Jerry A. Thornhill, DVM, DACVIM
There is an assumed differential diagnostic dilemma of Renomegaly (big kidneys) in cats, encountered by veterinarians in private practice, ER facilities, specialty clinics, and veterinary school teaching hospital settings. The standard thought process separates the anatomically enlarged Renal Structure(s) – noted on abdominal palpation, and confirmed by Abdominal Radiograph application – into Polycystic Kidney Disease (PKD), Renal Lymphoma, Hydronephrosis or Renal Amyloidosis, entities.
The tool in our collective Professional Toolbox for a much needed in-depth anatomical picture of the kidneys, to separate and identify Renomegaly candidates, unequivocally, is the application of an Abdominal Ultrasound (US) – which can be employed by an in-house machine, an assigned teleradiology contract, an ambulatory Radiology service, or a referral appointment to a specialty hospital.
There is, however, another differential diagnosis of Renomegaly cats, to bear in mind – the rarely documented Renomegaly condition of the “Feline Perinephric Pseudocystic Disease” condition. It is represented by progressive accumulation of transudative fluid build-up between the outer cortex of the kidney, and its respective capsule.
The kidney in man and animals is surrounded by a protective fibrous capsule, but unique to the feline species, the cortex (outer rim) of the kidney underneath the capsule is infiltrated with an extensive circulatory capillary network that has the proclivity in elderly cats to become entangled in cortical scar tissue associated the advancement of Chronic Kidney Disease (CKD). Subsequently, the entanglement of fragile capillaries can lead to bruising and leakage of a transudate (plasma ultrafiltrate) into the occupying space between the outer rim of the Kidney and its capsule, lifting the capsule off the surface of the kidney as a well of sieved transudate accumulates. Thus, the name given to the captured fluid accumulation – Feline Perinephric Pseudocystic Disease.
Feline patients being presented to veterinary hospital/clinic venues, with the Pseudocystic disorder (of one or both renal structures), would have grossly palpable Renomegaly on physical examination, accompanied, traditionally, by abdominal discomfort. As outlined above, in the discussion of separation of Renomegaly conditions – confirmation of the Renomegaly condition into Pseudocystic Disease, would be secured by an anatomical integrity study of the renal structures with Abdominal Ultrasound application.
Traditional treatment of the Pseudocystic Disease has been the employment of abdominal surgery, with extirpation (removal) of a major bulk of the capsule, to allow continued and sustained drainage of the sieved transudate from the cortical capillaries into the peritoneal cavity for absorption (Note: the sieved transudate never stops its flow, albeit at a slowed pace – and, the peritoneal membrane is more than capable to handle absorption of the sterile transudate back into the patient’s general circulation).
There is, of late, a new technique, developed by Dr. Mitch Robbins (Chief of Surgery at Veterinary Specialty Center), for snipping a permanent portion of the capsule away from the kidney (a window for transudate drainage) in cats with Pseudocystic Disease, by Laparascopy. This frees the need for invasive abdominal surgery as amelioration for the condition.