Imaging characteristics of intradural disc herniation: A comparison with large disc extrusion

To compare the computed tomography (CT) and magnetic resonance imaging (MRI) findings of lumbar intradural disc herniation (IDH) and disc extrusion mimicking IDH.

Between January 2015 and August 2018, 32 with surgically confirmed IDH or disc extrusion mimicking IDH were included. Age, sex, symptoms, herniated disc level, history of discectomy at the same site, and operative findings were investigated through the medical records. We evaluated the direction, type, migration, margin, and shape of disc herniation, the presence of an abrupt discontinuity of the posterior longitudinal ligament (PLL), Y-sign of ventral dura, disc material beyond the PLL, and disc calcification or ossification. In addition, maximum herniated disc diameter to central canal diameter (MHDD/CCD) ratios were calculated.

Twelve patients (8 males, 4 females; mean age 53.3 [21-83] years) were surgically confirmed to have lumbar IDH and 20 (11 males, 9 females; mean age 52 [19-78] years) had disc extrusion mimicking lumbar IDH. Margins and beak-like shapes of herniated discs, abrupt discontinuity of the PLL, Y-sign of ventral dura, disc material beyond the PLL, calcification or ossification of herniated discs, and MHDD/CCD ratios were significantly different in the IDH and non-IDH groups (p < 0.05).

Imaging findings of an ill-defined margin, a beak-like shape, herniated disc calcification or ossification, abrupt PLL discontinuity, Y-sign of ventral dura, disc material beyond the PLL and a high MHDD/CCD ratio were found to predict the presence of IDH.