Biomedical subjects

Peter K Nelson

Publications and source records attributed to Peter K Nelson.

6 recordsLinked to original sources

PubMed2006

Endovascular treatment of spinal cord arteriovenous malformations.

Spinal cord arteriovenous malformations are rare lesions that represent one-tenth of the brain arteriovenous malformations. Depending on their location and relationship to the dura, these lesions are divided into four categories. Their clinical manifestations may vary from mild symptoms to severe motor deficits. Spinal angiography remains the "gold standard" for diagnosing spinal cord vascular lesions. Although the type of shunting remains difficult to determine by the magnetic resonance imaging, it is well analyzed by spinal angiography. The cure of the shunting is not by itself a therapeutic goal, but the objective is the creation of a new hemodynamic equilibrium between the lesion and the spinal cord to decrease the risk of hemorrhage and prevent the progression of the spinal cord ischemia. The endovascular tools seem to be a reasonable therapeutic option for the treatment of the majority of the spinal cord arteriovenous malformations.

Arteriovenous Malformations↗

PubMed2006

Recent steps toward a reconstructive endovascular solution for the orphaned, complex-neck aneurysm.

OBJECTIVE: The purposes of this article are to summarize recent developments and concerns in endovascular aneurysm therapy leading to the adjunctive use of endoluminal devices, to review the published literature on stent-supported coil embolization of cerebral aneurysms, and to describe our experience with this technique in a limited subgroup of problematic complex aneurysms over a medium-term follow-up period. METHODS: Between January 2003 and June 2004, 28 individuals among 157 patients with cerebral aneurysms we evaluated were identified as harboring aneurysms with exceptionally broad necks. Out of these 28 patients, 16 were treated with a combination of stents and detachable coils, preserving the parent artery. Recorded data included patient demographics, the clinical presentation, aneurysm location and characteristics, procedural details, and clinical and angiographic outcome. RESULTS: Over an 18-month period, 16 patients with large cerebral aneurysms additionally characterized by neck sizes between 7 and 14 mm were treated, using combined coil embolization of the aneurysm with stent reconstruction of the aneurysm neck. Thirteen out of the 16 aneurysms were occluded at angiographic reevaluation between 11 and 24 months (mean angiographic follow-up, 17.5 mo). There were no treatment-related deaths or clinically evident neurological complications. Thirteen patients experienced excellent clinical outcomes, with good outcomes in two patients and a poor visual outcome in one patient (mean clinical follow-up, 29 mo). A single technical complication occurred, involving transient nonocclusive stent-associated thrombus, which was treated uneventfully with abciximab. CONCLUSION: Stent-supported coil embolization of large, complex-neck cerebral aneurysms seems to provide superior medium-term anatomic reconstruction of the parent artery compared with historic series of aneurysms treated exclusively with endosaccular coils. In the near future, increasingly sophisticated endoluminal devices offering higher coverage of the neck defect will likely enable more definitive endovascular treatment of complex cerebral aneurysms and further expand our ability to manipulate the vascular biology of the parent artery.

Blood Vessel Prosthesis↗

PubMed2005

Proximal intracranial internal carotid artery branches: prevalence and importance for balloon occlusion test.

OBJECT: The aim of this study was to determine the prevalence of angiographically identifiable skull base arterial branches that potentially serve as collateral conduits during a balloon occlusion test (BOT) of the internal carotid artery (ICA). The authors posited that neurological deficits in patients who had previously tolerated the occlusion test may be attributable to an unrecognized collateral support through these channels (operant during proximal ICA BOT) when permanent ICA occlusion was performed more distally. METHODS: In 481 cases (962 ICAs), cerebral angiograms obtained during routine Wada testing were retrospectively reviewed. Two hundred sixty-one patients had at least one angiographically identifiable ICA branch; 109 patients had two or more branches. A meningohypophyseal branch of the cavernous ICA was identified on the right side in 108 patients and on the left in 122. A vidian artery originated from the petrous portion of the ICA on the right side in 58 patients and on the left in 85. The inferolateral trunk revealed itself as a branch of the cavernous ICA on the right side in 17 patients and on the left in 33. A caroticotympanic artery arose from a left cavernous ICA. A persistent trigeminal artery was situated on the right side in two patients and on the left in three. More than half of the patients had angiographically identifiable and perhaps hemodynamically significant skull base branches of the ICA, and approximately one quarter had more than one identifiable branch. CONCLUSIONS: The authors recommend that patients be screened during angiography studies performed prior to BOT in branches of the proximal intracranial ICA and that the site of BOT be moved distally if such branches are identified.

Adolescent↗

PubMed2005

Flow changes caused by the sequential placement of stents across the neck of sidewall cerebral aneurysms.

OBJECT: The goal of this study was to quantify the reduction in velocity, vorticity, and shear stresses resulting from the sequential placement of stents across the neck of sidewall cerebral aneurysms. METHODS: A digital particle image velocimetry (DPIV) system was used to measure the pulsatile velocity field within a flexible silicone sidewall intracranial aneurysm model and at the aneurysm neck-parent artery interface in this model. The DPIV system is capable of providing an instantaneous, quantitative two-dimensional measurement of the velocity vector field of "blood" flow inside the aneurysm pouch and the parent vessel, and its changes at varying stages of the cardiac cycle. The corresponding vorticity and shear stress fields are then computed from the velocity field data. Three Neuroform stents (Boston Scientific/Target), each with a strut thickness between 60 and 65 microm, were subsequently placed across the neck of the aneurysm model and measurements were obtained after each stent had been placed. The authors measured a consistent decrease in the values of the maximal averaged velocity, vorticity, and shear stress after placing one, two, and three stents. Measurements of the circulation inside the sac demonstrated a systematic reduction in the strength of the vortex due to the stent placement. The decrease in the magnitude of the aforementioned quantities after the first stent was placed was remarkable. Placement of two or three stents led to a less significant reduction than placement of the first stent. CONCLUSIONS: The use of multiple flexible intravascular stents effectively reduces the strength of the vortex forming in an aneurysm sac and results in a decrease in the magnitude of stresses acting on the aneurysm wall.

Cerebrovascular Circulation↗

PubMed2004

Roles of uroplakins in plaque formation, umbrella cell enlargement, and urinary tract diseases.

The apical surface of mouse urothelium is covered by two-dimensional crystals (plaques) of uroplakin (UP) particles. To study uroplakin function, we ablated the mouse UPII gene. A comparison of the phenotypes of UPII- and UPIII-deficient mice yielded new insights into the mechanism of plaque formation and some fundamental features of urothelial differentiation. Although UPIII knockout yielded small plaques, UPII knockout abolished plaque formation, indicating that both uroplakin heterodimers (UPIa/II and UPIb/III or IIIb) are required for plaque assembly. Both knockouts had elevated UPIb gene expression, suggesting that this is a general response to defective plaque assembly. Both knockouts also had small superficial cells, suggesting that continued fusion of uroplakin-delivering vesicles with the apical surface may contribute to umbrella cell enlargement. Both knockouts experienced vesicoureteral reflux, hydronephrosis, renal dysfunction, and, in the offspring of some breeding pairs, renal failure and neonatal death. These results highlight the functional importance of uroplakins and establish uroplakin defects as a possible cause of major urinary tract anomalies and death.

Animals↗

PubMed2002

Interactive use of cerebral angiography and magnetoencephalography in arteriovenous malformations: technical note.

OBJECTIVE: To minimize the risks associated with treating cortical cerebral arteriovenous malformations (AVMs), we developed a technique combining functional imaging and cerebral angiography. The functional loci obtained by performing magnetoencephalography (MEG) are projected onto stereoscopic pairs of a stereotactically derived digital subtraction angiogram. The result is a simultaneous three-dimensional perspective of the angioarchitecture of an AVM and its relationship to the sensorimotor cortex. METHODS: Eight patients underwent multimodality brain imaging, including magnetic resonance imaging, functional mapping via MEG, and stereotactic angiography using a modified Compass fiducial system (Compass International, Rochester, MN). The coordinates derived by performing MEG were superimposed onto stereotactic, stereoscopic, angiographic pairs using custom-made distortion correction and coordinate transfer software. RESULTS: The magnetoencephalographic angiogram allowed simultaneous viewing of the angioarchitecture of the AVM nidus, the feeding vessels, and the draining veins and their relationship to the normal cerebral vasculature and functional cortex. This imaging technique was particularly valuable in identifying en passant vessels that supplied functional cortex and was used during the treatment of these lesions. CONCLUSION: The techniques of MEG and cerebral angiography were combined to provide simultaneous viewing of both modalities in a three-dimensional perspective. This technique can aid in risk stratification in the management of patients with cerebral AVMs. In addition, this technique can facilitate the selective targeting of vessels, thus potentially reducing the risks associated with embolization of these formidable lesions.

Adolescent↗