Lumbar extraosseous intraforaminal osteoblastoma: case report and review of the literature.

Osteoblastomas are rare primary bone tumors with a predilection for the spine. The extraosseous growth pattern is rare: to our knowledge, only two cases of fully extraosseous osteoblastomas have been previously reported.A 36-year-old man presented with a 7-month history of low back pain radiating to the gluteal area. On examination, a typical L5 radiculopathy was noted. The radiological examinations conducted in the previous months pointed out the rapid growth of an extraosseous mass occluding the right L5-S1 foramen. Partial laminectomy was performed in order to achieve gross total resection. Histological analysis was consistent with osteoblastoma.Osteoblastomas with extraosseous extension are uncommon, and an exclusively extraosseous presentation is anecdotal. This can lead to preoperative misdiagnosis when typical radiological characteristics of bone-forming tumors are missing. We describe the case of an extraosseous lumbar osteoblastoma whose clinical and radiological presentation was suggestive of malignancy.