"Beaded" osteoid osteoma: a possible transition between solitary and multicentric tumor.

An extremely rare example of an elongated (3 cm) osteoid osteoma is presented. The tumor demonstrated three focal enlargements connected by narrow areas, suggesting a "string of beads" in appearance. The elongated shape suggested the possibility that lesional tissue was stretched in a longitudinal fashion as a result of the rapid skeletal growth. The tumor closest to the growth plate was densely ossified, while the furthest lesion was almost completely lytic, suggesting that the tumor enlarged in a centripetal direction. This case is believed to illustrate a continuum from solitary to multicentric osteoid osteoma. The tumor was treated successfully with three separate percutaneous radiofrequency ablations during a single session.