Presentation
Female with a history of meningitis three months ago, intense headache, fever, positive Kernig and Brudzinski, stiff neck.
Patient Data
Irregularly shaped extra-axial lesion in the prepontine cistern with well-defined borders, showing intense signal on T1WI and intermediate signal on T2WI and slightly hyperintense signal relative to the pons on FLAIR. It does not exhibit diffusion restriction or post-contrast enhancement. The lesion surrounds the basilar artery without compressing it, fills the right cerebellopontine angle cistern and bulges into the right internal porus acusticus, surrounding the right facial and vestibulocochlear nerves and ending at the level of the glossopharyngeal and vagus nerves and proximal part of the right PICA.
A smaller lesion of the same character traverses the foramen magnum, abutting the right anterior aspect of the brainstem and communicating with the more superior lesion.
Case Discussion
A well-defined round mass with smooth margins, located anterior to the brainstem is the characteristic presentation of intracranial neurenteric cysts.
Wide range of signal intensity on T1 and T2 weighted images is attributed to its variable protein content; most frequent presentation is iso- to hyperintense signal with respect to brain parenchyma on T1 and hyerintense signal on T2. However, about 10% of cases show high signal intensity on T1 and intermediate intensity on T2, as in this case.
Absence of intralesional fat renders the diagnosis of a dermoid cyst less probable.
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