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Biomedical subjects

M G Hamilton

Publications and source records attributed to M G Hamilton.

At least 37 records · Page 2Linked to original sources
PubMed1994

The molecular weight and subunit organization of Helisoma trivolvis (Say) hemoglobin: light-scattering and scanning transmission electron microscopic studies.

The hemoglobin of the freshwater snail, Helisoma trivolvis has a molecular weight of 1.77(+/- 0.04) x 10(6) Da as determined by light-scattering measurements at 630 nm. Scanning transmission electron microscopic measurements gave nearly the same particle mass of 1.85(+/- 0.24) x 10(6) Da. The molecular weight of the denatured hemoglobin in 6.0 M GdmCl is found to be 3.96 x 10(5) Da, which is close to one-fifth of the mass of the parent hemoglobin. The molecular weight data based on light-scattering and STEM microscopy is consistent with a 10-subunit structure comprising five disulfide-linked dimers, as opposed to a 12-subunit assembly proposed by Ilan et al. (1986), which would necessitate a higher particle mass. Analysis of the molecular weight and the sedimentation data of H. trivolvis hemoglobin, suggests a compact two-layer ring structure of decamers of about 200 A to 250 A diameter, stabilized by disulfide-linkages between the subunits of the two pentameric layers.

Animals↗
PubMed1994

Cardiopulmonary bypass, hypothermic circulatory arrest and barbiturate cerebral protection for the treatment of giant vertebrobasilar aneurysms in children.

Intracranial aneurysms in the pediatric population are rare lesions with a significant proportion occurring as giant aneurysms involving the vertebrobasilar system. The complex anatomy of these lesions frequently creates an extremely difficult management dilemma. We present two patients, a 9-year-old and a 13-year-old, with giant fusiform vertebrobasilar aneurysms, to illustrate the utility of cardiopulmonary bypass, hypothermic circulatory arrest and barbiturate cerebral protection for successful surgical treatment of these complex intracranial vascular lesions in children.

Adolescent↗
PubMed1994

Variations in the anatomy of the rabbit cervical carotid artery.

BACKGROUND AND PURPOSE: A model for cerebral ischemia that requires injection of emboli into the internal carotid artery of the rabbit is commonly used. However, in our experience we have found the anatomy of the cervical carotid to be highly variable. If not appreciated, this may result in unexpectedly high variability in the severity of ischemic injury. We undertook this experimental protocol to determine whether it was possible to characterize the anatomy of the rabbit cervical carotid artery. METHODS: We examined and recorded the architecture of the cervical carotid arteries of 105 consecutive rabbits involved in experimental protocols to evaluate the role of tissue-type plasminogen activator during embolic stroke. RESULTS: Two basic patterns of origin of the internal carotid artery were identified: lateral origin, classified as type I, and dorsomedial origin, classified as type II. In addition, there were three subsequent variations in the origin and morphology of the occipital artery in relation to the internal carotid artery: origin from the external carotid artery (subtype A); origin proximal on the internal carotid artery (subtype B); and origin distal on the internal carotid artery (subtype C). CONCLUSIONS: The classification of the anatomy of the cervical carotid artery of the rabbit into these easily recognized types will assist those attempting to use this embolization model. Failure to recognize the origin of the occipital artery from the internal carotid artery can result in the misdirection of embolic material into the occipital artery and significantly reduce the effectiveness of this stroke model.

Animals↗
PubMed1994

A comparison of intra-arterial and intravenous tissue-type plasminogen activator on autologous arterial emboli in the cerebral circulation of rabbits.

BACKGROUND AND PURPOSE: The efficacy of thrombolytic therapy for treatment of embolic stroke has been a subject of both experimental and clinical examination. The aim of this study was to compare the efficacy, in regard to reduction of volume of ischemic brain, of two different modes of administration (ie, intra-arterial and intravenous) of tissue-type plasminogen activator (TPA) given 30 minutes after experimental embolic stroke in rabbits. METHODS: A randomized, blinded, controlled experimental trial was undertaken. Embolic stroke was simulated in rabbits by injecting fragments of autologous arterial thrombus into one internal carotid artery. Thirty minutes after embolization, the rabbits were blindly treated with 2 mg/kg intra-arterial TPA, 2 mg/kg intravenous TPA, or saline (all n = 10). Six hours after embolization the rabbits were killed. The brains were perfused with triphenyltetrazolium chloride and cut into 0.5-cm-thick coronal sections, and the areas of ischemia were measured. RESULTS: Administration of TPA resulted in a significant reduction in the volume of ischemic cerebral injury (P < .0001): control animals sustained ischemic injury to 20.1 +/- 4.6% (mean +/- SD) of total brain compared with 4.6 +/- 4.1% for animals treated with intra-arterial TPA and 3.4 +/- 2.6% for those treated with intravenous TPA. The difference between intra-arterial and intravenous TPA treatment was not significant (P = .786). CONCLUSIONS: In this rabbit model of embolic stroke, administration of TPA within 30 minutes resulted in a dramatic reduction in the amount of ischemic injury, with equal efficacy for the two modes of administration. These results favor the treatment of acute embolic stroke with intravenous TPA, given the rapidity with which intravenous therapy can be established in the clinical setting.

Analysis of Variance↗
PubMed1994

Venous thromboembolism in neurosurgery and neurology patients: a review.

Thromboembolism is a common problem in neurosurgery and neurology patients. Within this diverse population are subpopulations of patients with varying degrees of thromboembolic risk: low, moderate, and high. Patients at substantial risk for deep vein thrombosis and pulmonary embolism include those with spinal cord injury, brain tumor, subarachnoid hemorrhage, head trauma, stroke, and patients undergoing a neurosurgical operation. There are prophylactic strategies that can be applied to these various risk groups that will dramatically reduce the incidence of thromboembolism. The risk of pulmonary embolism or fatal pulmonary embolism typically exceeds the risk of severe or fatal bleeding from adequate prophylaxis, and these techniques should be applied on a routine basis. To adequately care for patients with deep venous thrombosis and pulmonary embolism, the physician requires a thorough understanding of the methods of diagnosis, the pharmacokinetics of heparin and warfarin, and a knowledge of their role in the treatment strategies that have proven efficacy and safety. In addition, an awareness of the low molecular weight heparins and heparinoids is becoming essential. These new agents have a potentially promising role in both the prophylaxis and treatment of patients with neurological disease. The principles concerning the prophylaxis, diagnosis, and clinical management of venous thromboembolic disease in neurosurgery and neurology patients are dealt with in this review.

Anticoagulants↗
PubMed1994

Isolated cerebellar lymphomatoid granulomatosis progressing to malignant lymphoma. Case report.

A 60-year-old man presented with progressive and unique neurological symptoms. Investigations identified an isolated cerebellar lesion. This lesion fulfilled the histological criteria for lymphomatoid granulomatosis, and in situ hybridization and deoxyribonucleic acid (DNA) dot blot techniques revealed significant amounts of Epstein-Barr virus DNA within the tumor cells. The patient underwent cranial radiation therapy, and 16 months after the initial presentation the lesion evolved into a malignant lymphoma. He subsequently died secondary to subdural empyema, bacterial meningitis, and bronchopneumonia. The unique clinical and etiological aspects of this case are addressed.

Cerebellar Neoplasms↗
PubMed1994

Petroclival lesions.

Explore the source record for details and available documents.

Cerebellar Neoplasms↗
PubMed1994

The prospective application of a grading system for arteriovenous malformations.

The decision-making process whereby treatment is offered to a patient with an arteriovenous malformation (AVM) must be supported by an understanding of the risks related to the natural history of the AVM and the risks related to the treatment of that particular AVM. The ability to estimate the treatment risk for an individual patient is hampered by the marked variability in the complexity of AVMs. In 1986, an AVM grading system was proposed to predict surgical morbidity and mortality. This system is based on the AVM size, the neurological eloquence of adjacent brain, and the pattern of venous drainage. Grade I malformations are small, superficial, and located in noneloquent cortex; Grade V lesions are large, deep, and situated in neurologically critical areas; and Grade VI lesions are considered inoperable AVMs. A retrospective application of this grading scheme demonstrated its correlation with the incidence of postoperative neurological complications. A prospective application of the AVM grading system has been performed in 120 consecutive patients who had a complete microsurgical excision of their AVM, with or without AVM embolization. The AVM grading system accurately correlated with both new-temporary (P < 0.0001) and new-permanent (P = 0.008) neurological deficits. The permanent major neurological morbidity rates for Grades I through III were 0%, increasing to 21.9% in patients with Grade IV and 16.7% in patients with Grade V AVMs (P < 0.0001). One patient with a Grade III AVM died from an esophageal hemorrhage 15 months after her AVM was treated.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1993

Supratentorial glioblastoma with spinal cord intramedullary metastasis.

A patient presented with myelopathy due to intramedullary thoracic spinal cord glioblastoma 10 months after treatment for a supratentorial glioblastoma. There was no supratentorial recurrence, and no evidence of gross leptomeningeal dissemination documented by CSF cytology, complete myelography, and MRI imaging. Gross examination of the spinal cord and arachnoid at the time of exploratory thoracic spinal surgery was normal. However, histological review of thoracic arachnoid demonstrated microscopic deposits of glial fibrillary acidic protein (GFAP) positive tumour consistent with malignant astrocytoma. Intramedullary spinal cord metastasis of cerebral glioblastoma rarely occurs, but may develop in association with leptomeningeal tumour dissemination. As local control of primary tumours improves, distant metastasis is likely to become a more common clinical problem. Leptomeningeal gliomatosis may be very difficult to document, even when clinically suspected and GFAP staining of a biopsy of arachnoid tissue can play an important role in confirming the diagnosis. This information can be critical to establish prognosis and develop an appropriate treatment strategy.

Aged↗
PubMed1993

Nervous system injuries in horseback-riding accidents.

A review of 156 horseback-riding accidents that occurred in southern Alberta over a 6-year period and resulted in nervous system trauma, including 11 deaths, is presented. The majority (81%) of accidents occurred during recreational activity and 81% were associated with falling or being thrown from a horse. Head injury occurred in 92% of patients and accounted for all of the 11 deaths. Spinal injury occurred in 13% of the patients and was associated with head injury in 40%. One peripheral nerve injury was identified. Helmets were used by only two victims. The 11 deaths that occurred as a consequence of severe head injury accounted for 79% of all deaths associated with horseback riding. This profile of neurologic injuries associated with horse-related accidents supports a need for use of protective headgear.

Adolescent↗
PubMed1993

Atlantoaxial dislocation as the presenting symptom of ankylosing spondylitis.

A 27-year-old woman presented with nontraumatic atlantoaxial dislocation that required a C1-C2 fusion. A comprehensive investigation initially failed to reveal any evidence of infectious or rheumatologic disease and she remained well for 3 1/2 years, at which time a diagnosis of ankylosing spondylitis was established. There are no other similar cases reported in the medical literature. When dealing with a patient who has experienced a spontaneous atlantoaxial dislocation, a thorough assessment looking for an underlying infectious or inflammatory etiology is mandatory. Furthermore, the authors recommend that any patient who has negative investigations be followed long-term; an underlying covert inflammatory cause may only become evident after significant delay.

Adult↗
PubMed1993

Chronic subdural hematoma: the role for craniotomy reevaluated.

The management of chronic subdural hematoma in the adult patient is approached with a variety of different surgical techniques. The trend in recent years has been toward treatment with burr holes or twist-drill holes rather than craniotomy. The rationale for this has been based on the assumption that burr holes and twist-drill holes offer equivalent efficacy and lower morbidity and mortality. This viewpoint is not, however, universally accepted, and many surgeons feel that craniotomy is superior to a burr hole for the management of this condition. In a review of 92 patients presenting over a 3-year period with 112 chronic subdural hematomas, 49 underwent craniotomy and 43 underwent burr-hole treatment. The recurrence of hematomas, requiring another operation, occurred in 8.6%; operative mortality was 2.2% at hospital discharge and 4.4% at follow-up. No patient died as a consequence of the operative procedure. There was no significant difference in the incidence of postoperative complications, hematoma recurrence, or operative mortality among the different surgical groups. Previous reports concerning the superiority of burr holes over craniotomy are not substantiated by this review. Although the issue concerning optimal therapy has not been resolved by this review, at this time, craniotomy remains a valid and safe technique for the management of patients with chronic subdural hematoma.

Adolescent↗
PubMed1992

Epstein-Barr virus-associated primary B-cell lymphoproliferative disorder of the cerebellum in an immune competent man.

BACKGROUND: The role of the Epstein-Barr virus (EBV) in lymphoproliferative lesions has been widely accepted. Most of these lesions occur in patients who have deficiencies in their immune status. Lymphomatoid granulomatosis (LG) is a lymphoproliferative disorder originally characterized as an angiocentric, necrotizing, pleomorphic infiltrate of mononuclear cells. The etiology of LG is unknown. It was originally hypothesized that LG may represent an unusual lymphoid response to an infective organism, possibly EBV. METHODS: Tissues from a previously healthy 60-year-old, healthy white man with primary cerebellar lymphomatoid granulomatosis were examined for the presence of EBV by nucleic acid hybridization. RESULTS: The original LG lesion was a polyclonal B-cell proliferation that contained detectable amounts of EBV. Peripheral blood leukocytes were negative for EBV by the same assay. After an 18-month remission, a tumor reappeared near the site of the primary lesion, which had the histologic appearance of a lymphoma. The cells showed restricted clonality and contained a similar amount of EBV-related DNA as the original lesion. Peripheral blood leukocytes at the time of recurrence were negative for EBV. The patient died approximately 2 months after the recurrent tumor was detected. CONCLUSIONS: This case demonstrated the development of a primary cerebellar B-cell lymphoproliferative disorder, histologically identical to lymphomatoid granulomatosis, that transformed into a lymphoma. The original tumor and the subsequent lymphoma contained, on average, several copies of EBV-related DNA per cell. Despite an extensive survey of the patient, no immune deficit was detected. Interpretation of the literature with the results of this case suggest that this instance of primary cerebellar LG arose as a consequence of an unusual EBV-associated B-cell lymphoproliferation. It is suggested that EBV may be a significant factor in the initiation of the abnormal proliferations of T-cells or B-cells reported in this disorder.

B-Lymphocytes↗
PubMed1992

Physical studies of the hemocyanin of the marine gastropod, Kelletia kelleti (Forbes).

1. The hemocyanin of the Californian whelk, Kelletia kelleti, investigated at pH and ionic conditions close to physiological, has a molecular weight close to 9.0 x 10(6) and a sedimentation constant of 114S, characteristic of the di-decameric structure of molluscan hemocyanins. Light-scattering measurements at pH 8.0, 0.05 M Mg2+, 0.01 M Ca2+ gave a molecular weight of 9.0 +/- 0.6 x 10(6), and scanning transmission electron microscopy produced nearly the same particle mass of 9.22 +/- 0.50 x 10(6) daltons (Da). 2. Light-scattering measurements on the fully dissociated monomers in the presence of 8.0 M urea and at pHs 10.6 and 11.0 gave molecular weights of 4.50 x 10(5)-4.91 x 10(5), that are close to one-twentieth of the mass of the parent di-decameric hemocyanin assembly. 3. Changes in pH produced a bell-shaped molecular weight profile, with molecular weights close to 9.0 x 10(6) in the pH region of about 5.5-8.0, and progressive dissociation to 4.5 x 10(5) Da monomers in the region below pH 4.0 and above pH 9.0 or 10, depending on the absence or presence of stabilizing Mg2+ ions (0.01 M). 4. In the absence of divalent ions some aggregation of hemocyanin was found at pHs close to 5.0, with observed molecular weights above 10 x 10(6) (investigated at a hemocyanin concentration of 0.10 g/l). The early studies of Condie and Langer (Science 144, 1138-1140, 1964) had shown that Kelletia kelleti hemocynanin aggregates at acidic pHs close to the isoelectric point, forming linear polymers of the hemocyanin di-decamers.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Pediatric spinal injury: review of 174 hospital admissions.

Injury to the spinal column and spinal cord occurs relatively infrequently in the pediatric population. A review of 174 pediatric patients is presented, representing 5.4% of all patients admitted with spinal injury. Spinal cord injury was present in 45% of patients. A distinct injury profile, explained by anatomical and biomechanical features, distinguishes the young patient with an immature spine from older adolescents with a more mature, adult-like spine. The younger patients, while less likely to have spinal injury, had a higher incidence of neurological injury, in addition to a higher frequency of both spinal cord injury without radiological abnormality and upper cervical cord injury. In addition, younger patients with spinal cord injury and no radiological abnormality were more likely to have complete or severe cord injury. Prognosis was determined by the severity of spinal cord injury. Patients with complete cord injuries showed little improvement, while patients with incomplete injuries generally fared much better, with 74% showing significant improvement and 59% experiencing a complete recovery of neurological functions. There were six deaths, but none was attributed solely to spinal injury. The authors conclude that outcome is quite good after pediatric spinal cord injury that does not produce a physiologically complete cord deficit.

Adolescent↗
PubMed1992

Pediatric spinal injury: review of 61 deaths.

Injury to the spinal column and spinal cord occurs relatively infrequently in the pediatric population. The authors present a unique review of 61 pediatric deaths associated with spinal injury. This group represented 28% of the total pediatric spine-injured population and 45% of the total pediatric spinal cord-injured group studied. The ratio of pediatric to adult spinal injury mortality was 2.5:1. Of the 61 children, 54 (89%) died at the accident scene. Thirty patients underwent a complete autopsy, 19 of whom had an Abbreviated Injury Scale Grade 6 injury (maximum score, untreatable). Spinal cord injury was found to be the cause of death in only eight children and was associated with injury to the high cervical cord and cardiorespiratory arrest. These children typically sustained severe multiple trauma. In this population, there appears to be little room for improved outcome through changes in treatment strategy.

Adolescent↗