This case provides an opportunity to discuss multiple possibilities for perihilar/perirenal mass as follow: 

The differential and what makes a diagnosis likely/unlikely is as follows:

1. Lymphoma - often bilateral, but may begin unilaterally; can have perihilar/perirenal infiltration as in this case. Despite the size and extent of the tumor, there is often mild obstruction of the urinary system as in this case. despite the size and location, vascular encasement with no thrombosis is more likely with lymphoma as in this case. Adenopathy would help to really favor this diagnosis. 
2. Renal cell carcinoma - usually heterogeneous, with vascular invasion and the main bulk mostly along renal parenchyma.
3. Urothelial carcinoma - It does not have such a large peri-renal component, and if extending to the hilum usually vascular pedicle involvement and thrombosis will be suggested.
4. RPF/IgG4 - RPF commonly starts near the aortic bifurcation, ascends along the aorta, medializes and obstructs the ureters.

Based on the appearance it would be appropriate to favor lymphoma in this case as the bulk of the soft tissue is around the hilum of the left kidney, the prominent retroperitoneal adenopathy, and lack of collecting system obstruction might tip you toward an alternative diagnosis from other differential diagnoses, Either way, this needs to be biopsied, which was performed with CT and confirmed high-grade b-cell lymphoma.