Rationale and Objectives: To retrospectively assess the value of spectral presaturation by inversion-recovery (SPIR) magnetic resonance (MR) imaging sequence after gadolinium injection to differentiate fibrotic scar tissue and tumoral infiltration within the mesorectal fat in patients with rectal carcinoma undergoing MR restaging after neoadjuvant chemo- and radiation therapy (CRT). Materials and Methods: Forty-three consecutive patients (mean age, 65.8 years; range, 46–85 years; male:female, 29:14) with locally advanced rectal carcinoma underwent CRT followed by surgery. MR imaging was performed before and after completion of CRT by using T2-weighted turbo spin-echo and T1-weighted SPIR sequences before and after gadolinium injection, and MR images were assessed by two radiologists in consensus. Logistic regression was conducted to test the significance of the MR image findings with histology. Results: AfterCRT the disease was either limited to the rectal wall (n = 18 patients) or presented perirectal infiltration (n = 25) on histology. In 21 patients, mesorectal enhancing strands were observed. Reticular-shaped enhancing strands reaching the mesorectal fascia presented the highest correlation with tumor infiltration of the mesorectal fat (OR 130.33, 95%CI: 4.1–4220.29; logistic regression), whereas linear-shaped enhancing strands either reaching or not reaching themesorectal fascia (OR 0.25 or 0.1, 95%CI: 0.024–2.6 or 0.01–1.07) revealed the lowest correlation. Conclusions: Reticular-shaped enhancing strands on SPIR MR imaging after gadoliniuminjection are associated with tumor infiltration of the mesorectal fat.
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