Temporal Changes in Mesorectal Fat Area After Bariatric Surgery: A Retrospective Cohort Study.

INTRODUCTION: Total mesorectal excision (TME) quality is critical for outcomes in mid- and low-rectal cancer. Larger mesorectal fat area (MFA) increases surgical difficulty and recurrence risk, yet interventions to reduce MFA remain unexplored. We examined temporal associations between bariatric surgery-associated weight loss and MFA. METHODS: We retrospectively reviewed 25 patients who underwent elective bariatric surgery at a university-affiliated center (2018-2023) with perioperative abdominal computed tomography imaging. Eligible patients had a computed tomography within 6 mo before and within 2 wk after surgery, plus a follow-up scan at 1-6, 6-12, or >12 mo. MFA was measured at the ischial spine level by subtracting rectal area from mesorectal package area. Absolute MFA change and percent excess weight loss (%EWL) were analyzed. RESULTS: Of 258 charts reviewed, 25 met inclusion criteria. The mean baseline body mass index was 46.2 ± 10.3 kg/m2 and MFA 20.9 ± 6.4 cm2. At 1-6 mo, MFA decreased by 5.0 ± 1.9 cm2 (-22.2%; P < 0.001) with %EWL 33.1% (P < 0.001). At 6-12 mo, %EWL increased to 47.2% (P = 0.003), while MFA declined an additional 3.8 ± 3.5 cm2 (-19.3%; P = 0.07). Beyond 12 mo, %EWL reached 80.2% (P < 0.001) with only modest further MFA change (-27.3% versus baseline; P < 0.001). Most MFA reduction occurred within 6 mo. CONCLUSIONS: Bariatric surgery-associated weight loss was associated with significant early declines in MFA, largely within 6 mo. These findings support further study of metabolic optimization strategies before rectal cancer resection requiring TME.