What is your diagnosis? Pancytopenia in a dog

Abstract: A 4‐year‐old male, castrated, mixed‐breed dog was presented to the Colorado State University Veterinary Teaching Hospital with a 1‐week history of polyuria, polydipsia, lethargy, fever, inappetence, weight loss, and soft mucoid stool. The dog was depressed and had pale, icteric mucous membranes. Results of a CBC included normocytic, normochromic, nonregenerative anemia, neutropenia, and thrombocytopenia, with 43% blast cells (200/μL), many of which contained fine azurophilic granules. Cytologic evaluation of the bone marrow aspirates revealed mild granulocytic hyperplasia that appeared to be left‐shifted in an apparent maturation arrest. A large population of blast cells comprised 35% of nucleated cells; the blasts had high nuclear to cytoplasmic ratios, deeply basophilic cytoplasm with vacuoles, and prominent nucleoli. Most cells also contained many fine azurophilic granules clustered in the paranuclear region. At necropsy, neoplastic cells were abundant in the bone marrow. Immunohistochemically the cells expressed CD3?, and an oligoclonal T‐cell rearrangement was found. The diagnosis was proliferative disorder of CD3⁺ granular lymphocytes, with associated pancytopenia. Because the blast cells were morphologically similar to myeloblasts and immunohistochemistry was required to confirm the diagnosis, T‐cell lymphoproliferative disease should be considered in dogs with pancytopenia presenting with similar clinical features.     

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? Hemorrhagic effusion in a dog

Abstract: A 2‐year‐old spayed female, German Shepherd dog was presented to the University of Illinois Veterinary Teaching Hospital with a history of intermittent lethargy. On physical examination, lung sounds were increased. The dog had a mild fever (103.7°F) and mild tachycardia (120 bpm). Thoracic ultrasound revealed a sternal mass and pericardial effusion, both of which were aspirated. On cytologic examination, the pericardial fluid contained a large amount of blood and was interpreted as a hemorrhagic effusion. Nucleated cells consisted mainly of macrophages containing phagocytized RBCs and hemosiderin and many clusters of reactive mesothelial cells. The majority of mesothelial cells contained variable amounts of rod‐shaped brown pigment granules that were suspected to be iron. The granules were positive for Prussian blue and carbol–fuschin, indicative of iron potentially mixed with lipofuscin. The granules stained negatively with Melan A, rhodamine, Hall's, and periodic acid‐Schiff. The iron within the mesothelial cells was likely secondary to hemorrhage, based on the erythrophagia and accumulation of hemosiderin in macrophages. Iron deposition and phagocytic activity in mesothelial cells has been reported previously in humans and rats, but not in dogs.     

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.