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Published on: September 25, 2009
A diagnostic pitfall for intracranial aneurysms in time-of-flight MR angiography: small intracranial lipomas
Andre Kemmling1, Ingo Noelte, Lars Gerigk
1Department of Neuroradiology, University Hospital Mannheim, University of Heidelberg, Theodor-Kutzer-Ufer 1-3, 68167 Mannheim, Germany. akemmling@web.de
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.
Materials And 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.
Conclusion:
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.
Insights
Small intracranial lipomas can mimic aneurysms on time-of-flight (TOF) MR angiography. The characteristic "india ink" artifact on out-of-phase TOF images helps differentiate lipomas from aneurysms, preventing misdiagnosis.
Area of Science:
- Neuroradiology
- Neuroimaging
- Medical Diagnostics
Background:
- Magnetic Resonance Angiography (MRA) has limitations in detecting small aneurysms (<3 mm).
- T1 hyperintense lesions on Time-of-Flight (TOF) imaging can be mistaken for vascular abnormalities.
- Intracranial lipomas can present diagnostic challenges on TOF imaging.
Purpose of the Study:
- To systematically analyze the characteristics of intracranial lipomas on TOF MRI.
- To identify imaging features that differentiate lipomas from aneurysms.
- To reduce diagnostic pitfalls in neuroimaging.
Main Methods:
- Retrospective search of 38,000 cranial MRI scans for intracranial lipomas.
- Analysis of TOF images from identified lipomas.
- In vitro MRI of lipomas and fatty specimens to assess TOF and chemical shift artifacts.
Main Results:
- Seventeen intracranial lipomas were identified (0.045% prevalence).
- Out-of-phase TOF images of lipomas showed a distinct dark peripheral fringe ("india ink" artifact) and hyperintense center.
- This "india ink" artifact was consistent across various lipoma sizes and textures.
Conclusions:
- Small intracranial lipomas are hyperintense on TOF MRI and can mimic aneurysms.
- The out-of-phase "india ink" artifact is a defining characteristic of lipomas on TOF images.
- This artifact aids in distinguishing lipomas from aneurysms, preventing misdiagnosis.
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