Presentation
Incidental finding on examination for vague headaches.
Patient Data
CSF enlargement of the left ambient cistern with mass effect on the medial aspect of the left temporal lobe is present. The collection follows CSF on all sequences. Coronal imaging will be of use to assess any effect on the left hippocampus. There is no susceptibility artifact to suggest blood products related to trauma. No diffusion restriction identified.
Conclusion:
Probable arachnoid cyst of the left ambient cistern.
Case Discussion
In many cases such as this, a histological confirmation is not possible, and one must rely on appearance and behavior. This patient has been scanned over a number of years with no change, and appearances are entirely consistent with an arachnoid cyst, albeit in a slightly unusual location.