Imaging diagnosis and fundamental knowledge of common brain tumors in adults.

The most common primary brain tumors in Japanese adults are meningiomas, gliomas, pituitary adenomas, and schwannomas, which together account for 84.0% of all primary brain tumors. The typical imaging findings of these tumors are well known by radiologists; therefore, the clinical and pathological issues, including terminology, genetics, and relation to hormones are discussed in this article. Other diseases important for the differential diagnoses are also mentioned. The molecular genetic analysis of brain tumors has recently become important. For instance, genetic analysis is important for differentiating oligodendroglial tumors from astrocytic tumors, and the gene mutation predicts response to chemotherapy for anaplastic oligodendrogliomas. Background factors such as hormones, history of cranial irradiation, and medications influence oncogenesis, tumor growth, and tumor appearances as seen by imaging modalities. A differential diagnosis with knowledge of the above may have some advantages over diagnoses based on imaging findings alone. Nonneoplastic diseases such as abscesses and demyelinating diseases may mimic gliomas. Pituitary adenomas may be confused with nonneoplastic conditions such as physiological hypertrophy and Rathke's cleft cyst. Such misdiagnoses would result in a treatment protocol very different from what would be suitable. Such conditions should be carefully distinguished from neoplasms.