Patterns and signal intensity characteristics of pelvic recurrence of rectal cancer at MR imaging.

Magnetic resonance (MR) imaging is becoming the cross-sectional imaging modality of choice for follow-up of patients with previous rectal cancer to diagnose pelvic recurrence and plan for surgery. The authors conducted a retrospective review of MR imaging examinations performed at their institution for evaluation of local recurrence of rectal cancer in 42 patients. Twenty-six patients had undergone rectal anastomosis and 16 had undergone abdominoperineal resection. The mean interval between initial surgery and recurrence was 2.5 years. Recurrence sites were axial (involving the anastomosis) (n = 19); lateral (sidewall) (n = 6); anterior (prostate or seminal vesicle [n = 2], bladder [n = 4], ureter [n = 3], vagina or uterus [n = 5]); or posterior (presacral fascia [n = 11], sacrum [n = 2]). Other recurrence sites included the pelvic floor (n = 7), sciatic nerve (n = 2), obturator nerve (n = 1), perineum (n = 1), abdominal wall (n = 1), or adnexa (n = 1). Recurrence was confirmed at surgery or by evidence of tumor growth at follow-up imaging. Recurrence patterns, signal intensity characteristics, findings of unresectability, potential MR imaging pitfalls, and the role of MR imaging versus other modalities in evaluating recurrent rectal carcinoma are discussed. Supplemental material available at https://radiographics.rsna.org/lookup/suppl/doi:10.1148/rg335115170/-/DC1.