Signalment:  

18-year-old, spayed female domestic short hair cat (Felis catus)This cat initially presented for abnormal gait, difficulty climbing stairs, and inappropriate urination for at least a month. The owner also reported an increase in water intake. Physical examination revealed a thin cat with unkempt hair coat, plantar stance, and a gallop heart rhythm. Additionally, abdominal masses were palpated. Fasting clinical chemistry, hematology and urinalysis samples were obtained and analyzed. The erythron was within normal limits, lymphocyte count was mildly low, and there was a mild azotemia. Electrolyte abnormalities included mildly low potassium and minimally increased calcium. Serum glucose was 360 mg/dl (Normal 64-170). Serum T4 and cortisol concentrations were within normal limits. Urinalysis showed trace protein, moderate glucosuria and bacteria, and large numbers of amorphous crystals with a specific gravity of 1.019. Insulin therapy and treatment for the urinary tract infection were initiated.

Ultrasound findings:
Several days after initial presentation, abdominal ultrasonographic evaluation was performed to investigate the abdominal masses. A mass in the location of the left adrenal measured 4.3 by 3.6 cm and a renal cortical mass measuring 3.2 by 2.6 cm were identified within and extending laterally from the right kidney. Due to poor prognosis and response to insulin therapy the animal was euthanized.

Gross Description:  

Abundant adipose tissue was present within the abdominal cavity. The right adrenal was not located; however, the left adrenal was markedly enlarged, multilobulated and pale yellow. The mass expanding from the right renal cortex measured approximately 3 x 3 x 2 cm and was multilobulated, pale pink and firm with several large vessels coursing over the surface. On cut section this discrete mass extended from the cortex and had numerous 1-2 mm diameter cysts containing clear fluid.

Histopathologic Description:

Expanding from and within the cortex, adjacent to the corticomedullary junction of the right kidney, was a moderately cellular, multilobulated mass. Lobules were often defined by bands of mature collagen. Numerous tubular structures lined by a single layer of cuboidal cells were supported by moderate amounts of loose collagenous stroma within the lobules (Fig. 1-1). The tubular lumena often contained a homogeneous eosinophilic material (proteinaceous fluid), and were dilated in several regions within the mass to several millimeters in diameter. The cuboidal cells lining the tubules were small to medium sized with slight anisocytosis and anisokaryosis with occasional crowding. Nuclei were round with finely stippled chromatin and a single medium-sized nucleolus. Mitotic figures rarely occurred and multinucleation was not noted. In several areas small extensions of neoplastic tubules pushed through the expansion capsule partially surrounding the mass. Rare, small foci of neutrophils were present within the supporting stroma and/or tubules. In the surrounding renal tissue, glomeruli had one or more of the following changes: moderately thickened basement membranes, senechia, thickened Bowmans capsule, and/or diffuse or nodular glomerulosclerosis characterized by hyaline thickening of capillary basement membranes and sclerosis of lobules within tufts and diffuse thickening of mesangium. Tubules also had thickened basement membranes and occasionally were dilated containing proteinaceous fluid. Multifocally the interstitium was expanded by accumulations of lymphocytes and plasma cells that were usually perivascularly oriented around medium-sized vessels. The interstitium throughout the section from papilla to capsule was diffusely expanded by increased amounts of mature collagenous stroma.

Morphologic Diagnosis:  

1. Severe, chronic, diffuse, membranous glomerulonephritis with glomerular sclerosis
2. Moderate, chronic, multifocal lymphoplasmacytic interstitial nephritis and pyelitis
3. Renal tubular carcinoma
4. Adrenocortical carcinoma (tissue not included)
5. Pancreatic islet amyloidosis (tissue not included)

Condition:  

Renal adenocarcinoma

Contributor Comment:  

The submitted renal mass was an incidental finding and unrelated to the clinical condition. Renal carcinomas are uncommon in domestic species with an incidence of up to 0.5 percent in cats although there are reports of lower incidences. Most commonly, renal carcinomas are unilateral, and there does not appear to be a sex or breed predilection. Although the morphology of the cells in the renal mass was relatively benign, the size of the mass and presence of lobules of neoplastic cells invading into vessels warrants a diagnosis of carcinoma rather than adenoma.(6,8)

Clinical diagnosis of diabetes mellitus in this animal was complicated by the presence of a well differentiated adrenal tumor (Fig. 1-2). This multilobulated adrenal tumor was densely cellular and composed of large polyhedral cells with abundant finely granular or vacuolated eosinophilic cytoplasm. Nuclei had finely granular chromatin and a single prominent nucleolus. These cells formed irregular trabeculae and nests supported by fine fibrovascular stroma. Mitotic figures were rare and the cells showed moderate anisocytosis and anisokaryosis. Binucleation was common. Multifocally there were areas of necrosis, and single necrotic cells were scattered throughout the mass. The size and histological features of this mass is consistent with a diagnosis of carcinoma.(3) Functional adrenocortical tumors in cats may produce cortisol, progesterone, aldosterone, or estradiol/testosterone. Most cats with hyperadrenocorticism, hyperaldosteronism or hyperprogesteronism are also hyperglycemic.(1,5,10) Unfortunately, many clinical signs for these endocrinopathies are vague and not useful in distinguishing between them. In this case, however, hyperaldosteronism is unlikely due to the mild hypokalemia which is more consistent with hypokalemia associated with an untreated diabetic state. The absence of cutaneous changes (alopecia, dermal fragility) (7) commonly reported in cats with cortisol and progesterone secreting tumors suggests that the mass was also not producing either of these hormones. Additionally, basal cortisol concentrations were within normal limits. Although not associated with hyperglycemia, a report of excessive production of sex steroids in cats increased aggression, thickened skin and vulval hyperplasia, (2) none of which were noted in this animal. Unfortunately due to the euthanasia of this animal prior to complete clinical evaluation, the contribution of the adrenal mass to the clinical condition is unknown. 

In the submitted case, pancreatic islet amyloidosis, a characteristic lesion of feline diabetes and Type 2 diabetes in humans (4,9) and in combination with hyperglycemia, strongly supported diabetes mellitus. This finding was characterized by replacement of islet cells throughout the pancreas by an amorphous, pale eosinophilic material consistent with amyloid (Fig. 1-3). The changes described above in the renal tissue surrounding the mass and urinalysis are also findings commonly identified in cases of chronic diabetes mellitus, including an ascending bacterial pyelitis.(4)

JPC Diagnosis:  

1. Kidney: Renal adenocarcinoma
2. Kidney: Nephritis, interstitial, lymphoplasmacytic, chronic, multifocal, moderate with fibrosis and pyelitis
3. Kidney, glomeruli: Glomerulonephritis, membranous, global, multifocal, moderate with tubular proteinosis

Conference Comment:  

There was extensive discussion in the post-conference session regarding the diagnosis of benign versus malignant renal tumor and acknowledgement that diagnosis may be difficult in some cases. As the contributor mentioned, renal tumors are fairly uncommon in cats, and they have not been extensively studied with a subsequent paucity of published literature. This case was reviewed by the AFIP Department of Genitourinary Pathology, and they agreed with the diagnosis of renal cell carcinoma.

Renal adenomas are rare tumors in domestic animals and are usually an incidental finding at necropsy. Grossly, adenomas are well circumscribed, individual tumors normally located in the cortex of the kidney.(8) Multiple adenomas can occur in dogs and cows. In German Shepherds with dermatofibrosis, multiple renal adenomas may be found as well as renal adenocarcinoma.(8) There are three distinct histologic patterns of renal adenomas: papillary, tubular, or solid.(8)

Renal carcinomas are an uncommon tumor encountered in veterinary medicine, and by the time these tumors manifest clinically in dogs, cats, and horses, they have usually metastasized. Most renal carcinomas are unilateral and often times are located at the pole of the kidney.(8) These tumors historically have been reported to be larger than 2 cm in diameter.(8) Carcinomas have been classified in the histologic subtypes mentioned previously, but the histologic subtype appears to have no bearing on tumor behavior.(8)

References:

1. Ash RA, Harvey AM, Tasker S: Primary hyperaldosteronism in the cat: a series of 13 cases. J Fel Med Surg 7:173-182, 2005
2. Boag AK, Nieger R, Curch DB: Trilostane treatment of bilateral adrenal enlargement and excess sex steroid hormone production in a cat. J Small Anim Pract 45:263-266, 2004
3. Capen CC: Tumors of the endocrine glands. In: Tumors in Domestic Animals, ed. Meuten DJ, 4th ed., pp. 607-696. Iowa State Press, Ames, Iowa, 2002
4. Charles JA: Pancreas. In: Jubb, Kennedy and Palmers Pathology of Domestic Animals, ed. Maxie MR, 5th ed. vol. 2, pp. 389-424. Elsevier Saunders, Philadelphia, Pennsylvania, 2007
5. Gunn-Moore D: Feline endocrinopathies. Vet Clin Small Anim 35:171-210, 2005
6. Henry CJ, et al: Primary renal tumors in cats: 19 cases (1992-1998). J Fel Med Surg 1:165-170, 1999
7. Hoenig M: Feline hyperadrenocorticism where are we now? J Fel Med Surg 4:171-174, 2002
8. Meuten DJ: Tumors of the urinary system. In: Tumors in Domestic Animals, ed Meuten DJ, 4th ed., pp. 509-546. Iowa State Press, Ames, Iowa
9. OBrien TD: Pathogenesis of feline diabetes mellitus. Mol and Cell Endoc 197:213-219, 2002
10. Rossmeisl JH, Scott-Moncrieff JKR, Siems J, Snyder PW, Wells A, Anothayanontha L, Oliver JW: Hyperadrenocorticism and hyperprogesteronemia in a cat with an adrenocortical adenocarcinoma. J Am Anim Hosp Assoc 36:512-517, 2000

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