The population in Western countries differs significantly from that in Eastern countries, and the prevalence of lateral
pelvic lymph node (LPLN) involvement in Western populations remains largely unknown due to the limited application
of LPLN dissection (LPLND). This discrepancy is primarily attributed to the higher body mass index commonly observed
in Western populations, which increases the risk of intraoperative complications. Consequently, the aim of this study is to
describe a specific Western clinico-radiological selection tool for LPLND, namely, the lateral pelvic lymph node positivity
(LPLNP) score.

This retrospective single center study was designed to elaborate the LPLNP score, which was further tested on
a prospective cohort of patients. Clinical and MRI factors associated with LPLN involvement were identified, and logistic
regression was used to establish the LPLNP score.

In the retrospective series, 120 patients underwent lateral pelvic lymph node dissection. After stepwise logistic
regression, five parameters were ultimately included in the LPLNP score. When tested on 66 prospectively selected patients,
40 with an LPLNP score > 0.23 (corresponding to the highest sensitivity and specificity) underwent LPLND: 22 patients
(55%) had pathologically confirmed positive LPLN. The negative predictive value of the LPLNP score was 96%, with a
sensitivity of 95.7% and a specificity of 58.1%.

The LPLNP score was developed based on the largest group of Western patients with locally advanced rectal
cancer. This scoring system demonstrated high sensitivity and specificity during validation on the prospective series, correctly
identifying LPLN involvement in 55% of cases.