Ten-year follow-up on the performance of a telemetric intracranial pressure sensor.

A permanently implanted epidural sensor has permitted long term telemetric intracranial pressure monitoring in selected neurosurgical patients. The sensor, consisting only of an inductance and a pressure-sensitive capacitance, has been implanted in 127 patients. Of these 127 patients, 13 have continued to have the sensor in place for 4 to 9 years (average, 6.8 +/- 0.44 years). The remaining patients were lost to follow-up or the sensor was removed. The sensor has been evaluated from the standpoint of accuracy, longevity, safety, and stability. Longevity was proven by successful monitoring over periods of years (in 1 patient, at least 9 years). The sensor has been a safe tool; the only morbidity has been two asymptomatic perisensor blood clots in 2 patients. There have been no infections in any of the 127 cases. The stability of the sensor was evaluated by measuring base line drift over time. This rate was 1.0 +/- 0.2 mm H2O/day. Causes of the drift and possible solutions are discussed, and the sensor is compared to other epidural telemetric monitoring systems.

Effects of occipital lobectomy upon eye movements in primate.

1. Eye movements were recorded before and after bilateral occipital lobectomy in six rhesus monkeys trained to fixate and to follow small targets. Striate cortex was completely removed in two animals; small islands islands remained in the others. In all animals portions of extrastriate cortex were also removed but the medial superior temporal area in the superior temporal sulcus was largely spared. Optokinetic nystagmus (OKN) was markedly altered but not abolished in all animals. The immediate pursuit component of OKN was eliminated leading to a poor response to stimuli comprised of high frequencies. The velocity-storage component of OKN was present, but the maximum value of OKN that could be achieved was decreased to 6 and 16 degrees/s in the two most severely affected animals (preop, 65-116 degrees/s). The residual OKN was similar to that of afoveate animals with a diminished response to high velocities of retinal-image motion and a temporal to nasal predominance during monocular viewing. 2. In the initial postoperative period all animals appeared completely blind. Within 1-6 mo, however, they regained an ability to make visually guided saccades to, and smooth pursuit of, small targets. Saccades were nearly as accurate as preoperatively, but saccade amplitudes were more variable and saccade latencies increased. In the two animals with a complete removal of striate cortex, gains (eye velocity/target velocity) of smooth pursuit during sinusoidal tracking (60 degrees/s, 0.5 Hz) were 0.9 and 0.95. During tracking of step-ramp (Rashbass) stimuli with 60 degrees/s ramps, the average acceleration of the eyes during the first 120 ms of smooth pursuit was 189-278 degrees.s-1.s-1 (preop range, 154-418 degrees.s-1.s-1). In other respects, though, smooth pursuit was not normal. Latencies were increased two- to threefold, and tracking was more variable. 3. Paradoxically, as visually guided saccades and pursuit recovered, some other ocular motor functions deteriorated. Spontaneous and gaze-evoked nystagmus developed 3-6 mo after occipital lobectomy; the time constant of the neural eye-position integrator dropped to values as low as 2.6-4.8 s. The maximum slow-phase velocity of OKN also decreased. 4. The findings immediately after occipital lobectomy indicate that in normal primates occipital cortex is necessary for visually guided saccades and smooth pursuit as well as for the immediate component of OKN. Occipital cortex also makes the predominant contribution toward the generation of the velocity-storage component of OKN.(ABSTRACT TRUNCATED AT 400 WORDS)

Traumatic internal carotid artery aneurysm with rupture into the sphenoid sinus.

A case of cavernous-internal carotid artery aneurysm with delayed rupture into the sphenoid sinus is presented, and the literature reviewed. We stress important diagnostic features such as epistaxis, which may require emergent use of epistaxis balloon catheters. Cervical carotid ligation and intracranial clipping of the internal carotid artery proximal to the ophthalmic artery controlled the bleeding and resulted in no neurologic sequelae.

Sclerosteosis: neurogenetic and pathophysiologic analysis of an American kinship.

We studied an American kinship with sclerosteosis, an autosomal-recessive disorder of bone remodeling and bone overgrowth of the calvaria, skull base, and tubular bones. Unlike osteopetrosis, which is attributed to abnormal immune and osteoclast function as well as bone resorption, sclerosteosis appears to be primarily a disorder of osteoblast (bone formation) hyperactivity. Related to cranial vascular and neural foraminal narrowing and reduced intracranial volume, affected patients with sclerosteosis demonstrate frequent seventh nerve palsy, progressive optic and cranial neuropathies, mixed hearing loss, brainstem compression, intracranial hypertension with increased elastance, and sudden, premature death. Management should involve early childhood identification of homozygotes, monitoring and aggressive treatment of intracranial hypertension, and extensive bone removal from skull, posterior fossa, and cervical spine.

Denervation study of synapses of organ of Corti of old world monkeys.

Fine structural characteristics of synapses in the spiral organ of Corti were examined, with reference to differences between inner and outer hair-cell systems, and to location of neurons of origin of efferent axons. Surgical interruption of crossed olivocochlear bundle, of vestibular nerve, of facial nerve, and excision of superior cervical ganglia were used to determine the pathways of different axons. Interruption of the vestibular nerve near the brainstem results in degeneration of all efferent terminals on outer hair cells. Mid-line lesions at, and caudal to, the facial colliculus result in degeneration of about half of these efferent terminals. Efferent synaptic bulbs to the inner hair-cell system are small, of the order of one micron, and form type 2 junctions with afferent dendrites. They tend to have more large dense-core vesicles (about 80 nm) than the large efferent terminals of the outer hair-cell system, and appear to be the terminals of axons in the habenula perforata, which exhibit varicosities laden with large dense core vesicles. The varicosities are unaffected by excision of the superior cervical ganglia. So far as our material can reveal, it appears that the varicosities in the habenula perforata do not survive vestibular root interruption, nor do the efferent processes in the internal spiral bundle or at the base of inner hair cells. Most interestingly, the afferent processes of the inner hair-cell system, as identified for example by their relation to pre-synaptic bodies in the inner hair cells, are subject to a trans-synaptic reaction after severance of the vestibular root. They undergo a dramatic cytological transformation, characterized by increase of volume, engorgement with microtubules, microfilaments, microvesicles of various sizes, and clusters of lysosomes. Thus, both the efferent and afferent terminals of the inner hair-cell system show marked cytological differences from the corresponding terminals of the outer hair cell system.

Continuous intracranial pressure recording in adult hydrocephalus.

An implantable intracranial pressure sensor was used to diagnose and monitor the treatment of 17 adults with hydrocephalus. The intracranial pressure sensor was implanted before shunting in most cases and patients were studied in a sleep laboratory for two nights during which the intracranial pressure was measured throughout the night. Cases included five examples of acute hydrocephalus secondary to tumor, subarachnoid hemorrhage or meningitis, and 12 cases of long standing hydrocephalus diagnosed as normal pressure hydrocephalus, aque-ductal stenosis, or hydrocephalus ex vacuo. Continuous intracranial pressure monitoring was a valuable adjunct in the diagnosis and management of these patients. Continuous overnight recordings of intracranial pressure were helpful in determining compromised cerebral compliance by observing the shape and the amplitude of the intracranial pressure waves during desynchronized sleep. A second method for checking cerebral compliance is also described.

Clinical evaluation of long-term epidural monitoring of intracranial pressure.

Forty-two epidural sensors for measuring intracranial pressure were implanted in 38 patients over the last four years. The sensor is a passive device consisting of an inductance and a pressure sensitive capacitance resonant at about 50 megahertz. The study involved 17 cases of hydrocephalus, nine of pseudotumor cerebri, and the remainder included cases of cranial trauma, brain tumors, and aneurysms. Four of the sensors failed in patients and were removed. Two of these had to be replaced to continue the pressure monitoring. The intracranial pressure is still being monitored in 22 patients, while 15 have been lost to follow-up for various reasons. Fourteen patients have been followed for about a year, and four for two years. The baseline drift rate in most sensors is between 1 and 2 mm H2O per day, with a few having greater rates of drift. Calibration errors were found in some of the sensors after implantation. These errors were corrected by direct measurement of the cerebral spinal fluid pressure via lumbar puncture. The sensors have proven to be a valuable adjunct in the management and diagnosis of neurosurgical patients by simplifying the intermittent and continuous recording of intracranial pressure. This was so despite the presence of calibration errors and a drift which necessitated an occasional lumbar puncture for making corrections.

Intracranial pressure in the normal monkey while awake and asleep.

Intracranial pressure (ICP) was recorded continuously by telemetry in seven normal monkeys trained to eat, sleep, and live in a primate chair. Electroencephalography, electromyography, and blood pressure were also measured by conventional means. During wakefulness and all stages of sleep except desynchronized sleep, the ICP record showed small short-term variations in pressure. However, during desynchronized sleep, the mean ICP rose on the average to 170 +/- 6 mm H2O above the ICP levels in the other states of sleep, and the pulsation pressure variation increased by a factor of three. The episodes occurred 10 +/- 2 times during the night and lasted for 6.8 +/- 1.4 minutes, during which the average systemic blood pressure decreased by 19 +/- 1.6 mm Hg. These ICP waves occurring during desynchronized sleep resemble the plateau waves described by Lundberg, but are of smaller magnitude and they appear to be a normal characteristic of sleep in the macaque monkey. Bilateral sympathectomy of the superior cervical ganglia in four of the monkeys did not alter significantly the duration, amplitude, or frequency of occurrence of the ICP waves during desynchronized sleep.

The effect of sleep upon the transmission of afferent activity in the somatic afferent system.

Macaque monkeys were trained to fall asleep while sitting in a primate chair with their heads restrained. A gentle vibratory stimulus was delivered to the glabrous skin of the hand; it did not provoke awakening or change the sleep cycle of the macaque. Postcentral neuronal response to the amplitude of a sine wave mechanical stimulus and neuronal spontaneous activity were observed repetitively during all the phases of normal night sleep cycles. One hundred six neurons which could be entrained by a cutaneous mechanical stimulus were studied during both waking and sleep. At threshold, cyclic entrainment of the discharges of postcentral neurons decreased to 81 +/- 0.25% during light sleep (S1 + S2), to 64 +/- 0.26% during deep sleep (S3 + S4), and to 9 +/- 0.98% during desynchronized sleep with rapid eye movements (REMs).

Thalamic EEG recordings in patients with chronic pain.

Thalamic EEG recordings were made in 10 patients; the therapeutic goal of the implantation was the electrical stimulation treatment for pain. The patients' ages ranged from 37 to 72 years; seven patients had thalamic pain (Dejerine-Roussy syndrome), two had chronic spinal arachnoiditis and one had facial anaesthesia dolorosa. Platinum-iridium electrodes were stereotaxically inserted; the ventrobasal complex of the thalamus including the ventral posterior zone was the target of the implant. Excessive thalamic slowing was found in four of seven patients with Dejerine-Roussy syndrome and also in two of three cases with other causes of pain. One patient had marked rhythmical intermittent delta activity in the thalamus which was often triggered by arousing stimuli. Thalamic spindle activity was sometimes noted without concomitant spindle activity on the scalp and would occasionally occur in states of early drowsiness.

Long-term intracranial pressure recording in the management of pseudotumor cerebri.

Long-term monitoring of intracranial pressure (ICP) was used as an aid for the management of four patients with pseudotumor cerebri. After the implantation of a small experimental pressure sensor in the skull, most of the subsequent (ICP measurements were made noninvasively by an external interrogator. During the initial study of the patient, baseline ICP recordings were made in the hospital before treatment. Pressure recordings on a 24-hour basis were continued during treatment, which, depending on the case, was with Diamox (acetazolamide), steroids, or the coperitoneal shunting. After discharge these patients returned weekly over 10 to 22 months for ICP measurement and for ophthalmological examination. Intracranial pressure before treatment showed irregular variations ranging from 100 to 500 mm H2O over a 24-hour period. The efficacy of treatments could be assessed in a few hours by the degree of ICP stabilization. Shunt malfunction was detected by a slow but continuous rise in pressure before full clinical signs were evident.

'Limbic spindles': a re-appraisal.

Respiration-linked spindles are frequently recorded from nasopharyngeal electrodes and these have been reported to represent neuronally generated limbic activity. Evidence is presented from sphenoidal and nasopharyngeal recordings suggesting that these spindles are artifactual, due to unstable electrode contacts that record palatal vibration during partial airway obstruction.

Effect of magnesium on epileptic foci.

Parenteral magnesium sulfate has been used to control acute convulsions of diverse etiologies and is currently a mainstay in controlling eclamptic convulsions. However, the site of this anticonvulsant action has remained controversial and not well studied in experimental epileptic models. Therefore we determined the effects of intravenously infused magnesium sulfate on the epileptic neural activity induced by topical application of penicillin G to motor cortex in anesthetized cats and dogs and in awake, undrugged primates. Magnesium sulfate was able to directly suppress neuronal burst firing and interictal EEG spike generation at serum levels below those producing paralysis. The degree of suppression corresponded to the serum magnesium concentration and was reversible. These results corroborate the clinical observations in patients that magnesium can produce an anticonvulsant effect apart from neuromuscular blockade and suggest it may have clinical applicability in treating a wider range of acute convulsions.