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? Intracranial mass in a dog

Abstract: A 9‐year‐old, spayed female Chihuahua was presented for evaluation of acute, progressive neurologic disease. On physical examination the dog was depressed and laterally recumbent. The dog had marked neutrophilia with a toxic left shift and monocytosis. Using computed tomography with contrast enhancement a large intracranial mass lesion was identified in the rostral portion of the brain. The mass extended from the central thalamic region rostral to the cribiform plate and obliterated the lateral ventricles. A fine needle aspirate of the mass contained moderately pleomorphic polygonal cells with many intranuclear cytoplasmic pseudoinclusions (ICPs). The primary differential diagnosis was meningioma, based on cell morphology and the presence of ICPs. At necropsy, the mass was well‐demarcated, unencapsulated, and densely cellular. Cells were arranged in papillary projections on fibrovascular stalks, and eosinophilic ICPs and nuclear folding were frequently seen. Cavitated areas of necrosis throughout the tumor mass were filled with intact and degenerated neutrophils. The histopathologic diagnosis was malignant papillary meningioma. ICPs are not frequently observed in Wright‐stained cytologic preparations but may be found in many types of neoplasms, including meningiomas.     

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.