Neurology India Medknow Publications on behalf of the Neurological Society of India ISSN: 0028-3886 EISSN: 1998-4022 Vol. 58, Num. 6, 2010, pp. 964-966

Neurology India, Vol. 58, No. 6, November-December, 2010, pp. 964-966

Letter to Editor

Thoracic intramedullary arachnoid cyst

Batuk Diyora, Hanmant Kamble, Naren Nayak, Praful Dugad, Alok Sharma

Department of Neurosurgery, L.T.M.G. Hospital, Mumbai, India

Correspondence Address:
Batuk Diyora
Department of Neurosurgery, L.T.M.G. Hospital, Mumbai
India
bddiyora@hotmail.com

Date of Acceptance: 22-Jul-2010

Code Number: ni10275

PMID: 21150077

DOI: 10.4103/0028-3886.73774

Sir,

Arachnoid cysts are benign developmental cysts that occur in the cerebrospinal axis in relation to the arachnoid membrane. A spinal arachnoid cyst is often encountered as an incidental finding and rarely causes spinal cord compression. ^[1] Spinal arachnoid cyst usually occurs in the pediatric population and is located in the thoracic or cervical cord. Intramedullary location of the arachnoid cyst is rare, with only a few cases reported in the literature. ^{[2],[3],[4],[5]}

A 45-year-old man presented with a history of midline thoracic back pain of 2 years' duration. Ten days prior to his presentation, he had noticed increased severity of pain and weakness in both the lower limbs, which progressed to paraplegia with urinary and fecal incontinence. Neurological examination revealed a flaccid paraplegia with absence of superficial and deep tendon reflexes. There was no muscle wasting. Below T6 level, all modalities of sensation were lost. Hematological and biochemical examinations revealed no abnormality. Lumbar cerebrospinal fluid (CSF) examination was unremarkable. Magnetic resonance imaging (MRI) of dorsal spine revealed a non-enhancing cystic intramedullary lesion at T4 to T5 level measuring 3.1×1.4 cm, which was hypointense on T1-weighted images and hyperintense on T2-weighted images [Figure - 1]. Screening of the cervical and lumbar regions of the spine showed no abnormality.

He underwent a T3 to T5 laminectomy. The cyst was identified just below the cord surface after a midline myelotomy. The cyst was bluish, thin walled; and clear fluid drained out under pressure. Cyst wall was partially excised as it was adherent at places to the spinal parenchyma. No communication with the subarachnoid space or an extramedullary component was present. Microscopic examination of the cyst wall showed fibrous connective tissue lined by arachnoid cells, consistent with the diagnosis of arachnoid cyst [Figure - 2]. Postoperatively, he had complete relief of pain, while his motor power improved to normal over a period of 6 weeks [Figure - 3].

Unlike intracranial arachnoid cysts, spinal arachnoid cysts are uncommon and may be located either intradurally or extradurally. Extradural cysts result from an extradural out-pouching of the arachnoid that is contiguous with the spinal subarachnoid space via a small dural defect. Intradural cysts are out-pouchings of arachnoid that, regardless of size, lie entirely within the dural space; these are more common than extradural cysts. Both these types may or may not communicate with the subarachnoid space. ^[6],[7]

Intramedullary arachnoid cysts are rare, and so far only 9 such cases have been reported. Aithala et al. reported the first case of intramedullary arachnoid cyst in a 7-year-old boy who presented with diffuse abdominal pain and progressive weakness of the lower extremities. ^[2] Literature review of reported cases shows that these lesions are commonly seen in the pediatric population in the first and second decades of life, more common in females as compared to males, and are located more commonly in the thoracic region than in the cervical region.

Regarding the etiology of these lesions, several theories exist, suggesting that the occurrence of these lesions is attributed to congenital defect, or to arachnoid adhesion due to inflammation because of various causes. ^[6],[7],[8] The hypothesis proposed by Hyndman and Gerber is that the cyst arises from misplaced cellular remnants as a result of the embryonic malformation. ^[9] Ball valve mechanism and fluid shifts as a result of pathological distribution of the arachnoid trabaculae have been postulated for increase in the size of extramedullary cyst. However, the cause for increase in the size of the intramedullary cyst needs to be established.

MRI plays a vital role in diagnosis and treatment planning of these lesions. The differential diagnoses of intramedullary cystic lesions include primary and secondary syrinx, tumor (astrocytoma, ependymoma, teratoma, ganglioglioma)-associated syrinx, epidermoid cyst and synovial cyst. With the widespread availability of MRI, more cases of asymptomatic intramedullary cyst are likely to be reported. However, a wait-and-watch policy appears to be justified for these cases.

Although percutaneous drainage of the cyst and shunting procedure have been reported in the management of spinal extramedullary arachnoid cysts, surgical excision is the treatment of choice for intramedullary cysts.

References

Copyright 2010 - Neurology India

The following images related to this document are available:

Photo images