Partial parotid sialoadenectomy in a horse with parotid ductal carcinoma: Surgical description and case report.

OBJECTIVES: To describe the surgical findings, histopathological features, and long-term outcome for a horse with parotid salivary carcinoma. STUDY DESIGN: Case report ANIMALS: Twelve year old American Quarter Horse gelding. METHODS: The gelding was presented for a 10 × 10 cm swelling below the base of the right ear. Ultrasonographic examination revealed a mass involving the right parotid salivary gland. Incisional biopsy was consistent with parotid carcinoma. The tumor was marginally excised. The lateral wall of the guttural pouch was excised with the mass and was reconstructed with a porcine small intestinal submucosal (SIS) sheet. Cisplatin beads were implanted in the wound bed prior to closure. Firocoxib (0.1 mg/kg orally, daily, every 24 h) treatment was initiated. RESULTS: Postoperative complications included right-sided facial nerve paralysis, difficulty with deglutition of fibrous feeds, and surgical site dehiscence. Wound healing was achieved by second intention. Partial improvement in nerve function was observed within the first 6 months. At 12 months postparotidectomy, no sign of tumor reoccurrence or metastatic disease was present, and the gelding returned to work. CONCLUSION: Partial parotid sialoadenectomy was performed with a favorable long-term outcome. Regional anatomic knowledge is crucial.

The use of methylene blue to assist with parotid sialadenectomy in dogs.

INTRODUCTION: There is an important morbidity associated with parotidectomy. The most commonly reported permanent complication is facial nerve injury. Methylene blue staining has been used as an intra-operative tool to improve tissue visualisation and preserve facial nerve integrity. OBJECTIVES: To describe the functionality and feasibility of the use of methylene blue for parotidectomy in dogs. MATERIALS AND METHODS: Retrospective study included seven client-owned dogs that underwent parotidectomy after injection of methylene blue from 2016 to 2019 in a referral centre. Cross-sectional imaging was used to confirm parotid gland surgical disease and for staging purposes. All dogs underwent parotid resection and removal of the parotid duct after injection of methylene blue. Methylene blue was either administered via cannulation of the parotid duct or directly injected into the abnormal gland. RESULTS: In all cases, the gland stained dark blue within seconds without any evident leakage. Complete parotid gland resection and removal of the parotid duct was achieved successfully in all dogs with a mean surgical time of 97 minutes. Subjectively, the staining was useful to identify innervation outside the coloured gland and facilitated dissection. No complications, including facial nerve injury, were recorded. CLINICAL SIGNIFICANCE: Methylene blue staining for complete parotidectomy was feasible, rapid and easy in these dogs. It can be used as an indirect facial nerve identification technique, and can therefore facilitate dissection and possibly reduce the incidence of post-operative facial nerve paralysis.

Malignant Myoepithelioma of the Parotid Gland in a Rat.

Myoepitheliomas of the salivary glands have been described in laboratory mice, but not in rats. A 20-week-old Wistar (Han) female rat developed a white to grey firm mass at the left side of the neck. Histologically, the mass was unencapsulated and infiltrated the adjacent tissue. The tumour parenchyma was cell rich without acinar or tubular architecture. The tumour showed a palisading basal cell pattern adjacent to blood vessels. There were areas of necrosis filled with cellular debris. The tumour cells showed strong immunohistochemical labelling for pan-cytokeratin types I and II (AE1/AE3), pan-cytokeratin (cytokeratins 1, 5, 6 and 8), cytokeratin 5, cytokeratin 14, vimentin and podoplanin, and only very slight positivity for cytokeratin 8 in small areas. There was no expression of smooth muscle actin. Based on the histological appearance and the immunohistochemistry, the tumour was diagnosed as a malignant myoepithelioma of the parotid gland originating from the parotid duct.

Epithelial-Myoepithelial Carcinoma in a Canine Salivary Gland.

A 7-year-old male cavalier King Charles spaniel was presented with a cervical subcutaneous mass. The mass had a multilobular growth pattern and each individual lobule contained ductal epithelial cells and myoepithelial cells surrounding the ductal cells. Immunohistochemically, the ductal epithelial cells were positive for cytokeratin (CK) 7 and CAM5.2 and the myoepithelial cells were positive for α-smooth muscle actin and p63. Both types of cells were positive for CK14, a myoepithelial cell marker. Ultrastructurally, the ductal epithelial cells were attached by desmosomes and contained abundant intracytoplasmic tonofilaments. Some ductal epithelial cells contained myofilaments characteristic of myoepithelial cells. Based on these findings, a diagnosis of epithelial-myoepithelial carcinoma was made. It is presumed that the tumour originated from an intercalated duct in a parotid salivary gland.

PAROTID CARCINOMA IN A FREE-RANGING CALIFORNIA SEA LION ( ZALOPHUS CALIFORNIANUS).

A free-ranging juvenile California sea lion ( Zalophus californianus) stranded on the coast of Vancouver, British Columbia, with signs of lethargy and emaciation in April 2016. An asymmetrical skull with a prominent superficial cervical lymph node was found on initial assessment. Fine-needle aspirates and biopsies of the lymph node were consistent with neoplasia and the animal was humanely euthanized and presented for necropsy. A metastatic parotid gland adenocarcinoma was diagnosed with regional lymph node and pulmonary metastases. Local invasion of contiguous skeletal muscle, bone, ear, and tonsils was extensive and likely accounted for the unilateral craniofacial deformity. Neoplasia of nonurogenital origin in juvenile California sea lions are reported infrequently. This is the first case of a parotid carcinoma in a California sea lion.

Parotid Salivary Gland Basal Cell Adenocarcinoma in a Big-eared Opossum (Didelphis aurita).

The opossum (family Didelphidae) is a marsupial endemic to the Americas. Apart from the South American short-tailed opossum (Monodelphis domestica) and the Virginia opossum (Didelphis virginiana), there is considerable lack of knowledge about the health and diseases of most opossum species. Among these, the big-eared opossum (Didelphis aurita) is found in Argentina, Brazil and Paraguay. Natural and experimental studies have shown this species to be susceptible to infectious agents with zoonotic potential and the animals may play a role in transmission of such agents. However, neoplasia appears to be uncommon in this species. We describe the gross, microscopical and immunohistochemical features of a parotid salivary gland basal cell adenocarcinoma in a free-living big-eared opossum. This case represents the first report of salivary gland neoplasia in opossums.

Primary intraparotid peripheral nerve sheath tumour with characteristics of benign schwannoma in a horse.

Schwannomas arising in the parotid gland are rare in man and are not documented in domestic animals. This report describes the clinical, morphological and immunohistochemical findings of a benign schwannoma in the parotid gland of a 12-year-old warmblood gelding. A slow-growing mass was surgically excised from the parotid gland and did not recur within the following 6 months. The tumour was well circumscribed and was composed of densely packed spindle cells partly arranged in an Antoni A pattern and intermixed with hypocellular areas resembling the Antoni B pattern. Tumour cells expressed vimentin, S100 protein, glial fibrillary acidic protein and variably neuron-specific enolase. Less than 5% of the neoplastic cells were immunolabelled with the proliferation marker Ki67. Although malignant melanomas frequently involve the parotid gland in horses, schwannomas should be included in the differential diagnosis of parotid masses.

Adenocarcinoma of the parotid salivary gland in a cow.

A 6-year-old Girolando dairy cow was presented for evaluation of a large subcutaneous facial mass. Fine-needle aspirates of the mass contained many neoplastic cells with high nuclear:cytoplasmic ratios arranged in sheets and loosely cohesive clusters with streaming erythrocytes and neutrophils in the background. Neoplastic cells were 13-25 µm in diameter and were round to cuboidal with variably distinct borders. Based on the signalment, anatomic location, and cytologic findings, differential diagnoses included salivary adenocarcinoma, squamous cell carcinoma, and mucoepidermoid carcinoma. The cow was euthanized and a necropsy was performed. The primary neoplasm arose from the left parotid salivary gland and meastatic tumor was found in the regional lymph nodes and lung. Histologically, the tumor was composed of anastomosing and irregular solid islets surrounded by scant stroma. Cells were negative for periodic acid-Schiff (PAS), PAS-diastase, and Alcian blue pH 2.5 stains, used to detect mucin. On immunohistochemical analysis, neoplastic luminal salivary gland cells expressed cytokeratin, but not S100, α-smooth muscle actin, or vimentin. Peripheral cells of neoplastic islets were immunoreactive for p63. The final diagnosis was nonsecretory adenocarcinoma of the parotid salivary gland.

Pleomorphic adenoma of the salivary gland in two dogs.

Pleomorphic adenomas of the salivary gland were diagnosed in two dogs. The tumours were single, firm and well circumscribed, with a smooth cut surface. Metastatic tumours were not detected. Histopathological examination revealed that the tumours contained multiple cysts lined with luminal epithelial cells and myoepithelial cells, and mucinous, myxochondroid and cartilaginous tissues. Immunohistochemical examination demonstrated labelling of luminal epithelial cells and myoepithelial cells, and mucinous, myxochondroid and cartilaginous tissues with antibodies to cytokeratin LU-5, AE1/AE3, CK-14, CALP, a-SMA, vimentin, GFAP, and S-100. Labelling for GFAP indicated stromal transformation into myxoid and chondroid tissues.

Parotid gland papillary cystadenocarcinoma in a Fischer 344 rat.

A spontaneous parotid gland tumor with histomorphologic features characteristic of cystic and papillary growth was found in a 72-week-old F344 rat. The tumor had a prominent cystic appearance and invasive growth into the dermis beyond the muscular layer of the skin. The cyst walls were lined by a single layer of cuboidal to tall columnar epithelium with prominent papillary projections continuous with the cyst lining. The tumor cells had mucoid, pale cytoplasm and medium to large nuclei. The myoepithelium did not appear to be associated with the tumor cysts and the papillae. Atrophic parotid gland tissues were seen between cysts and in the periphery of the cystic lesions. In light of these findings, the tumor was diagnosed as papillary cystadenocarcinoma of parotid gland; this is the first description of a salivary gland papillary cystadenocarcinoma in a rat.

Poorly differentiated carcinoma of the parotid gland in a six-week-old Sprague-Dawley rat.

A poorly differentiated spontaneous tumor was found in the parotid gland region of a 6-wk-old female Sprague-Dawley rat. The tumor consisted of undifferentiated cells forming dense clusters, well-defined nests, or compact sheets. In some areas, spindle-shaped cells were arranged in a fascicular fashion. Neither ductular nor acinar structures were seen. No keratinization was observed, either. Mitotic figures were frequent. All neoplastic cells were immunoreactive for pankeratin but negative for vimentin, alpha-smooth muscle actin and S-100 protein. Ultrastructurally, the tumor cells were characterized by desmosome-like junctional complexes, poorly developed cytoplasmic organelles, and microvilli-like cytoplasmic processes. Based on these findings and its anatomical location, the present tumor was diagnosed as a poorly differentiated carcinoma of the parotid gland.

T-cell-rich B-cell lymphoma in a cat.

T-cell-rich B-cell lymphoma is a neoplasm recognized in humans in which a neoplastic proliferation of large B lymphocytes is present amid a background of reactive T lymphocytes. A 13-year-old Domestic Shorthair cat developed a mass in the region of the left parotid gland. Histologically, the mass was composed of scattered large atypical cells within a dense background of uniform small lymphoid cells. Immunohistochemically, the large cells were uniformly labeled using antiserum directed against the B-lymphocyte marker BLA.36, whereas labeling of nearly all of the small cells was limited to the T-lymphocyte marker CD3. The histomorphologic and immunohistochemical features of this unique feline neoplasm are characteristic of T-cell-rich B-cell lymphoma of humans.

Parotid salivary gland adenocarcinoma with bilateral ocular and osseous metastases in a dog.

A case of primary parotid salivary gland adenocarcinoma is described in a three-year-old entire female great dane. The presenting complaint was sudden onset blindness concomitant with the development of bilateral hyphaema and anterior uveitis. A soft-tissue swelling of the left subaural region and right forelimb lameness were also present. A definitive diagnosis of primary parotid salivary gland adenocarcinoma with bilateral ocular metastases was made on post mortem examination. Metastases were also present in the right proximal humerus, left and right prescapular lymph nodes, left axillary lymph node, left retropharyngeal lymph node, bronchial lymph nodes and all lung lobes.

Adenocarcinoma of the salivary gland in a white Swiss mouse.

A salivary gland adenocarcinoma in a white Swiss mouse used in a titration of the scrapie agent is reported. The neoplasm originated from the serous cells of the parotid salivary gland. Retroviral particles were detected in the neoplastic salivary gland cells by electron microscopy.

Primary salivary gland neoplasia in three cows.

Salivary gland neoplasms in cattle are rarely reported. Three parotid gland carcinomas from slaughter cows are described. Based on light microscopic and ultrastructural appearances the neoplasms were classified as pleomorphic carcinomas in Cows 1 and 2 and as a squamous cell carcinoma in Cow 3.

Adenocarcinoma of the parotid gland in nude rats.

Seven of approximately 200 rnu/rnu nude rats developed adenocarcinomas of the parotid gland. The malignant neoplasms ranged from well differentiated (grade 1) to poorly differentiated (grade 3) adenocarcinomas. The age of affected rats varied from 6 months to 1 year. The appearance of salivary gland adenocarcinomas in rnu/rnu rats is unusual and may have important implications for human tumor xenotransplantation in these animals.