large migrated lumbar disc herniations predispose patients to dural tear , and unrecognized dural tears have been known to occur during discectomy for this condition2,8 ) . here , we report 2 cases of nerve root herniation into the intervertebral disc space through an unrecognized ventral dural tear . despite a relapse of severe sciatic pain after surgery , the diagnosis was delayed because of the existence of multilevel lumbar stenosis . a 56-year - old man presented with pain in the lower back , radiating from the left buttock to the anterior leg . 1 ) demonstrated a very large disc herniation at the left l4 - 5 level ( with upward migration evident on sagittal scans ) , spinal stenosis at the l2 - 3 , l3 - 4 , and l4 - 5 levels , and mild lateral recess stenosis at the left l5-s1 level . microscopic discectomy was performed at the left l4 - 5 level . the preoperative radiating pain from the left buttock to the anterior leg ten days later , he visited the outpatient clinic with severe pain radiating from the left buttock to the posterior thigh . he was unable to maintain a supine position because of the pain , which was most severe during position changes . the symptoms had started 1 week before presentation at the outpatient clinic and had worsened over time . 2b ) . because the patient continued to complain of left buttock pain , additional decompression for the left l3 - 4 and l5-s1 levels was performed ( fig . however , his buttock pain did not improve and continued to be most severe in the morning and during position changes . the symptoms worsened in spite of conservative treatments including oral analgesics , physiotherapy , and root block . eventually , the patient could not sit down or walk even 100 m because of severe pain radiating from the left buttock to the posterior thigh . finally , we found ventral herniation and entrapment of a nerve root at the l4 - 5 level on an mri rescan ( fig . 3 ) , a diagnosis that had been missed since his first visit to the outpatient clinic , with newly developed buttock and posterior leg pain following the first operation . after total laminectomy of l4 , a linear dural incision was made at the level of the l4 - 5 disc space . rootlet herniation through the ventral dural defect with severe adhesion between the rootlet , dura , and disc was observed ( fig . postoperative mri revealed complete release of the rootlet , and the patient 's symptoms markedly improved . the patient showed mild paresthesia of the left foot without any pain at the 6-month follow - up . a 64-year - old woman presented with pain in the lower back , radiating from the left buttock to the lateral leg . 5 ) showed paramedian extruded disc herniation at the left l2 - 3 level and spinal stenosis at the l3 - 4 and l4 - 5 levels . although the radiating pain greatly alleviated immediately after the surgery , it relapsed the next day . the pain was too severe for the patient to stand or even change her position while in the supine position , and the pain did not subside even after an opiate injection . the patient underwent additional decompression for the left l3 - 4 and l4 - 5 levels ( fig . mri performed 1 week after the surgery showed an epidural hematoma at the l2 - 3 level . we performed computed tomography ( ct)-guided needle aspiration to decompress the thecal sac ( fig . 6b , c ) , but this did not alleviate her pain , which had continued to worsen over time . eventually , she developed lower extremity motor weakness and muscle atrophy ( knee flexion , gr . 1 ; ankle dorsiflexion , gr . 4 ; and big toe dorsiflexion , gr . finally , we performed microscopic exploration at the l2 - 3 level and found that approximately 4 rootlets had herniated into the l2 - 3 disc space . we released the entrapped rootlets and repositioned them via the transdural approach , and the ventral dural defect was then closed with artificial dura . although the patient 's pain markedly alleviated after this surgery , she continued to experience knee flexion weakness , which has been ameliorating with rehabilitation . the patient showed improvement of the knee flexors with mild paresthesia of the lower extremities at the 6-month follow - up . a 56-year - old man presented with pain in the lower back , radiating from the left buttock to the anterior leg . 1 ) demonstrated a very large disc herniation at the left l4 - 5 level ( with upward migration evident on sagittal scans ) , spinal stenosis at the l2 - 3 , l3 - 4 , and l4 - 5 levels , and mild lateral recess stenosis at the left l5-s1 level . microscopic discectomy was performed at the left l4 - 5 level . the preoperative radiating pain from the left buttock to the anterior leg ten days later , he visited the outpatient clinic with severe pain radiating from the left buttock to the posterior thigh . he was unable to maintain a supine position because of the pain , which was most severe during position changes . the symptoms had started 1 week before presentation at the outpatient clinic and had worsened over time . 2b ) . because the patient continued to complain of left buttock pain , additional decompression for the left l3 - 4 and l5-s1 levels was performed ( fig . however , his buttock pain did not improve and continued to be most severe in the morning and during position changes . the symptoms worsened in spite of conservative treatments including oral analgesics , physiotherapy , and root block . eventually , the patient could not sit down or walk even 100 m because of severe pain radiating from the left buttock to the posterior thigh . finally , we found ventral herniation and entrapment of a nerve root at the l4 - 5 level on an mri rescan ( fig . 3 ) , a diagnosis that had been missed since his first visit to the outpatient clinic , with newly developed buttock and posterior leg pain following the first operation . after total laminectomy of l4 , a linear dural incision was made at the level of the l4 - 5 disc space . rootlet herniation through the ventral dural defect with severe adhesion between the rootlet , dura , and disc was observed ( fig . postoperative mri revealed complete release of the rootlet , and the patient 's symptoms markedly improved . the patient showed mild paresthesia of the left foot without any pain at the 6-month follow - up . a 64-year - old woman presented with pain in the lower back , radiating from the left buttock to the lateral leg . 5 ) showed paramedian extruded disc herniation at the left l2 - 3 level and spinal stenosis at the l3 - 4 and l4 - 5 levels . although the radiating pain greatly alleviated immediately after the surgery , it relapsed the next day . the pain was too severe for the patient to stand or even change her position while in the supine position , and the pain did not subside even after an opiate injection . the patient underwent additional decompression for the left l3 - 4 and l4 - 5 levels ( fig . mri performed 1 week after the surgery showed an epidural hematoma at the l2 - 3 level . we performed computed tomography ( ct)-guided needle aspiration to decompress the thecal sac ( fig . 6b , c ) , but this did not alleviate her pain , which had continued to worsen over time . eventually , she developed lower extremity motor weakness and muscle atrophy ( knee flexion , gr . 1 ; ankle dorsiflexion , gr . 4 ; and big toe dorsiflexion , gr . 3 ) . finally , we performed microscopic exploration at the l2 - 3 level and found that approximately 4 rootlets had herniated into the l2 - 3 disc space . we released the entrapped rootlets and repositioned them via the transdural approach , and the ventral dural defect was then closed with artificial dura . although the patient 's pain markedly alleviated after this surgery , she continued to experience knee flexion weakness , which has been ameliorating with rehabilitation . the patient showed improvement of the knee flexors with mild paresthesia of the lower extremities at the 6-month follow - up . incidental dural tear is a common complication of spinal surgery , and the reported incidence rates range from 3.1% to 14%3,11 ) . the risk of dural tears is increased by conditions such as fibrotic adhesion , scar tissue from prior surgery , eroded dura , or redundant dura in patients with large disc herniations2,8 ) . advanced patient age and the surgeon 's training level are other factors affecting the incidence9 ) . good long - term outcomes have been reported when incidental dural tears were recognized intraoperatively and repaired primarily3,5 ) . common sequelae associated with dural tear are headaches and wound infection in the short term and persistent cerebrospinal fluid ( csf ) leak , pseudomeningocele , neurologic deficits , and arachnoiditis in the long term3 ) . nishi et al.6 ) reported the occurrence of nerve root herniation into the facet joint through the arachnoid space after multiple laminectomies and discectomies . tppich et al.10 ) reported 2 cases of nerve root entrapment in the intervertebral space after lumbar discectomy . one of these cases was due to an unrecognized dural tear and the other from an incidental dural tear that was recognized and repaired using gelfoam and fibrin glue . the patients experienced temporary improvements immediately after surgery and then had sudden relapses of sciatic pain . ahn et al.1 ) summarized the typical symptoms of nerve root entrapment syndrome as follows : relapse of intractable radicular pain that may be either dermatomal or nondermatomal , resembles electric shock in nature , and depending on the location of the dural tear , is aggravated by walking or position change and is accompanied by various neurologic deficits . it is very important that the possibility of nerve root herniation be considered when a patient presents with these clinical features . when the dural tear is unrecognized , nerve root herniation is less likely to be diagnosed and treated with revision surgery if its presence is not strongly suspected . in the present cases , when postoperative mri confirmed the absence of hematoma , recurrent disc herniation , or infection , we misdiagnosed the patient 's relapse of sciatic pain after surgery as nerve root compression from remaining multiple lumbar stenoses . therefore , this report shows that nerve root herniation should be included as a differential diagnosis for new or recurrent sciatic pain after spinal surgery when there is no evidence of recurrence or infection on imaging studies1 ) . csf signal in the disc space on mri implies the presence of a dural tear . csf had collected in the disc space in the present cases , which we failed to recognize , but it had already been present immediately after surgery . since the csf collection was localized to the disc space , neither csf drainage through the wound drain nor csf collection in the posterior epidural space occurred . another important finding that can be observed on sagittal mri is nerve root displacement , which takes the shape of a gull 's wing . on retrospective review of the present cases , we could visualize this nerve root displacement through the ventral dural tear into the disc space . although a single rootlet is easy to overlook , a strong impression of its presence can be formed . it is our opinion that these 2 radiological findings are very useful for diagnosing nerve root herniation . in the present cases , we found a direct entrapment of the rootlet within the annulus of the intervertebral disc . several authors have reported dural tears in which the rootlet was irritated without direct entrapment1,10 ) , which induces pain only during movement . this can be diagnosed only by clinical manifestations and operative findings and not by imaging findings . patients who are at an increased risk for dural tears should be carefully examined when they complain of new or recurrent sciatic pain . although the imaging findings were highly suggestive of nerve root herniation , we focused on finding compressive lesions . this excessively narrow focus delayed diagnosis and treatment of these patients . re - exploration with repositioning of the herniated nerve root and repair of the dura with or without artificial dura must be performed as soon as possible . incidental dural tears do not adversely influence the long - term prognosis if they are properly repaired3 - 5 ) . in addition to nerve root herniation , unrepaired dural tears can lead to pseudomeningocele formation , persistent csf leakage , meningitis , or arachnoiditis7,11 ) . ahn et al.1 ) pointed out that unrecognized dural tears follow complex clinical courses because delayed widening of the dural opening by csf pressure can cause significant neural entrapment , which can not easily be detected . in the present cases , we found severe adhesion between the nerve root , the surrounding dura , and the intervertebral disc . since the diagnosis was delayed , the nerve root herniated through the ventral dura and closed the hole . while this stopped the csf leakage , inflammatory changes fixed the nerve root between the ventral dura and intervertebral disc . the most important aspects in the management of nerve root herniation are early recognition and prompt repair . clinicians must consider the possibility of nerve root herniation , especially in patients who are at risk for dural tears .
the authors report 2 cases of nerve root herniation after discectomy of a large lumbar disc herniation caused by an unrecognized dural tear . 
 patients complained of the abrupt onset of radiating pain after lumbar discectomy . 
 magnetic resonance imaging showed cerebrospinal fluid signal in the disc space and nerve root displacement into the disc space . 
 symptoms improved after the herniated nerve root was repositioned . clinical symptoms and suggestive radiologic image findings 
 are important for early diagnosis and treatment .