Metastatic Canine Phaeochromocytoma with Unusual Manifestation.

We report the clinical, pathological and immunohistochemical characteristics of a phaeochromocytoma (PCC) in a 9-year-old male neutered Golden Retriever dog. The dog presented with acute onset of deteriorating cervical pain but was otherwise normal on general physical and neurological examinations. Magnetic resonance imaging of the cervical spine revealed a focal, extramedullary, infiltrative, poorly demarcated, heterogeneous mass with moderate contrast enhancement at the left cranial articular process of C2, associated with osteolysis and pathological fractures of C2, and marked soft tissue trauma. Due to the severe lesions and grave prognosis, the dog was euthanized. Post-mortem examination revealed severe enlargement of the right adrenal gland due to a neoplasm of the adrenal medulla. C2 was lytic and there was a white, well-demarcated, firm neoplastic mass in the surrounding musculature. Neoplasms were also present in, and adjacent to, the prostate gland and in pulmonary lymph nodes. Histologically, the neoplasms were composed of dense sheets and nests of small, round to polyhedral cells with frequent palisading along fine connective tissue septa, karyomegaly, multinucleated cells and frequent mitotic figures. Immunohistochemically, neoplastic cells expressed chromogranin A and synaptophysin. Gross, microscopic and immunohistochemical findings support the diagnosis of PCC, originating from the right adrenal gland, with multiple metastases in the cervical spine, prostate gland and pulmonary lymph nodes. This case highlights the difficulty of intra-vitam diagnosis of PCC as its manifestation can be highly variable. PCC should be considered as a rare but possible differential diagnosis for painful vertebral masses in elderly dogs.