Atypical appearance of a premedullary cyst
Correspondence Address: Source of Support: None, Conflict of Interest: None DOI: 10.4103/0028-3886.246269
Source of Support: None, Conflict of Interest: None
Neuroenteric cysts (NEC) are uncommon, benign, extra-axial lesions of endodermal origin., Their intracranial occurrence is rare. They are usually seen ventral to the brainstem and in the cerebellopontine angle.,, Occasionally, NEC are present in supratentorial areas.,, Rarely, they occur in the foramen magnum region.
The radiological spectrum of NECs is wide, and an accurate preoperative diagnosis becomes difficult in occasional cases. In the present report, we describe one such atypical cyst at the foramen magnum area, which presented as a diagnostic dilemma as it was difficult to differentiate it from an exophytic cystic neoplasm.
A 26-year old lady presented with a 2-month history of insidious onset headache behind the left ear. The symptoms had worsened over a week's duration. The symptoms were also associated with recurrent episodes of vomiting. She had no neurological deficits. Magnetic resonance imaging (MRI) showed an extra-axial lesion predominantly occupying the left premedullary cistern, which was T1 hypointense, T2/fluid attenuated inversion recovery (FLAIR) hyperintense, and nonenhancing with gadolinium. Along the posterior aspect of the lesion, there was a fluid- fluid level (T1 hyperintense and T2 iso- to hyperintense) [Figure 1]. Also, there was marked T2 and FLAIR hyperintense signal noted in the pons and medulla, suggestive of edema. The possibility of NEC and other developmental cysts were considered. In view of brainstem edema, a low-grade cystic glioma was also kept as a differential diagnosis. The lesion was near-totally excised through the far-lateral approach. Intraoperatively, the lesion was cystic with a transparent wall and contained a milky white debris [Figure 2]. The portion attached to the vertebral artery was left behind. Histopathological examination of the cyst wall showed columnar mucinous epithelium consistent with a NEC. The patient had a symptomatic improvement after surgery.
A typical intracranial NEC is smooth, avascular, well-defined, thin-walled, round or lobulated lesion, iso-to-slightly hyperintense on T1 weighted images, hyperintense on T2/FLAIR images, and nonenhancing, located anterior to the pons/medulla. The signal intensities may differ (being hypointense, isointense or hyperintense on T1 and T2 weigted images) depending on the protein content of fluid. At times, the wall may partly enhance. On diffusion weighted imaging, they may show a mild restriction. Atypical forms with an enhancing mural nodule have also been reported. A NEC does not produce surrounding edema and this feature has never been reported earlier.
NEC occurring at the foramen magnum region are infrequent with less than 50 cases reported. In the present case, though NEC was considered in the differential diagnosis, there were a couple of atypical features that raised the suspicion of an intrinsic brainstem tumor with a large extra-axial cystic component. In the pontine and medullary area, T2/FLAIR hyperintense signals were noted, suggestive of brainstem edema. An extra-axial benign lesion is generally not expected to produce secondary signal changes in the brainstem. However, there have been reports in which extra-axial lesions that appeared apparently benign on radiology were proven to be of a malignant nature after a histopathological examination. Such instances, where a subtle imaging clue such as brainstem edema was overlooked, have been recently reported. Hence, we felt that it was prudent to consider a high-grade lesion in the differential diagnosis in these circumstances. The occurrence of the fluid- fluid level close to the brainstem suggested the possibility of an intrinsic brainstem neoplasm with bleeding into a large exophytic cystic component. However, the presence of an intracavitary bleed was ruled out on susceptibility weighted imaging.
In retrospect, this brainstem hyperintensity could possibly be attributed to reactive or inflammatory changes elicited by the protein content of the NEC in the adjacent brain parenchyma. It is known that the NEC may be adherent to the brainstem and surrounding neurovascular structures. Despite such adhesions, the radiological picture does not show apparent brainstem hyperintense signals. However, the present case had visible T2/FLAIR signal changes, which is unusual. The inspissated milky-white proteinaceous debris within the lesion could explain the presence of fluid–fluid levels.
NEC are frequently misdiagnosed as epidermoid cysts, especially the white atypical ones, which are T1 hyperintense.,,, They should also be differentiated from a neuroepithelial cyst, an arachnoid cyst, a dermoid cyst, a parasitic cyst, and a low-grade cystic glial neoplasm.,,, Rarely, craniopharyngiomas and colloid cyst at an ectopic location may cause a diagnostic confusion. Significant diffusion restriction and an irregularly appearing lesion insinuating into adjacent cisterns differentiates an epidermoid from a NEC., Arachnoid cysts usually present with cerebrospinal fluid like intensity in all MRI sequences. Tumors may show the enhancing wall in the areas composed of solid parts and may also reveal adjacent brain edema.
Total excision, when feasible, is the treatment of choice for NEC., However, it is not always possible, due to the adherence of the cyst to adjacent critical neurovascular structures. Recurrence is known and can occur from 4 months to as late as 14 years., Though other management modalities such as cyst aspiration, fenestration, biopsy, and partial cyst wall resection have been described, these are less recommended due to the high possibility of recurrence., Occasionally, chemical meningitis has been reported following the cyst excision, possibly secondary to spillage of its contents. Aspiration of the contents of the cyst before incising the cyst wall, packing the subarachnoid space with cotton patties, and irrigation with warm saline are recommended to prevent such a complication from occurring.
To conclude, the presence of fluid–fluid levels in a NEC is unusual. Furthermore, the associated parenchymal signal changes have not been described earlier. The report thus highlights an atypical imaging and adds to the varying radiological spectrum of a NEC.
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The authors certify that they have obtained all appropriate patient consent forms. In the form the patient has given her consent for her images and other clinical information to be reported in the journal. The patient understands that the names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.
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There are no conflicts of interest.
[Figure 1], [Figure 2]