Intradiploic encephalocele of the primary motor cortex in an adult patient: electrophysiological implications during surgery.

Encephaloceles are herniations of brain parenchyma through congenital or acquired osseous-dural defects of the skull base or cranial vault. Different types of symptoms, due to CSF fistulas, meningitis, or seizures, are often associated with this condition. The authors present a rare case of spontaneous right frontal parasagittal encephalocele in a 70-year-old man who was experiencing a spastic progressive paresis of his left lower limb. Results of routine electrophysiological workup (motor evoked potentials, somatosensory evoked potentials, and electroneuromyography), as well as those of MRI of the spinal cord, were normal. A brain MRI study detected a partial herniation of the right precentral gyrus through a meningeal defect into the diploe, embedding corticospinal fibers. The patient underwent navigated craniotomy. Intraoperative neuromonitoring of motor function with transcranial electrical stimulation and direct cortical stimulation indicated the presence of motor cortex inside the encephalocele. Thus, the brain parenchyma was carefully released without resection to preserve motor function and, finally, a cranioplasty was performed. After a few months, the patient demonstrated considerable improvement in his left lower-limb function and, after 1 year, he had fully recovered. Intraoperative electrophysiological monitoring and mapping allowed for the determination of the best surgical strategy for the isolation of the encephalocele and correlated well with preoperative multimodal MRI.