ANATOMIC AND CLINICAL INVESTIGATION OF A LOW SIGNAL PERIPHERAL LINE (BLACK LINE) AROUND THE LUMBAR HERNIATED NUCLEUS PULPOSUS ON MAGNETIC RESONANCE IMAGING

Abstract

It has been reported that a low signal peripheral line (black line) around the lumbar herniated nucleus pulposus (HNP) on magnetic resonance imaging (MRI) can be used for the evaluation of the interruption of the posterior longitudinal ligament (PLL). However, the previous reports have showed that different rates of agreement between MRI and surgical findings. In order to clarify this matter, the black line on MRI was assessed by a combined anatomic and clinical investigation. Three cadavers were used for the anatomic part of the study. For the clinical study, 11 patients with the diagnosis as HNP and 5 healthy volunteers were subjected to MRI to compare with the results from the anatomic study. The lumbo-sacral spine was dissected en bloc from the cadavers. The first imaging on MRI of the specimens was performed with the dural sac; the second imaging was performed after the dural sac and the nerve roots have been removed but with the PLL left; the third imaging was performed after the PLL was completely removed. After completion of imaging, the specimens were cut in sagittal and horizontal planes for histological evaluation. In the cadavers after removing the PLL histologically, the black lines were still shown on MRI. Finally, after changing encoding, the black lines were interrupted at some disc levels in the cadaver specimen, the patients with HNP, and healthy volunteers. Therefore the black lines could be interpreted as a chemical shift artifact. These results indicate that the continuity or the discontinuity of the black line is not appropriate sign to diagnose whether disruption of the PLL has occurred or not.