title: A diagnostic pitfall for intracranial aneurysms in time-of-flight MR angiography: small intracranial lipomas.
abstract: OBJECTIVE
  The sensitivity of MR angiography (MRA) for aneurysms smaller than 3 mm in diameter is limited. Diagnostic pitfalls may arise from primary T1 hyperintense lesions on time-of-flight (TOF) imaging adjacent to a vessel. Independently, three patients were referred from outside facilities for diagnostic workup of suspected aneurysms of the vertebrobasilar system on TOF images. The lesions were identified as small lipomas, which prompted us to systematically analyze characteristics of intracranial lipomas on TOF images.
  
  
  METHODS
  From our local database, 38,000 cranial MRI scans were searched for intracranial lipomas. If available, TOF images of identified lipomas were analyzed. In addition, in vitro MRI of excised cadaveric lipomas and other fatty specimens were examined for characteristics on TOF images and the presence of chemical shift artifacts.
  
  
  RESULTS
  Seventeen intracranial lipomas (0.045%) were identified. Out-of-phase TOF source images available in 12 identified lipomas showed a continuous dark peripheral fringe and a hyperintense center. In vitro out-of-phase chemical shift images of excised cadaveric lipomas revealed the same consistent fringe artifact, known as "india ink," independent of size, shape, surrounding fibrous capsule, or texture of the fatty specimen. In contrast, in-phase chemical shift artifact was variable.
  
  
  CONCLUSIONS
  Small intracranial lipomas close to a cerebral artery are hyperintense on TOF MR images and could be mistaken for partially thrombosed aneurysms and associated flow-related artifact. A defining characteristic of lipomas on TOF source images results from the out-of-phase india ink artifact. This dark fringe in the periphery of the lesions is characteristic and helps avoid potential diagnostic pitfalls.
authors: Department of Neuroradiology, University Hospital Mannheim, University of Heidelberg, Theodor-Kutzer-Ufer 1-3, 68167 Mannheim, Germany. akemmling@web.de
authors: Andre
authors: A
authors: Kemmling
authors: Ingo
authors: I
authors: Noelte
authors: Lars
authors: L
authors: Gerigk
authors: Stephan
authors: S
authors: Singer
authors: Christoph
authors: C
authors: Groden
authors: Johann
authors: J
authors: Scharf
mesh_terms: D000328:Adult; D000368:Aged; D016477:Artifacts; D001932:Brain Neoplasms / Q000150:complications / Q000175:diagnosis*; D002102:Cadaver; D003937:Diagnosis, Differential; D005260:Female; D006261:Headache / Q000209:etiology; D006801:Humans; D007091:Image Processing, Computer-Assisted; D002532:Intracranial Aneurysm / Q000150:complications / Q000175:diagnosis*; D008067:Lipoma / Q000150:complications / Q000175:diagnosis*; D018810:Magnetic Resonance Angiography; D008297:Male; D008875:Middle Aged; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D014717:Vertigo / Q000209:etiology