Rare case of Osteoblastoma of the Distal Radius: a report

New Delhi, India: Osteoblastomas are rare, benign, bone-forming neoplasms that represent less than 1% of all bone tumors and occur mostly in people aged 10 to 30 years. The vertebral column is the most frequent site. When they occur in long bones, the metadiaphyseal region is the most commonly involved. The femur is the second most common site (12%) after the spine, followed by the jaw bones (11%), tibia (10%), and foot and ankle region (9%). Only 11 cases have been reported to occur in the distal radius.

Akash Goel et al present the clinical, radiological, and histopathological findings of an osteoblastoma of the right distal radius in a 42-year-old woman for whom an open excisional biopsy with nidus removal comprised the treatment and produced a good outcome.

A 42-year-old woman presented with pain in the right wrist of 11 months' duration. The pain was insidious in onset and gradually progressive in intensity, not responding to nonsteroidal antiinflammatory drugs and hampering daily activities. There was no history of fever, weight loss, pain in other joints, or recent trauma. The patient had experienced a closed fracture of the distal radius in the same wrist approximately 15 years earlier, which was managed nonsurgically.

On examination, there was tenderness over the distal radius, with no obvious swelling and warmth. The overlying skin was normal. Wrist flexion and extension were near normal. Supination and pronation were restricted owing to pain by approximately 10 to 15 degrees each.

Plain radiographs of the wrist revealed sclerosis over the ulnar aspect of the distal radius in the metaphyseal region with a solid periosteal reaction. There was evidence of a malunited fracture of the distal radius and positive ulnar variance likely attributable to the previous injury.

A magnetic resonance imaging scan of the wrist revealed marked cortical thickening of the distal radius predominantly on the ulnar aspect of the distal radius with a well-defined intracortical lytic lesion. The lesion showed a hyperintense signal on T2 and an intermediate signal on T1 images with a central round hypointense structure on both T1 and T2 images, giving a target-like appearance and suggesting a partially mineralized nidus with a peripheral unmineralized component. Extensive soft tissue and bone marrow edema was noted adjacent to the lesion. Because the nidus was larger than 2 cm, the diagnosis of osteoblastoma was suggested. The differential diagnosis included an intracortical abscess with a central hypointense sequestrum.

Fine-needle aspiration cytology was inconclusive. An open biopsy of the lesion was done. During the exploration, no fluid or granulation tissue was observed. The curetted bone was sent for bacterial cultures, which were negative for growth.

Histopathology revealed strands of osteoid with osteoblastic rimming in a trabecular arrangement and numerous multinucleated osteoclastic giant cells. The cells showed insignificant mitotic activity and minimal cellular atypia. The pathologic diagnosis was osteoblastoma.

The postoperative period was uneventful. The wrist was immobilized for 2 weeks after which mobilization was started.

At 1- year follow-up, the patient was asymptomatic and had good range of motion (flexion of 750, extension of 800, supination of 800, and pronation of 850). She was able to return to daily household work comfortably. There were no signs of recurrence on radiographs of the wrist.

The authors opined that - the rare site of the lesion and the preexisting fracture of the distal radius made the diagnosis difficult. After the clinical examination and imaging, the possibility of a benign bone tumor or subacute osteomyelitis was considered. It was only after the biopsy that the diagnosis could be confirmed. Because the nidus was removed during the biopsy, the symptom of pain was largely addressed and no further treatment was required.

Further reading:

Osteoblastoma of the Distal Radius

Akash Goel(Ortho),Nishant Bhatia(Ortho), Vineet Dabas(Ortho),Anurag Mehndiratta(Radio),Meeta Singh(Path).

J Hand Surg Am. 2022;47(4):392.e1-e5

https://doi.org/10.1016/j.jhsa.2021.02.003