Marvin H. Bennett

The technique and results of treatment of tic douloureux by percutaneous retrogasserian glycerol rhizotomy ( PRGR ) were assessed in a series of 112 patients. All patients were refractory to or intolerant of medical therapy. Many of these patients had recurrent pain despite such surgical treatment as microvascular decompression (21%) or one or more percutaneous radiofrequency thermal rhizotomies (19%). The follow-up duration after glycerol rhizotomy ranged from 4 to 28 months. At the final assessment, 67% had complete pain relief; 23% were improved, with pan relieved by minimal drug therapy; and 10% had poor results with unsatisfactory pain relief even with medications. Before the final assessment, 19 patients required a second PRGR because of an initially suboptimal injection (10%) or recurrent pain (16.9%). Seventy-three per cent had no demonstrable change in facial sensation after operation. H akanson 's original procedure based on anatomic verification by cisternography provided precise localization, required no intraoperative stimulation or lesion generators, and allowed varied anesthetic options during operation. In contrast to thermal rhizotomy, PRGR offers patients relief of painful tic douloureux without altering facial sensation in most cases.

Brain retraction and induced hypotension are surgical adjuncts capable of compromising cerebral blood flow. To evaluate their effects upon brain function, cortical evoked potentials, neurological status and cortical histological changes were determined as a function of graded levels of brain retractor and systemic perfusion pressure in the dog. Somatosensory evoked potentials recorded from the site of application of brain retraction showed a decrement as a function of both the amount of retraction pressure and the systemic perfusion pressure. An electrode distant from the retractor site showed similar, though reduced and more variable changes in amplitude. For higher levels of brain retractor pressure, induced hypotension to 50 mm Hg systemic perfusion pressure produced greater reductions in evoked potentials than in normotensive subjects. It was demonstrated that a reduction of 50% of the evoked potential amplitude after sixty minutes brain retraction signaled, with high probability, the occurrence of postoperative sensory and/or motor deficits and cortical histopathology. It was concluded that cortical evoked potentials represent a reliable indicator of the functional effects produced by applied cortical retraction pressure at several levels of systemic perfusion pressure. It was suggested that the recording of evoked potentials would prove most useful during neurosurgical procedures employing induced hypotension and brain retraction.

Trigeminal evoked potentials and sensory thresholds in response to maxillary gum stimulation were obtained in patients with a complaint of unilateral face pain. The patients and the volunteer, normal control groups had undergone no prior surgical or other procedures involving cranial or cervical structures. For statistical purposes, patient data were analyzed with respect to the diagnostic classification of classical trigeminal neuralgia, atypical trigeminal neuralgia, or other face pain states in which the pain extended beyond the trigeminal nerve distribution. Latencies of trigeminal evoked potentials on the affected side were significantly increased (compared to normal control group responses) in patients with classical but not in those with atypical trigeminal neuralgia nor other face pain syndromes. All three patient groups had statistically significant threshold elevations on the affected side compared to the unaffected side. A high level of significance for this test was obtained for the classical trigeminal neuralgia group. Ratings for patients based upon the preoperative electrophysiological findings were highly correlated with long term results of microvascular decompression of the 5th nerve root for classical, but not for atypical trigeminal neuralgia patients. These results support the view that atypical and classical trigeminal neuralgia symptom complexes are caused by different types of physiological dysfunction and that classical trigeminal neuralgia is associated with compression of the trigeminal nerve root. It was suggested that the rating system may be a useful, objective, clinical adjunct in evaluating patients with classical trigeminal neuralgia.