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| LETTER TO EDITOR |
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| Year : 2012 | Volume
: 60
| Issue : 1 | Page : 123-124 |
Intramedullary arachnoid cyst: Report of two cases
Rashim Kataria, VD Sinha, Sanjeev Chopra
Department of Neurosurgery, SMS Medical College, Jaipur (Rajasthan), India
| Date of Submission | 29-Oct-2011 |
| Date of Decision | 20-Nov-2011 |
| Date of Acceptance | 25-Dec-2011 |
| Date of Web Publication | 7-Mar-2012 |
Correspondence Address:
Rashim Kataria
Department of Neurosurgery, SMS Medical College, Jaipur (Rajasthan)
India
 Source of Support: None, Conflict of Interest: None  | Check |
DOI: 10.4103/0028-3886.93618
How to cite this article:
Kataria R, Sinha V D, Chopra S. Intramedullary arachnoid cyst: Report of two cases. Neurol India 2012;60:123-4 |
Sir,
Arachnoid cysts are benign lesions and usually asymptomatic. The origin of arachnoid cysts is not clear. The hypothesis proposed by Hyndman and Gerber [1] suggests that the cysts arise from the misplaced cellular remnants. The degenerating cells of the arachnoid trabeculae leads to an increase in the osmotic effect within the cyst, causing its enlargement. [2] A valve-like mechanism for enlargement of the cyst is also postulated. Intramedullary arachnoid cysts are rare and only nine cases have been reported so far. All previously reported patients, except one, belonged to the pediatric age group and none involved the conus medullaris. [3],[4],[5],[6],[7],[8],[9],[10] Here, we report two cases with intramedullary arachnoid cyst in the conus, confirmed on histopathology examination.
A nine-year-old female child presented with a one-year history of low backache, dribbling of urine, and numbness in both lower limbs of six months duration. Examination showed weakness in both ankles, saddle anesthesia, and decreased anal tone. Magnetic Resonance Imaging (MRI) of the thoracolumbar spine showed an intramedullary, non-enhancing Cerebrospinal Fluid (CSF) intensity cystic lesion at the conus medullaris ([Figure 1]- preoperative). She underwent L1-L2 laminectomy, dorsomedian myelotomy, and cyst decompression. The cyst contained clear fluid. Partial removal of the cyst wall was done as it was adherent to the cord tissue. She showed gradual improvement in power at both ankle joints and improved bladder sensations at six weeks follow-up. A repeat MRI ([Figure 1]- postoperative) of the thoracolumbar spine at six-month follow-up did not show any evidence of cyst. | Figure 1: (a,b) Preoperative sagittal T1 and T2W MRI of the TL spine in Case 1, showing a cystic intramedullary lesion at the conus medullaris. The lesion is isointense to the CSF. (c) Postoperative MRI of the same patient at six-month follow-up confirms removal of the cyst
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Another case, a 40-year-old female presented with progressive paraparesis and urinary symptoms of six months duration. MRI of thoracolumbar spine [Figure 2] showed a well-defined intramedullary non-enhancing mass with CSF intensity at L1. A dorsomedian myelotomy was done and the cyst decompressed. The cyst contained a clear CSF-like fluid. As the wall was adherent to the cord, only partial excision of the wall could be done. She regained power in the bilateral ankle joints and was continent at the four-week follow-up. | Figure 2: Sagittal and axial preoperative T1W MRI of the thoracolumbar spine in Case 2 showing cystic intramedullary lesion at the conus medullaris
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Histopathological examination of the cyst wall in both patients revealed fibrous connective tissue lined by arachnoid cells, suggestive of an arachnoid cyst [Figure 3]. | Figure 3: Photomicrograph of a section of the cyst wall illustrating its histological features with fibrous wall lined by arachnoid cells. Hematoxylin and Eosin (H and E, ×40)
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The first case of intramedullary arachnoid cyst was reported by Aithala et al. [3] in 1999. Of the nine cases of intramedullary arachnoid cysts reported so far, eight were in the pediatric age group; thus, probable embryonic malformations can be speculated as an etiological factor [Table 1]. [3],[4],[5],[6],[7],[8],[9],[10] In a recent study of 10 symptomatic cervical spinal intradural arachnoid cysts carried out by Lee and Cho, [11] eight cysts were found to be in the pediatric age group, and none was intramedullary in location. The characteristic MRI findings of an intramedullary arachnoid cyst include a cystic lesion of CSF intensity, hypointense to the normal cord tissue in T1-weighted images and hyperintense on T2-weighted images with no contrast uptake and no perilesional edema. Important differential diagnosis of a cystic conus lesion includes a terminal (fifth) ventricle, [12] focal syringomyelia, epidermoid, and ependymoma. However, it is often not possible to differentiate radiologically between an arachnoid cyst, focal syrinx, and terminal ventricle. The major pathological difference among the terminal ventricle, arachnoid cyst, and focal syrinx is that the epithelial lining of an arachnoid cyst is made of arachnoid (meningothelial) cells. The terminal ventricle and focal syrinx are lined by ependymal cells and neuronal cells, respectively. | Table 1: Literature review of patients with spinal intramedullary arachnoid cyst
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Management of benign cystic conus lesions (arachnoid cyst, focal syrinx, and terminal ventricle) remains the same irrespective of the pathology. Hence, it is not always mandatory as well as not possible to establish the diagnosis preoperatively. The treatment of the symptomatic intramedullary arachnoid cyst includes dorsomedian or dorsal root entry zone myelotomy with wide decompression of the cyst and removal of the cyst wall as much as possible in order to improve the clinical symptoms. Complete excision of the cyst is often not possible because the wall is adherent to the cord. In both of our patients, the cyst was decompressed via a dorsal myelotomy and most of the cyst wall was removed, leaving behind a small portion of the wall adherent to the cord. The other treatment option is wide fenestration of the cyst with or without shunting to the subarachnoid space.
| » References | |  |
| 1. | Hyndman OR, Gerber WF: Spinal extradural cysts, congenital and acquired. Report of cases. J Neurosurg 1946;3:474-86. 
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| 2. | Sharma A, Sayal P, Badhe P, Pandey A, Diyora B, Ingale H. Spinal intramedullary arachnoid cyst. Indian J Pediatr 2004;71:1444-6.
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| 3. | Aithala GR, Sztriha L, Amirlak I, Devadas K, Ohlsson I. Spinal arachnoid cyst with weakness in the limbs and abdominal pain. Pediatr Neurol 1999;20:155-6.
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| 5. | Sharma A, Sayal P, Badhe P, Pandey A, Diyora B, Ingale H. Spinal intramedullary arachnoid cyst. Indian J Pediatr 2004;71:65-7.
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| 6. | Sharma A, Karande S, Sayal P, Ranadive N, Dwivedi N. Spinal intramedullary arachnoid cyst in a 4-year-old girl: a rare cause of treatable acute quadriparesis: case report. J Neurosurg 2005;102:403-6.
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| 8. | Guzel A, Tatli M, Yilmaz F, Bavbek M. Unusual presentation of cervical spinal intramedullary arachnoid cyst in childhood: case report and review of the literature. Pediatr Neurosurg 2007;43:50-3.
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| 10. | Medved F, Seiz M, Baur MO, Probst EN, Tuettenberg J. Thoracic intramedullary arachnoid cyst in an infant Case report. J Neurosurg Pediatrics 2009;3:132-6.
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| 12. | Liccardo G, Ruggeri F, De Cerchio L, Floris R, Lunardi P. Fifth ventricle: An unusual cystic lesion of the conus medullaris. Spinal Cord 2005;43:381-4.
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[Figure 1], [Figure 2], [Figure 3]
[Table 1]
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