Somatosensory evoked high-frequency oscillations recorded directly from the human cerebral cortex.

OBJECTIVE: To elucidate the generator sources of high-frequency oscillations of somatosensory evoked potentials (SEPs), we recorded somatosensory evoked high-frequency oscillations directly from the human cerebral cortex. SUBJECTS AND METHODS: Seven patients, 6 with intractable partial epilepsy and one with a brain tumor, were studied. With chronically implanted subdural electrodes, we recorded SEPs to median nerve stimulation in all patients, and also recorded SEPs to lip and posterior tibial nerve stimulation in one. High-frequency oscillations were recorded using a restricted bandpass filter (500-2000 Hz). RESULTS: For the median nerve oscillations, all oscillation potentials were maximum at the electrodes closest to the primary hand sensorimotor area. Most oscillations were distributed similar to or more diffusely than P20/N20. Some later oscillations after the peak of P20 or N20 were present in a very restricted cortical area similar to P25. We investigated the phase change of each oscillation potential around the central sulcus. One-third of the oscillations showed phase reversal around the central sulcus, while later oscillations elicited in a restricted cortical area did not. High-frequency oscillations to posterior tibial nerve and lip stimulation were also maximum in the sensorimotor areas. Most of the lip oscillations showed phase reversal around the central sulcus, but most of the posterior tibial nerve oscillations did not. CONCLUSION: High-frequency oscillations are generated near the primary sensorimotor area. There are at least two different generator mechanisms for the median nerve high-frequency oscillations. We suspect that most oscillations are derived from the terminal segments of thalamocortical radiations or from the primary sensorimotor cortex close to the generator of P20/N20, and some later oscillations from the superficial cortex close to the generator of P25.

Retrolabyrinthine presigmoid transpetrosal approach for selective subtemporal amygdalohippocampectomy.

The retrolabyrinthine presigmoid transpetrosal approach is a modification of the subtemporal approach which is suitable for complete amygdalectomy. By drilling away the retrolabyrinthine presigmoid petrosal bone, at least 1 cm more space below and 1 cm more space medially is obtained than in the subtemporal approach, and temporal retraction pressure is diminished when approaching from below. Operative results according to the Engel's classification of seizure control, and pre- and postoperative Wechsler Adult Intelligence Scale (WAIS), revised WAIS, and Wechsler Intelligence Scale for Children scores were measured in 16 patients treated by normal or modified subtemporal amygdalohippocampectomy. Postoperative follow-up ranged from 8 to 79 months. There has been no morbidity or mortality among these 16 patients, and postoperative seizure frequency has been diminished to less than 10% of the preoperative level in 15 of the 16. In eight patients, seizures have been eliminated totally. Subtemporal amygdalohippocampectomy achieved significantly increased performance and full scale intelligence quotient within 2 months after surgery, compared to preoperative levels. Subtemporal amygdalohippocampectomy is an alternative to the transsylvian approach, but is less invasive.

[Multiple myeloma presenting with a solitary cranial tumor with subdural extension: a case report].

We report a case of multiple myeloma presenting with a solitary cranial tumor in the frontal region, extending from subcutaneous tissue to subdural space. To our knowledge, invasion of a tumor beyond the dura mater has never been described in case of multiple myeloma presenting with a solitary calvarial tumor. In the present case, the subdural extension was clearly visualized by several diagnostic means. A 53-year-old female patient visited the clinic of our University Hospital, complaining of a left frontal mass in May 1991. The mass grew rapidly, and she was hospitalized in June. On admission, neurological examination showed nothing abnormal. Laboratory studies showed normocytic normochromic anemia. Protein electrophoresis disclosed hypergammaglobulinemia with S-spike, and serum paraprotein was specific to IgA with lambda light chains by immunoelectrophoresis. Urinary Bence-Jones protein was not detected. An osteolytic lesion visualized in the frontal bone on plain skull radiographs showed destruction of the frontal bone, and an enhanced mass extending from the epidural to subcutaneous space was shown by computed tomography. The mass had compressed the frontal lobe. T1-weighted magnetic resonance images of the area showed isointensity signals, homogeneously enhanced with gadolinium-diethylenetriamide pentaacetic acid. Subdural extension in the deep area of the tumor was suggested. At operation, we confirmed infiltration of the tumor from the dura mater into the subdural space. Postoperative biopsy of bone marrow of the iliac bone demonstrated myeloma cells. The tumor was histologically diagnosed as plasmacytoma. The patient was highly resistant to postoperative combined therapy, and started on a fatal course leading to respiratory insufficiency caused by interstitial pneumonia in April 1992.(ABSTRACT TRUNCATED AT 250 WORDS)