Spinal extradural arachnoid cyst: Rare cases from Indian Institutes.

BACKGROUND: Spinal extradural arachnoid cyst (SEDAC), accounting for approximately 1% of all spinal lesions, rarely causes compressive myelopathy. It is usually found at lower thoracic or upper lumbar levels in males in their forties to sixties. The standard surgical procedures include direct dural repair. CASE DESCRIPTION: A 37-year-old male presented with myelopathy attributed to a type I meningeal cyst (SEDAC) that was successfully managed with a laminectomy, cyst excision, and direct dural sleeve repair. Similar cases reported in the literature were also reviewed.
CONCLUSION: SEDACs, although rare, must be considered among the differential diagnoses for compressive myelopathy/neurogenic bladder. Copyright:

INTRODUCTION

Spinal extradural arachnoid cyst (SEDAC) is a rare cause of compressive myelopathy, accounting for approximately 1% of all spinal lesions.[1] Pathologically, they are comprised of herniation of arachnoid through an obvious or occult dural defect. These SEDACs can be congenital or an acquired due to trauma, infection, inflammation/arachnoiditis, or iatrogenic (e.g., postsurgical: (1) decompressive laminectomy for cervical compressive myelopathy or (2) after a simple lumbar puncture).[2] These lesions tend to enlarge secondary to progressive/recurrent trapping of cerebrospinal fluid within the “cystic” cavity.[1,2] They are found most typically in the lower thoracic or upper lumbar spinal levels and are more commonly seen among males in their twenties to fifties.[7]

Here, along with a literature review, we present a 37-year-old male with a SEDAC successfully managed with a laminectomy, excision of cyst, and defective dural sleeve repair.

CASE REPORT

A 37-year-old male presented with progressive lower extremity paraparesis of 3 years duration (motor power of 3/5 in both legs with a 0/5 left foot drop for 1 year). There were no history of back pain, significant trauma, spinal surgery/lumbar puncture, or tuberculosis.

The thoracic MR showed, on axial cuts, an arachnoid cyst with lateral extension into both neural foramina between the T12-L1 levels; no further lesions were noted on the cervical or lumbar MR studies.

Surgery

The patient underwent L1 preserving laminectomies from T11 to L2 [Figures 1-3], revealing a distended cyst. Thinning of the dura with arachnoid herniation was observed involving both T12-L1 neural foramina (e.g., especially on the right). The dural defect was directly repaired using a nonabsorbable monofilament suture made of expanded polytetrafluoroethylene (GORE-TEX) plus application of a small muscle patch graft. The wound was then routinely repaired in layers, with a drain placed in the epidural space.

Figure 1:

(a) T2-W MRI sagittal images disclose a well-defined uniformly hyperintense (identical to CSF) cystic multiseptate lesion extending from the lower end of the T10 vertebral body to the lower end of L2 vertebral body. The bulk of the lesion is seen to create a mass effect and compression over the cauda equina. (b) T1-W MRI sagittal images after contrast injection reveal a well-defined uniform hypointense multiseptate lesion with no evidence of enhancement within the substance or peripheral wall of the lesion. (c and d) T2-W MRI axial images, at the level of T12 and L2, disclose well-defined uniform hyperintense lesion with compression and displacement of conus as well as caudal roots at respective levels. The lesion is seen to be extended into intervertebral foramen at the level of T12.

Figure 3:

(a) Intraoperative picture after fenestration and decompression of the cyst, the collapsed wall is seen extending into neural foramina between T12 and L1 vertebral level, where the dural defect was identified and repaired using 4–0 Prolene with muscle patch and fibrin glue. (b) After complete excision of cyst, dura is noted to be adequately decompressed (no evidence of CSF leak on Valsalva maneuver subsequently).

(a) Intraoperative picture (under microscope) after T11-L2 laminectomy. Upper pole of large cystic lesion noted hanging over the underlying intact dura, while the inferior end is extending under L1 lamina which was preserved in tailored exposure. (b) Distended cyst wall is seen extending into the left neural foramina between T12 and L1 vertebral level. (c) Distinguished plane between cyst wall and native dura is clearly seen under the cranial pole of the cyst. (d) Distended cyst wall is seen extending into right neural foramina between T12 and L1 vertebral level.

Pathology

The histopathological examination revealed collagenous tissue within the wall of the cyst with occasional cuboidal and flattened cells, suggestive of a meningothelial reaction.

Postoperative course

Immediately after surgery, the patient had dramatic relief in his symptoms. The follow-up MRI 3 months later confirmed complete excision of cyst and thecal sac decompression. By 9 postoperative months, the patient was completely asymptomatic.

DISCUSSION

Nabors three part classification of spinal arachnoid cysts

According to Nabors classification,[3] spinal arachnoid cysts are of three types. Extradural cysts (SEDAC); without and with involvement of nerve root are Type I and Type II cysts, respectively. All intradural cysts are Type III cysts.

Clinical manifestations of SEDAC are usually myelopathy, radiculopathy, or neurogenic bladder. SEDAC can either be congenital in etiology or sporadic. The former is caused by mutations in the FOXC2 gene and is inherited as a part of lymphedema–distichiasis syndrome.

Various surgical strategies have been described ranging from complete microsurgical resection to simple fenestration followed by closure of dural defect.[1,2,5] Lee et al. demonstrated that recurrence of the cyst was dependent on the extent/ adequacy of dural closure and not on the completeness of surgical excision.[5] Dural defects are usually found around nerve root sleeves, possibly due to tension across the movable dural sac and relatively fixed nerve roots. As laminectomy increases the risk of future kyphotic deformity, some surgeons advocate a tailored laminectomy with cyst fenestration allowing for dural defect repair rather than attempting complete cyst resection and increasing the risk of instability.[4]

Review of seventy prior SEDAC cases

A total of seventy SEDAC cases have been reported, including 42 males and 28 females.[1-7] The predominant postoperative complication remains cyst recurrence [Table 1].

Table 1:

Summary of spinal extradural arachnoid cyst cases reported from India.

CONCLUSION

Type 1 meningeal cysts can cause compressive myelopathy in the thoracolumbar region. Here, it was successfully managed with laminectomy, cyst excision, and direct repair of the dural defect.