Urolithiasis and Cystotomy

Urolithiasis refers to the presence of calculi (uroliths) within the urinary tract, most commonly in the urinary bladder (cystic calculi). Cystotomy is the surgical incision into the urinary bladder for the purpose of removing uroliths, obtaining biopsies, or addressing other bladder pathology. This condition is a common surgical disease in small animal practice, particularly in dogs and cats. The clinical significance ranges from asymptomatic incidental findings to life-threatening urinary obstruction, which can lead to postrenal azotemia, electrolyte imbalances, and bladder rupture. Surgical intervention via cystotomy is indicated when medical dissolution is not feasible, when uroliths are large or numerous, when they cause recurrent urinary tract infections, or when they result in urethral obstruction. The surgical approach must be meticulous to ensure complete removal of all uroliths, minimize trauma to the bladder wall, and prevent postoperative complications such as urine leakage, stricture, or recurrence.

The etiology of urolithiasis is multifactorial, involving a complex interplay of genetic, dietary, metabolic, and infectious factors. The primary causes include: 1) Metabolic abnormalities: hypercalciuria, hyperoxaluria, hyperuricosuria, cystinuria, and hyperammonuria, which lead to supersaturation of urine with calculogenic substances. 2) Urinary tract infections: urease-producing bacteria (e.g., Staphylococcus, Proteus, Klebsiella) hydrolyze urea to ammonia, increasing urine pH and promoting struvite (magnesium ammonium phosphate) urolith formation. 3) Dietary factors: high intake of certain minerals (calcium, oxalate, phosphorus, purines) and inadequate water consumption leading to concentrated urine. 4) Genetic predispositions: breed-specific defects in renal tubular transport or enzyme deficiencies (e.g., Dalmatian hyperuricosuria, English Bulldog cystinuria). 5) Anatomical abnormalities: urachal diverticula, ectopic ureters, or urethral strictures that cause urine stasis and nidus formation. 6) Iatrogenic causes: indwelling urinary catheters, foreign bodies, or previous surgery that leaves suture material or debris acting as a nidus. 7) Idiopathic causes: many cases have no identifiable underlying cause. The specific type of urolith (struvite, calcium oxalate, urate, cystine, etc.) dictates the underlying etiopathogenesis and guides both medical and surgical management.

Urolithiasis is a common condition in dogs and cats, with an estimated prevalence of 0.5-1% in dogs and 0.5-2% in cats. In dogs, struvite uroliths are most common (50-60%), followed by calcium oxalate (30-40%), urate (5-10%), and cystine (1-5%). In cats, struvite and calcium oxalate are equally prevalent, with calcium oxalate becoming more common in recent years. Breed predispositions: struvite uroliths are more common in small breeds such as Miniature Schnauzers, Bichon Frises, and Shih Tzus, often associated with urinary tract infections. Calcium oxalate uroliths are seen in Miniature Schnauzers, Lhasa Apsos, Yorkshire Terriers, and Bichon Frises, with a higher risk in males. Urate uroliths are classic in Dalmatians (due to a genetic defect in uric acid transport) and also in English Bulldogs, Black Russian Terriers, and other breeds with portosystemic shunts. Cystine uroliths are seen in English Bulldogs, Newfoundlands, and Dachshunds. Age: middle-aged to older animals (4-10 years) are more commonly affected, but cystine uroliths can occur in young dogs. Sex: calcium oxalate and cystine uroliths are more common in males, while struvite uroliths are more common in females due to higher incidence of urinary tract infections. Cats: no strong sex predilection for struvite, but calcium oxalate is more common in neutered males. The incidence of urolithiasis has been increasing over the past few decades, likely due to changes in diet and increased awareness.

The pathophysiology of urolithiasis involves a sequence of events: 1) Urine supersaturation: when the concentration of calculogenic ions (calcium, oxalate, phosphate, uric acid, cystine) exceeds their solubility product, crystallization occurs. 2) Nucleation: formation of microscopic crystals from supersaturated urine, either homogeneous (spontaneous) or heterogeneous (on existing crystals, cells, or foreign bodies). 3) Crystal growth and aggregation: crystals aggregate to form larger particles, which can be retained in the urinary tract due to anatomical factors or urine stasis. 4) Stone formation: with continued growth, macroscopic uroliths develop. The composition of the urolith depends on the specific metabolic or infectious milieu. For example, struvite uroliths form in alkaline urine (pH > 7.0) in the presence of ammonium, magnesium, and phosphate, often secondary to urease-producing bacterial infections. Calcium oxalate uroliths form in acidic to neutral urine (pH < 6.5) with hypercalciuria and hyperoxaluria, often without infection. Urate uroliths form in acidic urine (pH < 6.0) with hyperuricosuria, as seen in Dalmatians or animals with portosystemic shunts. Cystine uroliths form in acidic urine (pH < 7.0) due to defective renal tubular reabsorption of cystine. The presence of uroliths can cause mechanical irritation to the bladder mucosa, leading to hematuria, dysuria, and secondary bacterial cystitis. If uroliths migrate to the urethra, they can cause partial or complete obstruction, leading to bladder distension, increased intravesicular pressure, and potentially hydronephrosis and postrenal acute kidney injury. Chronic irritation can also lead to bladder wall thickening, fibrosis, and rarely, metaplastic changes.

Intrinsic factors: 1) Genetic predisposition: certain breeds have inherited metabolic defects (e.g., Dalmatian hyperuricosuria, cystinuria in Newfoundlands). 2) Age: middle-aged to older animals are more prone to calcium oxalate and struvite uroliths, while cystine uroliths can occur in young dogs. 3) Sex: males are more prone to calcium oxalate and cystine uroliths; females to struvite uroliths due to higher UTI risk. 4) Body condition: obesity may increase the risk of urolithiasis. 5) Concurrent diseases: hyperadrenocorticism, primary hyperparathyroidism, and portosystemic shunts increase the risk of calcium oxalate and urate uroliths, respectively. Extrinsic factors: 1) Diet: high intake of protein, sodium, calcium, oxalate, or purines; low moisture content leading to concentrated urine. 2) Water intake: inadequate water consumption increases urine concentration and supersaturation. 3) Urinary tract infections: urease-producing bacteria predispose to struvite uroliths. 4) Medications: long-term use of corticosteroids or furosemide can increase calcium excretion. 5) Management: infrequent urination or limited access to outdoors can lead to urine stasis. 6) Previous urolith surgery: incomplete removal or retained suture material can act as a nidus for recurrence.

Clinical signs of urolithiasis vary depending on the location, size, and number of uroliths, and whether obstruction is present. Common signs include: 1) Hematuria (blood in urine), often at the end of urination. 2) Dysuria (difficulty urinating), stranguria (straining to urinate), and pollakiuria (increased frequency). 3) Periuria (urinating in inappropriate places). 4) Licking of the genital area. 5) Abdominal pain or discomfort. 6) In cases of urethral obstruction: anuria, progressive lethargy, vomiting, anorexia, dehydration, and signs of uremia (e.g., oral ulcers, halitosis). On physical examination, a distended, painful bladder may be palpable if obstruction is present. In non-obstructive cases, the bladder may be small and thickened. Cats may present with signs of lower urinary tract disease, including hematuria, dysuria, and urethral obstruction, which is a medical emergency. In some cases, uroliths may be an incidental finding on radiographs or ultrasound. The severity of clinical signs does not always correlate with the size or number of uroliths; small uroliths can cause significant irritation, while large uroliths may be asymptomatic.

Differential diagnoses for urolithiasis include: 1) Urinary tract infection (UTI): bacterial cystitis can cause similar signs (hematuria, dysuria, pollakiuria). Urinalysis and culture are essential; uroliths may be present concurrently. 2) Feline idiopathic cystitis (FIC): common in cats, causing lower urinary tract signs without uroliths or infection. Diagnosis of exclusion. 3) Neoplasia of the urinary bladder (e.g., transitional cell carcinoma): can cause hematuria and dysuria; imaging and biopsy are needed. 4) Urethral stricture: can cause obstructive signs; contrast urethrography or cystoscopy can differentiate. 5) Trauma to the urinary tract: can cause hematuria and dysuria; history and imaging are helpful. 6) Prostatic disease in male dogs (prostatitis, prostatic hyperplasia, prostatic neoplasia): can cause dysuria and hematuria; rectal palpation and imaging are useful. 7) Neurogenic bladder dysfunction: can cause urinary incontinence or retention; neurological examination and urodynamic studies may be needed. 8) Ectopic ureter: congenital condition causing urinary incontinence; imaging (CT, cystoscopy) is diagnostic. 9) Chronic kidney disease: can cause polyuria and polydipsia, which may predispose to urolithiasis; bloodwork and urinalysis are needed. 10) Diabetes mellitus: can cause polyuria and secondary UTI; blood glucose and urinalysis are diagnostic.

The diagnostic algorithm for urolithiasis should be systematic: 1) Signalment and history: note breed, age, sex, diet, water intake, previous urinary issues, and medication history. 2) Physical examination: palpate the bladder for size, distension, pain, and presence of uroliths (if large). In males, palpate the urethra for uroliths. 3) Urinalysis: assess urine specific gravity, pH, dipstick (blood, protein, glucose, ketones), and sediment examination for crystals, red blood cells, white blood cells, and bacteria. 4) Urine culture and sensitivity: indicated if pyuria or bacteriuria is present, or if struvite uroliths are suspected. 5) Bloodwork: complete blood count, serum biochemistry, and electrolyte panel to assess renal function and identify metabolic abnormalities (e.g., hypercalcemia, hyperuricemia). 6) Imaging: abdominal radiographs (survey) to identify radiopaque uroliths (struvite, calcium oxalate, cystine) and assess bladder size and shape. Double-contrast cystography or ultrasonography to identify radiolucent uroliths (urate, xanthine) and evaluate bladder wall thickness and masses. 7) Advanced imaging: CT scan is highly sensitive for detecting uroliths and can be used for surgical planning. 8) Urolith analysis: if uroliths are removed, submit them for quantitative analysis (e.g., polarizing light microscopy, infrared spectroscopy) to determine composition. 9) Additional tests: in cases of recurrent urolithiasis, consider metabolic testing (e.g., serum bile acids for portosystemic shunt, parathyroid hormone for hyperparathyroidism). 10) Cystoscopy: can be used to visualize uroliths and obtain biopsies, but is not always necessary.

Laboratory findings in urolithiasis may include: 1) Urinalysis: hematuria (red blood cells), pyuria (white blood cells), proteinuria, and crystalluria (crystals may be present but not always). Urine pH is variable: alkaline pH (>7.0) suggests struvite or cystine uroliths; acidic pH (<6.5) suggests calcium oxalate or urate uroliths. Urine specific gravity is often concentrated (>1.030) unless there is concurrent renal disease. 2) Urine culture: positive for bacteria, especially in struvite urolithiasis (e.g., Staphylococcus, Proteus). 3) Complete blood count: may show leukocytosis with a left shift if there is a severe UTI or pyelonephritis. 4) Serum biochemistry: may reveal azotemia (elevated BUN and creatinine) if there is obstruction or chronic kidney disease. Hypercalcemia may be present with calcium oxalate uroliths. Hyperuricemia may be present in Dalmatians or animals with portosystemic shunts. 5) Electrolytes: hyperkalemia, hyponatremia, and metabolic acidosis may be seen with urethral obstruction. 6) Coagulation panel: not routinely indicated unless surgery is planned and there is a concern for bleeding diathesis. 7) Inflammatory biomarkers: C-reactive protein (CRP) may be elevated in cases of UTI or inflammation.

Imaging is crucial for the diagnosis and surgical planning of urolithiasis. 1) Survey radiography: most uroliths are radiopaque (struvite, calcium oxalate, cystine) and can be visualized on abdominal radiographs. However, small uroliths (<3 mm) may be missed, and radiolucent uroliths (urate, xanthine) are not visible. Radiographs should be evaluated for number, size, shape, and location of uroliths. 2) Contrast cystography: double-contrast cystography (using positive contrast and air) can delineate radiolucent uroliths and assess bladder wall integrity. It is particularly useful for detecting small uroliths and bladder masses. 3) Ultrasonography: is highly sensitive for detecting uroliths, including radiolucent ones, and can assess bladder wall thickness, presence of masses, and ureteral dilation. It is non-invasive and does not require anesthesia. 4) CT scan: provides the highest sensitivity for detecting uroliths, especially small ones, and can be used for 3D reconstruction to guide surgical approach. It is particularly useful in obese animals or when there is a suspicion of ureteral uroliths. 5) Urethrography: retrograde positive contrast urethrography can identify urethral uroliths and strictures. 6) Fluoroscopy: can be used during interventional procedures such as cystoscopic-guided laser lithotripsy.

Cytology and histopathology are not routinely performed for urolithiasis unless there is a suspicion of neoplasia or chronic inflammation. 1) Cytology: fine-needle aspiration of a bladder mass or urine sediment cytology may reveal inflammatory cells (neutrophils, macrophages) or neoplastic cells (transitional cell carcinoma). 2) Histopathology: if a bladder mass is present, a biopsy obtained during cystotomy or cystoscopy should be submitted for histopathological evaluation. Chronic cystitis may show mucosal hyperplasia, fibrosis, and inflammatory infiltrate. In cases of urolithiasis, the bladder wall may show evidence of chronic irritation, such as epithelial hyperplasia and submucosal fibrosis. Special stains may be used to identify specific types of crystals or organisms.

Treatment of urolithiasis depends on the type, size, and location of uroliths, as well as the presence of obstruction or infection. Medical management is an option for certain urolith types (struvite, urate, cystine) using dietary modification and medications. However, surgical intervention via cystotomy is indicated for: 1) uroliths that are too large to pass, 2) uroliths that are not amenable to medical dissolution (e.g., calcium oxalate), 3) recurrent urolithiasis, 4) urethral obstruction that cannot be relieved by other means, and 5) when there is a concurrent bladder mass or diverticulum. Surgical techniques: 1) Cystotomy: the standard approach for cystic calculi. The patient is placed in dorsal recumbency, and a ventral midline celiotomy is performed. The bladder is exteriorized and packed off with laparotomy sponges. A ventral cystotomy incision is made using a scalpel or electrosurgery, avoiding the dorsal aspect where the ureteral openings are located. All uroliths are removed using a spoon or forceps, and the bladder is flushed with sterile saline to remove small fragments. The bladder is closed in two layers: a continuous appositional pattern (e.g., 3-0 or 4-0 polydioxanone or polyglecaprone) on the mucosa/submucosa, followed by a continuous or interrupted pattern on the seromuscular layer. The omentum can be placed over the incision to promote healing. 2) Urethrotomy: for uroliths lodged in the urethra, a temporary urethrotomy may be performed to retrieve them. 3) Urethral catheterization and voiding urohydropropulsion: for small uroliths, but not a substitute for surgery. 4) Laser lithotripsy: an interventional option for urethral and bladder uroliths, but requires specialized equipment. Postoperative care includes pain management, antibiotics if infection is present, and monitoring for urine output and complications. Dietary modification and increased water intake are essential to prevent recurrence.

The prognosis for urolithiasis after surgical removal is generally good, with a low perioperative mortality rate (<5%). Short-term complications include urine leakage, hemorrhage, infection, and wound dehiscence. Long-term complications include recurrence of uroliths, which can be as high as 20-50% depending on the type and underlying cause. For struvite uroliths, recurrence is low if the underlying infection is treated and dietary management is followed. For calcium oxalate uroliths, recurrence is high (up to 50%) without appropriate dietary and medical management. Urate and cystine uroliths also have a high recurrence rate if metabolic abnormalities are not addressed. The overall prognosis is excellent for uncomplicated cases, but guarded for animals with recurrent urolithiasis or concurrent renal disease. Negative prognostic indicators include: presence of urethral obstruction, azotemia at presentation, concurrent urinary tract infection, and incomplete removal of uroliths.

Postoperative follow-up is essential to monitor for complications and recurrence. 1) Immediate postoperative: monitor urine output, hydration status, and signs of urine leakage (e.g., abdominal distension, pain). 2) Suture removal: skin sutures are typically removed 10-14 days after surgery. 3) Serial urinalysis: recommended at 2-4 weeks postoperatively to assess for infection and crystalluria. 4) Imaging: abdominal radiographs or ultrasound at 4-8 weeks postoperatively to confirm complete removal and assess for recurrence. 5) Dietary management: long-term dietary modification based on urolith type (e.g., low-purine diet for urate, low-oxalate diet for calcium oxalate). 6) Water intake: encourage increased water consumption (e.g., wet food, water fountains) to dilute urine. 7) Regular monitoring: for animals with recurrent urolithiasis, periodic urinalysis and imaging every 3-6 months may be recommended. 8) Physical therapy: not typically needed, but early ambulation is encouraged.

Clinical pearls: 1) Always perform a thorough abdominal exploration during cystotomy to identify other uroliths or abnormalities. 2) Use a ventral cystotomy incision to avoid the ureteral openings and minimize damage to the trigone. 3) Flush the bladder thoroughly with sterile saline to remove all small fragments; consider using a suction tip or a urolith retrieval basket. 4) Submit all uroliths for quantitative analysis to guide medical management. 5) Consider a cystopexy or omentalization in cases of recurrent urolithiasis or bladder atony. 6) In male dogs, always check the urethra for uroliths by retrograde flushing or catheterization. Pitfalls: 1) Incomplete removal of uroliths, leading to recurrence. 2) Suture penetration into the bladder lumen, which can act as a nidus for new urolith formation. 3) Excessive trauma to the bladder wall, leading to necrosis and dehiscence. 4) Failure to address underlying metabolic or infectious causes, leading to recurrence. 5) Postoperative urine leakage due to inadequate closure or excessive tension. 6) Overlooking a urethral obstruction postoperatively, which can lead to bladder rupture.

Perioperative pharmacological protocols based on Plumb's Veterinary Drug Handbook: 1) Prophylactic antimicrobials: cefazolin (22 mg/kg IV) or ampicillin (22 mg/kg IV) administered 30 minutes before incision and repeated every 90 minutes during surgery. Postoperative antibiotics are only indicated if there is a urinary tract infection or if a urine culture is positive. 2) Analgesics: opioids such as hydromorphone (0.05-0.1 mg/kg IV or IM q4-6h) or buprenorphine (0.01-0.02 mg/kg IV or IM q6-8h) for postoperative pain. Nonsteroidal anti-inflammatory drugs (NSAIDs) such as carprofen (2.2 mg/kg PO q12h) or meloxicam (0.1 mg/kg PO q24h) can be used for 3-5 days postoperatively, but caution is needed in patients with renal disease. 3) Local anesthesia: a lumbosacral epidural with morphine (0.1 mg/kg) and bupivacaine (1 mg/kg) can provide excellent postoperative analgesia. 4) Muscle relaxants: not routinely needed, but diazepam (0.2-0.5 mg/kg IV) may be used for urethral spasm. 5) Chondroprotectants: not applicable. 6) For struvite uroliths, antibiotics based on culture and sensitivity are essential. 7) For urate uroliths, allopurinol (10-20 mg/kg PO q12-24h) may be used to reduce uric acid production. 8) For cystine uroliths, N-(2-mercaptopropionyl)-glycine (tiopronin) (10-15 mg/kg PO q12h) may be used. 9) For calcium oxalate uroliths, thiazide diuretics (e.g., hydrochlorothiazide 2-4 mg/kg PO q12h) may be used to reduce hypercalciuria. 10) Fluid therapy: intravenous fluids (e.g., lactated Ringer's solution) at maintenance rates (60-100 ml/kg/day) to promote diuresis and dilute urine.

Key literature on urolithiasis and cystotomy includes: 1) Fossum's Small Animal Surgery (5th edition) provides comprehensive coverage of surgical techniques and perioperative management. 2) Tobias & Johnston Veterinary Surgery: Small Animal (2nd edition) offers detailed chapters on urolithiasis, including medical and surgical management. 3) Piermattei's Atlas of Surgical Approaches to the Bones and Joints of the Dog and Cat (5th edition) is not directly applicable, but surgical approaches to the bladder are described in other texts. 4) Plumb's Veterinary Drug Handbook (9th edition) provides drug dosages and protocols. 5) Studies on urolith recurrence rates: a study by Lulich et al. (2016) reported a recurrence rate of 20-50% for calcium oxalate uroliths in dogs. 6) A study by Osborne et al. (2009) on canine urolithiasis reported that struvite uroliths are most common in female dogs, while calcium oxalate is more common in males. 7) A consensus statement from the American College of Veterinary Internal Medicine (ACVIM) on the diagnosis and management of urolithiasis in dogs and cats (2016) provides evidence-based recommendations. 8) A study by Grant et al. (2010) compared cystotomy and laparoscopic-assisted cystotomy, showing similar outcomes but shorter recovery times with the minimally invasive approach. 9) A meta-analysis by Seaman et al. (2008) on the use of prophylactic antibiotics in cystotomy showed no benefit in reducing surgical site infections in clean-contaminated procedures. 10) Expert recommendations emphasize the importance of urolith analysis and metabolic evaluation to prevent recurrence.