Lumbar disk herniation: correlation of histologic findings with marrow signal intensity changes in vertebral endplates at MR imaging.

Abstract

To compare findings at preoperative magnetic resonance (MR) imaging with data for tissue composition of herniated disks in patients after microsurgical removal of herniated material. Fifty-one patients underwent MR imaging before microsurgical removal of extruded lumbar disk herniation material. Marrow signal intensity changes along the cartilaginous endplates were classified according to Modic types 1-3. Severity of changes was evaluated with respect to extension along the endplate in the anteroposterior diameter (0%, <33%, 33%-66%, >66%). The existence of a dorsal vertebral corner defect was evaluated in relation to the existence of hyaline cartilage in the disk extrusion material. Mean tissue composition of herniated material in all patients was 63% anulus fibrosus, 30% nucleus pulposus, and 8% cartilaginous endplate. Twenty-five of the 51 patients had hyaline cartilaginous material in the extrusion (range, 5%-50%). Patients without marrow signal intensity changes along the cartilaginous endplate showed significantly less cartilaginous material in the extruded disk (P =.023, Fisher exact test). Mean percentage hyaline cartilage in patients without changes was 2% +/- 4 (SD) (Modic type 1, 16% +/- 15; type 2, 10% +/- 12). When the changes extended 33% of the vertebral endplate, there was cartilaginous endplate material in the extruded disk (P =.006). Cartilage from the endplate was present in the extruded disk material in 40% (16 of 40) of patients without a vertebral corner defect and in 82% (nine of 11) of patients with a vertebral corner defect (P =.019). Avulsion-type disk herniation seems to be common, and vertebral endplate marrow signal intensity changes on MR images are indicative of cartilaginous material in the extruded disk herniation material.