Excerpt from EEG in Brain Tumors

Synonyms, Key Words, and Related Terms: breach rhythm, brain neoplasms, electroencephalography, intermittent rhythmic delta activity, polymorphic delta activity

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Until the past 3 decades, localization of brain tumors and other focal lesions was difficult. Neuroimaging techniques consisted of skull radiography, which was usually negative, and pneumoencephalograms, which were invasive, painful, and often uninformative. In 1936, Walter, who introduced the term "delta waves," first identified the association between localized slow waves on EEG and tumors of the cerebral hemispheres. This established EEG as an important tool for localizing brain tumors. For the next 4 decades, electroencephalographers mounted an enormous effort to improve accuracy of localization and to seek clues to underlying pathological processes.

Experience has shown EEG to be somewhat reliable in localizing lesions involving superficial accessible portions of the cerebral hemispheres, though it is of limited value in deep-seated lesions, especially posterior fossa tumors. The role of EEG in detecting focal cerebral disturbances has undergone a significant change since the development of CT scan and MRI. Today EEG is used primarily to complement these studies by evaluating functional changes in the patient's condition; it demonstrates aspects of brain physiology that are not reflected in structural neuroimaging. Functional neuroimaging techniques, such as positron emission tomography (PET), single-photon emission computed tomography (SPECT), and functional MRI (fMRI), can exhibit physiologic changes but not with the temporal resolution of EEG. Furthermore, EEG provides the only continuous measure of cerebral function over time.

This article reviews the major EEG changes that occur with different brain tumors, as determined by location, histologic type, associated complications, and surgical and nonsurgical treatments. For excellent patient education resources, visit eMedicine's Cancer and Tumors Center and Procedures Center. Also, see eMedicine's patient education articles Brain Cancer and Electroencephalography (EEG).

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