Value of MRI and diffusion-weighted MRI for the diagnosis of locally recurrent rectal cancer

Abstract

Objectives: To evaluate the accuracy of standard MRI, diffusion-weighted MRI (DWI) and fusion images for the diagnosis of locally recurrent rectal cancer in patients with a clinical suspicion of recurrence.

Methods: Forty-two patients with a clinical suspicion of recurrence underwent 1.5-T MRI consisting of standard T2-weighted FSE (3 planes) and an axial DWI (b0,500,1000). Two readers (R1,R2) independently scored the likelihood of recurrence; [1] on standard MRI, [2] on standard MRI+DWI, and [3] on T2-weighted+DWI fusion images.

Results: 19/42 patients had a local recurrence. R1 achieved an area under the ROC-curve (AUC) of 0.99, sensitivity 100% and specificity 83% on standard MRI versus 0.98, 100% and 91% after addition of DWI (p = 0.78). For R2 these figures were 0.87, 84% and 74% on standard MRI and 0.91, 89% and 83% with DWI (p = 0.09). Fusion images did not significantly improve the performance. Interobserver agreement was κ0.69 for standard MRI, κ0.82 for standard MRI+DWI and κ0.84 for the fusion images.

Conclusions: MRI is accurate for the diagnosis of locally recurrent rectal cancer in patients with a clinical suspicion of recurrence. Addition of DWI does not significantly improve its performance. However, with DWI specificity and interobserver agreement increase. Fusion images do not improve accuracy.

Fig. 1

T2-weighted, b1000 diffusion-weighted and T2W+DWI fusion images of a male patient with a local tumour recurrence situated in the left gluteus muscle (arrows). On T2-weighted MRI (a), the signal of the tumour is isointense compared to the muscles. On the DWI (b) and fusion images (c) the tumour is visible as a lesion with high signal intensity, compared to the suppressed signal of the surrounding structures. Note the necrotic changes in the left internal obturator muscle (arrowheads), resulting in slightly increased signal intensity on the DWI and fusion images

Fig. 2

Receiver operator characteristics curves and areas under the ROC-curve (AUC) for reader 1 (R1) and reader 2 (R2) for detection of locally recurrent rectal cancer by using (1) standard MRI, (2) standard MRI+DWI, and (3) T2-weighted MRI+DWI fusion images, respectively. There were no significant differences in AUC between the three reading designs for either of the two readers

Fig. 3

Axial T2-weighted, b1000 diffusion-weighted and T2W+DWI fusion images of a male patient who had previously undergone a low anterior resection. On T2-weighted MRI (a) there is an area of intermediate signal intensity (arrows) that was erroneously interpreted as a tumour recurrence by the first reader. On the DWI (b) and fusion images (c), there is no focal high signal intensity in this area (circle) and the reader adjusted his score. Follow-up imaging revealed no tumour recurrence

Fig. 4

Axial T2-weighted, b1000 diffusion-weighted and T2W+DWI fusion images of a male patient who had previously undergone transanal endoscopic microsurgery. On T2-weighted MRI (a) there is a small area of intermediate signal intensity (arrow), that was overlooked by reader 2. On the DWI (b) and fusion images (c), there is a clear focal area of high signal intensity and the reader now identified the recurrence, which was later surgically removed and histologically confirmed

Fig. 5

CT, T2-weighted and T2W+DWI fusion images of a male patient who had previously undergone an abdominoperineal resection for a distally located rectal tumour. On CT (a) there is a presacrally located soft tissue mass. On CT it is not possible to discriminate between postoperative scar tissue and recurrent tumour. On the corresponding MRI (b) there is an area of hypointense signal intensity indicating fibrosis (arrowheads). Located anterior to this fibrosis, there is a bowel loop (*) This bowel loop was not opacified by the oral contrast on CT, because it was located distally from the patient’s ileostomy. On the fusion images (c) there are no areas of high signal intensity, suggestive of recurrent tumour. Follow-up imaging revealed no tumour recurrence