A case report of massive cutaneous histiocytoma in a 12-year-old intact bitch: Cytologic, radiologic, pathologic investigation.

Background: Facial masses in dogs can arise from infections, inflammation, or tumors. Histiocytoma, a common benign skin tumor in young dogs, originates from Langerhans cells. It appears as a small, round, hairless, and rapidly growing lump, present on the face or ears. Typically, histiocytomas regress spontaneously within a few months. While usually harmless, biopsy and monitoring are recommended to rule out malignancies like mast cell tumors or squamous cell carcinoma. Case Description: A 12-year-old, unspayed bitch presented with a huge histiocytoma on her frontonasal bone. The mass measured about ten centimeters across and had suddenly become bigger over the last few months. Microscopic examination of fine needle aspirates showed that there was proliferation of tumor cells composed of two cell types resembling neoplastic macrophages and dendritic cells, which corresponds to cutaneous histiocytoma confirmed by Hematoxylin-Eosin stain. Radiographic images also demonstrated a large subcutaneous mass with no evidence of lymph node metastasis. Removal of the growth through surgical excision was done, and the tissue sample submitted for histopathology showed a typical pattern of macrophage and dendritic cell proliferation without any signs suggesting malignancy. Enbloc excision resulted in an intact dog after six months post-surgery check with no evidence of clinical recurrence or relapse. Conclusion: This report underscores the need for a holistic diagnostic approach to diagnosis and management of canine cutaneous histiocytomas, stressing the role played by various radiological investigations, cytologic evaluations, and pathologic assessments while determining their size.