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Biomedical subjects

M K Morgan

Publications and source records attributed to M K Morgan.

At least 73 records · Page 4Linked to original sources
PubMed1989

Familial os odontoideum. Case report.

A familial asymptomatic os odontoideum with a Klippel-Feil type II fusion of C-2 and C-3 is reported. The pattern of inheritance within this family is consistent with that of autosomal dominance. The index case, a 16-year-old boy, was studied with plain cervical spine x-ray films, lateral cervical tomography in flexion and extension, fluoroscopic evaluation of the subluxation, and magnetic resonance (MR) imaging of the spine in flexion and extension. In spite of the subluxation noted on flexion and extension, there was no evidence of cord compression on MR imaging. The etiology and management of this condition are discussed.

Adolescent↗
PubMed1989

Management of spinal dural arteriovenous malformations.

Dura-based spinal arteriovenous malformations (AVM's) are being diagnosed with increasing frequency. The optimal management of such lesions remains a topic of discussion. In an effort to guide this discussion, the authors review their experience with 17 cases of spinal dural AVM treated between January, 1984, and July, 1987. All patients presented with a slowly progressive paraparesis. The abnormalities were initially identified on myelography and confirmed by selective spinal angiography. Fourteen patients underwent endovascular embolization as a primary treatment, and a total of 18 embolization procedures were performed. After all but two of these, obliteration was confirmed at angiography. Patients' symptoms improved following 15 or these procedures but early improvement was not sustained in 10 instances; patients were unchanged after two procedures and worse after one. Follow-up angiography was performed at varying intervals after 15 of the 18 procedures, and recanalization of the previously obliterated spinal dural AVM was demonstrated in 13 instances. Eight patients ultimately underwent surgical treatment of their dura-based spinal AVM. No patient suffered deterioration of symptoms following operation. While embolization may allow angiographic obliteration of a spinal dural AVM and early clinical improvement, for the majority of patients these are not sustained. The average time to treatment failure was 5 months. Newer embolization materials will be necessary to effect permanent treatment in many of these patients.

Aged↗
PubMed1988

Intracranial arteriovenous malformations: an 11-year experience.

A consecutive series of 107 patients with an intracranial arteriovenous malformation who were considered for surgical treatment over the 11-year period between 1974 and 1985 is analysed. In 71 (66.4%) patients complete obliteration (which in some cases was combined with pre- or peroperative embolization) by surgery was attempted and was achieved in all but two patients. Five patients were treated by embolization alone and three patients by radiotherapy alone. Twenty-eight patients were managed conservatively for one of four reasons: an expectation of a good outcome without treatment (six patients); the refusal of recommended surgical treatment (five patients); poor condition at presentation (eight patients); or the risks of operative treatment were thought to be too great (nine patients). There was a 9.9% mortality in the surgically-treated series and significant morbidity in 16 (22.3%) patients. In all but two of these 16 patients, morbidity was related directly to the initial intracerebral haemorrhage. The one-year mortality in the group that did not undergo operation was significantly higher than in those patients who were treated surgically. Some general guide-lines for the management of intracranial arteriovenous malformations are proposed.

Adolescent↗
PubMed1988

AIDS-related dementia: a case report of rapid cognitive decline.

Little is known psychometrically about the pattern of cognitive decline associated with acquired immunodeficiency syndrome (AIDS)-related dementia. Pre- and posttest results are presented to illustrate a case example of rapid cognitive decline. Increased psychometric assessment is recommended with additional examination of inconsistent results, which may be dismissed mistakenly as related to psychiatric symptoms. Implications for clinical practice and the role of the psychologist are discussed.

Acquired Immunodeficiency Syndrome↗
PubMed1988

Genetic organization and regulation of proteins associated with production of syringotoxin by Pseudomonas syringae pv. syringae.

Many strains of Pseudomonas syringae pv. syringae produce one of two low-molecular-weight, peptide-containing phytotoxins, either syringomycin (SR) or syringotoxin (ST). An analysis of Tn5-induced ST-mutants revealed alterations in the presence of two large proteins (ca. 470 and 435 kilodaltons). Apparent truncated forms of the 470 (ST1)- or 435 (ST2)-kilodalton proteins were observed in some mutants. Mapping of the Tn5 insertions and size determinations of truncated proteins suggested that both ST1 and ST2 are in the same transcriptional unit, with ST1 being directly upstream of ST2. When an ST-producing strain of P. syringae pv. syringae was grown under toxin-inducing conditions, ST1 and ST2 were first detected at the end of the exponential phase of growth, which was when the first accumulation of ST was observed. High iron levels were essential for efficient ST production. At concentrations of FeCl3 of between 0.2 and 5 microM, the amount of toxin accumulated was almost directly proportional to the iron concentrations. The amount of ST1 and ST2 present showed a corresponding increase in response to iron concentrations. Our genetic and physiological data implicate ST1 and ST2 in the biosynthesis of syringotoxin.

Bacterial Toxins↗
PubMed1988

Intracerebral hemorrhage after carotid endarterectomy.

A series of 14 patients with intracerebral hemorrhage after carotid endarterectomy is reviewed. This complication occurred in 0.6% of 2362 consecutive carotid endarterectomies performed at the Mayo Clinic from 1972 through 1986. All hemorrhages occurred within the first 2 weeks after operation and were ipsilateral to the side of the operation. Eight patients died, and only two made a good recovery. Significant risk factors are hypertension and chronic hemispheric hypoperfusion with impaired autoregulation. The "normal pressure-hyperperfusion breakthrough" syndrome was considered to be operative in 12 of the 14 patients. Nine patients had documented hyperperfusion (at least 100% increase of baseline cerebral blood flow) at the time of surgery. In an additional three patients, normal perfusion-pressure breakthrough was inferred by the clinical course and radiological findings, as well as by the absence of alternative explanations. Patients at risk for postendarterectomy intracerebral hemorrhage include those who have a clinical history suggestive of hemodynamic cerebral ischemia, severe carotid stenosis with limited hemispheric collateral flow, and postendarterectomy hyperperfusion, as measured by intraoperative cerebral blood flow. To minimize the risk of hemorrhage in these patients, strict maintenance of blood pressure at normotensive or even relatively hypotensive levels during the intraoperative and early postoperative periods is advised.

Aged↗
PubMed1988

Cerebrospinal fluid diversion in the treatment of benign intracranial hypertension.

Thirty-six patients from a consecutive series of 41 patients with benign intracranial hypertension (BIH) were treated by cerebrospinal fluid shunting. In 12 patients this was selected as the primary treatment due to the severe deterioration of vision or concern regarding the possible adverse effects of steroids; all 12 patients showed rapid and complete resolution of the disease, although eight patients still have a shunt in place. In 24 patients a shunt was inserted when other forms of treatment failed; all of these patients showed rapid resolution of the condition, although 20 patients still have a shunt in place. Three patients had the shunt removed without sequelae, and one patient in whom the shunt was removed because of low-pressure symptoms remains symptomatic with persistent papilledema (over 6 years). The percutaneous lumboperitoneal (LP) shunt was associated with the lowest revision and complication rates. Cisternal shunting to either the atrium or pleural cavity was next most effective, whereas valved LP shunts inserted via a laminectomy were least effective; ventricular shunts were used in only two cases. Shunting is therefore very effective in the treatment of BIH, but the significant complication rate and the possibility of inducing shunt dependence must be recognized.

Adolescent↗
PubMed1987

Moyamoya disease: presentation and treatment of two cases by surgery.

Stroke prophylaxis in patients with moyamoya disease has not been described previously in Australia. Two cases are presented in which superficial temporal to middle cerebral arterial bypass has been successful in halting the progress of the disease. The presentation, investigation and management of this occlusive vasculopathy are discussed.

Arterial Occlusive Diseases↗
PubMed1987

Vein of Galen malformation: diagnosis and management.

The vein of Galen malformation is a midline arteriovenous fistula with aneurysmal dilatation of the vein of Galen. The clinical details of diagnosis and treatment in 13 patients with such lesions together with a review of 232 cases collected from the literature are presented in this report. There were 132 males, 77 females, and 36 cases in which the sex was not stated. Eighty patients presented as neonates, 82 were 1 to 12 months old, 39 were 1 to 5 years old, 22 were 6 to 20 years old, and 22 were over the age of 20. The most common presenting symptoms were congestive cardiac failure (110 cases), raised intracranial pressure secondary to hydrocephalus (94 cases), cranial bruit (57 cases), focal neurological deficit (37), seizures (26 cases), and hemorrhage (25 cases). The most characteristic vascular supply to the midline fistula involved multiple bilateral vessels, although bilateral posterior cerebral and unilateral posterior cerebral supply was relatively common. The overall figures for treatment and outcome showed that 91 patients (37.1%) were treated by direct operation and 29 patients (11.3%) were treated by other forms of operation, predominantly shunting or remote vessel ligation. Forty-six patients (18.8%) were treated by medical means (digoxin, diuretics, and ventilatory support). In 79 patients (22.2%), there was no treatment or no details of treatment were available. There was an overall series mortality of 55.6% (no details were available in 33 cases) and a 37.4% mortality for surgically treated cases. After operation, there was a 46.3% incidence of significant morbidity in surviving patients. Neonatal patients fared worst, with an overall mortality of 64 of 70 cases (91.4%) where details were available. The outcome was equally bad for surgically and conservatively treated cases. Operation in the 1- to 12-month age group was more successful, but still carried a mortality of 31.7%, with a significant morbidity in approximately half of the surviving patients. Over the age of 1 year, the surgically treated patients had a 25.6% mortality and a 42.3% major morbidity in survivors. Consideration is given to some of the ways in which these figures may be improved, in particular a staged approach during the neonatal period, with the use of selective embolization or occlusion of vessels to reduce the volume of the arteriovenous shunt until the patient is older and better able to tolerate major operation.

Adolescent↗
PubMed1987

Intracranial carotid artery injury in closed head trauma.

Six patients with trauma to the intracranial internal carotid artery are reported. One patient died and two are permanently disabled due to ischemic sequelae. The incidence of this complication of trauma is unknown because of the infrequent use of angiography in head-injured patients. The pathology, clinical course, and management of this condition are discussed with reference to the 25 previously reported cases in addition to the six in this series.

Adolescent↗
PubMed1987

Cerebral arteriovenous malformations, steal, and the hypertensive breakthrough threshold. An experimental study in rats.

An experiment was designed to investigate the effects of arteriovenous (AV) fistula occlusion on cerebral autoregulation. A right carotid-jugular fistula was created in 63 rats in such a way as to produce an intracranial AV fistula with a loop extension into the neck. The fistula was occluded after an 8-week interval with the rats under both normotension and metaraminol-induced hypertension, and evidence of blood-brain barrier disruption was investigated with an Evans blue dye technique. The results indicate that an intracranial AV fistula may cause cerebral steal which is responsible for a reduction in the threshold for hypertensive breakthrough following fistula occlusion.

Animals↗
PubMed1986

Spinal arteriovenous malformation presenting at birth: case report.

A newborn with paraplegia and evidence of a subarachnoid hemorrhage was found to have a spinal arteriovenous malformation. The arteriovenous malformation was managed by direct surgical obliteration. This patient is the youngest ever reported to have this disorder and the youngest so treated.

Angiography↗
PubMed1985

Isolation and characterization of Tn5 insertion mutants of Pseudomonas syringae pv. syringae altered in the production of the peptide phytotoxin syringotoxin.

A syringotoxin-producing strain of Pseudomonas syringae pv. syringae (B457) was subjected to Tn5 mutagenesis by the transposon vector pSUP1011. Analyses of auxotrophs obtained suggested simple random insertions of Tn5. Syringotoxin-negative mutants arose at a frequency of about 0.28%. In a Southern blot analysis, the loss of toxin production was associated with Tn5 insertions into chromosomal EcoRI fragments of about 10.5, 17.8, and 19.3 kilobases. Data from a Southern blot analysis of SstI-digested DNA from these mutants suggest that the 10.5- and 17.8-kilobase EcoRI fragments may be adjacent to or near each other. Mutants that produced only 3 to 4% wild-type toxin levels also were identified.

Bacterial Toxins↗
PubMed1983

Isolation and Partial Characterization of Bacteriophages of the Phytopathogen Pseudomonas syringae.

Bacteriophages isolated from culture supernatants of Pseudomonas syringae pv. syringae and from sewage were identified. The DNA from each phage was isolated and digested with the restriction endonuclease EcoRI. Eight isolates were determined to be different, with two phage isolates from sewage having restriction patterns identical to two phages from culture supernatants. The sizes of the phage DNA ranged from 24 to49 kilobases for isolates from sewage and from 39 to 52.5 kilobases for the isolates from culture supernatants. Buoyant densities of phage particles in CsCl varied from 1.498 to 1.507 g/cm for isolates from sewage and from 1.506 to 1.516 g/cm for isolates from culture supernatants. Electron microscopy revealed four morphological types. Based on plaque-forming ability of culture supernatants, 31 out of 47 strains of P. syringae are probably lysogenic.

Journal Article↗
PubMed1982

Direct DNA repeat in plasmid R68.45 is associated with deletion formation and concomitant loss of chromosome mobilization ability.

Plasmid R68.45 has been useful in promoting the transfer of chromosomal markers in bacteria of many genera. In donors harboring R68.45, chromosome-mobilizing ability (Cma) may be lost without the loss of other plasmid markers. However, Cma can be somewhat stabilized by maintenance of the donors in the presence of kanamycin (Km). We isolated variants of R68.45 from four bacterial species of three genera. Plasmid variants isolated included those without Cma, without transfer function (Tra) and Cma, or without Tra, Cma, and Km resistance. In Erwinia carotovora subsp. atroceptica EA153, the loss of plasmid markers is dependent on the culture medium on which the donors are maintained. Restriction endonuclease analyses of the variant plasmids revealed that most are deletion mutants of R68.45. In all cases when the uncertainty in the ends of the deletions was not too great, one end of the deletion was shown to originate within or near the direct DNA duplication in R68.45 which is required for Cma and which maps close to the Km resistance determinant. Furthermore, the types of deletions observed are consistent with what might be expected for deletions generated by tandemly repeated insertion sequences. Therefore, we suggest that the DNA duplication is the source of much of the instability observed in R68.45. However, data are presented for E. carotovora subsp. atroceptica EA153 which suggest that another region of R68.45 may also play a role in its stability in this species.

Chromosomes, Bacterial↗