Kemmling Andre, Noelte Ingo, Gerigk Lars, Singer Stephan, Groden Christoph, Scharf Johann
Department of Neuroradiology, University Hospital Mannheim, University of Heidelberg, Theodor-Kutzer-Ufer 1-3, 68167 Mannheim, Germany.
AJR Am J Roentgenol. 2008 Jan;190(1):W62-7. doi: 10.2214/AJR.07.2517.
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.
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.
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.
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.
磁共振血管造影（MRA）对直径小于3mm的动脉瘤的敏感性有限。飞行时间（TOF）成像上与血管相邻的原发性T1高信号病变可能会导致诊断陷阱。另外，有三名患者从外部机构转诊来，针对TOF图像上疑似椎基底动脉系统动脉瘤进行诊断检查。这些病变被确定为小脂肪瘤，这促使我们系统地分析TOF图像上颅内脂肪瘤的特征。
从我们的本地数据库中搜索了38000例颅脑MRI扫描，以查找颅内脂肪瘤。如果有可用的资料，对已确定脂肪瘤的TOF图像进行分析。此外，对切除的尸体脂肪瘤和其他脂肪标本进行体外MRI检查，以了解TOF图像上的特征以及化学位移伪影的存在情况。
共识别出17例颅内脂肪瘤（0.045%）。12例已识别脂肪瘤中可获得的反相位TOF源图像显示出连续的暗外周边缘和高强度中心。切除的尸体脂肪瘤的体外反相位化学位移图像显示出相同的一致边缘伪影，即“印度墨水”，与脂肪标本的大小、形状、周围纤维囊或质地无关。相比之下，同相位化学位移伪影则是可变的。
靠近脑动脉的小颅内脂肪瘤在TOF MR图像上呈高强度，可能会被误认为是部分血栓形成的动脉瘤及相关的血流相关伪影。TOF源图像上脂肪瘤的一个决定性特征是由反相位印度墨水伪影导致的。病变周边的这种暗边缘具有特征性，有助于避免潜在的诊断陷阱。
