The patient was a 16-year old, 3.8kg, female spayed, Domestic Short Haired cat that presented with a 1-month history of lethargy, polyuria/polydipsia and weight loss. The patient had been diagnosed with hyperthyroidism 12 months previously and was being treated with thiamazole tablets. The patient’s appetite was normal and the owner had not observed any episodes of vomiting or diarrhoea.
On presentation, the patient was responsive but exhibited significant weakness. Rectal temperature was 38.4°C. Body condition score was 3/9 with apparent generalised muscle atrophy. There was no palpable goitre. Oral mucous membranes were pink and moist with a capillary refill time of <2 seconds. A grade 2/6, left-sided systolic cardiac murmur was detected on thoracic auscultation. The patient’s heart rate was 240 beats per minute with no pulse deficits. Her respiratory rate was 32 breaths per minute with no adventitious lung sounds detected, but an increased respiratory effort with a slight abdominal component was observed. On abdominal palpation, a firm, spherical mass was palpable in the cranial to mid-abdomen. The patient’s coat was in poor condition with the presence of significant grease and scale.
Haematology and biochemistry indicated hypernatremia, hypokalaemia, azotaemia with a normal packed cell volume (PCV) and marginally elevated serum creatinine kinase. On urinalysis, specific gravity was 1.017 with the presence of 2+ protein and pH 6.5 on dipstick evaluation. The patient’s blood pressure was 220/130mmHg.
An abdominal ultrasound examination was performed in the conscious patient to further evaluate the palpable mass in the cranial to mid-abdomen. On ultrasonography, the kidneys have an increased cortical echogenicity with poor corticomedullary distinction bilaterally (Image 1). However, the primary finding is a well-defined, spherical mass of mixed echogenicity in the region of the right adrenal gland. This mass measures 2.91 x 3.34 cm (Image 2). This mass does not appear to be invading the caudal vena cava. The left adrenal gland is not visualised. All other abdominal organs have a normal ultrasonographic appearance.
The initial list of possible differential diagnoses for this case included primary hyperaldosteronism due to an adrenocortical carcinoma, phaeochromocytoma, adrenal adenoma and chronic renal failure.
The presumptive diagnosis based on clinical presentation (lethargy, weakness, respiratory distress, polyuria/polydipsia and systemic hypertension), laboratory findings (hypernatremia and hypokalaemia) and abdominal ultrasound appearance of an adrenal mass was primary hyperaldosteronism due to an adrenocortical carcinoma (Conn’s syndrome) with concurrent hyperthyroidism and chronic renal failure.
Further investigation including determination of serum aldosterone and plasma renin concentrations was discussed with the owner. Treatment options including conservative medical management or surgical removal of the adrenal mass (right adrenalectomy) were also discussed with the owner. The owner declined further diagnostics and treatment and opted for euthanasia.
The patient was euthanised and the owner requested a post-mortem examination to be performed to confirm the presumptive diagnosis. The gross and histopathological reports confirmed a diagnosis of right adrenocortical carcinoma.
Image 1- Ultrasound image of the kidneys (open arrows) demonstrating increased cortical echogenicity and poor corticomedullary distinction. A right adrenal mass is also visible (solid arrow).
Image 2 – Ultrasound image of the right adrenal mass with measurements.