Question:medium
A 11-year-old boy presented with complaints of pain in the right arm near the shoulder. X-ray examination revealed an expansile lytic lesion in the upper third of the humerus. What is the most likely diagnosis?
A 11-year-old boy presented with complaints of pain in the right arm near the shoulder. X-ray examination revealed an expansile lytic lesion in the upper third of the humerus. What is the most likely diagnosis?
Show Hint
Expansile lytic lesion in the metaphysis near an open growth plate in a child points to a simple (unicameral) bone cyst.
Updated On: Jul 8, 2026
- Giant cell tumor
- Unicameral bone cyst
- Osteochondroma
- Parosteal osteosarcoma
Show Solution
The Correct Option is B
Solution and Explanation
Step 1: Build a short list of proximal humerus lesions.
In a growing child, a lytic area near the shoulder end of the humerus usually comes from one of four lesions: unicameral bone cyst, giant cell tumor, osteochondroma or parosteal osteosarcoma. The trick is matching the age and the X-ray pattern to the right one.
Step 2: Use age as the first filter.
This boy is $11$ years old, meaning his epiphyseal plate is still open. Giant cell tumor needs a fused, mature epiphysis to spread into, so it almost never appears before the growth plate closes. That removes giant cell tumor from the list.
Step 3: Use the X-ray pattern as the second filter.
Osteochondroma sticks out from the surface of the bone as a capped bony stalk, and parosteal osteosarcoma sits on the outer cortex as a dense sclerotic mass. Neither of these fits an expansile lytic lesion inside the shaft. That leaves the lesion sitting centrally in the metaphysis.
Step 4: Confirm the classic site.
The proximal humeral metaphysis, right under the growth plate, is the single most common location for a unicameral bone cyst in the body. The cyst is filled with clear fluid, thins the cortex from within, and can make the bone expand, which matches the X-ray description exactly.
Step 5: State the answer.
The lesion is a unicameral bone cyst.
\[ \boxed{\text{Unicameral bone cyst}} \]
In a growing child, a lytic area near the shoulder end of the humerus usually comes from one of four lesions: unicameral bone cyst, giant cell tumor, osteochondroma or parosteal osteosarcoma. The trick is matching the age and the X-ray pattern to the right one.
Step 2: Use age as the first filter.
This boy is $11$ years old, meaning his epiphyseal plate is still open. Giant cell tumor needs a fused, mature epiphysis to spread into, so it almost never appears before the growth plate closes. That removes giant cell tumor from the list.
Step 3: Use the X-ray pattern as the second filter.
Osteochondroma sticks out from the surface of the bone as a capped bony stalk, and parosteal osteosarcoma sits on the outer cortex as a dense sclerotic mass. Neither of these fits an expansile lytic lesion inside the shaft. That leaves the lesion sitting centrally in the metaphysis.
Step 4: Confirm the classic site.
The proximal humeral metaphysis, right under the growth plate, is the single most common location for a unicameral bone cyst in the body. The cyst is filled with clear fluid, thins the cortex from within, and can make the bone expand, which matches the X-ray description exactly.
Step 5: State the answer.
The lesion is a unicameral bone cyst.
\[ \boxed{\text{Unicameral bone cyst}} \]
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