Electrical stimulation of the cerebral visual system in man

In patients undergoing thalamotomy for intractable pain, multi-contact platinum electrodes were stereotaxically implanted so that the striate cortex and geniculocalcarine tract could be stimulated to evaluate the feasibility of a visual prosthesis. The parameters of stimulation were 50–300 Hz, 0.1–1 msec pulse duration and 0.1–5 mA/phase. Phosphenes were evoked in 7 out of the 17 cases studied. The projection in space of the phosphene depended upon the site of stimulation. The configuration, color and brightness of the phosphene varied from a simple white or colored light to occasionally a multicolored complex pattern. Some phosphenes appeared to blink or flutter, some were stable in position, others appeared to move away radially from the fixation point. Histological studies on 6 of the brains suggested that the phosphenes were more often evoked from the striate cortex than from the geniculocalcarine fibers.

Thalamotomy for alleviation of intractable pain

17 patients had thalamotomies for alleviation of pain due to malignancy since January, 1970. In 12 of them, thalamic electrodes were implanted through occipital burr holes for subsequent radiofrequency thalamotomies. In 4 cases, the lesions were made by the bifrontal approach and 1 case was approached from the left occipital and right frontal. In 13 cases, the thalamic lesions were made in the vicinity of pulvinar, ventrocaudalis, parvocellularis, centromedianum and/or the adjacent structures. The size of histologically verified lesions in 7 specimens was 3 × 4 × 47 mm maximum and 4 × 3 × 4 mm minimum. Three of the 17 cases required no analgesics between thalamotomy and death or at least 6 months. In these cases, thalamic lesions were made in the vicinity of the posterior medial portion of thalamic nuclei and in one case the lesion was extended to the anterior thalamic radiation. In 7 cases requiring nonnarcotic analgesics, the lesions were located in the vicinity of the posterior median portion of thalamic nuclei, involving pulvinar, ventrocaudalis posterior, centromedian, internal medullary lamina or medial mass of thalamus. The remaining 8 thalamotomies in 7 patients required narcotics. In 4 of them, the lesions were made outside the posterior medial portion of thalamic nuclei. Histological confirmation is available in 6 cases.

Carotid-cavernous fistula: a controlled embolus technique for occlusion of fistula with preservation of carotid blood flow. Technical note

✓ A case is described in which a carotid-cavernous fistula was eliminated successfully with preservation of the carotid circulation by a small ball-shaped muscle embolus introduced via an arteriotomy in the cervical carotid. The intent is to lodge the embolus in the fistula without occluding the carotid siphon. A long thread is attached to the embolus to permit its withdrawal if its position in the siphon proves unsatisfactory. Neither the intracranial nor cervical carotid artery is ligated.