Findings: A large soft tissue mass is seen on the plantar aspect of the right foot displacing the normal fat planes. On the AP view, mixed lytic and sclerotic lesions of the second and third metatarsal diaphyses separate the second metatarsal from the first and the third metatarsals.

Diagnosis: Desmoid fibromatosis.

Discussion: Fibromatosis is a category of several entities all describing 8 x 9 lesion born by various amounts of myofibroblasts and collagen. The different types of fibromatosis include palmar and plantar fibromatosis, Peyronie's disease (penile fibromatosis). Intra-abdominal fibromatosis includes pelvic fibromatosis, mesenteric fibromatosis and Gardner's syndrome. Another entity within the fibromatosis is the desmoid type tumor. These include extra-abdominal fibromatosis as well as abdominal fibromatosis. While still being considered a benign lesion, the desmoid type tumor is noted for the insidious infiltration of the surrounding tissues, especially when located in extra-abdominal sites. This extensive infiltration surrounding tissues often makes complete resection impossible. With the difficulty in complete resection, recurrences are common.

The osseous changes seen in the above x-ray are due to pressure erosions on the bone as well as cortical destruction due to mass effect. Another common finding seen in bone adjacent to fibromatosis is a frond-like periosteal reaction.

References:
Kirks DR. Practical Pediatric Imaging: Diagnostic Radiology
of Infants and Children, 3rd Edition. Lippincott-Raven,
Philadelphia; 1998:224, 410.

Resnick D, Nuwayama G. Diagnosis of Bone and Joint Disorders,
2nd Edition. W. B. Saunders, Philadelphia, 1988;4188.

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