Perirenal lipoma in a 14-year-old spayed female dog: A rare diagnosis.

Adipose tumors are common in older dogs. Most of these tumors present as benign subcutaneous lipomas; however, intracavitary lipomas, particularly those within the retroperitoneal space, are rarely documented in veterinary medicine. This case report describes a 14-year-old spayed mixed-breed dog with a history of recurrent urinary tract infections, hind-limb weakness, and prior subcutaneous lipomas that was presented because of polyuria, polydipsia, and behavioral changes. Abdominal ultrasound and subsequent computed tomography revealed a left-sided perirenal mass with fat, fluid, and soft-tissue components. Given the mass's location, vascularity, and associated organ displacement, malignant differential diagnoses were prioritized. Exploratory laparotomy with left nephrectomy and adrenalectomy was completed due to the mass's indistinct margins. Histopathology revealed a benign perirenal lipoma with necrosis, inflammation, and abscessation. The embedded adrenal gland was histologically normal. Postoperative azotemia developed but later stabilized. This case represents a rare instance of a benign retroperitoneal lipoma closely associated with renal and adrenal structures, mimicking more aggressive pathology on imaging. To the authors' knowledge, this may be the first reported case of perirenal lipoma in a dog. Although uncommon, intracavitary lipoma should be considered as a differential diagnosis of retroperitoneal masses, to better inform treatment decisions and prognoses. Key clinical message: This case highlights the rare occurrence of a perirenal lipoma in a dog, emphasizing the importance of considering benign adipose tumors in the differential diagnosis of retroperitoneal masses, even when imaging suggests malignancy. Early recognition can guide more informed treatment decisions and improve patient outcomes.