intradural disc herniation ( idh ) is a rare disease and its incidence is reported as 0.26 - 0.30% of all disc herniations16 ) . idhs primarily occur as a result of chronic degenerative diseases and rarely occur due to traumatic events1,14 ) . traumatic lumbar spine lesions usually result in bony fractures and paraspinal soft tissue injuries rather than isolated disc herniations . in this report , we present a rare case of a patient who exhibited an intradural mass lesion at l1 , which initially mimicked a spinal subdural hematoma ( sdh ) and was later determined to be an idh without an accompanying lumbar spine bony fracture after a traumatic event . a 52-year - old man presented at the hospital with numbness in his left calf and ankle after falling accident two days ago . the patient was initially admitted at another medical center after the accident but transferred to our hospital at his request . a motor power grade was intact with slightly decreased sensation along the left l5 dermatome . bladder and bowel functions were intact , and no other significant abnormalities were found upon neurological examination . in his medical history , he had visited our hospital six weeks ago with complaints of radiating pain in his right leg along the l5 dermatome after falling down from 2 m height . at that time , his lumbar spine magnetic resonance image ( mri ) scan exhibited diffuse bulging intervertebral disc in l4 - 5 ( fig . 1 ) . the patient had received a conservative treatment with a non - steroidal anti - inflammatory drug and discharged with the improvement of symptoms . at this time , the patient 's plain radiography did not present bony abnormalities such as fractures or dislocations . in his lumbar computed tomography ( ct ) scan , a small calcified lesion was found at the l1 - 2 level , posterior to the disc ( fig . 2 ) . on his lumbar t2-weighted mri , a high signal intensity with an amorphous shape lesion was located intradurally and it compressed the spinal cord anteriorly at the l1 level ( fig . 3c ) and it presented heterogeneous low signal intensity in the gradient echo ( gre ) image ( fig . we considered the lesion to be a spinal sdh , and decided to perform a conservative treatment . at the follow up mri scan after two weeks of treatment , the lesion still remained unchanged without any improvement of numbness , so we decided to operate . a subtotal laminectomy was performed at l1 , which revealed an out - punching whitish soft particle on the dorsal dura . the particle was thought to be a ruptured disc material and removed gently , then sent for pathology . the pathologic results determined the particle to be degenerating fibrocartilagenous tissue corresponding to an intervertebral disc . after removing the extradural lesion , a midline durotomy was done from the dura defect uncovering large , cartilaginous disc particles in the middle of the intradural space ( fig . , a hard bony lesion remained adhesively to the ventral dura and a small ventral dura defect was identified around the bony lesion ( fig . the hard bony lesion was thought to be a calcified lesion at the posterior l1/2 intervertebral disc in his lumbar spinal ct scan . we tried to repair the dura defect to protect a leakage of cerebrospinal fluid ( csf ) , but the ventral dura tear could not be repaired due to its severe adhesion . a watertight closure on dorsal dura after the operation , the patient 's numbness in his left leg has gradually improved . two weeks after surgery , the patient was discharged from the hospital with free of symptoms . idhs are rare clinical diagnoses that typically occur in patients aged in their fifties11 ) . dandy4 ) first reported an intradural lumbar disc herniation in 1942 and the incidence of idhs is reported between 0.04 and 0.33% of all reported lumbar disc herniations9 ) . the most common site of intradural lumbar disc herniations is the l4 - 5 ( 55% ) area , followed by l3 - 4 ( 16% ) , and l5-s1 ( 10% ) , far fewer occur at l1 - 2 and l2 - 311,13,15 ) . furthermore , traumatic idhs are rarer events and the incidence rate has not yet been reported in the literature . most traumatic disc herniations in the lumbar spine frequently have severe bony injuries such as fractures and dislocations8 ) . in our case , however , we found an idh after a traumatic event without fractures or dislocations . although the mechanisms that cause disc herniations to pass the dura mater are unclear , the widely accepted hypothesis states that adhesion between the ventral dura and posterior - longitudinal ligament ( pll ) leads to the successive perforation of these firmly adhesive tissues , including the annulus fibrosus , due to the increased intradiscal pressure1,4,9,10 ) . dandy4 ) explained that sudden pressure on the protruded disc might erode and then penetrate the overlying ventral dura . other reports have suggested that dense adhesion , whether it is congenital or acquired , fixate the dural sac1,14 ) . diagnosing an idh is difficult due to its rarity . diagnosis using radiological images is a difficult task , because lumbar idhs can have various radiological and clinical features3,17 ) . furthermore , lesions may be ignored in simple radiography and ct scans , which are one of the most frequently used radiologic examinations in the diagnosis of spinal injuries . hidalgo - ovejero et al.6 ) reported that the presence of epidural gas in a ct scan could be a clue of the presence of an idh . in our case , however , we could not find epidural gas on the ct scan . since wasserstrom et al.18 ) made the first idh diagnosis using a gadolinium - enhanced mri in 1993 , the rim enhancement of herniated discs has been accepted as a typical mri finding in idhs . furthermore , choi et al.2 ) presented the loss of pll continuity and a sharp beak - like feature on a t2-weighted image as indicators of idh . in our case , we also observed a peripheral rim enhancement pattern on the gadolinium - enhance t1 mri , but it was not enough to consider the idhs due to the small size of portion ( fig . moreover , the loss of pll continuity was not definite on our initial lumbar spine mri . therefore , our initial impression of the intradural mass at l1 was a spinal sdh , although a traumatic spinal sdh is also very rare12 ) . on mri , the spinal sdh yielded high signals on both t1 and t2 , but the signal intensity of the spinal sdh on the mri also depend on the duration7 ) . in our case , 3a , b ) and an isosignal on the t1 scan . on the gre scan , however , the intradural lesion had a high signal - intensity with a low signal void inside the intradural lesion ( fig . an intradural abscess could be considered as another differential diagnosis , but we excluded it because there were no signs of infection such as fever or leukocytosis . additionally , the patient had visited our hospital six weeks previously for radiating pain in his right lower leg . at that time , the patient checked a lumbar mri scan , and was diagnosed with a diffuse bulging disc in l4 - 5 and there was no intradural mass lesion . compared with the mri from that visit , de - novo intradural lesion was detected . moreover , the height and the signal intensity of the intervertebral disc of l1 - 2 had decreased in the recent study ( figs . we assumed that a strong vertical pressure had been applied to cause the intervertebral disc rupture , then the ruptured particles penetrated the pll , ventral dura , and through dorsal dura to the epidural space . according to the clues mentioned above , we could assume that the idh developed from a trauma rather than a degenerative condition . we experienced a rare case of a lumbar idh after trauma without an accompanying bony fracture or dislocation . for patients with an intradural lesion at the lumbar spine after trauma as with the patient in this report , idhs should be considered as differential diagnoses and prompt removal of the intradural mass is necessary .