Ossification of the ligamentum flavum associated with osteoblastoma: a report of three cases

We report three cases of spinal osteoblastoma with ossification of the liga mentum flavum (OLF) adjacent to the tumor. The patients in this report, all young adults, had no symptoms except for back pain. Computed tomography (C T) demonstrated a typical radiolucent nidus in the spinal pedicle/lamina wi th a dense sclerotic rim. In addition, ectopic bone formation at the insert ion point of the ligamentum flavum adjacent to the tumor was clearly illust rated. Magnetic resonance imaging (MRI) revealed the tumor and surrounding inflammatory responses, but OLF was not detected clearly. Histological exam ination revealed endochondral ossification of the ligamentum flavum that is quite unusual for normal young adults. Immunohistochemical assays in one c ase demonstrated that bone morphogenetic protein (BMP)-2/4 was expressed in the osteoblastic tumor cells. This case raises the possibility that BMPs s ecreted from the tumor cells triggered ectopic ossification in the spinal l igament.