Biomedical subjects
Publications and source records attributed to R E Latchaw.
MR imaging has become the definitive diagnostic procedure for the evaluation of suspected spinal dysrhaphic processes. Techniques for spinal MR imaging are discussed and MR findings in patients with surgically verified dysrhaphic spinal lesions are reviewed.
The absence of cerebral blood flow is a valuable adjunct confirming clinical criteria of brain death. However, current methods to confirm absent cerebral blood flow have problems that limit their clinical use. We reviewed cerebral blood flow data obtained with xenon-enhanced computed tomography in nine patients who were being evaluated for brain death. In eight patients who met clinical criteria for brain death, mean cerebral blood flow was 1.6 +/- 2.0 mL X 100 g X min. This value was within the range of error inherent in the method, and therefore represented absent flow. In a patient with persistent respiratory efforts, flow values compatible with absent flow were obtained in the supratentorial compartment, while mean flows as high as 24 mL X 100 g X min were measured in selected regions of interest in the infratentorial compartment, correlating with the clinical evidence of residual function of the brain stem. Xenon-enhanced computed tomography may be a useful test to confirm the absence of cerebral blood flow in patients being evaluated for brain death.
Operative intervention remains controversial for patients with transient nonhemispheric symptoms with occlusive disease of both the anterior and posterior cerebral circulations. In addition to the standard evaluation of these patients, we have used stable xenon-enhanced computed tomographic mapping of cerebral blood flow (Xe/CT CBF). This relatively new and potentially widely available CBF methodology, by measuring approximately 30,000 CBF values within each of three CT levels, provides a readily interpretable means of evaluating extremes of hemodynamic compromise within any or all vascular territories. In the past 30 months, Xe/CT CBF studies in 300 patients with occlusive vascular disease have identified nine patients with global low flow and nonhemispheric symptoms (vertigo, lightheadedness, and/or blurred vision). Blood pressures determined by ocular pneumoplethysmography of Gee were markedly abnormal with reduced ocular/brachial ratios. Each patient had a combination of both segmental carotid and vertebrobasilar occlusive disease. Each patient had a flow-augmenting procedure performed on the anterior circulation in an attempt to improve global flow: carotid endarterectomy (two patients), subclavian-external carotid bypass (one patient), and superficial temporal artery-middle cerebral artery bypass (six patients). In each case disabling transient symptoms were relieved. There were no operative deaths, but one stroke occurred, probably as a result of a brief period of postoperative hypotension. Postoperative Xe/CT CBF studies show a long-term improved global CBF in all patients.
A computer software program (Seapit) was developed for precise determination of intracranial targets identified by stereotactic computed tomography (CT). This program was added to the software of a GE 8800 CT scanner to perform the following operations: millimetre precise calculation and display of the rectilinear coordinates of a target identified on axial CT images; preplotting of phantom target trajectories on the CT images or electronic radiographs; calculation of probe angles required to achieve various trajectories; display of a coordinate scale on each CT image to allow direct target determination without mathematical calculations; calculation of the intercommissural plane for functional neurosurgery. In a series of 100 patients undergoing stereotactic surgery, the Seapit program proved to be a superior and accurate method of target coordinate calculation. Preview display on the CT images of 'phantom' probes significantly enhanced the safety of stereotactic intervention.
Twelve patients with neurofibromatosis affecting the spine and paraspinal regions were examined with magnetic resonance (MR) imaging performed using a 1.5-T magnet, surface coils, and spin-echo pulse sequences. In all 11 patients with neurofibromas, these tumors had slightly greater signal intensity than muscle on T1-weighted images and markedly increased signal intensity on T2-weighted images. In seven patients central areas of decreased signal intensity within the neurofibromas were demonstrated on T2-weighted images. In one patient these central areas corresponded pathologically to relatively fibrous components of the tumors surrounded by myxoid matrix. Five patients had extensive plexiform neurofibromatosis, one had lateral meningoceles, one had a neurofibrosarcoma, three had extradural spinal cord compression, and two had cystic intramedullary tumors of the spinal cord. The ability to obtain high-resolution, multiplanar images in a noninvasive fashion makes surface coil MR imaging an ideal technique for evaluating neurofibromatosis involving the spinal cord, spinal canal, and paraspinal soft tissues.
Fourteen institutions performed 1,830 computed tomographic (CT) cerebral blood flow (CBF) examinations with 32% inhaled stable xenon. Respiratory rate delay greater than 10 seconds occurred in 3.6% of patients, with 83% of the delays lasting 10-15 seconds. There was no incident of prolonged respiratory difficulty. Headache (0.4%), seizures (0.2%), nausea and vomiting (0.2%), and change in neurologic status (0.1%) were uncommon, and there were no transient ischemic attacks. The CT CBF method with 32% inhaled stable xenon is thus associated with an acceptably low incidence of adverse reactions.
The exposure and operative management of the petrous and upper cervical internal carotid artery (ICA) in 29 patients is detailed. Twenty-seven of these patients had extensive cranial base neoplasms (benign or malignant), 1 had an inflammatory cholesteatoma, and 1 had an aneurysm of the upper cervical ICA immediately proximal to the carotid canal. Preoperative studies useful in the evaluation of these patients included computed tomography, magnetic resonance imaging, cerebral and cervical angiography, and a balloon occlusion test of the ICA with evaluation of neurological status and of cerebral blood flow. The exposure of the upper cervical and petrous ICA was useful to obtain proximal control of the cavernous ICA, aided in the operative approach to extensive petroclival, intracavernous, and parapharyngeal neoplasms, and enabled the total resection of 23 of 27 such tumors. A subtemporal and preauricular infratemporal fossa approach was most commonly used for the exposure of the artery. Intraoperative arterial management consisted of exposure and decompression only, dissection from encasing neoplasm, resection of the invaded arterial segment and vein graft reconstruction, or intentional arterial occlusion. Vascular complications included 1 stroke due to delayed arterial occlusion, 1 stroke and death due to infection spreading from the nasopharynx with bilateral ICA rupture, and 1 pseudoaneurysm formation secondary to wound infection necessitating postoperative balloon occlusion of the ICA. Nonvascular complications included facial nerve paralysis in 10 patients (usually temporary), glossopharyngeal and vagal paralysis in 13 patients requiring Teflon injection of the vocal cord in 9, temporary difficulties with mastication in 9 patients, and wound infection in 3. The surgical exposure and management of the upper cervical and petrous ICA may permit a total operative resection of extensive cranial base neoplasms and is also an alternative for the management of vascular lesions involving these segments of the artery. With malignant neoplasms extending from the nasopharynx, postoperative infection remains a problem and may best be resolved by the use of a vascularized rectus abdominis muscle flap to reconstruct defects of the nasopharynx. Bilateral ICA encasement by neoplasms is also a major problem to be solved. The value of such an aggressive approach to the management of malignant neoplasms remains to be proven.
Modern stereotaxic surgery is dependent upon compatible advanced imaging tools, including computerized tomography (CT) scanning and magnetic resonance (MR) imaging. The authors describe three cases in which the patients underwent stereotaxic surgery for mass lesions identified by both MR imaging and CT scans. Identical target coordinates were defined by both techniques, and accuracy was confirmed by intraoperative CT. In comparison to stereotaxic CT, MR provided superior contrast resolution, allowed direct multiplanar imaging and target determination, and permitted accurate correlation of the image with histological features. The operative set-up and technique are described. Stereotaxic surgery with MR imaging may permit more accurate histopathological definition of tumor margins and ultimately lead to better dosimetry for therapeutic procedures such as interstitial brachytherapy.
Intracranial lipoma is an uncommon lesion that has been well described in both the neurosurgical and neuroradiological literature for many years. This lesion is usually only an incidental finding, but it may be symptomatic. The authors describe a case of symptomatic intracranial lipoma of the superior medullary velum with emphasis on the correlation between computerized tomography and magnetic resonance imaging in evaluation of the lesion.
To define tumor boundaries prior to radiation therapy, 13 patients with intracranial glial neoplasms had tumor biopsies using magnetic resonance imaging (MRI)--computed tomography (CT) stereotactic technique. Precise histologic sampling of the lesion volume was correlated with the MRI and CT-defined 'lesion'. Tumor boundaries extended beyond the CT or MRI margin in 4 of 4 cases of glioblastoma, 1 of 3 cases of anaplastic astrocytoma, and 1 of 6 cases of well-differentiated astrocytoma. While stereotactic MRI is superior to stereotactic CT in the visualization of glial neoplasms, accurate tumor biopsy is mandatory to define both tumor type and margins before pre-operative radiation therapy.
Xenon/CT cerebral blood flow (CBF) analysis has been utilized in the evaluation of 35 patients sustaining severe cranial trauma. The patient population included closed head injury, focal hematoma, and the sequelae of trauma including coma, persistent alteration of consciousness, and brain death. Xe/CT CBF analysis has proven helpful in the determination of appropriate degrees of hyperventilation therapy for the head injured patient. The technique is helpful for determining both local and remote changes of CBF as an aid in deciding upon surgical intervention. Severely decreased flows, compatible with brain death, can be demonstrated. The technique shows promise in the evaluation of physiologic changes accompanying therapy for the injured brain.
CT scanning performed before and sequentially during the inhalation of stable xenon (32%), coupled with end-tidal xenon measurements, has made possible the routine construction of regional cerebral blood flow (rCBF) maps with resolution that approximates that of the CT scanner. The capability of obtaining quantitative flow maps with direct anatomic correlation is now available with a commercial package of hardware and software adapted to the General Electric 9800 scanner. The ability to distinguish between normal and reduced rCBF in specific vascular territories has proved useful in the management of cerebrovascular disease. Specific clinical dilemmas that have been addressed with rCBF information from xenon-enhanced CT scanning include the following: In the patient with asymptomatic occlusive disease, is normal rCBF preserved? Is there adequate collateral flow? Are cerebrovascular symptoms a result of emboli or chronic regional low flow? In the patient with complex multivessel occlusive disease, which revascularization procedure is indicated first? Did operation improve rCBF? Should a further procedure be added? May a diffusely diseased but patent artery, which is the source of emboli, be sacrificed safely without compromising rCBF? On the basis of experience with 155 patients, the management and understanding of cerebrovascular disease has been aided substantially by the incorporation of rCBF mapping by xenon-enhanced CT scan in the evaluation of these patients.
Minimal neck injury produced vertebral artery damage in two women and three men, 20 to 57 years of age. Serious neurologic deterioration occurred in two patients when positioned for roentgenographic procedures. Dissection or thrombosis of one or both vertebral arteries while in the transverse foramina occurred in three, one at the site of an osteophyte. The arteriogram of one patient showed a traumatic aneurysm at C-7, and a second patient had segmental arterial stenosis with bilateral traumatic aneurysms at C-5. The location of the arterial injury is not restricted to the occipitoatlantoaxial level but includes the course through the transverse foramina. The use of anticoagulation appears to be important in the immediate management of this process.
This study was performed to determine the effects of osmotic and oncodiuretic therapy on CT-brain density (CT-BD) and on intracranial pressure (ICP) in normal monkeys. CT scans were obtained before therapy then hourly for six hours. ICP was measured before therapy and was continuously monitored thereafter. Four monkeys in group I received oncodiuretic therapy (furosemide-albumin) for the first five hours, then osmotic therapy (mannitol) was added for one hour. Four monkeys in group II received mannitol during the first hour of therapy, then oncodiuretic therapy was added for the remaining four hours. CT-BD was increased and ICP decreased one hour after mannitol but not after oncodiuretic therapy. CT-BD and ICP correlated inversely during osmotic therapy but not during oncodiuretic therapy. The effects of mannitol on CT-BD indicate that it lowers ICP by dehydrating normal brain. Oncodiuretic therapy did not reduce ICP nor consistently increase CT-BD in these six hour experiments on monkeys without cerebral oedema.
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Until recently, in standard hospital settings the tissue blood supply could be inferred only from indirect measures such as assessment of the clinical signs and intracranial pressure (ICP) monitoring. This critical parameter can now be imaged directly with stable xenon-enhanced computed tomographic (CT) imaging. The procedure requires only an additional 10 minutes after a standard head study, yet it provides potentially vital information about tissue perfusion. We describe here a patient in whom a frontal lobe hematoma produced a direct mass effect, causing an element of central herniation with relative sparing of lateral and posterior cortical regions. Although the ICP recordings remained unchanged, symptoms of brain stem compression became apparent. Xenon/CT cerebral blood flow (CBF) mapping demonstrated a flow decrease mainly within the left frontal lobe and throughout central ganglionic structures. After removal of the left frontal hematoma, both clinical status and local and central flow improved. Because the xenon/CT method combines direct anatomical information with blood flow information in one examination, it may be a valuable clinical tool in providing a better understanding of pathophysiology in patients with head injuries and other mass lesions.
The charts of 750 patients were reviewed to determine the value of routinely removing cerebrospinal fluid at the time of myelography and cisternography for chemical and cytologic examination. In most patients cerebrospinal fluid findings were normal. In the few abnormal studies, the findings were often uninformative, superfluous, or insufficient for appropriate diagnosis. In no instance did routine analysis of cerebrospinal fluid uncover occult disease. Routine removal of cerebrospinal fluid for analysis in radiologic spinal taps seems to be inappropriate, and removal should be dictated by the clinical context in which the procedure is performed.
Xenon computerized tomography (Xe CT) blood flow studies were conducted in 25 patients referred for a possible extracranial-intracranial bypass procedure for occlusive vascular disease in one or more extra- or intracranial vessels. These studies were helpful in selecting eight candidates for surgery. The Xe CT studies were performed at one or two brain levels using a prototype Xe CT system for measurement of cerebral blood flow which was designed in collaboration with the General Electric Co., and adapted for the GE 9800 scanner. In those patients selected to undergo operation, Xe CT demonstrated compromise of flow reserve regionally, globally, and/or in the watershed area. All eight patients who underwent the procedure showed a favorable clinical response postoperatively, and seven had a dramatic increase in flow. The 17 patients whose baseline CT studies showed no reduction of flow with the Xe CT method were not selected for surgery. All 25 patients have remained neurologically stable to date. Case studies of three of the eight patients undergoing bypass surgery are presented. This limited but consistent experience suggests that Xe CT blood flow mapping makes possible the recognition of brain regions in which flow reserves are compromised. This is due to the relatively high degree of spatial resolution that this technique provides and to the fact that mapping can be correlated directly with the anatomy. Used in combination with a careful clinical examination and an accurate medical history, this study method appears to be a useful guide in the selection of patients who are most at risk from hemodynamic instability and those who are most likely to benefit from flow-augmentation surgery.