Surgical removal of a choroid plexus oncocytoma in an adult cat.

An 11-year-old male castrated domestic shorthair cat presented with left central vestibular dysfunction. Magnetic resonance imaging of the brain revealed a large, extra-parenchymal, strongly contrast-enhancing mass at the level of the left cerebellopontine angle and compressing the cerebellum and brainstem. The mass was surgically excised via left rostral and sub-tentorial craniectomies and histopathology revealed an epithelial neoplasm composed of anastomosing cords of neoplastic cells that contained large amounts of finely granular hypereosinophilic cytoplasm and round nuclei. The cytoplasmic granules were variably positive with periodic acid-Schiff and modified Gomori trichrome. Immunohistochemical staining with anti-cytokeratin AE1/AE3 was diffusely positive. Electron microscopy revealed neoplastic cells that were full of electron-dense organelles consistent with mitochondria. This is the first case of a choroid plexus oncocytoma in the central nervous system of any domestic animal species and highlights the role of successful surgical intervention in extra-parenchymal neoplasia in the central nervous system.

Oncocytic carcinoma of the salivary gland in a dog.

A 3-y-old male miniature Dachshund was presented with an ~0.8 cm diameter mass in the right mandibular region. Fourteen months later, the mass was 5 × 4 × 3 cm. Grossly, the mass was encapsulated and was homogeneously gray-white on cut surface. Microscopically, the mass was composed of large, round to polygonal tumor cells that were arranged in solid nests and cords separated by a fibrovascular stroma. Tumor cells had large, round, hypochromatic nuclei containing large prominent nucleoli and abundant eosinophilic cytoplasm containing dark blue granules visible with phosphotungstic acid-hematoxylin stain. Metastasis was observed in the mandibular lymph node. Immunohistochemically, tumor cells were positive for CK AE1/AE3, low-molecular-weight CK (CAM5.2), E-cadherin, mitochondria ATPase beta subunit, and S100, but were negative for vimentin, carcinoembryonic antigen, p63, CK14, CD10, and chromogranin A. Ultrastructurally, tumor cells contained numerous mitochondria. Therefore, the tumor was diagnosed as an oncocytic carcinoma of the mandibular gland.

Canine mammary minute oncocytomas with neuroendocrine differentiation associated with multifocal acinar cell oncocytic metaplasia.

Two solitary and minute tumors of 1 and 1.5 mm diameter were identified by microscopy in the left fourth mammary gland of a 13-year-old female Labrador Retriever dog, in addition to multiple mammary gland tumors. The former tumors were well circumscribed and were composed of small-to-large polyhedral neoplastic oncocytes with finely granular eosinophilic cytoplasm, and were arranged in solid nests separated by fine fibrovascular septa. Scattered lumina of variable sizes containing eosinophilic secretory material were evident. Cellular atypia was minimal, and no mitotic figures were visible. One tumor had several oncocytic cellular foci revealing cellular transition, with perivascular pseudorosettes consisting of columnar epithelial cells surrounding the fine vasculature. Scattered foci of mammary acinar cell hyperplasia showing oncocytic metaplasia were also observed. Immunohistochemically, the cytoplasm of neoplastic cells of the 2 microtumors showed diffuse immunoreactivity to anti-cytokeratin antibody AE1/AE3, and finely granular immunoreactivity for 60-kDa heat shock protein, mitochondrial membrane ATP synthase complex V beta subunit, and chromogranin A. One tumor also had oncocytic cellular foci forming perivascular pseudorosettes showing cellular membrane immunoreactivity for neural cell adhesion molecule. The tumors were negative for smooth muscle actin, neuron-specific enolase, vimentin, desmin, S100, and synaptophysin. Ultrastructural observation confirmed the abundant mitochondria in the cytoplasm of both neoplastic and hyperplastic cells, the former cells also having neuroendocrine granule-like electron-dense bodies. From these results, our case was diagnosed with mammary oncocytomas accompanied by neuroendocrine differentiation. Scattered foci of mammary oncocytosis might be related to the multicentric occurrence of these oncocytomas.

Laryngeal rhabdomyoma in a dog.

A 3-year-old, female spayed Australian Shepherd dog was presented to Veterinary Healthcare Associates in Winter Haven, FL with a history of respiratory stridor, difficulty swallowing, and a change in bark for approximately 3 months. Radiographs revealed a soft tissue mass caudal to the epiglottis. Oral and computerized tomographic (CT) examinations were performed under general anesthesia and revealed a small firm mass in the caudal larynx on the right side. Cytologic evaluation of a fine-needle aspirate of the mass revealed cells consistent with a rhabdomyoma, oncocytoma, or granular cell tumor. Histopathologic interpretation was rhabdomyoma or oncocytoma. Histochemical staining with periodic acid-Schiff was mostly negative with a low number of weakly positive cells and with phosphotungstic acid-hematoxylin was strongly positive with visible cross striations. Tumor cells did not express pancytokeratin AE1/AE3, were strongly immunoreactive for myoglobin and muscle-specific actin, and did not express vimentin except for a low number of weakly immunoreactive cells. These findings confirmed a diagnosis of rhabdomyoma. Primary neoplasia of the larynx is rare, and widely varying types of neoplasms have been documented in this location. Due to the cytologic and histologic similarities between rhabdomyoma, oncocytoma, and granular cell tumor, these neoplasms should be differentiated using histochemical staining and immunohistochemical analysis.

Nasopharyngeal oncocytoma in a cat.

A 5-year-old male neutered Siamese cat was referred because of nasal swelling, nasal discharge, and oral respiration. Computed tomography and necropsy following euthanasia revealed a firm tan mass in the nasopharynx, occluding the nasal passage. Histologically, the nasopharyngeal mass was composed of solid nests, anastomosing cords, and closely packed glands separated by a delicate fibrovascular stroma. Individual neoplastic cells were cylindrical to polyhedral in shape, had distinct cell borders, and contained moderate amounts of finely granular eosinophilic cytoplasm and round to oval nuclei. The cytoplasmic granules were positive on phosphotungstic acid-hematoxylin staining. Immunohistochemically, the neoplastic cells were positive for cytokeratin and negative for chromogranin A, neuron-specific enolase, and vimentin. Ultrastructurally, the neoplastic cells contained numerous mitochondria.

Oncocytoma in the mandibular salivary gland of a cat.

A cat was referred for investigation of a soft tissue mass caudal to the left mandible. Initial investigations suggested a malignant salivary gland tumour, and the mass was removed by extracapsular resection of the mandibular gland. Histopathology showed an oncocytoma within the salivary gland. An oncocytoma is a neoplastic transformation of oncocytes. Oncocytes are cells with a small nucleus and intense eosinophilic granular cytoplasm due to numerous mitochondria, which proliferate during ageing in exocrine and endocrine glandular tissues. Physiological proliferation occurs next to oncocytosis, oncocytoma, and oncocytic carcinoma. This is the first report of an oncocytoma in a feline mandibular salivary gland, and the first report of long-term survival after surgical removal.

Nasal oncocytoma in a domestic shorthair cat.

An oncocytoma was diagnosed in the nasal cavity of a 12-year-old Domestic Shorthair cat who presented with periocular swelling and sneezing. Histologic examination from biopsy material revealed monomorphic sheets, anastomosing cords, tubules, and acini composed of large polygonal to oval cells that contained abundant finely granular eosinophilic cytoplasm. No vascular or lymphatic invasions were noted. Histochemical stains revealed positive staining of tumor cells with periodic acid-Schiff (PAS) (before and after diastase digestion) and phosphotungstic acid-hematoxylin. Immunohistochemical evaluation of the tumor cells demonstrated positive staining for cytokeratin and negative staining for vimentin, desmin, S-100, glial fibrillar acidic protein, and neuronal specific enolase. Ultrastructurally, the tumor cells contained large numbers of mitochondria within their cytoplasm, which confirmed a diagnosis of oncocytoma.

The histology and growth kinetics of canine renal oncocytoma.

A renal oncocytoma was diagnosed in a 10-year-old English springer spaniel with a 5-month history of anorexia, vomiting and weight loss. The tumour, which was localized to the kidney, was treated by simple nephrectomy and the dog made a full recovery. Histologically, the tumour consisted of cells with abundant eosinophilic cytoplasm forming acini and alveolar nests set within a loose fibrovascular stroma. The results of cell kinetic studies (AgNOR score 2.68, PCNA index 5.2%) were comparable with findings reported for benign human renal tumours. This appears to be the first reported case of renal oncocytoma in a dog.

Bilateral renal oncocytoma in a Greyhound dog.

A bilateral, locally invasive renal oncocytoma was diagnosed in a 10-year-old spayed female Greyhound dog. The diagnosis was based on positive staining of the tumor with the periodic acid-Schiff reaction prior to diastase treatment, on the immunohistochemical expression of cytoplasmic cytokeratin, and on the prominence of mitochondria in the tumor cells.

Imprint and brush cytology in the diagnosis of canine intranasal tumours.

Fifty-four dogs with nasal tumours were included in this study. Based on histopathology 52 tumours were malignant (36 epithelial and 16 mesenchymal) and two were benign (one oncocytoma and one pleiomorphic adenoma). Malignancy was significantly more frequently diagnosed by imprint cytology (81 per cent of the cases) than by brush cytology (56 per cent). Brush cytology was a significantly more sensitive technique in epithelial than in mesenchymal tumours, while the sensitivity of imprint cytology was not affected by the histological type. Brush cytology determined an epithelial origin in 88 per cent of epithelial tumours, and imprint cytology in 90 per cent. In mesenchymal tumours, the scores were significantly lower, the histological type being determined in only 20 per cent and 50 per cent, using brush and imprint cytology, respectively.