[74] Myxochondroid Fibrous Pseudotumor: A Distinctive, Previously Undescribed Pseudoneoplasm of the Foot with a Predilection for Adolescent Males

Wonwoo Shon, Andrew L Folpe. Mayo Clinic, Rochester, MN

Background: Cartilaginous tumors of soft tissue are uncommon, with benign chondromas of soft parts greatly outnumbering rare soft tissue chondrosarcomas. Over the past several years we have seen in consultation a distinctive, benign-appearing chondroid soft tissue tumor of the foot, that differs in a number of respects from chondroma of soft parts. Herein we report our experience with this distinctive lesion.
Design: A retrospective review of all cases from the foot in our soft tissue consultation archives identified 6 similar cases, most often previously coded as "fibroconnective tissue with chondroid metaplasia". All cases were submitted in consultation due to concern for a neoplastic process, in particular chondroma of soft parts or fibroosseous pseudotumor of the digits. Clinical information, including patient follow-up, was obtained from the referring pathologists and clinicians.
Results: The patients were 4 adolescent males (ages 11-18 years, mean 14 years) and 2 older women (ages 49 and 65 years). All cases occurred in the soft tissue of the feet, including 4 cases confined to the toes, and presented as non-specific, variably painful masses. Radiographic studies, available in 3 cases, did not show bone involvement. The lesions were characterized by a variably cellular proliferation of bland fibroblastic cells in a fibromyxoid background, and in areas showed distinct basophilia and a chondroid appearance. Intralesional cystic change and a variety of reactive changes in the surrounding connective tissue were present. Features of chondroma of soft parts, such as true cartilaginous foci with lacunae, flocculent calcification, and giant cells, or of fibrosseous pseudotumors of the digits, such as woven bone production, were absent. Clinical follow-up (6 patients, 2-67 months, mean 27.6 months) showed all patients to be without recurrent disease.
Conclusions: We have identified a morphologically distinctive lesion of the foot, most often occurring in adolescent males, termed "myxochondroid fibrous pseudotumor". The clinical and histopathological features of this lesion strongly suggest that it is a reactive, pseudoneoplastic process, rather than a true neoplasm. Awareness of the unique features of this lesion should allow its ready distinction from chondroma of soft parts, fibroosseous pseudotumor of the digits, and other cartilage-forming lesions of the foot, such as calcifying aponeurotic fibroma.
Category: Bone & Soft Tissue

Tuesday, March 5, 2013 9:15 AM

Proffered Papers: Section G, Tuesday Morning


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