Cristina Cercato

ABSTRACT PURPOSE To retrospectively assess the value of spectral pre-saturation inversion-recovery (SPIR) MR imaging sequence after gadolinium injection to identify some imaging findings which could be predictors of mesorectal fascia infiltration in patients with rectal carcinoma undergoing MR restaging after neoadjuvant chemo- and radiation therapy (CRT). METHOD AND MATERIALS Fifty-eight consecutive patients (mean age: 65.8 years; range: 46 - 85 years; M:F 39:19) with locally advanced rectal carcinoma involving the higher, middle or lower rectum underwent CRT followed by surgery. MR imaging was performed before and after completion of CRT by using T2-weighted fast spin-echo and T1-weighted SPIR sequences before and after gadolinium injection. MR images were assessed by two radiologists in consensus. The evidence of reticular (interwoven strands within the mesorectal fat creating a meshwork) or linear-shaped enhancing strands (strands travelling separately through the mesorectal fat) on MR images were retrospectively correlated to the histopathologic findings. RESULTS After CRT the disease was either limited to the rectal wall (n=28 patients) or presented mesorectal fat infiltration (n=30) on histology. In 5 patients a positive circumferential resection margin after total mesorectal excision was found. In 31 patients reticular (n=21 patients) or linear-shaped (n=10 patients) mesorectal enhancing strands were observed. The evidence of enhancing strands, without any reference to their shape, was not predictor of mesorectal fat (OR=1.84, 95% CIs: 0.65-5.19; P>0.05) or mesorectal fascia infiltration (1.39, 0.21-9.01; P>0.05). Reticular-shaped mesorectal enhancing strands were predictors of mesorectal fat (8.17, 2.27-29.36; P<0.05) and fascia infiltration (3, 0.45-19.59; P<0.05). The reticular enhancing strands reaching the mesorectal fascia represent an even better predictor of mesorectal fascia infiltration (3.61, 0.99-13.15; P<0.05). Linear-shaped enhancing strands either reaching or not reaching the mesorectal fascia were not predictors of infiltration (0.25 or 0.1; 0.01-1.07; P<0.05). CONCLUSION Reticular-shaped enhancing strands on SPIR MR imaging sequence after gadolinium injection were predictors of mesorectal fascia infiltration. CLINICAL RELEVANCE/APPLICATION The evidence of reticular-shaped mesorectal enhancing strands reaching the mesorectal fascia represents a predictor of mesorectal fascia infiltration and should suggest to intensify the CRT.