History: A 59-year-old man initially presented to an outside hospital with right flank pain and gross hematuria due to a partially obstructing right ureteral calculus.
病史：59岁男性，最初因右输尿管结石导致右腹痛、肉眼血尿在外院就诊。
Findings
Coronal CT image (a) demonstrates a well-circumscribed homogeneous fat-attenuating intravascular mass (arrows) extending from the renal veins to the inferior vena cava (IVC). Axial T2 MR image (b) shows a hyperintense round mass in the IVC that subtracts out on postcontrast T1 fat-saturated axial (c) and coronal (d) MR images, as well as demonstrates chemical shift artifact on out-of-phase coronal MRI (e). The lesion is space filling, nonenhancing and nearly all fat, most compatible with an intravascular lipoma.
影像表现：
冠状CT（图a）可见一边界清楚呈均匀脂肪密度的血管内肿物（箭），范围从肾静脉至下腔静脉。
轴位T2WI（图b）示下腔静脉内见一高信号类圆形肿物，轴位及冠状T1增强（图c、d）压脂图像上呈低信号，冠状反相位图像（图e）上可见化学位移伪影。
病变填充血管腔，无强化，几乎均为脂肪密度，符合血管内脂肪瘤表现。
Diagnosis: Intravascular lipoma of the renal vein
诊断：肾静脉血管内脂肪瘤
Learning points
Intravascular lipoma
- On imaging, an intravascular lipoma is seen as a well-defined, homogeneous, nonenhancing, fat-attenuating mass without areas of soft tissue, hemorrhage or necrosis. A hyperintense signal on T2 imaging that subtracts on fat-saturated images confirms the diagnosis.
- Intravascular lipomas must be distinguished from their more malignant counterpart — liposarcomas — given that a subset of lipomas can have soft-tissue components and may be indistinguishable on imaging alone.
- Although benign, intravascular lipomas may require surgery depending on concern for obstructive complications.
知识点（血管内脂肪瘤）
影像表现：边界清楚，密度均匀，无强化，脂肪密度肿物，无软组织成分、出血或坏死。T2WI呈高信号，脂肪抑制信号减低。
需要和对应的恶性肿瘤（脂肪肉瘤）相鉴别，一小部分脂肪瘤可以有软组织成分，仅凭影像不易鉴别。
尽管是良性的，但考虑到会导致相关血管阻塞后的并发症，仍需手术切除。