Preoperative Planning

One promising clinical application for fMRI is in preoperative planning and risk assessment. Since fMRI allows for the creation of maps of brain activity corresponding to the performance of a specific task, one natural use of fMRI is in identifying areas of the brain that are functionally important and therefore should be carefully avoided during neurosurgery. It should be emphasized that it is the creation of maps specific to the individual patient in question (rather than maps based on averages across many subjects) that is of use to the surgeon. Functional MRI is particularly well suited to the creation of such individualized maps.

Intractable focal epilepsy is sometimes treated by excising the epileptogenic focus surgically. In this context, "intractable" means "not successfully treated with drugs,'' and "focal" means that there is a single site that appears to be the source or trigger for the epileptic seizures.) The areas to be removed are often close to brain areas critical to language (so-called "eloquent" cortex), so surgeons must exercise extreme caution lest their patients acquire severe language impairments as a result of the operation. For most adults, language function is strongly lateralized, meaning that damage to one hemisphere (typically the left) has much greater consequences for language comprehension and production than damage to the other (typically the right) hemisphere. Approximately 95% of right-handed individuals are left lateralized for language, whereas left-handed individuals show a much more variable language lateralization (both in left versus right and in the degree of lateralization). Historically, the best procedure for assessing the side and degree of language lateralization in an individual patient has been the Wada test. In this procedure, amobarbitol is injected unilaterally into the left or right carotid artery, resulting in the anesthetization of the corresponding hemisphere of the brain. Both sides are tested in this way. If the subject is relatively unimpaired on language and memory tasks performed during the anesthetization of one hemisphere, then it is deemed safe to operate on that hemisphere. Functional MRI offers several advantages over the Wada test: It is completely noninvasive, and it provides a better estimate of areas important to language within each hemisphere. In the early days of attempting to use fMRI to assess language lateralization, the results were equivocal. Today, fMRI is a robust measure of language lateralization. On the other hand, fMRI has not been demonstrated to be as sensitive a measure of memory function as the Wada test, but progress is being made. At least one hospital in the United States has replace the Wada test with fMRI for presurgical planning, but use of this alternative is not widespread. Notwithstanding this slow start, it can be speculated that the first generally accepted clinical application of fMRI will be as a replacement for Wada test.

More detailed functional maps are being developed for presurgical planning and risk assessment relevant to other brain areas (besides eloquent cortex). For instance, during the surgical removal of tumors and other abnormalities near the central sulcus, one risk is the unnecessary removal of portions of primary motor cortex, resulting in serious impairments of motor control. Functional MRI has been used to map the boundaries of primary motor cortex in order to help weigh the risks and benefits of various treatment options. Obtaining an accurate, individualized functional map in this instance is particularly important because brain abnormalities in question often displace structures and make anatomical landmarks ambiguous as well as potentially disturbing the underlying functional maps of normal brain structures. Depending on the type of tumor, if fully resecting a tumor would endanger primary motor cortex, then partial resection might be in the patient's best interest. If, on the other hand, the entire tumor can be safely removed without endangering primary motor areas, then it is in the patient's best interest to remove the entire tumor.

Breaking Bulimia

Breaking Bulimia

We have all been there: turning to the refrigerator if feeling lonely or bored or indulging in seconds or thirds if strained. But if you suffer from bulimia, the from time to time urge to overeat is more like an obsession.

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