Mapping of the Motor Cortex

Abstract

The resection of brain tumors located within or near the eloquent tissue has a higher risk of postoperative neurological deficits. The primary concerns include loss of sensory and motor functions in the contralateral face, upper and lower extremities, as well as speech deficits. Intraoperative neurophysiological monitoring (IONM) techniques are performed routinely for the identification and preservation of the functional integrity of the eloquent brain areas during neurosurgical procedures. The IONM modalities involve sensory, motor, and language mapping, which helps in the identification of the boundaries of these areas during surgical resection. Cortical motor Mapping (CmM) technique is considered as a gold-standard technique for mapping of the brain. We present the intraoperative CmM technique, including anesthesia recommendations, types of electrodes, as well as stimulation and recording parameters for successful monitoring.

Keywords: brain tumor; cortical mapping; eeg; electrocorticography; ionm; motor mapping; neuro-monitoring; neuro-surgery.

Figure 1. Subdural grids.

Schematic presentation of the subdural cortical grids. A: Eight-contact grid (2 x 4); B: Eight-contact grid (1 x 8).

Figure 2. Bipolar probe.

Schematic presentation of a bipolar ball tip handheld probe.

Figure 3. Motor mapping: Penfield method.

Motor mapping responses after bipolar handheld stimulation using a Penfield 50 Hz method. Multiple responses are present in leg muscles (green arrow). Face (Orbicularis Oris), Tongue, Arm (Deltoid/Biceps Brachii), Forearm (Brachioradialis/Flexor Carpi Ulnaris), Hand (Abductor Pollicis Brevis/Abductor digiti minimi), Leg (Tibialis Anterior), and Foot (Abductor Hallucis) muscles.

Figure 4. Monopolar probe.

Schematic presentation of a handheld ball tip monopolar probe.

Figure 5. Motor mapping: Taniguchi method.

Motor mapping responses after monopolar handheld stimulation using a Taniguchi high-frequency method. Motor evoked responses are present in the right Flexor Carpi Ulnaris (red arrow) and First Dorsal Interosseous (orange arrow) muscles.

Figure 6. Motor mapping stack: Taniguchi method.

Motor mapping responses in stack view after monopolar handheld stimulation using a Taniguchi high-frequency method. Motor evoked responses are stacked in the right Flexor Carpi Ulnaris, First Dorsal Interosseous, and Abductor Pollicis Brevis muscles.

Figure 7. Electrocorticography.

Electrocorticography (ECoG) recordings showing stimulation artifact induced after discharges (white arrows).

Figure 8. Multimodality mapping.

Multimodality motor mapping with responses after monopolar handheld stimulation using a Taniguchi high-frequency method. A: Motor evoked responses are present in the right Flexor Carpi Ulnaris, and Abductor Pollicis Brevis muscles. B: Electrocorticography (ECoG), and C: Electromyography (EMG).