CT in the diagnosis of supratentorial tumors

Abstract

T HE computed tomogram (CT) is approximately 98% accurate in detecting intracranial lesions,” and thus is one of the most effective detection systems utilized in medicine. In comparison, radionuclide scans detect about 75%80%” of intracranial masses. While they are especially effective in detecting higher grade astrocytomas, meningiomas, and abscesses, radionuclide scans are ineffective in low grade astrocytomas and cystic abnormalities. CT scanning is also highly useful in the evaluation or analysis of a lesion, not only permitting localization, but often yielding definitive information about its character. At the time of clinical presentation, many intracranial lesions have produced a definite mass. The mass may be solid or cystic, may be surrounded by edema, and may have variable inherent neovascularity. Furthermore, tumor may cause obstruction of the cerebrospinal fluid pathway, leading to hydrocephalus, which is clearly shown by CT. The tumor itself may calcify to a variable degree. It is well known that a high percentage of oligodendrogliomas calcify and that astrocytomas, especially those of lower grade, may also have associated calcification. Calcification is shown on plain radiographs in lo%-20% of meningiomas. We have been severely limited in our ability to discern this calcification in the past. CT has a greater sensitivity to differences in contrast and therefore allows detection of lesser concentrations of calcification than may be seen on plain skull films or even on conventional tomograms. CT detection of intracranial masses is based on changes related to the above-mentioned characteristics of intracranial lesions. Normal brain tissue has an EMI number ranging from approximately 8 to 20. Intracranial masses may or may not have