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Images in Neurology
May 2000

Functional Magnetic Resonance Imaging Localization of Motor Function

Arch Neurol. 2000;57(5):749. doi:10.1001/archneur.57.5.749

A 44-YEAR-OLD right-handed woman had a 4-year history of simple partial seizures (focal motor activity involving the left side of the face and mouth) and rare secondary generalized tonic-clonic seizures associated with a right frontal lobe mass. After 4 years, the slowly enlarging lesion led to patient referral to us for evaluation. Taking antiepileptics, she had no generalized seizures but several partial seizures per month. Routine magnetic resonance imaging (MRI) (Figure 1, A) revealed a nonenhancing lesion of the right frontal lobe. Blood-oxygen level–dependent functional MRI during left wrist flexion was localized (Figure 1, B). Functional MRI reveals disproportionate changes in blood flow related to oxygen use in response to neocortical activation. An increase in blood flow increases the amount of deoxygenated (paramagnetic) hemoglobin, leading to higher MRI signals from the activated tissue. Concern that the tumor might be adjacent to or involve motor cortex led to placing a 64-contact subdural grid over the lesion for seizure localization and functional mapping (Figure 1, C) before planned resection. Spontaneous seizures originated from the posterior margin of the tumor near contacts 38 and 46 (Figure 1, C, crosses) near the motor cortex representing the left side of the face. Functional mapping of the motor cortex by sequential stimulation of the subdural grid contacts revealed that the arm and hand movements localized to a region of cortex that included the region identified by functional MRI, providing excellent correlation of the 2 mapping modalities. On tumor resection, pathological examination revealed a low-grade oligodendroglioma. Postoperatively she had no motor deficits and has had only 1 simple partial seizure in over 18 months since surgery.

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