Cortical stimulation mapping of phantom limb rolandic cortex. Case report

Findings of intraoperative rolandic cortex mapping during awake craniotomy for a tumor in a patient with a contralateral upper-extremity amputation are presented. This patient sustained a traumatic amputation at the mid-humerus 24 years previously. Initially he had experienced rare painless phantom limb sensations but none in the past 10 years. Functional mapping during an awake craniotomy was performed to maximize safe tumor resection. Typical temporal and frontal speech areas were identified; motor representation of face and jaw extended more superiorly than sensory representation. Shoulder movements were evoked more laterally than usual at the superior aspect of the craniotomy. A small region of precentral gyrus, between the jaw and shoulder representations, elicited no detectable effect when stimulated. Somatosensory mapping showed a similar topographical distribution of face and mouth cortex; however, posterior and inferior to the shoulder motor cortex, right arm and hand (phantom) sensations were evoked. Evidence suggests that significant motor reorganization occurs following an amputation, with expansion of neighboring homuncular representations without loss of somatosensory representation, despite a long period of time without any sensation referable to the amputated limb. Contrary to models of sensory cortex plasticity, the plasticity of the adult cortex may be system specific, with reorganization present in motor, but not in sensory, cortical systems.