Papers by Dr. Michael Lawton
Evaluation of Insecticides for Cat Flea Control Inside Urban Dwellings, 1982
Insecticide and acaricide tests, 1983
The residual control of cat fleas indoors with Dursban LO, Ficam W, Knox Out, Safrotin and some m... more The residual control of cat fleas indoors with Dursban LO, Ficam W, Knox Out, Safrotin and some mixtures with insect growth regulator Precor was evaluated in apartments and single family dwellings in coastal areas of southern California. Residences with active flea infestations were obtained through the cooperation of Western Exterminator Company. Residences where studies were made were surveyed 24 h before treatment and 30 and 60 days post-treatment. Pretreatment and posttreatment counts were obtained with a Hoover Portapower vacuum cleaner modified with a special cloth filter attachment inserted in the collection hose. Fleas could be readily vacuumed from accessible floor space, including carpets and bare floors. Filters with fleas and debris were placed into plastic bags that were sealed and were returned to the laboratory to be evaluated. The contents were carefully examined and adult fleas unable to jump or crawl were considered to be moribund. Although larvae and dead adult fleas were occasionally collected, only living adult fleas were counted. Treatments were applied by professionals at 40 psi from a B & G compression sprayer equipped with a coarse fan nozzle. Ficam and Knox Out were applied at approximately 3.8 liters of finish spray/74m2 (1 gal/800ft2) while Dursban and Safrotin were applied at 1.9 liters/74m2. About 0.8ml of Precor was mixed with 3.8 liters of Safrotin and Knox Out and applied at the above rates. Safrotin provided excellent residual control for at least 60 days and the lowest percentage of complaints within 30 days after treatment. Even though Knox Out also provided excellent residual control, residents frequently mentioned the lack of rapid activity and the odor within 2-3 wk after treatment. The addition of 0.8 ml Precor per 3.8 liters of Safrotin or Knox Out did not appear to enhance their performance at 30 and 60 days. Ficam did not provide satisfactory control of cat fleas and all the residences needed another treatment within 2 wk.
Speak Up!: A Quantitative Exploration of the Long-term Impacts of Competitive Forensics
Three seventeenth century versions of the story of Palamon and Arcite
Operative neurosurgery (Hagerstown, Md.), Jan 17, 2017
The Superior Cerebellar Artery Aneurysm: A Posterior Circulation Aneurysm with Favorable Microsurgical Outcomes
Neurosurgery, Jan 24, 2017
Superior cerebellar artery (SCA) aneurysms are usually grouped with aneurysms that arise from the... more Superior cerebellar artery (SCA) aneurysms are usually grouped with aneurysms that arise from the upper basilar artery or more broadly, the posterior circulation. However, the SCA aneurysm has distinctive anatomy that facilitates safe surgical management, notably few associated perforating arteries, and excellent exposure in the carotid-oculomotor triangle. To demonstrate the outcomes of patients treated with microsurgery in a continuous surgical series. Sixty-two patients harboring 63 SCA aneurysms were retrospectively reviewed from a prospectively maintained database, focusing on clinical characteristics, surgical techniques, and clinical outcomes. Of 31 patients (49%) presenting with subarachnoid hemorrhage, the SCA aneurysm was the source in 16 (25%). Thirty-three aneurysms were complex (52%) and 43 patients (59%) had multiple aneurysms. Fifty-seven SCA aneurysms (90.5%) were clipped and 5 were bypassed/trapped or wrapped. Complete angiographic occlusion was achieved in 91.7%. P...
Neurosurgery, Jan 13, 2017
High-risk components of brain arteriovenous malformations (BAVMs) can be targeted to reduce the r... more High-risk components of brain arteriovenous malformations (BAVMs) can be targeted to reduce the risk of lesion rupture. To evaluate targeted embolization of aneurysms against other means of treatment with a case-control analysis; we previously investigated this approach associated with BAVMs. Retrospective analysis of patients with BAVMs was performed, identifying patients treated with intention to occlude only an aneurysm associated with a BAVM. For each targeted aneurysm embolization (TAE) patient identified, 4 control patients were randomly selected, controlling for rupture status, age, and Spetzler-Martin plus Lawton-Young supplemental score. Analysis was performed to compare rates of adverse events (hemorrhage, new seizure, and death) between the 2 groups. Thirty-two patients met inclusion criteria, and 128 control patients were identified, out of 1103 patients treated during the study period. Thirty-four adverse events occurred (15 ruptures, 15 new seizures, and 11 deaths) dur...
PloS one, 2017
To compare the validity of diagnosis of urinary tract infection (UTI) through urine culture betwe... more To compare the validity of diagnosis of urinary tract infection (UTI) through urine culture between samples processed in routine health service laboratories and those processed in a research laboratory. We conducted a prospective diagnostic cohort study in 4808 acutely ill children aged <5 years attending UK primary health care. UTI, defined as pure/predominant growth ≥105 CFU/mL of a uropathogen (the reference standard), was diagnosed at routine health service laboratories and a central research laboratory by culture of urine samples. We calculated areas under the receiver-operator curve (AUC) for UTI predicted by pre-specified symptoms, signs and dipstick test results (the "index test"), separately according to whether samples were obtained by clean catch or nappy (diaper) pads. 251 (5.2%) and 88 (1.8%) children were classified as UTI positive by health service and research laboratories respectively. Agreement between laboratories was moderate (kappa = 0.36; 95% confi...
Stroke, May 21, 2017
Brain arteriovenous malformation (bAVM) is an important risk factor for intracranial hemorrhage. ... more Brain arteriovenous malformation (bAVM) is an important risk factor for intracranial hemorrhage. Current therapies are associated with high morbidities. Excessive vascular endothelial growth factor has been implicated in bAVM pathophysiology. Because soluble FLT1 binds to vascular endothelial growth factor with high affinity, we tested intravenous delivery of an adeno-associated viral vector serotype-9 expressing soluble FLT1 (AAV9-sFLT1) to alleviate the bAVM phenotype. Two mouse models were used. In model 1, bAVM was induced in R26CreER;Eng(2f/2f) mice through global Eng gene deletion and brain focal angiogenic stimulation; AAV2-sFLT02 (an AAV expressing a shorter form of sFLT1) was injected into the brain at the time of model induction, and AAV9-sFLT1, intravenously injected 8 weeks after. In model 2, SM22αCre;Eng(2f/2f) mice had a 90% occurrence of spontaneous bAVM at 5 weeks of age and 50% mortality at 6 weeks; AAV9-sFLT1 was intravenously delivered into 4- to 5-week-old mice. ...
Neurosurgery, 2006
The incidence of de novo aneurysm formation is unknown. The risk of recurrent hemorrhage in treat... more The incidence of de novo aneurysm formation is unknown. The risk of recurrent hemorrhage in treated patients with a previous aneurysmal subarachnoid hemorrhage or incidental aneurysm is reported to be higher than in the general population. It seems that the incidence in the younger age population may be higher than in the older population. We review a consecutive series of young patients to determine their risk for de novo aneurysm formation. METHODS: We report a series of 378 patients treated between 1976 and 2000 who presented with a subarachnoid hemorrhage secondary to a saccular aneurysm or an incidental aneurysm in patients ranging in age from 9 to 39 years at presentation. Thirty-nine of these patients died from initial hemorrhage or from other causes, leaving 339 patients for follow-up. RESULTS: Of 121 patients who had repeat arteriograms, new aneurysms were seen in 15 (12.4%). Findings in 16 other patients included the development of a neck remnant or growth of a known previous neck remnant, regrowth of a previously thrombosed aneurysm, rupture of a previously explored infundibulum, and recurrence of a previously clipped aneurysm. CONCLUSION: Although the follow-up of the remaining patients is ongoing, it seems that de novo aneurysm formation or recurrent growth of existing aneurysm is significant. Close angiographic follow-up in patients below the age of 40 years is recommended.
World Neurosurgery, 2017
Background: Complex aneurysms of the anterior cerebral artery (ACA) may require a bypass procedur... more Background: Complex aneurysms of the anterior cerebral artery (ACA) may require a bypass procedure as part of their surgical management. Most current bypass paradigms recommend technically demanding side-to-side anastomosis of pericallosal arteries or use of interposition grafts, which involve longer ischemia times. The purpose of this study is to assess the feasibility of an anterior temporal artery (ATA) to ACA end-to-side bypass. Methods: Fourteen cadaveric specimens (17 ATAs) were prepared for surgical simulation. The cisternal course of the ATA was freed from perforating branches and arachnoid. The M3-M4 junction of the ATA was cut and the artery was mobilized to the interhemispheric fissure. The feasibility of ATA bypass to the pre-and post-communicating ACA was assessed in relation to the cisternal length and branching pattern of the middle cerebral artery. Results: Successful anastomosis was feasible in 14 ATAs (82%). Three ATAs did not reach the ACA. These ATAs were branching distally and originated from the M3 (opercular) middle cerebral artery. In specimens where bypass was not feasible, the average cisternal length of the ATA was significantly shorter than the rest. Conclusions: ATA-ACA bypass is anatomically feasible and may be a useful alternative to other revascularization techniques in selected patients. It is technically simpler than A3-A3 in situ bypass. ATA-ACA bypass can be performed through the same pterional exposure used for the ACA aneurysms, sparing the patient an additional interhemispheric approach, required for the A3-A3 anastomosis.
World Neurosurgery, 2017
Background: Identification and protection of the cochlea during anterior petrosectomy is key to p... more Background: Identification and protection of the cochlea during anterior petrosectomy is key to prevent hearing loss. Currently, there is no optimal method to infer the position of the cochlea in relation to the Kawase quadrangle, therefore damage to the cochlea during anterior petrosectomy remains a substantial risk. Objectives: To identify and define landmarks available during anterior petrosectomy to locate the cochlea and prevent its damage. Methods: Kawase approach was simulated in eleven specimens. After a subtemporal craniotomy, foramen spinosum and ovale were identified. Anterior petrosectomy was performed and the upper dural transitional fold (UDTF) was identified. Two virtual lines, from foramen spinosum (Line A), and the lateral rim of the foramen ovale (Line B), were projected to intersect the UDTF perpendicularly. The cochlea was exposed and the distances between Lines A and B and the closest point of the outer rim and membranous part of the cochlea were measured. The average distance between Line A to the bony and membranous edges of the anteromedial cochlea was -0.62±1.38 mm and 0.38±1.63 mm, respectively. The average distance between Line B to the bony and membranous edges of the cochlea was 1.82±0.99 mm and 2.78±1.29 mm, respectively. Line B (cochlear safety line) never intersected the cochlea. The cochlear safety line is a reliable landmark to avoid the cochlea during the Kawase approach. When expanding the anterior petrosectomy posteriorly, the "cochlear safety line" may be used as a reliable landmark to prevent exposure of the cochlea, therefore preventing hearing loss.
Journal of Clinical Neuroscience, 2016
While brainstem cavernous malformations were once considered inoperable, improvements in patient ... more While brainstem cavernous malformations were once considered inoperable, improvements in patient selection, surgical exposures, intraoperative MRI-guidance, MR tractography, and neurophysiologic monitoring have resulted in good outcomes in the majority of operated patients. In a consecutive series of 104 patients with brainstem cavernous malformations, only 14% of patients experienced cranial nerve or motor dysfunction that was worse at late follow-up, relative to their preoperative condition. Outcomes were predicted by several factors, including larger lesion size, lesions that crossed midline, the presence of a developmental venous anomaly, older age, and greater time interval from lesion hemorrhage to surgery. The 14% of patients who experienced a persistent neurological deficit as a result of surgery, while substantial from any perspective, compares favorably with the risks of observation based on a meta-analysis published by Horne et al. 2016. Curative resection is a safe and effective treatment for brainstem cavernous malformations that will prevent re-hemorrhage in symptomatic patients.
World neurosurgery, Jan 5, 2016
The objective of this study is to classify patients using federally mandated categories of ethnic... more The objective of this study is to classify patients using federally mandated categories of ethnicity and race and to determine if subgroups are associated with patient outcomes and aneurysmal subarachnoid hemorrhage (SAH). The American College of Surgeons National Surgical Quality Improvement Program database from 2008 to 2013 was utilized to identify patients undergoing treatment of an intracerebral aneurysm. Ethnicity and race were combined to create subgroups. A descriptive statistical analysis was performed and a multivariable logistic regression model was tested if ethnic and racial subgroups were associated with SAH. A total of 686 patients met the study criteria. There were no endovascular cases reported. Four subgroups were identified, which included: non-Hispanic Whites (n=504, 73.47%, NH Whites), Hispanic Whites (n=38, 5.54%, H Whites), non-Hispanic Blacks (n=109, 15.89%, NH Blacks) and non-Hispanic Asians (n=35, 5.10%, NH Asians). Significant statistical associations were...
Journal of clinical neuroscience : official journal of the Neurosurgical Society of Australasia, 2016
The full utility of diagnostic cerebral angiography, an invasive cerebrovascular imaging techniqu... more The full utility of diagnostic cerebral angiography, an invasive cerebrovascular imaging technique, is currently debated. Our goal was to determine trends in diagnostic cerebral angiography utilization and associated complications from 1999 through 2009. The National Inpatient Sample (NIS) was used to identify patients who received primary cerebral angiography from 1999-2009 in the United States. We observed trends in discharge volume, total mean charge, and post-procedural complications for this population. Data was based on sample projections and analyzed using univariate and multivariate regression. There were a total of 424,105 discharges indicating primary cerebral angiography nationwide from 1999-2009. The majority of these cases (65%) were in patients older than 55years. Embolic stroke was the most frequent complication, particularly in the oldest age bracket, occurring in 16,304 patients. The risk for complications increased with age (p<0.0001) and with other underlying h...
The transsylvian approach for resection of insular gliomas: technical nuances of splitting the Sylvian fissure
Journal of Neuro-Oncology, 2016
Insular gliomas represent a unique surgical challenge due to the complex anatomy and nearby vascu... more Insular gliomas represent a unique surgical challenge due to the complex anatomy and nearby vascular elements associated within the Sylvian fissure. For certain tumors, the transsylvian approach provides an effective technique for achieving maximal safe resection. The goal of this manuscript and video are to present and discuss the surgical nuances and appropriate application of splitting the Sylvian fissure. Our hope is that this video highlights the safety and efficacy of the transsylvian approach for appropriately selected insular gliomas.
Journal of Neurosurgery: Pediatrics, 2016
Mutations in the smooth muscle–specific isoform of alpha actin (ACTA2) cause smooth muscle dysfun... more Mutations in the smooth muscle–specific isoform of alpha actin (ACTA2) cause smooth muscle dysfunction in arteries. This rare loss-of-function mutation may cause a diffuse occlusive cerebral arteriopathy, resulting in stroke. While ACTA2 arteriopathy is often described as moyamoya-like, it has a distinct phenotype characterized by dilation of the proximal internal carotid artery (ICA) and occlusion of the terminal ICA and proximal middle cerebral artery. Intracranial arteries have an abnormally straight course, often with small aneurysms. There is limited experience with revascularization procedures for ACTA2 arteriopathy, and the safety and efficacy of these procedures are unknown. In this paper the authors present a symptomatic 6-year-old patient with ACTA2 cerebral arteriopathy who underwent both indirect revascularization and direct cerebrovascular bypass. Postoperatively, the patient suffered an ischemic infarct in a neighboring vascular territory. While direct cerebrovascular ...
Journal of Cerebral Blood Flow & Metabolism, 2016
Cerebral aneurysms are weakened blood vessel dilatations that can result in spontaneous, devastat... more Cerebral aneurysms are weakened blood vessel dilatations that can result in spontaneous, devastating hemorrhage events. Aneurysm treatment aims to reduce hemorrhage events, and strategies for complex aneurysms often require surgical bypass or endovascular stenting for blood flow diversion. Interventions that divert blood flow from their normal circulation patterns have the potential to result in unintentional ischemia. Recent developments in computational modeling and in vivo assessment of hemodynamics for cerebral aneurysm treatment have entered into clinical practice. Herein, we review how these techniques are currently utilized to improve risk stratification and treatment planning.
JAMA Neurology, 2016
To the Editor Amin-Hanjani el al 1 identified an important distinction in the natural history of ... more To the Editor Amin-Hanjani el al 1 identified an important distinction in the natural history of atherosclerotic vertebrobasilar occlusive disease by separating the diagnosis of stenosis/ occlusion with hemodynamic insufficiency. Could this be used to stratify patients more likely to benefit from intervention? Cautious optimism exists in the shadow of previous attempts to justify interventions based on hemodynamic compromise, like the Carotid Occlusion Surgery Study. 2 Unlike the Carotid Occlusion Surgery Study, which used an indirect method of blood flow measurement to identify atrisk patients, the Vertebrobasilar Flow Evaluation and Risk of Transient Ischemic Attack and Stroke investigators used their own quantitative magnetic resonance angiography platform to directly measure blood flow. Seventy-four percent of patients with normal distal flow had severe stenosis or occlusion. This emphasizes the disconnect between stenosis and distal blood flow because territory downstream from a stenosis can have robust collateral blood supply, particularly in the vertebrobasilar circulation. The etiology for stroke in a low-flow state is yet to be elucidated, and many questions remain related to this. Historically, interventions to prevent stroke in disease related to stenosis relied on measurement of the degree of stenosis, and this has been the standard to identify future stroke risk based on thousands of patients with carotid stenosis in randomized clinical trials. 3,4 In severe carotid stenosis, the pathologic turbulence resulting from stenosis, along with plaque instability, is thought to result in arter y-to -arter y thromboembolism. The same may not be true for vertebrobasilar stenosis, and hypoperfusion may be the leading pathologic mechanism. In our experience, many patients present as medically refractory, meaning that they return with serial, symptomatic ischemic events over a relatively short period despite antiplatelet agents. Revascularization is successful in arresting these crescendo scenarios, suggesting that restoration of blood flow is helpful, and supports the hypothesis of a hypoperfusion-based pathology in vertebrobasilar ischemia. The authors emphasized endovascular angioplasty and stenting in their conclusion 1 , but it is also important to emphasize microsurgical bypass. Although bypass is more invasive and taxing on these patients than endovascular therapies, we have observed dramatic results in a limited experience with posterior circulation bypasses that include the superficial temporal artery-to-posterior cerebral artery, vertebral artery-toanterior inferior cerebellar artery bypass, and occipital arteryto-anterior inferior cerebellar artery bypasses. 5 In all of these patients, endovascular revascularization was considered first but there were no viable options. Further work with quantitative magnetic resonance angiography may determine the hemodynamic effect of intervention and further validate intervention in patients who otherwise have a threatening natural history.
World neurosurgery, Jan 4, 2016
Aneurysms of the anterior pontine segment of the anterior-inferior cerebellar artery (AICA) are u... more Aneurysms of the anterior pontine segment of the anterior-inferior cerebellar artery (AICA) are uncommon. Their treatment is challenging because critical neurovascular structures are adjacent to it and the available surgical corridors are narrow and deep. Although endoscopic endonasal approaches are accepted for treating midline skull base lesions, their role in the treatment vascular lesions remains undefined. The present study is aimed to assess the anatomic feasibility of the endoscopic endonasal transclival (EET) approach for treating anterior pontine AICA aneurysms and compare it with the subtemporal anterior transpetrosal (SAT) approach. Twelve cadaveric specimens were prepared for surgical simulation. The AICAs were exposed using both EET and SAT approaches. Surgical window area and the length of the exposed artery were measured. The distance from the origin of the artery to the clip applied for proximal control was measured. The number of AICA perforators exposed and the ana...
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Papers by Dr. Michael Lawton