Biomedical subjects
Publications and source records attributed to W A Friedman.
Stereotactic angiography has long been the imaging database for the radiosurgical treatment of arteriovenous malformations (AVM). The following analysis reveals systematic shortcomings in the methodology, resulting in errors in determining target shape, errors in determining target size, and errors in the identification of the true AVM "nidus."
OBJECTIVE: To determine the value of multimodality-evoked potential recordings in predicting outcome in comatose children. DESIGN: Prospective series and literature review. SETTING: Pediatric ICU in a university hospital. PATIENTS: Forty-one children with a Glasgow Coma Scale score of less than 8, who were admitted to the pediatric ICU between 1984 and 1989. INTERVENTIONS: Forty-one patients underwent brainstem auditory-evoked potential testing within 72 hrs of admission. Of these patients, 37 also had somatosensory-evoked potential testing at the same time. Four patients did not receive somatosensory-evoked potential testing for various nonmedical reasons. MEASUREMENTS AND MAIN RESULTS: Multimodality-evoked potential recordings were used to predict outcome in these comatose children. Outcomes were categorized as bad (death or chronic vegetative state) or good (all other outcomes). Survivor outcomes were determined at discharge and on subsequent follow-up visits from 1 to 3 yrs later. There were no false pessimistic predictions, and two false optimistic predictions in this series. A comprehensive literature review of coma outcome prediction, using multimodality-evoked potential recordings, revealed 20 series with 982 additional patients in whom the predictive errors of false optimism and false pessimism could be determined. Five cases of false pessimism and 99 cases of false optimism were identified in the 982 additional patients. If neonates are excluded, the false pessimism number is reduced to three. CONCLUSIONS: A bad outcome can be reliably predicted using multimodality-evoked potential recordings with little chance of a false pessimistic prediction. The acceptable error of false optimism occurs frequently, since patients often die of progressive neurologic and nonneurologic problems that may or may not be present at the time of the evoked potential recordings. Thus, in comatose children, multimodality-evoked potential recordings are a useful adjunct to clinical examination and other diagnostic aids in predicting outcome and in making decisions regarding the degree of intervention to offer.
Somatosensory evoked potentials (SEPs) were monitored during 53 procedures for aneurysms of the middle cerebral artery (MCA). "Significant" changes were reported to the surgeon, who took corrective action when possible. Changes in the SEPs were categorized as follows: Type I, no change; Type II, significant change with complete return to baseline; Type III, significant change with incomplete return to baseline; Type IV, complete loss with no return; and Type V, no response at baseline. Only 1 of 37 patients with a Type I SEP had a new neurological deficit, and this was a patient who could not be examined for several days after surgery because he was in a pentobarbital coma. All 4 patients with Type III and IV changes had new postoperative neurological deficits. Perhaps of greater importance, 4 of 5 patients with Type II changes had no new deficit. These patients all had changes in SEPs that were completely reversible by clip adjustment (2), prompt removal of temporary clips (1), and inducing hypertension after aneurysm trapping (1). These cases may, therefore, represent instances in which SEP monitoring allowed the clinicians to prevent a neurological deficit. The MCA supplies the area of the somatosensory cortex that controls the hand. Median nerve SEPs are, therefore, a theoretically ideal monitor during surgery for MCA aneurysms. This study suggests that the results of MCA aneurysm surgery may be accurately predicted and improved with SEP monitoring.
Stereotactic radiosurgery has become a major force in the treatment of arteriovenous malformations (AVMs) of the brain. After treatment, obliteration of flow through the malformation occurs in 75%-85% of cases within 2 years, assuming the entire AVM nidus can be encompassed by the radiation field. Because the follow-up period is relatively long, a noninvasive means to assess residual transnidus blood flow is desirable. The authors report favorable findings after a comparative analysis of 85 posttreatment magnetic resonance images and 27 follow-up cerebral arteriograms in 34 patients treated with stereotactic radiosurgery. The authors found that transnidus flow can be determined from apparent signal intensity differences between tandem two-dimensional gradient-recalled echo images obtained first without and then with gradient moment nulling (flow compensation), with empirically derived pulse parameters. This method provides a means to monitor the reduction in AVM matrix size and to assess the extent of persistent arteriovenous shunting (ie, blood flow) across the nidus.
Nucleus caudalis dorsal root entry zone lesions (open trigeminal nucleotomy) are a surgical procedure which can achieve pain control without major complications in the difficult clinical setting of deafferentation-type facial pain. Two patients are reported, who had relief of pain, but also experienced neurological complications. One patient succumbed to pulmonary complications, which provided the opportunity for anatomic analysis of the lesioned area, which is discussed in detail. Potential modifications of the surgical technique are suggested.
As radiosurgery evolves into a widely available treatment modality for a variety of intracranial lesions, the need for basic research concerning the radiobiology of high-dose single-fraction ionizing radiation becomes crucial. A device especially designed for experimental radiosurgery in the cat is described. It incorporates basic parts of the Kopf stereotactic frame for accurate target positioning. A motorized pendular movement of the machine is used to describe a radiation arc, while the radiation source (either a linear accelerator or a cobalt machine) remains stationary. The pathway of the different radiation arcs is modified by rotation of the animal platform around the machine isocenter. Mechanical accuracy tests have shown a maximal alignment error of 0.15 mm, comparing favorably with that reported for modern clinical radiosurgical systems.
Previously reported suboccipital transcerebellar stereotactic biopsy methods, performed with the patient in the prone position, have required general endotracheal anesthesia. A technique is described for performing such biopsies with the patient in the lateral decubitus position, under local anesthesia. Phantom planning and routine computerized tomography graphics allow the selection of a safe entry point and intra-axial trajectory to the lesion. The time required for data acquisition and the operative procedure itself compares well with that of more routine biopsy techniques.
Neurophysiologic tests currently used in the diagnosis and treatment of peripheral nerve trauma include EMG, NCV, late responses, SEPs, and intraoperative NAPs. The physiologic basis of these tests has been reviewed. Examples of typical applications have been provided. The interested reader is referred to the listed references for more detailed information.
Forty-three patients with chronic pain disorders of different causes were selected for spinal cord stimulation. All underwent implantation of a ribbon electrode through a small laminotomy, under general anesthesia. Thirteen patients (30%) failed to obtain significant pain relief during a period of trial stimulation, and their electrodes were removed. The remainder underwent a definitive implant and were followed for a mean of 13 months (range, 3-33 months). Nineteen of them (63%) continued to experience pain relief. A detailed analysis of this series, as well as a literature review, is presented.
During the past decade, multiple linear accelerator (LINAC) radiosurgical systems have been developed. By measuring beam energy, beam accuracy, and dose gradient, it is possible to compare them to the older radiosurgical device, the gamma knife. LINAC systems appear to be advantageous in terms of cost, variety of collimator sizes available, and currently available sophistication of computerized dose planning. In the near future, the development of conformal LINAC treatment may change the entire field of radiosurgery significantly by offering improved dose plans for irregularly shaped lesions. In addition, LINAC systems may be adapted for stereotactically focused fractionated radiotherapy and for radiosurgical treatment of lesions elsewhere in the body.
A new, linear accelerator based radiosurgical system has been designed and tested. It incorporates a mechanical system of precision bearings to control all patient and accelerator movements. The dosimetry system allows near real-time examination of the isodose distributions in any computed tomography plane such that any treatment plan can be quickly optimized. Extensive testing shows a radiation beam accuracy of .2 +/- .1 mm. The dose gradient between the 90% and 10% isodose distributions compares favorably with any previously published radiosurgical method.
Despite the widespread availability of image-guided stereotactic biopsy, the need for such procedures in patients with "clear-cut" clinical and radiographic diagnoses is still frequently discussed. In an attempt to ascertain the incidence of unexpected pathological findings, 100 consecutive stereotactic biopsies have been reviewed. Twelve patients were found to have diagnoses of pathological conditions that preoperatively were considered unlikely, or not considered at all. The details of these "diagnostically discordant" cases are discussed.
Children with achondroplasia may be at increased risk of developing apneic episodes and of dying unexpectedly. The risks seem to be related to neural axis compression by an abnormal cranial base and may be complicated by the development of hydrocephalus. We used magnetic resonance imaging to study five children with achondroplasia. All of them demonstrated a discrepancy between the size of the brain stem and the foramen magnum. Comprehensive prospective assessment of infants with achondroplasia, including the use of new imaging techniques, will provide important information concerning the natural history of the relationship of the neural axis to the bony posterior fossa and upper cervical spine in this condition. It may also help to identify those patients at risk before the development of life-threatening medullary compression.
Total surgical excision is the main goal of therapy for intracranial meningiomas. The controversy today involves the efficacy of postoperative radiation therapy. To evaluate this question, 132 patients with benign intracranial meningiomas, treated between October 1964 and April 1985, were evaluated. All patients had a minimum 2-year follow-up. The actuarial local control rates at 10 years for the three treatment groups were as follows: subtotal excision alone, 18%; subtotal excision plus postoperative radiation therapy, 82%; and total excision alone, 77%. The actuarial determinate survival rates at 10 years were 49%, 81%, and 93%, respectively. Postoperative radiation therapy was also effective for patients treated at the time of the first recurrence, with an actuarial local control rate at 10 years after salvage treatment of 30% for patients treated with surgery alone and 89% for patients receiving postoperative radiation therapy at the time of salvage. This analysis suggests that radiation therapy has a significant role in the treatment of subtotally excised and recurrent intracranial meningiomas.
Separate somatosensory evoked potentials (SEPs) were monitored from each lower extremity during instrumentation for a spinal fracture. The SEP disappeared from the right lower extremity after instrumentation, but not from the left lower extremity. The predicted hemi-spinal cord injury was pathologically confirmed. The merits of sequential, as opposed to simultaneous, stimulation of multiple extremities during surgical monitoring are discussed.
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Because short-latency evoked potentials are relatively resistant to anesthetic agents, they can be used to monitor neural pathways during surgical procedures. The use of median nerve somatosensory evoked potentials to localize the central sulcus is an established aid of indisputable value in neurosurgical procedures involving cortical incisions for resection of certain epileptic foci, vascular malformations, or neoplasms near the central area of the brain. Likewise, recording of intraoperative nerve action potentials is currently regarded as indispensable in management of the neuroma-incontinuity after peripheral nerve trauma, as this evoked potential monitoring technique provides the only reliable method of distinguishing between axonotmetic and neurotmetic lesions. Evoked potential monitoring has been of value during many other types of surgical procedures, including cerebral aneurysm clipping, carotid endarterectomy, aortic procedures, microvascular decompression for trigeminal neuralgia and hemifacial spasm, acoustic neuroma resection, and a variety of spinal procedures. A detailed review of the literature is presented on the use of evoked potential monitoring for one of the more common indications: scoliosis surgery. Many orthopedic surgeons use the "wake-up test" only if the somatosensory evoked potentials change during surgery. A detailed review of the few reported cases of "false negative" evoked potentials is presented. The dearth of convincing reports of such phenomena in the face of so many positive experiences should persuade even the skeptical that monitoring of evoked potentials is a highly reliable and helpful intraoperative tool.
Searching the medical literature for persistent memory loss following section of the anterior fornix in humans, 13 reports were found and reviewed. They comprised 193 patients of whom 180 underwent fornicotomy for the treatment of epilepsy, and 13 underwent removal of third ventricle colloid cysts. Only 4 were reported to have persistent memory loss postoperatively and they were in the colloid cyst group. Within the limitations inherent to this type of analysis and to the problems of detection and quantification of memory deficits, the reviewed material supports the hypothesis that with anterior fornix section we are only interfering with a part of the structural system subserving memory and that the tumor, the surgical trauma, or other destructive pathology, or a combination of factors including the variability of neural localization, may cause persistent memory loss by additional damage to structures other than the anterior fornix. Language and geographical barriers may explain the apparent failure in communication between early investigators.