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 .
 intradural lumbar disc herniation is a rare disease . according to the reports of intradural lumbar disc herniations , 
 most cases have developed as a chronic degenerative disc diseases . 
 traumatic intradural lumbar disc herniations are even rarer . 
 a 52-year - old man visited our emergency center with numbness in his left calf and ankle after falling accident . 
 initial impression by radiologic findings was a spinal subdural hematoma at the l1 level . a follow up image two weeks later , however , did not demonstrate any interval change . 
 the patient was decided to have an operation . in operative findings 
 , a ruptured disc particle penetrating the ventral and dorsal dura was indentified after laminectomy . 
 it was assumed to be a traumatic outcome not a degenerative change . 
INTRODUCTION
CASE REPORT
DISCUSSION
CONCLUSION