Case description: A 5.5-year-old 0.929-kg spayed female domestic ferret (Mustela putorius furo) underwent serial abdominal ultrasonographic and clinicopathologic examinations after multiple renal cysts were detected bilaterally during a routine examination.
Clinical findings: The ferret was apparently healthy at the start of the monitoring period and had no clinical signs for > 20 months. Four months after the initial examination, the largest cyst became increasingly mineralized; 17 months after detection, it had increased in size and become amorphous, and the ferret's plasma BUN concentration was mildly high. Within 21 months after the first visit, a nodule was detectable, and hydronephrosis developed in the kidney with the largest cyst. Findings for fine-needle aspirates from the nodule were consistent with renal carcinoma.
Treatment and outcome: Contrast-enhanced CT revealed severe unilateral nephromegaly with no contrast uptake in the affected ureter. Following surgical removal of the affected kidney, histologic examination identified renal adenocarcinoma replacing the entire renal cortex and medulla. The ferret was euthanized postoperatively because of declining condition. On necropsy, metastasis to a mesenteric lymph node was identified; comorbidities included 2 other neoplasms and acute, severe injury of the contralateral kidney.
Clinical relevance: Neoplastic transformation of a renal cyst was suspected in the ferret of this report on the basis of observed ultrasonographic changes over time and extensive infiltration of the neoplasm throughout the affected kidney. Renal cysts are linked to renal neoplasia in other species, and the findings for this patient supported the need for periodic monitoring of renal cysts in ferrets.