Spontaneous shrinkage of solitary osteochondromas.

OBJECTIVE: Osteochondromas are the most common benign bone tumors, and thus far, their spontaneous shrinkage is considered a rare phenomenon. This study was designed to investigate the exact ratio of remission to progressive or stable cases and analyze the mechanism of tumor regression on the basis of existing theories.

MATERIALS AND METHODS: We retrospectively collected images of solitary osteochondromas in patients from 1992 to 2013, excluding cases involving short-term follow-up periods and follow-up periods that ended before growth plate closure. A total of 121 patients were diagnosed and screened for study inclusion. Tumor shrinkage was measured by assessing three points on tumor contours to determine if they had regressed or vanished. Patterns of shrinkage were further divided on the basis of mechanisms described as incorporation, absorption, and fracture.

RESULTS: Seventeen patients (mean age at initial diagnosis 13.1 years) met the study inclusion criteria. Tumor morphological classifications were pedunculated (10 cases) and sessile (7 cases). Osteochondroma shrinkage was the most common outcome (8 cases), followed by stable osteochondromas (6 cases), and osteochondromas that had progressed (3 cases). Tumors with sessile morphology were more prone to shrinkage (6 of 7 cases) compared with those of pedunculated morphology (2 of 10 cases; p = 0.015). Among pedunculated cases, tumor shrinkage was via absorption. The timing of tumor growth cessation was related to the pattern of tumor shrinkage. Absorption mostly followed tumor growth cessation, whereas incorporation mostly preceded tumor growth cessation.

CONCLUSION: The shrinkage of osteochondromas appears less rare than was originally thought.