Paracaval lipoma

Clinical History

A 91-year-old woman was hospitalized with ischemic stroke in the right posterior cerebral artery territory. Known cardiovascular risk factors were arterial hypertension and atrial fibrillation. Initial workup included angio-CT which showed a 90% stenosis of the right internal carotid artery. A PET-CT was requested to search for hypermetabolism within this atheromatous plaque.

Imaging Findings

No hypermetabolism was detected within the severely stenosing right carotid artery plaque. However the PET-CT included coverage of the thoraco-abdominal region, and post-contrast axial slices of the abdomen showed a 1.4 cm well deliniated round lesion of homogenous fat attenuation (-100 HU) projecting onto the inferior veina cava lumen. Fig. 1 shows this lesion, at the level of the proximal right hepatic vein, surrounded by opacified blood. Coronally reconstructed images (Fig. 2) allowed confirmation of the extravascular origin of the lesion, with a stalk connecting it to surrounding fatty tissue. No other suspicious lesion was seen.

Discussion

Paracaval lipoma is a normal anatomic variant with focal protrusion of pericaval fatty tissue into the lumen of the intrahepactic portion of the inferior vena cava (IVC). Without clinical significance, it mimics an intracaval intrinsic mass lesion, or thrombus. Partial volume effect can make it appear more dramatic. The variant has been described to occur in 0.5% of adults undergoing abdominal CT [1].
Paracaval lipoma is typically observed adjacent to the medial or posterior aspect of the IVC, at or superior to, the confluence of the hepatic veins and the IVC, above the caudate lobe [1-5]. It has been observed that the variable appearance of paracaval lipoma, on serial CT, results from differences in respiratory depth or intrathoracic pressure during the scans [1, 6]. It was proposed that the changing imaging appearance results from the proximity of the diaphragm, notably to the medial aspect of the IVC, with differences in IVC angulation explaining the phenomenon [3]. A physiologic narrowing of the IVC may also exist at this level [4, 7]. The phenomenon can be more pronounced in concomitant liver disease, for example cirrhosis, anatomic variations, or obesity [8]. In cirrhosis, pericaval fat accumulation may be increased and the vessel further tilted because of shrinking of the right hepatic lobe [7].
An erroneous interpretation of the image may occur if analysis is confined to axial images, where a bland thrombus (the leading cause of IVC obstruction) or even a neoplasm may be suspected (renal cell carcinoma [RCC], hepatocellular carcinoma and adrenocortical carcinoma having the biggest rates of intracaval extension) [7]. Only coronal and sagittal reconstructions may show continuity of the fatty tissue with paracaval fat collections, via a stalk. In addition to neoplasms or thrombi, another pitfall to consider is flow phenomenon in the IVC lumen, where there may be an admixture of opacified renal venous blood with unopacified blood arriving from the lower limbs. Opacified blood may also reflux into the hepatic IVC in cases of heart failure or high injection rates >3 ml/s [7]. Alternatively to reformatted images, ultrasound may also help to confirm the extravascular origin of the image seen on abdominal CT [4].
In conclusion, paracaval lipoma is an anatomic variant with possibly changing appearance on serial exams. Knowledge and awareness of the variant are important in order to not confound it with intrinsic pathology of the IVC, and multiplanar reconstructions help in doubtful cases.

Differential Diagnosis List

Final Diagnosis

Paracaval lipoma

URL:	https://www.eurorad.org/case/13766
DOI:	10.1594/EURORAD/CASE.13766
ISSN:	1563-4086