental oxygen enhancement if necessary as well as continued anti-tussive therapy (Hycodan) and anti-inflammatories (Prednisone). Post-operative antibiotics are prescribed if a concurrent airway infection is documented or suspected.  Stone Disease and Urinary Obstruction in Dogs and Cats Are Minimally Invasive Alternatives an Option for your Patient? Allyson C. Berent, DVM, DACVIM This talk will focus on the management of urinary stone disease in dogs and cats, focusing on some of the newer minimally invasive options using interventional endoscopy techniques. Each minimally invasive treatment is explained and each stone type is discussed. It is important to realize which options are available for your patients based on stone location, stone size, stone type, patient size and patient signament. Key Ideas
Clinical Signs: Dependent on stone location 1. Kidney Stones
Interventional Endoscopy (IE) involves the use of endoscopic equipment (with other contemporary imaging modalities, such as fluoroscopy to perform minimally invasive procedures in virtually any part of the body accessed endoscopically (gastrointestinal, biliary, respiratory, urinary tract, etc). Currently, an expanding investigation of the use of some novel techniques in veterinary medicine has been undertaken and its use for the management of urinary stone disease has been vast. Many of these interventional procedures are considered the standard-of-care in human medicine, and are currently being performed in veterinary medicine. The use of these techniques are expanding as these modalities are becoming more widely available. The invasiveness and side-effects associated with some traditional surgical or medical techniques (i.e. surgery of the ureter for ureteral obstructions) makes the use of minimally invasive alternatives using IE appealing. Kidney and Ureter Percutaneous Nephrolithotomy (PCNL) Kidney stones or proximal ureteral obstructions secondary to ureteroliths can result in progressive renal failure, intractable infections, ureteral pain, and bleeding. If the stone is small enough it may pass, however others require surgery to relieve the obstruction or avoid permanent nephron damage. The surgeries to fix this can be prolonged, invasive, and complicated, potentially resulting in significant morbidity. In people, percutaneous nephrolithotomy is considered the standard-of-care for kidney stones too large to be treated with shockwave lithotripsy or retrograde ureteroscopy with laser lithotripsy, and has recently been performed successfully in clinical veterinary cases. This minimally invasive procedure aims to minimize morbidity, and preserve as much renal function as possible while gaining access into the kidney for stone removal. 
ESWL for Nephro/Ureterolithiasis Extracorporeal shock-wave lithotripsy (ESWL) is another minimally invasive alternative for the removal of upper tract calculi in the renal pelvis, or ureters. ESWL uses external shockwaves that is passes through a water medium directed under fluoroscopic guidance in 2 planes. The stone is shocked anywhere from 1000-2500 times at different energy levels to allow for implosion and powdering of a stone. The debris is then left to pass down the ureter into the urinary bladder over a 1-2 week period. This procedure can be performed safely in nephroliths smaller than 2 cm, and ureteroliths. In larger stone burdens (>1 cm) or in the case of ureteral obstruction from stone disease an indwelling double pigtail ureteral stent is placed prior to ESWL to aide in stone debris passage. For stones of larger sizes PCNL is recommended. 
Ureteral stenting is performed for a variety of disorders to divert urine from the renal pelvis into the urinary bladder. This technique can be useful in patients with ureteral obstruction and due to ureteral stones, ureteral or trigonal obstructive cancer, following ureteroscopy, for post-operative ureteral anastomosis, ureteral tears, ureteral spasm, or ureteral inflammation. In addition, the presence of the ureteral stent results in subsequent passive ureteral dilation to permit passage of previously obstructive ureteroliths, or allow passage of the flexible ureteroscope for appropriate ureteral intervention. This technique is currently under investigation for use in veterinary patients with ureterolith-induced obstructions, particularly in cats. Ureteral stenting is also ideal in patients with nephroliths or ureteroliths that are undergoing ESWL to aid in fragment passage following treatment. Stent placement in the ureter for bladder tumors causing obstruction is now being performed routinely. 
Urinary Bladder and Urethra Laser lithotripsy is an innovative technique involving the intracorporeal fragmentation of bladder and urethral stones (and rarely ureteral or kidney stones), which is assessed using a rigid or flexible cystoscope or ureteroscope. The stone is fragmented until the pieces are small enough to be removed normograde through the urethral orifice, either via voiding urohydropropulsion or with the assistance of a stone basket. This process is useful for ureteral, cystic and urethral calculi. All stone types are able to be fragmented using laser lithotripsy. Other urologic applications for laser lithotripsy include incision of urethral and ureteral strictures; ablation of superficial transitional cell carcinoma/prostatic adenocarcinoma within the urethral lumen, laser ablation of urinary polyps. Bladder polyps are common findings in dogs and can be associated with chronic, recurrent urinary tract infections, cystolith formation, and are often misinterpreted for cystic neoplasia. Using cystoscopy and baskets or laser lithotripsy the polyps can be removed without surgical intervention by cauterizing the stalk. 
Percutaneous Cystolithotomy (PCCL) is a new minimally invasive technique, which combines cystic and urethral stone retrieval in any size, sex or species, and is very easy to perform in both cats and dogs. With this technique the need for urethrotomy for stone disease is nearly obsolete and makes all animals a candidate, since lithotripsy has patient and stone size and stone number limitations. This procedure is performed with a small ventral midline skin incision made over the bladder apex until 1 finger is inside the abdomen for bladder identification. A trocar is advanced into the bladder lumen and a rigid cystoscope is advanced through the trocar into the urinary bladder for stone removal with an Endoscopic stone basket. The entire mucosal surface of the bladder and entire urethra are visualized and stones stuck inside the urethra can be removed as well, without the need for urethrotomy. During this procedure the bladder can be explored carefully for polyps or masses and removed with the laser or biopsied if necessary. Once the scope and trocar are removed the incision is closed. Calcium Oxalate stones have become the most common type of stone seen in small animal patients over the past few decades with all ages, breeds and sex's being represented. Terrier dogs are more commonly seen to have stones and clinical signs usually present more commonly in male than female dogs. Some risk factors for calcium oxalate stone formation include: excessive dietary calcium, animal protein, and vitamin D consumption; medications that cause increase calcium elimination from urine (furosemide, prednisone/steroids), vitamin B6 deficiency, hyperparathyroidism, hyperadrenocorticism, and excessive oxalate exretion from excessive dietary intake of oxalate, and ascorbic acid. Treatment
Infection-induced Struvite: Urinary tract infections with urease-producing bacteria (especially Staph/Strep, Proteus, and Ureaplasmas) in dogs. This results in a unique combination of conditions favoring formation of uroliths containing struvite, calcium apatite, calcium phosphate, and calcium carbonate. Sterile Struvite: Dietary and/or metabolic factors may be involved in the genesis of sterile struvite stones, but the mechanism of sterile struvite formation in dogs and cats is unclear. Treatment
Treatment
Treatment
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