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Year : 2001  |  Volume : 11  |  Issue : 2  |  Page : 95-96
Intraspinal/extradural lumbosacral arachnoid cyst causing bone erosion & nerve root compression - Ct myelography findings

Dhwani Kiran Diagnostic Pvt. Ltd, Sangli, India

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How to cite this article:
Joshi A, Kulkarni A. Intraspinal/extradural lumbosacral arachnoid cyst causing bone erosion & nerve root compression - Ct myelography findings. Indian J Radiol Imaging 2001;11:95-6

How to cite this URL:
Joshi A, Kulkarni A. Intraspinal/extradural lumbosacral arachnoid cyst causing bone erosion & nerve root compression - Ct myelography findings. Indian J Radiol Imaging [serial online] 2001 [cited 2021 Feb 26];11:95-6. Available from:

We have reported a symptomatic histopathologically proved and operated case of posterior extradural arachnoid cyst (Tarlov cyst) in the lumbo-sacral region with an unusual bone pressure erosion.

A forty-years-old woman presented with a history of low back pain and progressive paraplegia with unstable gait and diminished sensation below the knee of six months duration with no history of trauma. On examination she was found to have weakness of the calf muscles with exaggerated ankle reflexes, more on the left side. There was no wasting of muscles. The SLR was positive on either side (Rt. 80, Lt. 70). All the routine investigations including hemogram and ESR were within normal limits.

The plain radiograph of the spine showed non-specific degenerative changes. No pressure erosive changes in vertebral bodies or appendages were obviously appreciated in the AP and lateral radiographs.

Lumbar myelography [Figure - 1] with nonionic contrast media revealed displacement of the thecal sac in the L5/S1 region antero-medially from the right side with caudal narrowing. All the roots filled well & revealed normal axillary angles except L5 root on the right side, which showed opening of the axillary angle. This was further evaluated with a CT examination, which was done immediately following myelography (MCT).

The CT examination revealed an extradural cystic lesion containing low attenuation tissue in the L5/S1 region on the right side in the extradural space extending posteriorly. Due to indentation of the sacrum and low attenuation values of the lesion on CT, a long standing benign cystic lesion was suspected causing compression of the theca, effacing the nerve roots of the L5/S1 region on the right.

During surgery, the cystic lesion was noted arising from the right L5 nerve root communicating with the CSF space with a well identifiable neck. The cystic lesion was resected and fenestrated followed by laminectomy. The patient regained power in both lower extremities as well as had an uneventful recovery in the post-operative period.

Histologically, the cyst membrane was arachnoid and therefore was diagnosed as a spinal arachnoid cyst.

Extra-dural arachnoid cysts are small cystic dilatations of nerve root sheaths, commonest in the cervical and lumbo-sacral regions []. In the latter, they may reach several centimeters. They may fill slowly with contrast medium and differentiation from an intrasacral meningocele may be difficult - if the neck is not seen clearly. The sacral cyst may occasionally cause compression [2]. Earlier these dilatations were considered as normal variants in a large majority of patients [2]. The expansion of the lesion in the spinal canal may occur since they communicate with subarachnoid space. They cause symptoms by compressing the spinal cord or roots.

The pathogenesis of arachnoid cysts is unclear, although congenital, traumatic & inflammatory causes have been postulated. The cyst may arise in relation to the nerve root, within the subarachnoid space or even outside the dura mater - accordingly these are classified as either extra or intradural.

Almost all intradural arachnoid cysts lie posteriorly [3], they are most commonly in the thoracic region and very occasionally cause cord compression. They are often demonstrated best with the patient supine. There may be hold up of contrast at the base of the cyst and while contrast medium enters a cyst easily, it leaves with great difficulty.

Extradural cysts are rare. The cyst communicates through a small defect in the dura mater and characteristically lies posterior. The usual presentation is with spinal cord compression. Plain radiographs may demonstrate focal expansion of the spinal canal. In the prone position the cord may show compression. The present case falls in this category; the cyst caused pressure indentation over the sacrum - a rare finding. Complete relief by surgery is reported in literature; recovery has been upto 87 % for intradural arachnoid cysts.

The differential diagnosis includes avulsion of root which occurs following trauma - road traffic accident & is usually associated with fractures. All of them will have various degree of sensory & motor losses. The myelogram in these cases show characteristic traumatic pseudomeningocele [4]. Pressure bony erosion are not seen in avulsion of the nerve root injury.

   References Top

1.Tarlov I.M. (1953) Sacral nerve root cysts. Springfield: Thomas  Back to cited text no. 1    
2.Larsen et al: 1980 - Arachnoid diverticula & cyst like dilatations of the nerve root sheaths in lumbar myelography - Acta Radiol, 21 (141-145).  Back to cited text no. 2    
3.Rimmelin et al.:Department of radiology 2 & neurosurgery, university hospital of strasbourge of thoracic & lumbar spinal extradural arachnoid cysts: neuroradiol: 1997 M.39 (3), 203-6.   Back to cited text no. 3    
4.Chin CH et al: Institute of orthopaedics & traumatology, hospital, Kaula Lumpur, Malaysia. Lumbo sacral nerve root avulsions injury: 1997 Nov-Dec; 38(9-10): 674-8.  Back to cited text no. 4    

Correspondence Address:
A Joshi
Dhwani Kiran Diagnostic Pvt. Ltd, Sangli
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Source of Support: None, Conflict of Interest: None

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[Figure - 1], [Figure - 2], [Figure - 3], [Figure - 4]


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