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24 July 2013 - Case of the Week #280
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Case of the Week #280
A 15 year old girl presented with left hip pain for a few months. CT scan showed a well circumscribed mass of the left sacroiliac bone with no soft tissue invasion.
What is your diagnosis?
Chondromyxoid fibroma is a rare benign cartilaginous bone tumor arising in young adults aged 15-25 years (Hum Pathol 2010;41:208). It presents with a dull, achy pain, and often occurs in the metaphysis of long tubular bones or in the small bones of the feet. Radiographs show an extremely well circumscribed lytic defect with a scalloped, sclerotic margin similar to metaphyseal fibrous defect.
At gross exam, the tumor is 3-8 cm, well circumscribed, solid and glistening. It is often lobulated with zonation. Older tumors are more hyalinized. Microscopic examination reveals well circumscribed, hypocellular lobules of poorly formed hyaline cartilage composed of chondroblasts with abundant pink cytoplasm, and myxoid tissue with fibrous septae containing spindle cells and osteoclasts. Atypia is common, including large, hyperchromatic nuclei. Scattered calcification and osteoclast-like giant cells are present. At the periphery, the tumor is more cellular and vascular (Mod Pathol 1999;12:514). There is no / rare mitotic activity. Tumors often have 6q13 rearrangements, with recurrent 6p25 and 6q25 anomalies (Mod Pathol 2009;22:1499).
The differential diagnosis includes:
Chondroblastoma: usually epiphysis (open) or apophysis; compact polyhedral chondroblasts with well defined cell borders, abundant pink cytoplasm, hyperlobulated nuclei with grooves in mineralized, chicken-wire matrix that surrounds chondroblasts; may be a related entity, since both have similar expression profile for skeletal development markers (Mod Pathol 2012;25:1452)
Chondrosarcoma: similar histology but malignant radiologically, no hypocellular center, infiltrates surrounding tissue
Fibromyxoma: usually older adults, no cartilaginous areas
Fibrous dysplasia with myxoid change: curvilinear trabeculae (Chinese letters) of metaplastic woven bone in hypocellular fibroblastic stroma; not lobulated
Chondromyxoid fibroma is benign, although 25% recur after curettage. They may erode through the bone cortex, but there are no distant metastases.
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