Presentation
Incidental finding
Patient Data
The computed tomography shows a cystic structure in the posterior fossa, behind the vermis that communicates with the fourth ventricle, hydrocephalus is observed with the involvement of the fourth ventricle and supratentorial ventricles. There is a deviation of the nasal septum of right convexity.
Case Discussion
This patient presented to the emergency room with a history of head trauma secondary to a motorcycle accident, with no previous significant history. He was referred for a CT to rule out intraparenchymal contusion and fractures, which were ruled out, however, a cystic image was accidentally found in the fossa posterior behind the vermis that communicates with the fourth ventricle, which is shown dilated in the same way as the supratentorial ventricles.
Possible differential diagnoses that can be mentioned mega cisterna magna is an enlarged cistern that measures more than 10 mm, with bone involvement but without the involvement of the vermis and normal fourth ventricle.
The arachnoid cyst is located behind or below the vermis in the medial sagittal region, the latter could be related to the case. For further assessment and differential diagnosis MRI can be utilized.
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