A large extraskeletal osteochondroma of the foot.

Osteochondromas are very common benign tumors composed of cartilage and bone. They are usually found at the end of the growth plate of long bones, most often at the area of the joints, and are contiguous with the medullary cavity. Extraskeletal osteochondromas, the same as their namesake, are composed of cartilage and bone. However, unlike typical osteochondromas, extraskeletal osteochondromas are not contiguous with bone, as their name implies. They usually arise from the synovial tissue and tendon sheaths. Although rare, extraskeletal osteochondromas have been reported to occur within the knee and around the hip; however, they are more commonly reported to occur in the hands and feet. When found in the hands or feet, these new growths are often very small and only occasionally symptomatic. We present the case of a 49-year-old female who had a slow-growing mass of 4 years' duration, located on the plantar aspect of her left foot. The mass was slowly becoming more palpable as it increased in size and was progressively causing pain and discomfort during ambulation. Imaging studies revealed an ossified mass bearing no connection to any other structure on the plantar aspect of her foot. An excision biopsy was performed, and the easily dissectible mass, although much larger than its usual presentation, proved to be an extraskeletal osteochondroma.