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Ventriculus terminalis or conus medullaris arachnoid cyst: a diagnostic dilemma
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  1. Sergio G Núñez Báez1,
  2. Orlando De Jesus1,
  3. Eduardo J Labat2 and
  4. Caleb E Feliciano1
  1. 1Neurosurgery, University of Puerto Rico Medical Sciences Campus, San Juan, Puerto Rico
  2. 2Department of Radiological Sciences and Diagnostic Radiology, Neuroradiology, University of Puerto Rico Medical Sciences Campus, San Juan, Puerto Rico
  1. Correspondence to Dr Orlando De Jesus; drodejesus{at}aol.com

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Description

A woman in her late 30 s complained of leg paraesthesias more prominent on the left, mild gait imbalance and bilateral leg spasms for the last 2 years. The symptoms aggravated during the prior month, and she was consulted at the emergency department. She denied urinary or faecal incontinence. The physical examination revealed numbness in the left leg and mild gait imbalance but no leg weakness. A thoracolumbar spine MRI with contrast showed a large non-enhancing cyst at the level of T11 with local compression of the conus medullaris (figure 1). Because of the progressive symptoms, the patient was taken to the operating room to drain the cyst. Under intraoperative neuromonitoring, a T11 bilateral laminectomy with a midline durotomy was completed with exposure of a supero-dorsally displaced conus medullaris due to a tense intramedullary cyst (figure 2). The cyst was fenestrated with a small midline myelotomy achieving adequate cyst drainage, decompression of the conus medullaris, and improved craniocaudal cerebrospinal fluid flow. A cysto-subarachnoid shunt using a 4 cm segment of an MRI compatible epidural catheter was introduced into the cyst cavity to minimise the probability of cyst recurrence. It was sutured to the overlying arachnoid layer with a prolene 6–0 suture. No changes in neuromonitoring were observed during the procedure. No cyst wall tissue was obtained to avoid an additional neurological deficit. In the early postoperative period, she showed improvement in leg spasms with fewer paraesthesias. Three months later, she continued improving her gait with fewer leg spasms.

Figure 1

(A) Preoperative MRI sagittal T2-weighted image showing the large cyst (yellow arrow) at the T11 level compressing the conus medullaris; (B) sagittal FLAIR image showing the cyst and depicting the neural tissue around it (yellow arrow); (C) axial T2-weighted image showing the cyst expanding the conus medullaris (yellow arrow).

Figure 2

(A) Intraoperative photo showing the enlarged conus medullaris due to the intramedullary cyst (black arrow); (B) small central myelotomy and cyst wall fenestration (black arrow); (C) cysto-subarachnoid shunt introduced into the cyst cavity through the fenestration (black arrow).

Although the MRI suggested that the cyst could be intramedullary, it was not possible to reach a specific diagnosis between an intramedullary arachnoid cyst (AC) versus cystic dilation of the ventriculus terminalis (VT). These two lesions are rare cystic lesions encountered in the conus medullaris region.1 2 The VT and intramedullary AC appear identically in the MRI, showing a hypointense signal in T1-weighted sequences and hyperintense in T2-weighted sequences with fluid characteristics similar to cerebrospinal fluid without cyst wall enhancement.3–6 A histopathological examination is the only way to differentiate them. The cyst wall of the AC is composed of arachnoid cells, and the cyst wall of the VT is composed of ependymal cells.6–9 Although imaging does not provide a specific preoperative diagnosis, other characteristics may support one diagnosis over another. Studies have reported a more eccentrical location for intramedullary AC than a midline location for VT.4 8 The management of these two benign cysts is similar, with fenestration of the cyst if it causes neurological deficits. A cystic VT classification system that considers the clinical presentation and symptom progression has been reported to offer adequate management strategies.5 6 For patients with progressive non-specific complaints, focal neurological deficit, or sphincter dysfunction, surgical treatment is the most appropriate option. Although the histopathological examination of the cyst wall can provide a final diagnosis, the risks of tissue sampling must be weighed against any benefits and should only be performed if the cyst wall shows enhancement.

Learning points

  • Ventriculus terminalis (VT) and intramedullary arachnoid cyst (AC) exhibit identical features on MRI with a hypointense signal on the T1-weighted sequences and hyperintense in T2-weighted sequences similar to cerebrospinal fluid.

  • A histopathological examination can differentiate between these two entities. The ventriculus terminalis cyst wall exhibits ependymal cells, while the AC wall is composed of arachnoid cells.

  • Cyst wall sampling must be weighed against any benefits. It should only be performed if the cyst wall enhances, suggesting the possibility of neoplasia.

Ethics statements

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References

Footnotes

  • Contributors Drafting the article: SNB, ODJ, EJL and CEF. Revising the manuscript: SNB, ODJ, EJL and CEF. Final approval of the manuscript: SNB, ODJ, EJL and CEF.

  • Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

  • Case reports provide a valuable learning resource for the scientific community and can indicate areas of interest for future research. They should not be used in isolation to guide treatment choices or public health policy.

  • Competing interests None declared.

  • Provenance and peer review Not commissioned; externally peer reviewed.