Final answer:
A mass causing anterior displacement of the renal structure and retroperitoneal fat is likely located in the retroperitoneal space, which houses the kidneys and related structures.
Step-by-step explanation:
The characteristics of anterior renal displacement, anterior dilated ureter displacement, anterior displacement of the retroperitoneal fat ventrally and often cranially, and anterior vascular displacement suggest the presence of a mass located in the retroperitoneal space.
This space is located posterior to the peritoneum, and contains the kidneys, ureters, and associated structures such as the renal hilum, which is the entry and exit site for structures servicing the kidneys. The kidneys themselves are protected and anchored by the renal fascia, adipose tissue known as the renal fat pad, and the overlying peritoneum.