Introduction

Giant cell tumor (GCT) of bone is a benign, locally aggressive tumor composed of mononuclear stromal cells and osteoclast-like multinucleated giant cells. While GCT most commonly affects the distal femur, proximal tibia, and distal radius, involvement of the distal ulna is uncommon [1,2]. It represents approximately 5% of all primary bone tumors and commonly affects skeletally mature individuals between the second and fourth decades of life [3]. The tumor typically arises in the epiphysis of long bones, with the distal femur, proximal tibia, and distal radius being the most frequently involved sites. Rarely, GCT may occur in the sacrum (4%-9%), pelvis (3%-6%), small bones of the hands and feet (1%-2%), and lumbar vertebrae (<1%) [3,4]. GCTs of the distal ulnar metaphysis are extremely rare, accounting for only 0.45% to 3.2% of all GCT cases, and GCTs crossing interosseous margins account for <1% of all cases.

Although histologically benign, GCT can demonstrate aggressive local behavior and may recur following treatment. Distant metastasis occurs in a small percentage of patients, most commonly involving the lungs. However, contiguous extension to adjacent bones is extremely uncommon.

Due to the rarity of distal ulna GCT and the possibility of unusual local spread, accurate imaging evaluation and complete surgical excision are crucial. We present a rare case of distal ulna GCT with contiguous involvement of the distal radius, managed successfully with en bloc resection.