Primary hyperparathyroidism due to a cystic parathyroid adenoma in a cat

Abstract

A 15-year-old neutered female domestic shorthair cat was presented for weight loss, polydipsia/polyuria, and lethargy. A large fluctuant mass was palpated in the ventral right cervical region. Biochemistry results were consistent with primary hyperparathyroidism. Parathyroid hormone level in the fluid was higher to that observed in the plasma, consistent with a cystic parathyroid lesion. Right parathyroidectomy and thyroidectomy were performed without complications. Ionized calcium normalized within a few hours. Histopathology yielded a diagnosis of cystic parathyroid adenoma. Follow-up showed complete recovery of clinical signs and normalization of ionized calcium. This case shows an uncommon presentation of feline primary hyperparathyroidism secondary to a cystic parathyroid adenoma and is, to our knowledge, the first case presented with a large palpable mass in which parathyroid hormone concentration was measured. This report highlights the value of selective hormonal analyses of the cystic fluid to confirm the origin of the cystic lesion pre-operatively.

Keywords: Adenoma; Calcium; Cyst; Hyperparathyroidism; Parathyroid hormone.

Fig. 1.. Photograph of the cat presented with a large mass in the ventral right cervical region.

Fig. 2.. Ventrodorsal radiography of the neck showing a large homogeneous right cervical soft-tissue mass with marked lateral deviation of the cervical trachea to the left.

Fig. 3.. Transverse (A) and sagittal (B) CT images of the cervical region, respectively, before and after IV contrast media administration, showing a well-defined, non-enhancing fluid-filled mass, surrounded by a thin enhancing wall, measuring 6.4 cm craniocaudally and 4.2 cm lateromedially and ventrodorsally, deviating the trachea, esophagus, and surrounding vascular structures to the left. The right lobe of the right thyroid gland was displaced ventrally and caudally and localized along the ventral wall of the mass, in its caudal half (A, arrow). Agglomerated slightly hyperattenuating cellular material was observed in the dependent part of the lumen of the cyst, consistent with a blood clot, likely secondary to the fine-needle aspiration previously performed (B, arrow). No invasion of surrounding structures was observed.

Fig. 4.. Photograph of the mass obtained during surgery. The mass is well-encapsulated and measured 8 cm × 5 cm.

Fig. 5.. Microphotograph of the cystic parathyroid adenoma. Within the severely atrophic parathyroid parenchyma, a 2 cm in diameter encapsulated round cystic tumor with compressive growth was observed. The tumor (arrow) includes a large cyst (C) containing an organizing hematoma. A diffuse atrophy of the right thyroid gland (arrowhead) was observed, consistent with mass compression. Hematoxylin–eosin–saffron stain, bar = 1,000 μm.