Preoperative CT scan of the head. A preoperative CT scan of the head with intrathecal contrast was done to localize the CSF leak. The frontal view is shown here. The scan shows a defect in the cribriform plate with confluent CSF extension into several bilateral ethmoid air cells, evidenced by the higher intensity signal of the contrast. Secondarily, there is mucosal thickening in the ethmoid and maxillary sinuses.