Large solid heterogeneous mass with a necrotic center in the right upper abdomen, exerting mass effect on the IVC, liver, porta hepatis, pancreas, and right kidney. The mass is most likely extrahepatic-retroperitoneal, although an intraperitoneal component cannot be confidently ruled out. The mass undergoes heterogeneous enhancement. The solid component at its posteroinferior aspect engulfs the renal accessory vessel. Retroperitoneal-perirenal fat edema is present.
The liver is of normal size and contour. Its medial aspect and porta hepatis are compressed by the mass. Diffuse hepatic fatty infiltration. Heterogeneous hepatic enhancement at the arterial phase, most probably due to mass effect on the hepatic vessels. No focal intrahepatic mass.
The gallbladder contains numerous tiny calculi.
The spleen is enlarged, 16.4 cm in the craniocaudal plane.
Small simple cortical cysts in both kidneys.
Status post bariatric surgery. The duodenum is displaced by the mass and there is no separation plane between them.
No enlarged intra-abdominal lymph nodes.
Venous collaterals coursing in the abdominal wall.
Conclusion
Solid, partially necrotic, right upper abdominal mass displacing adjacent organs. Impression of disrupted venous drainage due to compression of the IVC. The mass is most probably extrahepatic-retroperitoneal; an intraperitoneal component cannot be ruled out.
Differential diagnosis includes a duodenal GIST, retroperitoneal sarcoma, or other solid fibrous/mesenchymal tumor.