Initial evaluation of a patient with symptoms and signs suggestive of an intracranial mass lesion should consist of either a CT or MRI examination. If CT is the initial imaging study and an intracranial mass suspicious for glioma is shown, or if a normal or nonspecific CT examination is obtained in the setting of strong clinical suspicion for a mass, an MRI scan is usually obtained for complete evaluation.

Although MRI is well recognized to be a more sensitive imaging technique, CT is an acceptable alternative for the initial evaluation of many patients for several reasons. CT is less costly, is a more rapid imaging modality, and is generally more available compared with MRI. CT is also useful in patients who, because of severe claustrophobia, would need heavy sedation for an MRI examination. Patients with contraindications to MRI, such as a cardiac pacemaker or intracranial aneurysm clips, can also be studied with CT.

CT is often essential as a complementary study for patients with MRI-demonstrated intracranial lesions. CT provides detailed evaluation of bony anatomy and morphology for proper positioning of a craniotomy bone flap, for determining the number and placement of radiotherapy ports, and for evaluating patients with lesions adjacent to or invading the skull base or calvarium.

CT can also detect the presence of calcification associated with a mass lesion, which can help narrow the differential diagnostic possibilities. For example, peripheral calcification along the rim of a mass may indicate the correct diagnosis in cases of giant aneurysm that may mimic an intracranial neoplasm.

CT combined with the intravenous administration of an iodinated contrast agent provides additional information. The presence or absence of enhancement together with the pattern of enhancement helps to characterize a mass lesion. Small focal cerebral lesions such as metastases, and subependymal or leptomeningeal tumor extension may only be visualized following contrast injection. In cases of multiple lesions or lesions that incompletely or inhomogeneously enhance, the best site for biopsy is indicated by the brightest area of enhancement, which generally is the zone of the most actively growing tumor cells. Finally, postoperative tumor recurrence and radiation necrosis are both best detected on postcontrast imaging studies.