Extra-axial Tumors

A variety of different neoplasms are united in the category of extra-axial brain tumors, ranging from benign to highly malignant entities, which often occur in distinct anatomical locations. Imaging features may include visibility of a CSF cleft or meningeal tumor base, and for some lesions, growth in the ventricular system is typical. Aggressive extra-axial tumors may invade the adjacent skull or brain. In many cases, the combination of patient demographics, lesion site, and image signal generates a narrow list of differentials, or even a single diagnosis. Cancers and nonneoplastic conditions may mimic certain benign tumors and are in some cases identifiable through subtle morphological differences. The following sections will discuss meningeal neoplasms, pineal region tumors, intraventricular tumors, and cranial nerve tumors with a focus on the value of clinical neuroradiology in their diagnosis. By the end of this chapter, readers will be familiar with characteristic and nonspecific imaging appearances of extra-axial tumors on different radiological techniques, able to devise a suitable imaging protocol based on lesion site, and to provide a comprehensive diagnostic report that can guide surgical planning and follow-up.