Renal cysts are thought to arise as a result of underlying infections (e.g. microabscesses) from ascending infections (e.g. cystitis), as a consequence of tubular obstruction, or from congenital diseases such as renal dysplasia and nodular dermatofibrosis.
Some dogs are asymptomatic and renal cysts may be an incidental finding on ultrasonography or postmortem.
Seriously affected dogs often present with a protracted history of hematuria, polyuria, polydipsia and vomiting. Depending on the cyst size, a palpable mass may be evident in the dorsal abdomen, sometimes with concurrent pain and tenderness in the loin region.
Ultrasonic imaging usually reveals small kidneys with a loss of normal architecture and poor corticomedullary distinction. The cyst often appear as anechoic spaces with sharply demarcated, thin-walled, round structures containing anechoic fluid.
Diagnosis can be made presumptively on ultrasonographic findings of renal contour distortion and presence of hyperechogenic fluid-filled cysts, which may be present unilaterally or bilaterally.
A differential diagnosis would include polycystic kidney disease, renal carcinoma, nephroblastoma, Echinococcus spp infections, renal hypoplasia (Ask-Upmark kidney), X-linked hereditary nephropathy (in Cocker Spaniels), familial juvenile glomerulonephropathy (autosomal-recessive in French Mastiff and Bull Terrier).
Solitary renal cysts are frequently benign and in the majority of instances asymptomatic and do not require treatment. Nevertheless, treatment may be required if abdominal discomfort or pain, hypertension, infection or renal outflow obstruction occur.
Canine renal cysts may be successfully managed in some instances by a single ethanol injection and in severe cases ureteronephrectomy may be considered in unilateral cases where renal tissue is extensively compromised.
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