What is your diagnosis? Intracranial mass in a cat

Abstract: A 14‐year‐old female spayed cat was presented with a 3–4‐month history of circling to the left and intermittent head pressing. Neurologic examination findings localized the lesion to the left supratentorial region. Using magnetic resonance imaging, an extra‐axial mass was found on the dorsal aspect of the brain at the level of the frontal and parietal lobes, compressing and displacing the brain ventrally and caudally. Craniectomy was performed and the mass was submitted for cytologic and histopathologic evaluation. Impression smears revealed abundant cholesterol crystals and loose clusters of mildly pleomorphic spindle cells, compatible with a meningioma. The histopathologic diagnosis was meningioma with psammoma bodies and numerous cholesterol clefts. Abundant cholesterol crystals within meningiomas in cats may present a diagnostic challenge when nucleated cells are scant. Other differential diagnoses for abundant cholesterol crystals in an intracranial mass include cholesterol granulomas and keratinizing cysts.     

What is your diagnosis? Lingual mass in a dog

A 3.5-year-old female spayed Rat Terrier was presented for evaluation of a submucosal lingual mass. Fine-needle aspiration of the mass revealed a population of neoplastic cells composed predominantly of small, round cells and large, round to spindle-shaped cells, which occasionally had blunt cytoplasmic borders and multiple nuclei. The neoplastic cells had moderate to marked anisocytosis and anisokaryosis. The cytologic interpretation was malignant neoplasia, most likely sarcoma. Histopathologic examination of a biopsy specimen revealed an unencapsulated, poorly demarcated, moderately cellular neoplasm composed of individualized, infiltrative spindle cells. Elongate skeletal muscle cells with prominent, rectangular borders (strap cells) were observed. A morphologic diagnosis of rhabdomyosarcoma was made. Staining with phosphotungstic acid-hematoxylin revealed haphazardly arranged skeletal muscle cross-striations. Immunohistochemical staining results for vimentin, Myo D1, desmin, and myoglobin were positive, though staining intensity of tumor cells varied with the degree of differentiation. Using transmission electron microscopy, irregular, disorganized Z-bands were identified. Rhabdomyosarcomas are uncommon tumors in the dog, and rarely may involve the tongue or oral cavity. Cytologic evaluation of a rhabdomyosarcoma may reveal a pleomorphic population of cells and definitive diagnosis may require histologic examination, immunohistochemical staining, and electron microscopy.     

What is your diagnosis? Vertebral mass in a dog

Abstract: A 1‐year‐old, castrated male, mixed‐breed dog was presented for sporadic episodes of kyphosis, tremors, and vocalizing. On neurologic examination, the lesion was localized to spinal cord segments T3–L3. Magnetic resonance imaging of the spine showed an expansile mass occupying most of the ventral aspect of the spinous process of T6. Fine‐needle aspirates of the mass were examined cytologically. A moderately cellular population of pleomorphic spindle cells and abundant mucinous matrix were observed. The cytologic diagnosis was spindle cell neoplasia, with myxosarcoma and fibrosarcoma as the primary differential diagnoses. The dog was euthanized. Histopathologic evaluation of the mass and surrounding tissue confirmed a low‐grade spindle cell sarcoma, with severe compressive myelopathy and mild neutrophilic inflammation. The neoplastic cells stained positive for mucopolysaccharides with Alcian blue, resulting in a final diagnosis of low‐grade (grade 1) myxosarcoma. Fine‐needle aspiration was useful in making a preliminary diagnosis of myxosarcoma in this case. Myxosarcoma should be included in the differential diagnosis for a vertebral mass in a young dog.     

What is your diagnosis? Ventral neck mass in a dog

Abstract: A 14‐year‐old male Labrador Retriever was presented for lethargy and collapse. On physical examination, numerous abnormalities were found, including a large ventral neck mass (100 cm³) in the area of the thyroid gland. Fine‐needle aspirates revealed 2 apparent populations of cells: one suspected to be a well‐differentiated thyroid carcinoma, and the other consisting of large pleomorphic to spindloid cells suggestive of sarcoma. Two days later, the dog died at home. A full necropsy was not performed, but examination of the head and neck revealed a well‐encapsulated mass adjacent to the cranial trachea and larynx. A section of the mass was evaluated histologically and a diagnosis of anaplastic thyroid carcinoma was made. Immunohistochemical evaluation with antibodies to thyroglobulin, cytokeratin, and vimentin confirmed distinct populations of malignant epithelial and malignant mesenchymal cells, and the diagnosis was amended to thyroid carcinosarcoma. Thyroid carcinosarcoma is a rare neoplasm in dogs in which the cell type comprising the mesenchymal component can vary. Immunochemistry to demonstrate the 2 cell types may be necessary to differentiate thyroid carcinosarcoma from anaplastic thyroid carcinoma.