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A 7-month-old castrated French bulldog was presented with a left-sided mandibular tumor. The initial tumor biopsy diagnosis was ameloblastoma. The owner brought this dog the Kitasato University Veterinary Teaching Hospital for more detailed examination and treatment. Computed tomography revealed a tumor on the left lateral mandibular gingiva from the caudal third of the incisor tooth to the right canine tooth, associated with severe amorphous osteolysis of the mandibular bone. The tumor was surgically excised and diagnosed as papillary squamous cell carcinoma. Currently, 2514 d (6.9 y) since the operation, the dog is healthy, without recurrence. Key clinical message: Although papillary squamous cell carcinoma is rare, many cases have been reported in the oral cavity of medium-to large-sized dogs. Based on this report, papillary squamous cell carcinoma can occur in small dogs such as young French bulldogs and a good prognosis can be achieved with proper resection., (Copyright and/or publishing rights held by the Canadian Veterinary Medical Association.)

In the present study, follicle-sinus complexes (FSCs) were harvested from the muzzle skin of 123 dogs with suspected canine rabies, and the sensitivity and specificity of FSC analysis were compared with those of brain tissue immunohistochemistry analysis. In the FSCs, viral antigen was detected from Merkel cells. Sensitivity was 97.3%, specificity was 100%, and the coefficient κ was 0.88. These results reconfirm that FSCs are very useful for the postmortem diagnosis of canine rabies, and suggest that 5 FSCs can yield results that are almost equivalent to those derived from brain tissue analysis in rabid dogs.

Recently, we reported that follicle-sinus complexes (FSCs) in the muzzle skin are useful for postmortem diagnosis of rabid dogs. Here, we compared the sensitivity and specificity of detecting the viral antigen in the brain and FSCs of 226 suspected rabid dogs, and assessed whether the FSC harbored the virus genome and particles. The viral antigen was detected in 211 of 226 samples with 100% sensitivity and specificity. Viral RNA and particles were observed in the cytoplasm of Merkel cells (MCs). These results suggest that MCs are targets of virus infection and FSCs are useful material for diagnosing rabies.

The direct fluorescent antibody test (dFAT) on fresh brain tissues is the gold standard for rabies virus antigen detection in dogs. However, this method is laborious and holds a high risk of virus exposure for the experimenter. Skin biopsies are useful for the diagnosis of humans and animals. In mammals, the tactile hair, known as the follicle-sinus complex (FSC), is a specialized touch organ that is abundant in the muzzle skin. Each tactile hair is equipped with more than 2,000 sensory nerve endings. Therefore, this organ is expected to serve as an alternative postmortem diagnostic material. However, the target cells and localization of rabies virus antigen in the FSCs remain to be defined. In the present study, muzzle skins were obtained from 60 rabid dogs diagnosed with rabies by dFAT at the Research Institute of Tropical Medicine in the Philippines. In all dogs, virus antigen was clearly detected in a part of the outer root sheath at the level of the ring sinus of the FSCs, and the majority of cells were positive for the Merkel cell (MC) markers cytokeratin 20 and CAM5.2. Our results suggest that MCs in the FSCs of the muzzle skin are a target for virus replication and could serve as a useful alternative specimen source for diagnosis of rabies., (Copyright © 2016 Elsevier B.V. All rights reserved.)

A 15-year-old, female mixed-breed dog presented with abdominal distention. An exploratory laparotomy revealed a large left ovarian mass (20 × 15 × 12 cm). Histopathological examination of the mass revealed a mixed myxoid liposarcoma and a well-differentiated leiomyoma. Four months after surgical removal of the mass, the dog died due to multiorgan metastasis. The metastasis was composed solely of the liposarcoma component. The liposarcoma component was Alcian Blue- and Oil red O-positive, and demonstrated immunoreactivity with S-100, adipophilin and vimentin. Electron microscopy revealed that the tumor cell cytoplasms were packed with lipid vacuoles and dilated rough endoplasmic reticulum. To our knowledge, this is the first report of myxoid liposarcoma and leiomyoma co-existing in a canine ovary.

Rabies is a zoonotic disease caused by the rabies virus. While the salivary glands are important as exit and propagation sites for the rabies virus, the mechanisms of rabies excretion remain unclear. Here, we investigated the histopathology of the salivary glands of rabid dogs and analyzed the mechanism of excretion into the oral cavity. Mandibular and parotid glands of 22 rabid dogs and three control dogs were used. Mild to moderate non-suppurative sialadenitis was observed in the mandibular glands of 19 of the 22 dogs, characterized by loss of acinar epithelium and infiltration by lymphoplasmacytic cells. Viral antigens were detected in the mucous acinar epithelium, ganglion neurons and myoepithelium. Acinar epithelium and lymphocytes were positive for anti-caspase-3 antibodies and TUNEL staining. In contrast, no notable findings were observed in the ductal epithelial cells and serous demilune. In the parotid gland, the acinar cells, myoepithelium and ductal epithelium all tested negative. These findings confirmed the path through which the rabies virus descends along the facial nerve after proliferation in the brain to reach the ganglion neurons of the mandibular gland, subsequently traveling to the acinar epithelium via the salivary gland myoepithelium. Furthermore, the observation that nerve endings passing through the myoepithelium were absent from the ductal system suggested that viral proliferation and cytotoxicity could not occur there, ensuring that secretions containing the virus are efficiently excreted into the oral cavity.

An 11-year-old mixed breed dog was presented with signs of anorexia. Radiographic and ultrasound examinations revealed a large mass in the heart, between the right atrium and the right ventricle. Upon gross inspection, a multilobulated tumor arising from the right atrial wall and occupying the right atrium was identified. Microscopical analysis demonstrated that this tumor consisted of neoplastic cells with granular cytoplasm, which were separated into nests by fine fibrovascular stroma and were negative for Grimelius's method. Immunohistochemical examinations revealed that the neoplastic cells expressed chromogranin A, synaptophysin and neuron specific enolase. Electron microscopy revealed that the cytoplasm of the neoplastic cells held secretory granules. Based on these pathological findings, the tumor was diagnosed as a paraganglioma. This report is a rare case of primary paraganglioma deriving from the right atrium and provides a detailed characterization of its morphological features.

A 13-year-old castrated male Labrador retriever dog presented with a mass caudal to the first molar of his left mandible. Although the tumor was excised, a recurrent tumor was detected one month later and resected. Both tumors displayed invasive growth and were composed of neoplastic proliferation arranged in irregular lobules, nests and cords continuous with mucosal epithelium. The most prominent feature of the tumors was the presence of many proliferating spindle cells admixed with palisading basal-like cells, acanthocytes and stellate cells. In immunohistochemical examinations, the spindle cells were found to be positive for vimentin; cytokeratin AE1/AE3, 5/6, 14 and 19; and p63. The other neoplastic cells were positive for all of these markers shown above except vimentin. Based on these findings, the tumors were diagnosed as spindle cell ameloblastic carcinoma.

Extraskeletal myxoid chondrosarcoma was found in a five-month-old male Irish setter dog. At necropsy, the largest mass, measuring 15 × 13 × 13 cm, was found in the right caudal lobe of the lung, and metastatic small masses were observed in multiple organs. Microscopically, the tumor comprised mainly atypical mesenchymal cells and myxoid stroma, which stained positively with Alcian blue. Immunohistochemically, the tumor cells stained positively for vimentin, S-100 protein, neuron-specific enolase, calretinin, and chromogranin A. Ultrastructurally, the cytoplasm of the tumor cells was comprised abundant rough endoplasmic reticulum, mitochondria, Golgi complex, free ribosomes and short irregular microvillous processes extending from the cytoplasm. Based on these pathological findings, this tumor was diagnosed as extraskeletal myxoid chondrosarcoma.

Traumatic neuroma of the cervical spinal cord was diagnosed in a 14-year-old male mixed-breed dog. A gross view showed two intradural extramedullary masses, measuring 1 and 0.6 cm in length and 0.7 and 0.4 cm in diameter, attached to the left side of the spinal cord at the level of the sixth and seventh cervical vertebrae. Microscopically, the cervical spinal masses comprised interlacing fascicles of axons and Schwann cells surrounded by collagenous stroma. Immunohistochemically, the fascicles were stained positively for neurofilament and S-100 proteins. Ultrastructurally, variably sized myelinated fibers and onion bulb-like structures were observed. To our knowledge, this is the first report of a traumatic neuroma in the cervical spinal cord of a dog.

A solitary mass, 2.5 cm x 2.5 cm x 2.0 cm in size, was found in the subcutis adjacent to the ischial tuberosity of an 8-year-old male German shepherd dog. The excised mass was not encapsulated and the cut surface was solid, grey-white and had multiple red areas suggestive of haemorrhage. Microscopically, the neoplasm was composed of epithelioid cells interspersed with venous vessels of various sizes and irregular bundles of spindle-shaped tumour cells with mucinous stroma. The nuclei showed anisokaryosis and many mitotic figures were noted. Immunohistochemically, the majority of tumour cells were positive for alpha smooth-muscle actin and vimentin, but negative for cytokeratin, desmin, S-100 and factor VIII-related antigen. Ultrastructurally, the tumour cells contained irregular nuclei, few mitochondria, few rough endoplasmic reticulum, cytoplasmic myofilaments of intermediate density, pinocytotic vesicles and distinct basal lamina. Based on these pathological findings, the diagnosis was malignant glomus tumour.

Of 197 cases of canine oral malignant melanoma, 29 cases with myxoid, cartilage, and osteoid formation were studied pathologically and immunohistochemically. Tumor tissues were classified into spindle cell type (13 cases), epithelioid cell type (1 case), and mixed type (15 cases). Myxoid matrixes (29 tumors) were formed mainly in the tissues of spindle cell type and were positive for Alcian blue (pH 2.5). Cartilaginous matrixes (12 tumors) were formed in the myxoid tumor tissues. The morphology of atrophied neoplastic cells, which were embedded in the cartilage cavities, significantly differed from that of spindle cells proliferating in surroundings. There were reticular areas in the process of transitioning from myxoid to cartilaginous matrixes. Osteoid matrixes were not continuous with myxoid or cartilaginous matrixes, and arose as eosinophilic trabeculae in the dense collagenous connective tissues. A calcified bone trabecula was present among the osteoid trabeculae in a case. Melanin-producing melanocytes were proliferating in the collagenous matrixes, while amelanotic cells were in the osteoid matrixes. Immunohistochemistry demonstrated proliferating neoplastic cells as melanocytes. All cells in/out of these three matrixes were positive for Melan-A, S-100 protein, NSE, and vimentin. From these results, it is suggested that cartilage and osteoid matrixes are produced by dedifferentiated melanocytes.

A solitary mass of 6 x 6 x 5 cm was found in the smooth muscle layer of the pyloric part in the stomach of a Shetland sheepdog. The excised mass was solid, gray-white in color, and had central necrosis with hemorrhages. Microscopically, the neoplasm was composed of irregular bundles of spindle-shaped tumor cells and round tumor cells. A few multinucleated cells and gangliocyte-like cells were observed. The nuclei exhibited a high degree of atypia and many cells contained mitotic figures. Immunohistochemically, tumor cells were positive for vimentin and desmin, but negative for c-kit antibody. Ultrastructurally, tumor cells contained cytoplasmic myofilaments and pinocytotic vesicles. Based on these pathological findings, the tumor was diagnosed as gastric pleomorphic leiomyosarcoma.

A 5-year-old, male French bulldog with bradycardia, dyspnea, and decerebrate rigidity was necropsied. Macroscopic findings were restricted to the brain, and a single mass, 1.5 x 2.0 x 1.5 cm in size, was observed mainly at the right cingulum with prominently protruding into the dilated right lateral ventricle. The mass was grayish white in color, soft and gelatinous, but not clearly delineated. Microscopically, the mass consisted of diffuse proliferated neoplastic oligodendroglial cells characterized by small, round, and hyperchromatic nuclei with clear cytoplasm and the cells aggressively invaded into the adjacent parenchyma. Immunohistochemistry demonstrated that most of the neoplastic cells were positive for S-100 protein, vimentin, neuron specific enolase (NSE), and neurofilament protein (NFP). From these findings, the mass was diagnosed as oligodendroglioma.