MRI Detection of Extramural Venous Invasion in Rectal Cancer: Correlation With Histopathology Using Elastin Stain

OBJECTIVE. The purpose of this article is to evaluate the diagnostic performance of MRI for detection of extramural venous invasion (EMVI) compared with histopathologic analysis using elastin stain. MATERIALS AND METHODS. Forty-nine patients with rectal cancer who had undergone surgical resection with preoperative MRI were identified. Thirty-seven patients had received preoperative chemoradiation therapy (CRT). Sixty-nine MRI studies were independently reviewed by two blinded radiologists for EMVI using a score of 0-4. Comparison was made with histopathologic results obtained by two pathologists reviewing the elastin-stained slides in consensus. EMVI status was also correlated with other tumoral and prognostic features on imaging and pathologic analysis. Statistical analysis was performed using Fisher exact and McNemar tests. RESULTS. EMVI was present in 31% of the pathology specimens. An MRI EMVI score of 3-4 was 54% sensitive and 96% specific in detecting EMVI in veins 3 mm in diameter or larger. Inclusion of a score of 2 as positive for EMVI increased the sensitivity to 79% but decreased the specificity to 74%, with poor positive predictive value. Preoperative CRT had no significant effect on the diagnostic performance of MRI. Contrast-enhanced MRI increased reader confidence for diagnosis or exclusion of EMVI compared with T2-weighted imaging. EMVI status correlated with depth of extramural invasion and proximity to mesorectal fascia. CONCLUSION. Despite an anticipated increase in sensitivity for EMVI detection by histopathologic analysis using elastin compared with H and E staining, MRI maintains a high specificity and moderate sensitivity for the detection of EMVI.