title: Can the Windkessel Hypothesis Explain Delayed Intraparenchymal Haemorrhage After Flow Diversion? A Case Report and Model-Based Analysis of Possible Mechanisms.
abstract: BACKGROUND
  Delayed ipsilateral intraparenchymal haemorrhage is a recently recognised complication after endovascular flow diversion for intracranial aneurysms. Although the mechanism of this phenomenon is not understood, one proposed explanation (the windkessel hypothesis) is that removal of aneurysmal compliance increases distal pulse pressure.
  
  
  METHODS
  We present a case of delayed haemorrhage after placement of a Pipeline stent, discuss the proposed mechanisms, and describe a novel electrical analogue model that was used to evaluate the likely haemodynamic effect of stent placement.
  
  
  RESULTS
  Model-based analysis suggests that stenting is not likely to produce a significant change in distal pulse pressure. Moreover, basic fluid dynamics principles suggest that a local reduction in disturbed flow in the region of the aneurysm could produce only a minor increase in distal pressure (a few mmHg), which is unlikely to be the main cause of the observed haemorrhage.
  
  
  CONCLUSIONS
  The windkessel hypothesis is unlikely to explain the occurrence of delayed ipsilateral intraparenchymal haemorrhage after flow diversion; however, other mechanisms involving altered haemodynamics distal to the treated aneurysm may play a role. Further studies involving the assessment of haemodynamic changes after flow diversion would be useful to understand, and eventually mitigate, this currently unpredictable risk.
authors: Department of Clinical Neurosciences, and; Department of Radiology, Foothills Medical Centre, Calgary, Alberta, Canada. Electronic address: amitha@ucalgary.ca.
authors: Alim P
authors: AP
authors: Mitha
authors: Biomedical Simulation Laboratory, Department of Mechanical & Industrial Engineering, University of Toronto, Toronto, Canada; Heart Research, Clinical Sciences, Murdoch Children's Research Institute, Melbourne, Australia.
authors: Jonathan P
authors: JP
authors: Mynard
authors: Department of Clinical Neurosciences, and.
authors: John A
authors: JA
authors: Storwick
authors: Department of Clinical Neurosciences, and.
authors: Zaher I
authors: ZI
authors: Shivji
authors: Department of Clinical Neurosciences, and; Department of Radiology, Foothills Medical Centre, Calgary, Alberta, Canada.
authors: John H
authors: JH
authors: Wong
authors: Department of Radiology, Foothills Medical Centre, Calgary, Alberta, Canada.
authors: William
authors: W
authors: Morrish
mesh_terms: D002543:Cerebral Hemorrhage / Q000209:etiology / Q000473:pathology / Q000503:physiopathology / Q000601:surgery; D002560:Cerebrovascular Circulation; D057510:Endovascular Procedures / Q000009:adverse effects*; D005260:Female; D006801:Humans; D002532:Intracranial Aneurysm / Q000473:pathology / Q000503:physiopathology / Q000601:surgery; D008875:Middle Aged; D008955:Models, Cardiovascular; D011183:Postoperative Complications / Q000473:pathology / Q000503:physiopathology / Q000601:surgery; D015607:Stents
keywords: Flow diversion; Intracranial aneurysm; Intraparenchymal haemorrhage; Mathematical model; Pipeline stent; Windkessel Effect