A 10-year-old male presents with nighttime tibial pain; radiographs show a 1 cm radiolucent nidus surrounded by osteosclerosis. The most likely diagnosis is

• A. Osteosarcoma.
• B. Bone cyst.
• C. Osteoblastoma.
• D. Osteoid osteoma.

Answer: (D)

A small, radiolucent nidus about 1 cm with surrounding reactive sclerosis in a child who has nighttime bone pain is classic for osteoid osteoma. The nidus represents a focused osteoid-producing lesion, and the surrounding sclerosis reflects reactive bone formation. The intense nocturnal pain is driven by prostaglandin production within the nidus, which explains why it often responds dramatically to nonsteroidal anti-inflammatory drugs.

Other lesions don’t fit this pattern. Osteosarcoma typically shows aggressive bone destruction, cortical disruption, and periosteal reaction rather than a tiny, well-circumscribed nidus. A simple bone cyst is just a fluid-filled cavity without a focal nidus and the associated sclerosis. Osteoblastoma can resemble osteoid osteoma but is usually larger (often over 2 cm), less likely to cause night pain that is dramatically NSAID-responsive, and more often involves the spine or other locations outside the typical small, focal nidus pattern.

So, the presentation aligns best with osteoid osteoma.