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Biomedical subjects

Michael K Morgan

Publications and source records attributed to Michael K Morgan.

11 recordsLinked to original sources
PubMed2006

Responses of arteriovenous malformations to radiosurgery: ultrastructural changes.

OBJECTIVE: To examine the ultrastructural changes in arteriovenous malformations (AVMs) after radiosurgery and to explore the possible mechanisms of posttreatment obliteration and hemorrhage. METHODS: Twenty-two specimens, among them three irradiated AVMs (size, 3-6 cm), 15 nonirradiated AVMs, and four normal controls were processed for ultrastructural study immediately after removal. Transmission electron microscopy was used to compare the vasculature of irradiated AVMs with nonirradiated AVMs and normal controls. RESULTS: Thirty-three months postradiosurgery, partial vaso-occlusion (36-74% lumen) occurred by coagulation of cytoplasmic debris and proteinaceous material leaking from the endothelium. Forty-eight months postradiosurgery, heterogeneous thrombus formation (86-96% lumen) with fibrinoid and proteinaceous materials was observed. Sixty-four months postradiosurgery, complete luminal closure (90-100% lumen) by a fibrin thrombus was seen in vessels with diameters up to 5.5 mm including feeding arteries and draining veins. In occluded vessels, there was extensive degeneration of endothelial cells, subendothelial fibroblasts, and myofibroblasts. Neoproliferation and endothelialization of smooth muscle cells with Weibel-Palade bodies was observed in arteries. CONCLUSION: Radiosurgery causes irreversible cellular damage of the vascular wall. Partial vaso-occlusion that increases blood flow in remaining vessels and degenerative changes on the blood-brain barrier may contribute to hemorrhage at early stage postradiosurgery. Radiosurgery stimulates neoproliferating and endothelializing smooth muscle cells in vessel walls, which might lead to narrowing of the vessel lumina. Complete vaso-occlusion achieved 64 months postradiosurgery suggested a minimum follow-up duration of 5 years to determine final outcome of radiosurgery. Histological end point of vaso-occlusion of AVMs takes longer time than neuroimaging endpoint of complete obliteration.

Adolescent↗
PubMed2006

Ultrastructure of perinidal capillaries in cerebral arteriovenous malformations.

OBJECTIVE: The ultrastructure of perinidal capillaries in cerebral arteriovenous malformations (AVMs) was examined to clarify their pathomorphological features. METHODS: Fifteen AVM specimens were dissected and divided into perinidal and intranidal groups and processed for ultrastructural study immediately after surgical removal. Eleven of the patients had presented with hemorrhage. Tissue from four normal controls was also studied. Electron microscopy was used to compare features of the blood-brain barrier and endothelial cells (ECs) of capillaries in perinidal, intranidal, and controls. RESULTS: Perinidal capillaries demonstrated abnormal ultrastructure of the blood-brain barrier with no basement membranes and astrocytic foot processes. ECs had fenestrated luminal surfaces. Large gaps were observed at endothelial intercellular junctions. ECs contained numerous filopodia, large numbers of cytoplasmic processes, numerous micropinocytotic vesicles, and the cytoplasm contained more filaments than those observed in controls. Pericytes were rich in pinocytotic vesicles, vacuoles, and filaments. Their processes were in close contact with ECs. Weibel-Palade bodies were present in perinidal ECs. CONCLUSION: The absence of blood-brain barrier components in perinidal capillaries may contribute to extravasation of red blood cells into the surrounding brain in the absence of major hemorrhage and explain the gliosis and hemosiderin occasionally seen around AVMs. Cellular differentiation and proliferation in perinidal capillaries should be included in a systematic study aimed at a better understanding of the mechanisms underlying the recurrence of surgically removed AVMs.

Adolescent↗
PubMed2005

Ultrastructural characteristics of hemorrhagic, nonhemorrhagic, and recurrent cavernous malformations.

OBJECT: Ultrastructural characteristics of hemorrhagic, nonhemorrhagic, primary, and recurrent central nervous system cavernous malformations (CMs) were examined in an attempt to clarify their pathological mechanisms. METHODS: Thirteen specimens (nine from samples of CMs and four from healthy control tissue) were processed for ultrastructural study immediately after surgical or postmortem removal, by fixation in glutaraldehyde/formalin and postfixation in OsO4. Transmission electron microscopy was used to examine the vascular walls, endothelium, subendothelium, and cytoplasmic organelles. The vascular walls in CMs demonstrated abnormal ultrastructure with no basement membranes and astrocytic foot processes. Pericytes were rarely seen. Single-layer lining endothelial cells showed fenestrated luminal surfaces. Large gaps were observed at intercellular junctions between endothelial cells, and large vesicles with extremely thin plasma membranes bordering the lumen were common in the lesions that had previously hemorrhaged. Endothelial cells of recurrent CMs had more Weibel-Palade bodies, filopodia, cytoplasmic processes, micropinocytotic vesicles, and filaments than those in primary lesions and normal control tissues. CONCLUSIONS: The absence of the blood-brain barrier, normal supporting wall structure, and large vesicles bordering the lumen of CM vessels may explain leakage of red blood cells into surrounding brain in the absence of major hemorrhage. Proliferation of residual abnormal endothelial cells may contribute to the recurrence of surgically removed CMs.

Adolescent↗
PubMed2004

Bifurcation geometry and the presence of cerebral artery aneurysms.

OBJECT: The angles of arterial bifurcations are governed by principles of work minimization (optimality principle). This determines the relationship between the angle of a bifurcation and the radii of the vessels. Nevertheless, the model is predicated on an absence of significant communication between these branches. The circle of Willis changes this relationship because the vessels proximal to the ring of vessels have additional factors that determine work minimization compared with more distal branches. This must have an impact on understanding of the relationship between shear stress and aneurysm formation. The authors hypothesized that normal bifurcations of cerebral arteries beyond the circle of Willis would follow optimality principles of minimum work and that the presence of aneurysms would be associated with deviations from optimum bifurcation geometry. Nevertheless, the vessels participating in (or immediately proximal to) the circle of Willis may not follow the geometric model as it is generally applied and this must also be investigated. METHODS: One hundred seven bifurcations of the middle cerebral artery (MCA), distal internal carotid artery (ICA), and basilar artery (BA) were studied in 55 patients. The authors analyzed three-dimensional reconstructions of digital subtraction angiography images with respect to vessel radii and bifurcation angles. The junction exponent (that is, a calculated measure of the division of flow at the bifurcation) and the difference between the predicted optimal and observed branch angles were used as measures of deviation from the geometry thought best to minimize work. The mean junction exponent for MCA bifurcations was 2.9 +/- 1.2 (mean +/- standard deviation [SD]), which is close to the theoretical optimum of 3, but it was significantly smaller (p < 0.001; 1.7 +/- 0.8, mean +/- SD) for distal ICA bifurcations. In a multilevel multivariate logistic regression analysis, only the observed branch angles were significant independent predictors for the presence of an aneurysm. The odds ratio (OR) (95% confidence interval) for the presence of an aneurysm was 3.46 (1.02-11.74) between the lowest and highest tertile of the observed angle between the parent vessel and the largest branch. The corresponding OR for the smallest branch was 48.06 (9.7-238.2). CONCLUSIONS: The bifurcation beyond the circle of Willis (that is, the MCA) closely approximated optimality principles, whereas the bifurcations within the circle of Willis (that is, the distal ICA and BA) did not. This indicates that the confluence of hemodynamic forces plays an important role in the distribution of work at bifurcations within the circle of Willis. In addition, the observed branch angles were predictors for the presence of aneurysms.

Angiography, Digital Subtraction↗
PubMed2003

Prospective study of neuropsychological and psychosocial outcome following surgical excision of intracerebral arteriovenous malformations.

In this prospective study the neuropsychological and psychosocial function of 64 patients undergoing surgical resection of cerebral arteriovenous malformations was examined prior to surgery (T1), one month post-surgery (T2) and one year post-surgery (T3). A mild but widespread cognitive decline was observed pre-operatively. There was a trend toward decreased neuropsychological function at T2. All neuropsychological tests showed a trend toward improvement at T3 compared with both pre-operative (generally not statistically significant) and early post-operative values (generally significant). Patients were assessed for change between testing times. At T2 patients were more likely to have deteriorated than improved, whereas at T3 the group which had altered from baseline were more likely to have improved than deteriorated. Deterioration in some verbal/language tasks was more common for left sided AVMs. Outcome did not differ significantly for patients presenting with haemorrhage. Psychosocial function was unchanged at late follow-up for the majority of patients.

Activities of Daily Living↗
PubMed2003

Barbiturates for acute neurological and neurosurgical emergencies--do they still have a role?

A number of clinical studies have reported poor clinical outcomes for patients treated with barbiturate therapy in acute neurological and neurosurgical emergencies. Barbiturate therapy, as currently practised with thiopentone and pentobarbitone at least, is also associated with a prolonged post-infusion period of clinical unresponsiveness. Hence, the popularity of barbiturate therapy for sedation of critically ill neurological and neurosurgical patients has declined over the past decade. A retrospective study of traumatic brain injury patients treated at the Royal North Shore Hospital, Sydney, with high-dose thiopentone therapy between 1987 and 1997 has found disappointing results with a 1-month mortality outcome of 50% (14 of 28 patients). Nevertheless, barbiturate therapy remains a consideration for patients with severe cranial trauma in whom preferred treatments have failed to control intracranial or cerebral perfusion pressures. More favourable results ( approximately 10% 1-month mortality rate) were encountered for patients with refractory vasospasm complicating subarachnoid haemorrhage or intracerebral haemorrhage complicating supratentorial arteriovenous malformation resection. A well designed, prospective and randomised controlled trial may be of value in further determining the role of barbiturate therapy in acute neurovascular emergencies refractory to standard therapy.

Barbiturates↗
PubMed2003

Delayed hemorrhage following resection of an arteriovenous malformation in the brain.

OBJECT: Between 1989 and 2002 the authors treated 416 cases of angiographically confirmed arteriovenous malformations (AVMs) of the brain. METHODS: Three hundred fifty-five patients underwent resection of an AVM; 2% died and 12% experienced a permanent morbidity (1.7% experienced a deterioration of modified Rankin Scale [mRS] score of 3-5). Patient outcomes in this series were based on the Spetzler-Martin grade. For patients with Grade I and II AVMs the rate of permanent morbidity was 1% and the rate of mortality was 0.5%. For patients with Grade III AVMs the morbidity rate was 18.9% (2.7% experienced a deterioration of mRS score of 3-5) and the mortality rate was 2.7%. For patients with Grade IV and V AVMs the morbidity rate was 25.6% (5.1% experienced a deterioration of mRS score of 3-5) and the mortality rate was 7.7%. No patient with a Spetzler-Martin Grade I or II lesion had a worsened outcome due to delayed hemorrhage, whereas 3.6% of patients with a Grade III and 12.8% of patients with Grade IV and V AVMs experienced delayed hemorrhage that led to a permanent downgrade in function. With the introduction of an aggressive postoperative blood pressure protocol (for AVMs with grades > II and sizes > 3.5 cm in diameter) the incidence of delayed postoperative hemorrhage leading to mortality or permanent morbidity decreased from 4.4 to 1%. This difference was significant. Neither case selection nor complications other than delayed hemorrhage changed between these two periods. CONCLUSIONS: In selected cases an aggressive postoperative blood pressure protocol is likely to reduce delayed hemorrhage following AVM resection.

Adolescent↗
PubMed2002

High-grade arteriovenous malformations and their management.

The aim of this study was to compare operatively and non-operatively managed high-grade arteriovenous malformations (AVMs) and to identify risk factors for surgical morbidity. Three hundred and ninety-one consecutively enrolled patients with AVMs were graded using the Spetzler Martin grading scheme. Forty-six of these patients had grade 4 or 5 AVMs. Twenty-nine patients underwent surgery and 17 were conservatively managed. During an average of 33 months follow-up the non-operative group experienced a decline in function in 27% of cases followed. These deteriorations were due to haemorrhage, progressive neurological deficits and seizures. In the surgical group completing treatment there was a mortality and morbidity impacting on self-care of 15%. In those without deep perforating arterial supply the morbidity was 10% and with deep perforating arterial supply or deep meningeal recruitment there was a combined morbidity and mortality of 44%. This difference in outcome was statistically significant (P<0.01). We conclude that high-grade AVMs have a high operative morbidity. However, these lesions often have a poor natural history and with careful selection (based on the presence or absence of deep perforating arterial supply) a group can be selected that benefits from surgery. Grade 4 and 5 AVMs with supply from lenticulostriate, choroidal, thalamic deep perforating arteries or deep meningeal recruitment may be best treated conservatively or possibly by multimodality treatment utilising radiotherapy and embolisation combined with surgery.

Adult↗
PubMed2002

Bypass to the intracranial internal carotid artery.

Extracranial to intracranial internal carotid artery bypass surgery with vein is well described for a number of diverse conditions. They provide high blood flow with good initial patency. However, long term patencies for specific graft types remains unknown. This is an analysis of consecutive interposition saphenous vein bypass cases between the common carotid artery (CCA) and the intracranial internal carotid artery (ICA) where the distal anastomosis was placed end-to-end immediately proximal to the posterior communicating artery in 55 patients undergoing 57 bypass procedures (bilateral in 2 cases). Twenty-five patients underwent grafting for planned vessel obliteration where the pathology required vessel sacrifice. Twenty-eight patients had bypass grafting for stroke risk reduction in the setting of threatening stroke and 4 patients had bypass grafts for emergency revascularisation in the setting of stroke in evolution. Patients were assessed preoperatively and at follow-up with modified Rankin scores. Procedural related complications included a 7% mortality and 7% functional decline. Early graft occlusion occurred in 5% of grafts leading to death in each case. A further patient died of rupture at the distal anastomosis site. In surviving patients, patency was present in 100% at last follow-up (mean 5 years and maximum 11 years) with no patient sustaining new hemispheric ischemic events. One patient developed a delayed asymptomatic stenosis within the vein graft requiring stenting. Because of the high initial management risks this technique of common carotid to intracranial internal carotid artery saphenous vein bypass surgery should be reserved for patients at considerable risk by alternate management. However, once the acute postoperative period is past the bypass appears to be robust and capable of supplying the entire distribution of a normal internal carotid artery.

Adolescent↗