Efficiency of apparent diffusion coefficients in differentiation of colorectal tumor recurrences and posttherapeutical soft-tissue changes

Abstract

Objective: To evaluate effectiveness of apparent diffusion coefficient (ADC) values measured by diffusion-weighted magnetic resonance imaging (DW-MRI) in differentiation of colorectal tumor recurrences and posttherapeutical soft tissue changes.

Methods: For this prospective study, 30 patients (22 males, 8 females; age range 30-81 years; mean age 61±12 years) who underwent surgery for colorectal tumors and had a mass detected by computed tomography (CT) and/or MRI during follow-up examinations were divided into 2 groups [17 patients (Group 1) with recurrence and 13 patients (Group 2) with benign fibrosis/granulation tissue]. Final diagnoses were based on histopathological examination in 14 patients and clinical follow-up at least 6 months in the remaining 16. In the latter, the diagnosis of recurrence was made in cases in which the lesion was larger on follow-up CT and MRI; recurrence was ruled out in cases of stable or shrinking lesions without any increase in tumor markers. DW-MRI was performed in the axial plane, for two different b values (b=0 and 800 s/mm(2)). The mean apparent diffusion coefficient (ADC) values were measured by manual delineation of regions of interest on ADC maps.

Results: The median ADC values were 1.07 × 10(-3)mm/s(2) (min: 0.82, max: 2.05) and 1.91 × 10(-3)mm/s(2) (min: 1.51, max: 2.22) in Groups 1 and 2, respectively. A statistically significant difference was detected between the two groups (P<0.001). When the threshold value used to determine whether the lesions recurred was 1.48 × 10(-3)mm/s(2) based on ROC analysis, the sensitivity was 82% and the specificity was 100%. There were three patients with a false-negative diagnosis, and the primary histopathological diagnosis of all was mucinous adenocarcinoma.

Conclusions: Because recurrences in mucinous adenocarcinomas have high ADC values, they may show overlap with benign lesions. In the detection of the local recurrence of colorectal neoplasms, with the exception of mucinous adenocarcinomas, ADC measurements are reliable imaging techniques.

Keywords: Colorectal neoplasms; Diffusion-weighted imaging; Local recurrence; Rectum and diagnosis.