Changes in retroperitoneal anatomy of the lumbar spine in supine, prone, and lateral lumbar spine MRIs.

Abstract

To investigate the changes in anatomy of the retroperitoneal (RP) space and lumbar lordosis based on magnetic resonance imaging (MRI) acquired in different positions. Twelve adults underwent MRI in the right-lateral decubitus, prone, and supine positions. At each lumbar disc space, the cross-sectional area (CSA) of the psoas, RP space CSA, distance to the great vessels, and lumbar lordosis were measured. At L2-3, the CSA of the RP space was increased in the lateral position compared to the prone position (11.4cm² vs 7.5cm², P=0.0071), and at L3-4 the RP space was significantly smaller in the lateral position compared to the supine position (6.9mm² vs 10.3mm², P=0.0157). When stratified by sex, males had a larger left RP space in the lateral position at L2/3 (18.7 cm²) compared to prone (11.9 cm², P=0.0042) and supine (13.0 cm², P=0.0148). Females had a larger RP in the supine position at L2/3 (5.4 cm²) compared to prone (3.1 cm², P=0.008), supine L3/4 (5.4cm²) compared to lateral L3/4 (2.9 cm², P=0.0046) and supine L4/5 (13.4 cm²) compared to prone L4/5 (11.0cm², P=0.0049) and lateral L4/5 (8.7cm², P<0.0001). In the lateral decubitus position, there was a lower lumbar lordosis when compared to the two other positions (P<0.05). This study found that the size of the RP space varies depending on patient positioning and sex, while also demonstrating a flattening effect as RP CSA decreased at L3/4 in the lateral position. A nuanced understanding of the RP anatomy may influence a surgeon's decision-making regarding intraoperative patient positioning to exploit safe operative corridors.