FIG 4. Case 2: 5-year-old boy with arachnoid cyst.

A, Axial T2-weighted FSE (4000/92/2) MR image reveals a cystic-appearing right petrous apex lesion with CSF signal intensity contiguous with Meckel's cave (black arrows). Also noted is an ipsilateral mastoid effusion (open arrow).

B, Enhanced axial T1-weighted SE (450/12/2) MR image shows a lesion in the apex with CSF signal intensity (white arrows). Open arrow denotes complex effusion.