Fibroma of the tendon sheath in the dorsum of the foot: A case report.

Fibroma of tendon sheath (FTS) is a rare soft tissue tumor that usually occurs in the upper extremity. Moreover, of the few cases reported in the feet, nearly all occur in the plantar region. We report the case of a large FTS in the dorsum of the left foot that grew quickly into a 4 cm-diameter lesion. The 44-year-old Japanese man noticed the tumor incidentally one year before presentation and could not recall any possible cause. Physical examination showed an elastic hard mass that spread over the third to fifth metatarsal bones. MRI showed iso-intense signals with central hypo-intensity on T1-weighted images and hypo-intense signals on T2-weighted images. Since a biopsy did not reveal any malignant findings, the lesion was excised surgically. The tumor was found to be multilocular, encapsulated, and to arise from the extensor digitorum brevis tendon. Histopathology showed scattered spindle fibroblasts and slit-like vascular structures within the dense collagenous matrix. The tumor was diagnosed on the basis of the clinical, demographic, surgical, and histopathological findings as an FTS arising from the extensor digitorum brevis tendon. A review of the literature revealed seven cases of FTS of the dorsum of the foot, which indicates its rarity. More than one-half of these cases were from Japan. While the cause of FTS remains unclear, trauma has been implicated. We suggest that the cultural background of the patient, which could promote kneeling-induced dorsal foot trauma, may have contributed to the onset/progression of our case. Level of Clinical Evidence: 4.