Light-bulb sign in X-ray shoulder is seen in:
**Core Concept**
The light-bulb sign in X-ray shoulder refers to a specific radiographic finding characterized by a dense, rounded, and well-defined lesion in the humeral head, resembling the shape of a light bulb. This sign is typically associated with a specific type of bone lesion.
**Why the Correct Answer is Right**
The light-bulb sign is classically seen in cases of a Campanacci lesion, also known as a giant cell tumor of the bone. These tumors arise from the epiphyseal plate of the bone and are characterized by an abundance of giant cells, leading to a lytic lesion in the bone. The tumor often causes a well-defined, rounded, and sclerotic lesion in the humeral head, which radiographically resembles a light bulb. The tumor's growth pattern and cellular composition lead to the characteristic appearance seen on X-ray.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the "light-bulb sign" is not typically associated with osteosarcoma, which is a malignant bone tumor characterized by an aggressive and destructive growth pattern, resulting in a different radiographic appearance.
**Option B:** This option is incorrect because the "light-bulb sign" is not characteristic of a simple bone cyst, which is a benign fluid-filled lesion that typically appears as a well-defined, rounded lucency in the bone, but lacks the sclerotic border seen in Campanacci lesions.
**Option C:** This option is incorrect because the "light-bulb sign" is not typically associated with an aneurysmal bone cyst, which is a benign, expansile lesion that often contains fluid-filled spaces and has a more irregular appearance on X-ray.
**Clinical Pearl / High-Yield Fact**
Remember that the light-bulb sign is a classic radiographic finding in giant cell tumors of the bone, and its presence should prompt consideration of this diagnosis in cases of a well-defined, rounded, and sclerotic lesion in the humeral head.
**Correct Answer: C. Giant cell tumor of the bone.**