Fig 2. Patient 4. CT underestimates defect size by 2 mm. Sagittal MPR image from 1.25-mm axial dataset demonstrates a 13-mm defect in the posterior wall of the right frontal sinus with soft tissue suggestive of encephalocele protruding through the defect. At endoscopy, this was a 15-mm defect. MR was performed preoperatively and showed no encephalocele.