Presentation
Headache, dizziness, no focal neurological symptoms.
Patient Data
There is a cystic lesion of extra-axial origin with unclear borders, located in the posterior fossa, just below the cerebellar vermis and the floor of the 4th ventricle, extending to the cisterna magna and foramen magnum. This mass displays a signal similar to cerebrospinal fluid on all imaging sequences, specifically low on T1, FLAIR, and high on T2W, GRE, with no restriction of diffusion (low on DWI and ADC).
The mass exerts a mass effect on adjacent structures, causing compression of the brainstem and cerebellar hemispheres.
Case Discussion
The findings on MRI are consistent with a posterior fossa arachnoid cyst, accompanied by a mass effect on the brainstem and cerebellum.
This is a common extra-axial cystic lesion of the central nervous system, often discovered incidentally and asymptomatic. When the lesion is large and exerts a mass effect in locations such as the posterior fossa, sellar/suprasellar regions, quadrigeminal area, and cerebellopontine angle, it may cause clinical symptoms. These lesions are benign, and if they lead to significant symptoms, consideration can be given to open surgery (fenestration or resection) or placement of a cyst-peritoneal shunt. A rare complication to note is spontaneous rupture into the subdural space.
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