History of arachnoid cyst. Yearly follow up to evaluate change in size. There is redemonstration of a cystic lesion centered on the right aspect of the quadrigeminal plate cistern measuring 3.2 x 2.4 cm, which is unchanged in size. The lesion follows CSF signal characteristics on all sequences. There is no nodularity within the lesion. There is associated significant flattening of the right posterolateral midbrain and the right cerebellar vermis to a similar degree as prior exams. The cerebral aqueduct remains effaced, however, the ventricles are unchanged in size and configuration.There is no evidence of intracranial hemorrhage or acute infarct. The brain parenchyma appears unremarkable. The ventricles and basal cisterns are unchanged in size and configuration. There is no midline shift or herniation. The skull and extracranial soft tissues are unremarkable. There is left maxillary sinus mucosal thickening and some fluid within the left mastoid air cells. There is prominence of the adenoid tonsillar tissue which can be normal in this age group.
No significant change in size or appearance of a cystic lesion occupying the right aspect of the quadrigeminal plate cistern, most compatible with an arachnoid cyst. 