The 'padlock sign' in computed tomography of the head.

In computed tomography (CT) of the head, some lesions may enhance after intravenous injection of contrast material as semisolid or semicystic lesions resembling a padlock. Thirty-five patients whose scans showed padlock-shaped enhancement patterns were followed up and proved to have the following: 12 gliomas, 9 abscesses, 8 metastases, 3 tuberculomas, 1 craniopharyngioma, 1 meningioma and 1 cystic prolactinoma. The sign is probably caused by excentric cavitation in a solid lesion, or partial-volume averaging of the capsule in an irregularly shaped cystic lesion.