Fig 5. A–E, A 38-year-old woman (patient 24) with a history of meningitis 2 months ago. After sudden onset of a headache, the axial CT (A, B) shows a fluid level within the sphenoid sinus and subarachnoid air in the right prepontine and suprasellar cistern. At 14 days later after referral for further evaluation, sagittal CT (C) shows an aerated sinus and a small osseous defect within the posterior wall of the sphenoid sinus (arrow). Sagittal T2 and T1-weighted MR images (D, E) depict a small lesion (arrow) that herniates into the sphenoid sinus. Only in the clinical setting of CSF rhinorrhea the lesion is suspected to correspond to arachnoid herniation.