Which surface would a renal abscess most likely extend into if located posteriorly along the medial aspect of the kidney?

A renal abscess located posteriorly along the medial aspect of the kidney is most likely to extend into the psoas fascia. The psoas fascia covers the psoas major muscle, which is located adjacent to the kidney. The proximity and position of the kidney relative to the psoas muscle mean that any infection or abscess could easily spread through the fascial planes surrounding the muscle.

The psoas fascia serves as a conduit for infection to travel, allowing it to extend away from the kidney and potentially affect nearby structures. This anatomical relationship highlights why the psoas fascia is the most likely area affected by a posterior renal abscess.

In contrast, although the transverse abdominal fascia and the quadratus lumborum fascia are also adjacent to the kidney, they do not have the same direct relationship as the psoas fascia. The latissimus dorsi, being further away from the renal area, would be less likely to be involved in the spread of a posterior renal abscess. Thus, the anatomical positioning and the continuity of the fascial planes make the psoas fascia the most likely surface for extension in this scenario.