title: Collar Sign in Incompletely Occluded Aneurysms after Pipeline Embolization: Evaluation with Angiography and Optical Coherence Tomography.
abstract: Flow diversion with the Pipeline Embolization Device has emerged as an attractive treatment for cerebral aneurysms. Processes involved in aneurysm occlusion include changes in intra-aneurysmal hemodynamics and endothelialization of the device. Here, we call attention to a radiographic sign not previously reported that is detected in incompletely occluded aneurysms after treatment with the Pipeline Embolization Device at angiographic follow-up and referred to as the "collar sign."
  
  
  
  A retrospective review of all patients who underwent placement of a Pipeline Embolization Device for cerebral aneurysms between January 2014 and May 2016 was performed. All aneurysms found to show the collar sign at follow-up were included. Optical coherence tomography was performed in 1 case.
  
  
  
  One hundred thirty-five aneurysms were treated in 115 patients. At angiographic follow-up, 17 (10.7%) aneurysms were found to be incompletely occluded. Ten (58.8%) of these aneurysms (average diameter, 7.9 ± 5.0 mm) were found to have the collar sign at angiographic follow-up (average, 5.5 ± 1.0 months). Four (40.0%) of the aneurysms underwent a second angiographic follow-up (average, 11.0 ± 0.9 months) after treatment, and again were incompletely occluded and showing the collar sign. Two patients underwent retreatment with a second Pipeline Embolization Device. Optical coherence tomography showed great variability of endothelialization at the proximal end of the Pipeline Embolization Device.
  
  
  
  The collar sign appears to be indicative of endothelialization, but continued blood flow into the aneurysm. This is unusual given the processes involved in aneurysm occlusion after placement of the Pipeline Embolization Device and has not been previously reported.
authors.affiliation: From the Neurosurgical Service, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts. christoph.griessenauer@gmail.com.
authors.forename: C J
authors.identifier: 0000-0002-2952-3812
authors.initials: CJ
authors.lastname: Griessenauer
authors.affiliation: From the Neurosurgical Service, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts.
authors.forename: R
authors.identifier: 0000-0002-5497-3241
authors.initials: R
authors.lastname: Gupta
authors.affiliation: From the Neurosurgical Service, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts.
authors.forename: S
authors.identifier: 0000-0001-9010-7431
authors.initials: S
authors.lastname: Shi
authors.affiliation: From the Neurosurgical Service, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts.
authors.forename: A
authors.identifier: 0000-0003-0508-9609
authors.initials: A
authors.lastname: Alturki
authors.affiliation: From the Neurosurgical Service, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts.
authors.forename: R
authors.identifier: 0000-0001-7540-5019
authors.initials: R
authors.lastname: Motiei-Langroudi
authors.affiliation: From the Neurosurgical Service, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts.
authors.forename: N
authors.identifier: 0000-0002-8668-7629
authors.initials: N
authors.lastname: Adeeb
authors.affiliation: From the Neurosurgical Service, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts.
authors.forename: C S
authors.identifier: 0000-0003-4600-8545
authors.initials: CS
authors.lastname: Ogilvy
authors.affiliation: From the Neurosurgical Service, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts.
authors.forename: A J
authors.identifier: 0000-0003-4412-3152
authors.initials: AJ
authors.lastname: Thomas
mesh_terms: D000328:Adult; D000368:Aged; D002533:Cerebral Angiography; D004621:Embolization, Therapeutic / Q000295:instrumentation*; D057510:Endovascular Procedures / Q000295:instrumentation*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D002532:Intracranial Aneurysm / Q000000981:diagnostic imaging* / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D019233:Retreatment; D012189:Retrospective Studies; D041623:Tomography, Optical Coherence; D016896:Treatment Outcome