INTRODUCTION
Intradural disc herniation (IDH) was originally described by Dandy [1] in 1942 and is defined as the intervertebral disc nucleus pulposus displacement into dural sac. IDH comprises only 0.26% to 0.3% of all disc herniations, 92% of it occur in the lumbar region, of which 55% is seen in the L4–5 disc space followed by L3–4 (16%) and then by L5–S1 (10%) [2].
CASE REPORT
1. History
Patient was a 42-year-old male, he presented with severe acute low back pain radiating to the right lower limb with paresthesia and numbness. He had difficulty standing and walking, even after a few steps. The patient had bowel and bladder deficits. There had no history of fever or trauma. He had a history of L4–5 discectomy performed 5 years back for L4–5 disc herniation. Written informed consent was obtained from the patient for the publication of this case report.
2. Physical Examination
Bilateral paravertebral muscle spasm was noted. Passive straight leg raising was possible upto 30° on the right side and 50° on the left side. Neurological examination revealed absence of sensation in the S1, S2 dermatomes in right lower limb.
3. Radiological Findings
Magnetic resonance imaging showed a central disc bulge with right posterolateral herniation at L4–5 level (Figure 1).
5. Surgical Procedure
Posterior stabilization with laminectomy was done at L4–5 level. During laminectomy, adhesions were found on the dorsal dura. Adhesions were released from the dura with adequate care of dura. After achieving thorough decompression around the dura and the nerve roots, we could not encounter the disc fragment seen on magnetic resonance imaging (MRI) and disc like material was still palpable beneath the dura. This discrepancy prompted us to incise the dorsal dura, which revealed sequestered disc fragments within the dura (seen in Figure 2). Complete removal of sequestered disc fragments was done, followed by suturing of the incised dura.
This changed our diagnosis into “recurrent disc herniation L4–5 with intradural disc extrusion with cauda equina syndrome.”
Figure 3 is a postoperative x-ray showing L4–5 posterior stabilization with interbody fusion.
6. Postoperative Period
The patient had complete resolution of radicular pain in the lower limb, immediately after surgery. The patient was mobilized on the 3rd postoperative day. Perianal sensation returned on the 4th postoperative day with persistence of bowel and bladder incontinence. He was discharged with urinary catheter in situ after was educated about bladder training in the form of intermittent clamping.
The patient was evaluated through periodic follow-up. The patient began to appreciate the bladder sensation after 1 week. By the 15th postoperative day, the patient was able to achieve bowel control. The urinary catheter was removed, and intermittent self-catheterisation was advised on 40th postoperative day.
DISCUSSION
In our case, the dissection of dural sac was difficult and amount of disc fragment obtained was less than the expected after studying the MRI and palpating the disc fragments.
Autopsies have shown presence of adhesions between ventral dural sheath and posterior longitudinal ligament (PLL) which are loose in most cases. Adhesions may become resistant, unable to be separated through sharpless dissection, becoming an important predisposing factor and they are more common at L4–5 [4].
Possible attachment between anterior dura and annulus fibrosus, could facilitate the nucleus pulposus herniation into dural sac [3-5]. Congenital reduction of dural thickness, vertebral canal, congenital stenosis and previous surgeries are other predisposing conditions [6].
Despite the advancement and refinement in neuroimaging techniques, final diagnosis of IDH is made mostly during the intraoperative period [2]. Differential diagnosis of IDH can be neurofibroma, lipoma, meningioma, arachnoid cyst, epidermoid tumor, arachnoiditis and metastasis [7]. Prognosis is related to the duration of symptoms, kind of symptoms and history of previous surgery [2].
There are certain signs related to IDHs which can be appreciated in contrast enhanced MRI scans like the Crumble-disc sign, Y-sign and the Hawk-beak sign. These signs can help us in diagnosing IDHs preoperatively in cases with high suspicion.
Crumble-disc sign: Peripheral contrast enhancement seen in MRI after Gadolinium injection, the extradural part is compact at the entry into dura and intradural part seems to be less compact, with crumbled appearance, irregular borders and no contrast enhancement [8].
Y-sign: Sagittal image of an MRI shows hypointense structure seen splitting the ventral dura and arachnoid mater. Seen along with it are displacement of nerve roots and secondary soft tissue spinal canal stenosis [9].
Hawk-beak sign: In MRI, loss of continuity of PLL shown in sagittal acquisitions. Sagittal T2-weighted MRI shows like an extradural lesion like a hawk’s beak. T2 weighted axial sections show a triangular aspect of herniated disc, compressed laterally by the cartilaginous edges of annulus fibrosus which shows enhancement with Gadolinium injection [10].
CONCLUSION
Intradural disc extrusion is a rare pathology and confirmed intraoperatively. The typical symptoms include acute exacerbation of chronic back pain, and there is a higher incidence of cauda equine syndrome in IDH than in extradural herniation [3,11,12]. History of previous surgery (especially at L4–5 level), difficult dissection around the dura, palpable disc material even after complete decompression, discrepancy between preoperative radiological examination and intraoperative clinical findings should spark the need to consider ruling out intradural disc herniation. Prompt decompression surgery is necessary to steer treatment towards favorable prognosis.
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