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R M Crowell

Publications and source records attributed to R M Crowell.

At least 73 records · Page 4Linked to original sources
PubMed1982

Superior temporal gyrus approach to middle cerebral artery aneurysms: technique and results.

Aneurysms of the bifurcation of the middle cerebral artery (MCA) can be approached through a small incision in the anterior portion of the superior temporal gyrus. The pterion and the lateral aspect of the lesser wing of the sphenoid bone are removed. The aneurysm is approached, using microsurgical techniques, by following the main divisions of the MCA to the parent trunk and the base of the aneurysm. Once the parent vessel and the origin of the major divisions are clearly identified, it is usually preferable to dissect and mobilize the entire aneurysmal complex to elucidate the anatomy and prepare the neck for clipping. This approach offers the advantages of minimal brain retraction and minimal manipulation of the main trunk and perforators of the MCA. In addition, it allows a more complete exposure of the aneurysmal complex and facilitates dissection behind the aneurysm, which is more difficult when the aneurysm is approached from the front by opening the sylvian fissure medially to laterally. A potential disadvantage of this method is that proximal control is not obtained until the base of the aneurysm is reached, but this has not been a problem in our experience. Other disadvantages are the need for a slightly larger bone flap and the potentially increased risk of epilepsy. This approach is not suitable when the main trunk of the MCA is short and the aneurysm is in front of the insula. It is also not recommended for the rare cases in which the aneurysm points back over the insula. During a 6-year period, this approach was used in 49 of 58 cases of MCA aneurysm. The only deaths in this group occurred in patients who were in deep coma before operation. Two patients were made worse by operative complications, and 2 more worsened as a result of postoperative vasospasm. There was a significant incidence of thrombophlebitis and pulmonary embolism in this series.

Cerebral Arterial Diseases↗
PubMed1982

Effect of mannitol on experimental focal ischemia in awake monkeys.

The effect of mannitol on focal cerebral ischemia in cynomolgus monkeys was studied. After the implantation of a snare ligature about the right middle cerebral artery (MCA) and of deep electrodes for measurement of cerebral blood flow, unanesthetized animals underwent 4-hour MCA occlusion. Ten monkeys were untreated, and 12 animals received mannitol (1.2 g/kg i.v.) 20 minutes after occlusion. The preocclusion and postocclusion deep hemispheric cerebral blood flows (mean CBFs) were similar in the treated and untreated groups. Occlusion produced an average decrease in flow of about 50% in both groups. In the mannitol-treated group the mean CBF of 30.0 fell to 15.8 ml/100 g/minute, and in the untreated group the mean CBF of 29.5 fell to 12.5 ml/100 g/minute. Several animals showed increased CBF after mannitol treatment, and there was an average 21% increase in CBF in the mannitol group after treatment, but this was not a statistically significant difference from the untreated group. With regard to clinical status, there was no significant difference between the mannitol group and the untreated group after MCA occlusion. In individual animals, mannitol treatment caused no significant improvement. Two weeks after occlusion, brains were evaluated for infarct size; there was no significant difference between the mannitol and the untreated groups. In this study, treatment with mannitol (1.2 g/kg) 20 minutes after MCA occlusion failed to modify significantly the mean hemispheric CBF, clinical status, or the pathological effects of 4-hour focal cerebral ischemia.

Animals↗
PubMed1981

Correlation of spectral phonoangiography and carotid angiography with gross pathology in carotid stenosis.

Spectral phonoangiography, a noninvasive method for measurement of the residual-lumen diameter of carotid stenosis by bruit analysis, was compared with x-ray angiography and direct measurement of the pathological specimen at carotid endarterectomy in 39 bifurcations from 36 patients. In six studies, the bruit was too faint to analyze. In 31 of the other 33 studies, the phonoangiogram predicted the residual-lumen diameter to within 0.5 mm of the measured value. Of the 39 contrast angiograms, 35 showed residual lumens within 0.5 mm of the value measured in the specimen, two showed lumens between 0.5 and 1 mm, and the sizes of two could not be estimated because of vessel overlap in all planes. Spectral phonoangiography and contrast angiography are both accurate methods for evaluation of carotid stenosis. Since phonoangiography is noninvasive, it may be of particular value in determining the natural history in patients with carotid bruits.

Auscultation↗
PubMed1981

John R. Green M.D.

Explore the source record for details and available documents.

History, 20th Century↗
PubMed1981

Variability and reversibility of focal cerebral ischemia in unanesthetized monkeys.

To assess reversibility of focal cerebral ischemia, we performed a neurologic and pathologic study of 27 monkeys subjected to temporary middle cerebral artery occlusion. An implanted snare ligature occluded the artery in awake monkeys for 30 minutes, 4 hours, 8 hours, 16 hours, 24 hours, or permanently. Serial neurologic observations were made for 2 weeks, and systematic neuropathologic examination estimated extent of infarction. Deficits from ischemia were commonly reversible at 30 minutes and 4 hours, but were rarely reversible after 8 hours. Neurologic deficit and infarct size showed remarkable variability. Maximum irreversible infarction evolved in about 4 to 8 hours in most awake monkeys. Variability and reversibility of focal ischemia were probably related to variable collateral circulation. The results suggested that emergency surgical revascularization might help some cases of acute ischemic stroke.

Animals↗
PubMed1981

Thresholds of focal cerebral ischemia in awake monkeys.

An awake-primate model has been developed which permits reversible middle cerebral artery (MCA) occlusion during physiological monitoring. This method eliminates the ischemia-modifying effects of anesthesia, and permits correlation of neurological function with cerebral blood flow (CBF) and neuropathology. The model was used to assess the brain's tolerance to focal cerebral ischemia. The MCA was occluded for 15 or 30 minutes, 2 to 3 hours, or permanently. Serial monitoring evaluated neurological function, local CBF (hydrogen clearance), and other physiological parameters (blood pressure, blood gases, and intracranial pressure). After 2 weeks, neuropathological evaluation identified infarcts and their relation to blood flow recording sites. Middle cerebral artery occlusion usually caused substantial decreases in local CBF. Variable reduction in flow correlated directly with the variable severity of deficit. Release of occlusion at up to 3 hours led to clinical improvement. Pathological examination showed microscopic foci of infarction after 15 to 30 minutes of ischemia, moderate to large infarcts after 2 to 3 hours of ischemia, and in most cases large infarcts after permanent MCA occlusion. Local CBF appeared to define thresholds for paralysis and infarction. When local flow dropped below about 23 cc/100 gm/min, reversible paralysis occurred. When local flow fell below 10 to 12 cc/100 gm/min for 2 to 3 hours or below 17 to 18 cc/100 gm/min during permanent occlusion, irreversible local damage was observed. These studies imply that some cases of acute hemiplegia, with blood flow in the paralysis range, might be improved by surgical revascularization. Studies of local CBF might help identify suitable cases for emergency revascularization.

Anesthesia↗
PubMed1980

Subarachnoid hemorrhage secondary to ruptured intracranial aneurysm: prognostic significance of cranial CT.

Computed tomographic (CT) findings in 50 patients with subarachnoid hemorrhage due to proven intracranial aneurysms were analyzed for prognostic significance in relation to the clinical grade and severity of vasospasm that developed preoperatively. Only patients who had CT within 4 days after the documented hemorrhage were included in the study. CT scans were classified according to the extent of subarachnoid bleeding. There was direct correlation between the extent of blood and the clinical grade, and between the extent of blood and the severity of vasospasm that developed. The importance of abnormal contrast enhancement was also investigated and found to be of no significance. Scans soon after subarachnoid hemorrhage can assist in identifying patients at risk for preoperative neurologic deterioration.

Adult↗
PubMed1979

Clinical and radiologic remission in reticulum cell sarcoma of the brain.

Two patients with cerebral reticulum cell sarcoma (CRCS) are reported in whom neurologic abnormalities and radiologic (computerized tomographic [CT] scan) evidence of tumor remitted. In one patient, remission followed craniectomy and corticosteroid therapy and lasted for eight months. In the other patient, at least four remissions occurred over a span of seven years, each in conjunction with the administration of corticosteroids. Corticosteroids may favorably alter the biologic activity of tumor tissue in some cases of CRCS, predisposing to clinical remission and disappearance of tumor on CT scan.

Adult↗
PubMed1976

Computed tomographic evaluation of hemorrhage secondary to intracranial aneurysm.

Angiography in patients with subarachnoid hemorrhage secondary to aneurysm gives precise information on the location and size of the aneurysm and the aneurysm and the presence of spasm but gives incomplete information on ventricular size, size and location of hematoma, and extent of infarction. CT demonstrates precisely brain or intraventricular hematoma and, at times, subarachnoid hemorrhage, indicates the extent of infarction; and rapidly documents the degree of hydrocephalus. Infarction secondary to spasm, hematoma, and hydrocephalus are readily differentiated. The CT examination may be repeated as often as necessary without patient discomfort or morbidity. Serial scans allow rapid assessment of change in ventricular size, development and persistence of infarction, and change in size of hematoma.

Adult↗
PubMed1975

Surgical treatment of extracranial carotid occlusive disease.

This report has reviewed the preoperative evaluation, operative technique, postoperative care, results, and representative pathological findings in 225 carotid endarterectomies. Surgery is generally indicated in patients with: 1. TIA's, and carotid stenosis (lumen diameter less than 2 mm.) or an ulcerated plaque. 2. A stable, mild to moderate neurological deficit with or without TIA's, and carotid stenosis (lumen diameter less than 2 mm.) or an ulcerated plaque. 3. An acute progressive or fluctuating neurological deficit, and carotid stenosis (lumen diameter less than 2 mm.) or carotid occlusion. Surgery should be considered in some patients with: 1. TIA's, and ipsilateral carotid occlusion. 2. An acute partial persistent neurological deficit, and carotid stenosis (lumen diameter less than 2 mm.) or occlusion. 3. No symptoms, and carotid stenosis (lumen diameter less than 2 mm.). Surgery is generally not indicated in patients with an acute severe persistent neurological deficit, and carotid stenosis or occlusion.

Aged↗