Ex vivo MR imaging of colorectal carcinoma before and after formalin fixation: correlation with histopathologic findings

Abstract

Purpose: We aimed to assess and compare ex vivo MRI of resected colorectal carcinoma before and after formalin fixation.

Methods: We enrolled 45 consecutive patients (47 carcinomas) who underwent colorectal carcinoma surgery. Specimens underwent two MR scans at 1.5 T (after resection and 24 h after formalin fixation). Two radiologists evaluated all MR images independently regarding T-staging and the subserosal linear architecture. T-stage accuracy and frequency of linear architecture were calculated. A third radiologist measured vertical tumor distance and contrast-to-noise ratio (CNR) of the mucosa, submucosa, muscularis propria, subserosa, and tumor.

Results: T-stage accuracy compared to histopathology by the two readers was 91.5% and 87.2% before fixation and 91.5% and 85.1% after fixation, respectively. Linear architecture was observed in 11.1% of T2 tumors and 100% of T3 tumors by both readers. The vertical tumor distance between histopathological and MRI findings was well correlated before and after fixation. The measurement error of the vertical tumor distance between before and after fixation was within 3 mm. CNR of the tumor was significantly lower than those of the submucosa and subserosa before and after fixation (p < 0.05). CNRs of the tumor and muscularis propria were decreased after formalin fixation (p < 0.05).

Conclusions: Subserosal linear architecture represented fibrosis with tumoral invasion, suggesting a T3-4 tumor. The submucosa and subserosa showed high intensity and the mucosa and muscularis propria showed low intensity compared with tumor. CNRs of the tumor and muscularis propria were decreased by formalin fixation.

Keywords: Colorectal carcinoma; Desmoplastic reaction; Ex vivo imaging; Formalin fixation; Magnetic resonance imaging; T-staging.