Non-Oncological Progression of an Aneurysmal Bone Cyst (ABC) in a Puppy Following Surgical Treatment.

Aneurysmal bone cysts (ABCs) are benign but locally aggressive osteolytic lesions that are rarely reported in dogs and may progress or recur following surgical treatment. This case report describes the diagnosis, surgical management, postoperative progression, and long-term outcome of an ABC affecting the left ulna of a four-month-old Labrador Retriever. Radiography and computed tomography revealed a rapidly progressive, expansile osteolytic lesion with marked cortical thinning. Histopathological examination supported the diagnosis of ABC, with no evidence of malignancy. Initial treatment consisted of corticotomy, intralesional curettage, autologous bone grafting, and stabilization of the cortical segment with lag screws. Despite complete clinical resolution of lameness, surveillance radiographs six weeks postoperatively demonstrated progression of the lesion proximal to the original surgical site. Revision surgery involving a larger cortical window and more extensive curettage was subsequently performed, followed by bone grafting. Histopathology again confirmed ABC without malignant transformation. The dog regained normal limb function, and serial radiographic and computed tomographic examinations demonstrated progressive osseous remodeling with no evidence of further progression or recurrence through 35 months of follow-up. This case highlights the importance of adequate surgical excision and scheduled postoperative imaging, as ABC progression may occur despite apparent clinical recovery.