Cryptic osteoid osteoma of the cranium: case report. Osteoid osteoma is an uncommon benign tumor of bone that rarely involves the cranium. If often causes local pain that is worse at night, characteristically relieved by aspirin, and does not correlate with the size of the lesion. The diagnosis depends on skull radiographs and computed tomography. This report describes a case in which radiographs showed nothing abnormal. The diagnosis and operative localization were accomplished with radionuclide bone scanning. Thus, the possibility of radiographically cryptic lesions must be considered in the evaluation of atypical head pain syndromes. 