Clinical, Cytologic, Histopathologic, and Diagnostic Imaging of a Malignant Peripheral Nerve Sheath Tumor in the Renal Pelvis of a Border Collie Dog

A 12-year-old female spayed Border Collie dog was presented for evaluation of 6 months of intermittent hematuria and weight loss. A highly vascularized right renal mass deforming the renal architecture and paraneoplastic hypertrophic osteopathy were found. Cytologic evaluation of the mass obtained by fine-needle aspiration guided by ultrasound revealed mesenchymal cells with a moderate amount of bluish cytoplasm, moderately defined cell borders, and spindle to stellate or roundish morphology. The nuclei were centrally located, with a coarse chromatin pattern, round to oval, and occasionally bean-shaped. Usually, a single distinct nucleolus per nucleus with minimal size variation was noted. Anisocytosis and anisokaryosis were moderate. The cytologic interpretation was mesenchymal proliferation with moderate atypia, most consistent with soft tissue sarcoma. Right ureteronephrectomy was performed. Histologic evaluation showed a neoplastic proliferation located beneath the lamina propria of the transitional epithelium of the renal pelvis and infiltrating the renal medulla. Immunohistochemistry for protein S-100, laminin, and desmin was performed to further characterize the lesion as a nerve sheath tumor. The hematuria disappeared 4 days after the surgery; 5 months later, no alterations were observed in the general examination, and the paraneoplastic hypertrophic osteopathy mildly improved. This is the first cytologic description of a primary renal malignant nerve sheath tumor in the renal pelvis of a dog with paraneoplastic hypertrophic osteopathy.