J Korean Neurosurg Soc 52 | August 2012 MRI is regarded as the most reliable method for diagnosing ILDH, and indeed for diagnosing any IDH. A study by Choi et al.4) presented a T2-weighted image showing the PLL’s loss of continuity and its sharp, beak-like appearance, which presages an IDH. Wassestrom et al.21) reported an IDH with a rim en- hancement pattern visible on a gadolinium-enhanced MRI. In spite of these diagnostic modalities for ILDH, the preoperative diagnosis of ILDH is difficult due to gadolinium-enhanced MRI being in limited use and to ILDH’s rarity and nonspecific pre- sentation9,16). In our case, we also observed a peripheral rim en- hancement pattern on the gadolinium-enhanced MRI, but it depicted only a small, inferior portion of the mass. Mut et al.15) classified IDH into types A and B. Type A is disc herniation into the dural sac, while type B is disc herniation into the dural sheath, in the preganglionic region of the nerve root. However, classifying IDHs into type A or B presents diffi- culties, not only because ILDH detection most often occurs in- cidental to other surgery, but also because Mut et al.15) based their classification on operative field findings2,17). In our case, we located an intradural mass-like lesion at the level of the L2 vertebral body and extending into the L2-L3 disc space. Because most of the mass was at the level of the L2 verte- bral body and totally within the thecal sac, we thought the mass might be an intradural extramedullary spinal tumor, such as a neurinoma, meningioma, ependymoma, or dermoid. Interest- ingly, however, biopsy revealed the mass to be an ILDH. While Sarliève et al.17) reported the first case of an intradural cranial migration of disc material, the patient in their case had undergone previous spinal surgery. Therefore, that patient had fibrosis and cicatricial arachnoiditis around the dura mater. 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