dense external adhesions between the ventral dura and posteri- or longitudinal ligament (PLL). However, not only the dural sheath but also annulus of L2/3 intervertebral disc and PLL had no apparent defects or tearing. Upon making a longitudinal incision in the dura, we detected a 1×2 cm, yellowish mass occupying the thecal sac, with periph- eral displacement of the nerve roots (Fig. 3). Moreover, superior portion of the mass contacted the conus medullaris. After carefully microdissecting the mass from the surround- ing nerve roots and inner aspect of the ventral dura, the mass was totally removed. Although the ventral dura showed a dense adhesion to the PLL, no dural defects or tearing existed at the level of the mass. We sent a section of the mass for a frozen sec- tion biopsy, which ultimately confirmed it comprised degenera- tive nucleus pulposus, without any cellular elements. The sur- gery concluded upon primary closure of the durotomy site. The patient had no complication and his pain resolved significantly. He was discharged 1 week after the operation. DISCUSSION Intradural herniation of an intervertebral disc is a rare clinical entity, generally detected during surgery, and 92% of such intra- dural disc herniations (IDHs) are seen at the lumbar level9,17). ILDH’s reported incidence is 0.04-0.33% of all lumbar disc her- niations9,12,16). The most commonly affected site is L4-5 (55%), followed by L3-4 (16%) and then L5-S1 (10%)8,17). Although some authors, including Han et al.9), have reported ILDHs at the L2-3 level, such are quite rare. Moreover, intradural migra- tion of disc fragment, to the level of the vertebral body from the level of ruptured intervertebral disc space, is particularly rare. Although researchers are not certain of IDH’s disease mecha- nism, the most widely accepted hypothesis states that adhesion between the ventral dura and PLL leads to the subsequent per- foration of these firmly adhesive tissues, including the annulus fibrosus, due to the increased intradiscal pressure5,10,11,13). Floeth and Herdmann7) have reported that the herniated fragments work like a fingertip and the relative movements of the lumbar spine lead to a repetitive impression of the fixed dural sac and subsequent to a chronic inflammation and erosion process with thinning of the dura. Finally, the ligament and the adherent dura sheets are perforated and free disc material can herniate into the dural sac. Furthermore, some studies suggest that dense adhesions, whether congenitally formed or caused by trauma, previous surgery, inflammation, or osteophyte or disc protru- sion, fixate the dural sac3,6,15). Many previous studies report see- ing ILDH most frequently at the L4-5 level; the fact that the L4-5 level shows the densest adhesions between the PLL and ventral dura supports the hypothesis8,14,17). ILDH’s clinical symptoms generally include long-lasting low back pain and signs of cauda equina syndrome12,17). ILDH above the conus medullaris seems to lead to neurological dysfunction more rapidly than does ILDH below the conus medullaris. How- 157 Intradural Lumbar Disc Herniation | HS Kim, et al. A B Fig. 1. Preoperative MRI. A : A 10×23 mm sized isointense mass-like le- sion on sagittal T1-weighted image (arrow) B : Inhomogenous signal in- tensity on T2-weighted image. Fig. 2. Gadolinium-enhanced axial image shows peripherally enhanced of the lesion. Fig. 3. Intraoperative photograph. Yellowish mass occupying the thecal sac (white arrow) and peripheral displacement of the adherent cauda equine nerve roots (black arrow). ever, cases may present solely with signs of root compression17). Myelography and myelo-computed tomography can accu- rately reveal this pathology, typically showing a complete block- age of the contrast medium, but these imaging methods do not allow the physician to characterize the compression’s nature18,19). Although CT can provide valuable information, it cannot reli- ably identify intradural disc ruptures4). Benyamin et al.2) report an incidental diagnosis of ILDH that occurred during a discog- raphy. In that case, the physicians saw the annular fissure and extrusion of the injected contrast medium into the intrathecal space on the discography.