ABSTRACT
Neoplastic cysts and cyst-like tumors In some patients, mass lesions of the brain cause their symptoms not by growth of tumor cells but by enlargement of a fluid-filled cyst. Some of these cysts are associated with neoplasms; others are not but must be considered in the differential diagnosis of neoplasm. Table 12.8 classifies these cysts. Many such cysts that accompany brain tumors, such as pilocytic astrocytomas and hemangioblastomas, are discussed in the chapters on those primary neoplasms. Cysts of infectious origin, such as cysticercosis and ex-vacuo cysts, i.e. those that result from loss of brain substance, are not
discussed in this book except in the context of differential diagnosis. The cysts discussed here fall into two large categories, those lined by neuroepithelium which secretes CSF and those that have a non-neuroepithelial lining secreting a fluid different from CSF; some of these latter lesions occasionally become true neoplasms. Lesions in these two categories can often be distinguished by MR scan (see below).
