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Fig 4: Histological section from the proximal femur highlighting nests of neoplastic cells within the marrow cavity and osteoclastic resorption of bone. Resorption of bone is characterised in this image by an osteoclast present within a shallow, scalloped osseous trabecula (arrowhead). Note the mitotic figure (arrow) and the dyskeratosis (cytoplasmic hypereosinophilia) within the neoplastic population of squamous cells. Haematoxylin and eosin, bar=30 m.
Focally effacing the vertebral endplate and underlying
Fig 3: a) Post mortem frontal plane section of the right femur; proximal is to the top of the image. The thick arrow points to the greater trochanter of the femur and the thin arrow points to marked periosteal proliferation. b) Sagittal plane section of the same femur fromFigure a; proximal is to the top of the image. Notice the focally extensive tan discoloration of the medullary cavity (arrow points to normal marrow). c) Sagittal section of the fourth and fifth cervical vertebrae. Cranial is to the left. There is focal loss of bone and herniation of disc material in the cranial aspect of the fifth cervical vertebral body with surrounding osteosclerosis (arrow). Squamous cell carcinoma was confirmed by histopathology at both sites. Bar = 1 cm.
limits. Sagittally transected, the cervical vertebral canal revealed a focal lytic lesion present in the cranial aspect of the vertebral body of the fifth cervical vertebra (C5) surrounded by sclerotic bone (Fig 3c). Fibrocartilage of the intervertebral disc was focally protruded through the vertebral body endplate, collapsing into the lytic lesion of C5. No SCC tumour recurrence was observed on the preputial sheath. Histopathology of the affected tissues was performed.
Multifocally effacing marrow spaces, infiltrating into adjacent cortical bone and extending into the periosteum was an unencapsulated, sparsely cellular neoplasm composed of nests of polygonal cells widely separated by reactive fibrous connective tissue (Fig 4). Neoplastic cells rarely formed nests around central aggregates of lamellated keratin (keratin pearls). Neoplastic cells were polygonal with variable amounts of eosinophilic cytoplasm and indistinct cell borders. Nuclei contained finely stippled and peripheralised chromatin with distinct, centrally located nucleoli. Eleven mitotic figures were counted in 10 fields at 400× magnification. The periosteal surface was expanded by proliferation of reactive bone and periosteal fibrosis.
trabecular bone of the fifth cervical vertebra was an unencapsulated, poorly demarcated, sparsely cellular neoplasm composed of epithelial cells arranged in islands and trabeculae surrounded by abundant reactive fibroplasia. The vertebral end plate was focally disrupted on the cranial aspect of C5 in an area that measured 9mm and contained protruded disk material (Schmorl’s node, Fig 5) that penetrated up to 12mm into the vertebral body in an area disrupted by tumour and osteolysis. The protruded disk material was surrounded by abundant fibrous tissue with rare islands of tumour cells. A diagnosis of metastatic squamous cell carcinoma of the right femur and fifth cervical vertebra was made with vertebral disc protrusion. Examination of the muscle in the region of the proximal
femur revealed a focally extensive area in which the skeletal muscle fibres were replaced by oedema and fibrin with an abundancy of myxomatous stroma separating the remaining myocytes. A specific cause of the ventral abdominal and preputial oedema was not found.
Discussion
This case is unique in that it describes a case of multiple SCC skeletal metastases from a suspected penile origin affecting both the axial and appendicular skeletons. While it is relatively common for penile SCC to metastasise to regional lymph nodes, distant metastasis in the horse is rare (van den Top et al. 2011). When distant metastasis occurs, it is usually to other soft tissues within the thorax or abdomen, most notably the lungs, liver and heart (Cramer et al. 2011). In man, systemic metastasis to lungs, liver, bone and brain occur late in the disease process and are also uncommon with only 1–10% reported in most large case studies (Pow-Sang et al. 2010). Skeletal metastasis appears to be a very rare location for SCC in horses, with only a single case report in the literature (Patterson et al. 1990). The infrequency of reported skeletal
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