John L. Fox

Effect of cerebrospinal fluid shunts on intracranial pressure and on cerebrospinal fluid dynamics 2. A new technique of pressure measurements: results and concepts 3.A concept of hydrocephalus

Part 2 describes measurements of intracranial cerebrospinal fluid (CSF) pressure in 18 adult patients with CSF shunts, all pressure measurements being referred to a horizontal plane close to the foramina of Monro. All 18 patients had normal CSF pressure by lumbar puncture; however, in one patient an intracranial pressure of +280 mm was subsequently measured after pneumoencephalography. Twelve patients had pre-shunt CSF pressures measured intracranially: 11 ranged from +20 to +180 mm H2O and one was +280 mm H2O in the supine position. In the upright posture nine patients had values of −10 to −140 mm H2O, while three others were +60, +70, and +280 mm H2O. After CSF shunting in these 18 patients the pressures were −30 to +30 mm H2O in the supine position and −210 to −370 mm in the upright position. The effect of posture on the siphoning action of these longer shunts in the erect, adult patient is a major uncontrollable variable in maintenance of intracranial pressure after shunting. Other significant variables are reviewed. In Part 3 a concept of the hydrocephalus phenomenon is described. Emphasis is placed on the pressure differential (Pd) and force differential (Fd) causing pre-shunt ventricular enlargement and post-shunt ventricular size reduction. The site of Pd, which must be very small and not to be confused with measured ventricular pressure, P, must be at the ventricular wall.

The use of laser radiation as a surgical “light knife”

Abstract An investigation into the effects of continuous wave (CW) infrared laser radiation on skin, muscle, skull, brain, liver, and small bowel was carried out on 24 dogs. A unique articulating arm was utilized by the surgeon to conveniently direct the energy to the exposed target. About 30 watts of power focused to a 2-mm. diameter spot size readily cut through skin and muscle without significant bleeding. When vessels more than 1 mm. in diameter were encountered, bleeding usually occurred since the energy caused vaporization of the vessel wall without sealing off the opening. Such bleeding was troublesome in attempting to cut through brain and liver. As soon as a film of blood covered the surgical field the laser energy was absorbed by the blood, preventing deeper penetration. The skull bone could be incised down to a depth of about 3 mm. at which point charring occurred and further penetration was not practical since the deeper layers could not be exposed to the energy by retraction of superficial layers (unlike soft tissue). Healing of canine abdominal skin wound incisions deteriorated during the sixth to tenth day after laser radiation causing wound edge separation. Healing by secondary intention then rapidly ensued. Gross and histologic examination of knife and laser wounds during the first week and during the third through the sixth week failed to reveal significant differences. Use of laser radiation as a “light knife” by the clinical surgeon has some practical hazards which include accidental radiation of unintentional targets. At present, except for some select applications, the disadvantages to the use of laser radiation in surgery outweigh any advantages.

THE EFFECTS OF LASER IRRADIATION ON THE CENTRAL NERVOUS SYSTEM. I. PRELIMINARY STUDIES.

This study of the effect of laser radiation on the brain was made to further our understanding of the interaction of light with living matter and to provide a basis for the possible uses of laser energy in biology and medicine. The physics and engineering aspects of lasers are adequately treated elsewhere (1–3). Light produced by lasers differs from that of conventional sources in that it is strongly coherent and emitted in a narrow, collimated monochromatic beam which can be focused to produce high energy and power densities which are destructive to tissues. The ability to produce sharply circumscribed superficial lesions has been demonstrated (4) and suggests the application as an ablative tool in neurosurgery and neurophysiological research. Using equipment similar to ours, Fine et al. (4, 5) found that 75 per cent of mice died within 24 hours when a single 1-millisecond focused or unfocused laser pulse of about 100 joules struck the brain of the mouse through the intact scalp and skull. In earlier experiments we (G) were able to kill nearly every mouse within a few minutes, using only a single 1-millisecond, 20-joule pulse focused within the brain through the scalp and skull. The lethal mechanism was not explained by the small focal lesions. The occurrence of isolated hemorrhages in the base of the brain away from the site of impact had been thought to be an artifact produced during the removal of the brain from the cranium. If laser light had actually penetrated to that depth in sufficient intensity to produce hemorrhage, a continuous lesion would be expected.

Effects of laser irradiation on the central nervous system. II. The intracranial explosion.

One of the more interesting aspects of our study of the effects oflaser radiation on intracranial structures has been the search for the mechanism of immediate death of guinea-pigs following passage of a single pulse train of laser energy through the intact skull. Laser light is a form of electromagnetic radiation but differs from other light sources in several important respects (Lengyel, 1962; Schawlow, 1963; Troup, 1963; Brotherton, 1964; Heavens, 1964). Laser light exhibits strong temporal coherence: the energy is emitted in a very narrow frequency bandwidth so that the wavelength does not vary. Because the electromagnetic waves are nearly all in phase from one point in time to the next (constant frequency), the light is extremely monochromatic, yet intense. This light also exhibits spatial coherence: the electromagnetic waves are almost all in phase laterally from one point in space to the next. This coherent beam can thus be brought to an extremely small focus by a lens system affecting very high energy concentration. Finally, by using a pulsed system rather than a continuous emission (continuous wave) system, it is possible to deliver the energy in an extremely short period of time, thereby increasing the power by several orders of magnitude. One of the effects of this latter phenomenon is that the heat generated at the living tissue target is absorbed faster than it can be conducted away. Fine, Klein, Nowak, Scott, Laor, Simpson, Crissey, Donoghue, and Derr (1965) and Earle, Carpenter, Roessmann, Ross, Hayes, and Zeitler (1965) demonstrated that pulsed laser irradiation of sufficient energy-density was lethal to these animals when the intact cranium was radiated. At the Armed Forces Institute of Pathology we set out to find the mechanism of death in these animals (Fox, Hayes, Stein, and Green, 1966a; Fox, Stein, and Hayes, 1966b; Hayes, Fox, and Stein, 1967; Fox, Hayes, Stein, Green, and Paananen, 1967). The results of these studies indicated that, when a single pulse train containing 12 to 24 cal* of 694 nmt wavelength laser energy and lasting 1V5 to 2 5 msec intercepts the exposed intact skull of a guinea-pig, extremely high intracranial pressures exceeding 10 atmospheres for 1 msec are attained. This occurs even though only 10% of the energy actually reaches the brain through the skull. This leads to brain-stem herniation and immediate, permanent respiratory arrest. The heart continues beating for about 10 minutes until anoxic arrest occurs. When the exposed brain was radiated the animal did not immediately die since, although 10 times as much energy struck the brain, the intracranial cavity was not closed. The rapidly expanding vapours were dissipated into the open air. We elected to study further the intracranial pressure phenomenon using high speed cinematography.

A new method of stereotaxis.

Implantation of an electrode or probe into the brain by stereotaxis requires accurate biplane radiography to define the target. The x-ray image of the target may be seen directly (e.g., an ancurysm filled with contrast medium) or, as is usually the case, indirectly by measurements from coordinate points outlined by contrast medium (e.g., in parkinsonism the ventrolateral nucleus of the thalamus midway between the anterior and posterior commissures on the lateral film). The intracranial target usually is approached by a specialized probe passed through a burr hole in the skull. A major problem from a radiologic point of view has been transposition of radiographically distorted measurements from the images on biplane x-ray films to the real stereotaxic frame and hidden target. The many methods, instruments, and calculations used by stereotaxic centers testifies to the lack of a satisfactory stereotaxic technic generally accepted by most centers. The system of rectangular coordinates originated with Horsley ...