Pre-surgical Functional Brain Mapping

Among the issues that MEG/MSI, as well as all the other functional imaging techniques are called to address, is the identification of the brain regions mediating sensation, movement, language and memory. Advance knowledge of these regions facilitates surgical planning and reduces morbidity associated with resection of eloquent cortex, especially in cases of epilepsy surgery. Such knowledge was typically sought through invasive means such as the Wada procedure and direct cortical stimulation either intraoperatively or extraoperatively via implanted electrodes or subdural electrode grids. These invasive methods of brain mapping are now supplemented or replaced by non-invasive functional imaging techniques such as MEG/MSI and functional MRI.

Fig 2
Preoperative MRI scan from a patient with a left posterior inferior temporal cyst. Clusters of MSI-derived activity sources obtained in the context of two repetitions of a word recognition task are shown as red or yellow circles. Crossed lines indicate sites of effective intraoperative electrical stimulation documented.


TMS is being used to preoperatively map the location and extent of the motor cortex when a brain tumor or the epileptogenic focus is in close proximity to the motor cortex or the eloquent cortex, and surgery is considered. Preoperative motor mapping with TMS is becoming an important tool available to neurologists and neurosurgeons in planning surgeries. The TMS lab at Le Bonheur Children's Hospital has been operational since July 2012. In the figures below, Cases 1 and 2 are examples of presurgical mapping performed at Le Bonheur Children's Hospital. In addition, these Cases 3 and 4 demonstrate the utility of TMS in studying plasticity in the motor system.


Case 1: A 52 year old female diagnosed with a tumor in the left motor cortex. Motor mapping indicted that the mouth motor cortex was in the vicinity of the tumor while the hand motor cortex was not (left panel). The tumor was found to be near speech production areas (Broca’s area) (right panel).

Case 2: A 21 year old male whose tumor in the right frontal lobe was removed, continued to have seizures. His seizure focus was in the margins of the resection cavity. Motor mapping indicted that the hand motor cortex was along the posterior margin of the cavity.


Case 3: A 6 year old female had onset of seizures at 5 months of age and diagnosed with right hemisphere dysplasia and developmental delay. Patient underwent a right functional hemispherectomy at age 3. Presently patient continues to have seizures characterized by bilateral arm movements. The locations of primary motor cortex that innervate the right adductor pollicis brevis (APB) and adductor digiti minimi (ADM) muscles are normally located along the left precentral gyrus (blue and purple circles respectively). The cortical location of cortex that innervates the left brachioradialis (Brac) muscle is located in the left post central gyrus, (shown in yellow). The MEPs are shown in the right panel.

Case 4: A 6 year old male sustained a traumatic brain injury at 15 months of age, resulting in extensive encephalomalacia of the right cerebral hemisphere with secondary mental retardation and refractory partial seizure disorder. The patient currently has a limited use of his left arm, with no signs of muscular wasting. The locations of primary motor cortex that innervate the right hand muscles are located along the left precentral gyrus and post central gyrus (orange pegs). The cortical locations of cortex that elicited MEPs in both hands (indicating innervation of the left hand as well) are located in the left post central gyrus, (yellow pegs).

References

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Contact Us

Clinical Neurosciences
Department of Pediatrics
UTHSC College of Medicine
and
The Neuroscience Institute
Le Bonheur Children's Hospital
777 Washington Ave.
Memphis, TN 38105

Holly Smith, RN, BSN, CPN
MEG Coordinator
901-287-7126 (phone)
901-287-4540 (fax)
Holly.Smith@lebonheur.org