Local staging of sigmoid colonic cancer using MRI

Objectives: Locally advanced colon cancer has a poor prognosis. Preoperative chemotherapy is effective in a number of gastrointestinal cancers, including rectal cancer. Preoperative imaging is important to identify patients with locally advanced colon cancer. The aim was to evaluate the diagnostic accuracy of preoperative MRI in identifying locally advanced sigmoid colon cancer and poor prognostic factors correlated with postoperative histopathologic findings. Secondly to evaluate the inter-observer variation of the tumour apparent diffusion coefficient (ADC) values of diffusion-weighted imaging (DWI). Methods: The MRI scanning was carried out using a 1.5 Tesla (T) MRI unit. No contrast enhancement was used. Diffusionweighted imaging was performed perpendicular to the tumour. Five different b values were used, applying diffusionsensitive gradients; b = 0, b = 200, b =400, b = 600, and b = 800 s/mm2. Regions of interest (ROIs) on the ADC map were drawn manually within the solid tumour part containing slices. The size and position of the ROIs was selected to cover the entire tumour area on a single section containing the largest available tumour area. The ADC values were blindly compared between two observers. Observer 1: Resident in Radiology and observer 2: Experienced gastrointestinal Radiologist. A complete postoperative histopathological examination was regarded as the gold standard, none of the patients had any neoadjunvant therapy. Early tumours were defined as T0 to T3ab. T3cd or T4 tumours were classified as advanced tumours. Results: The study population included 35 patients with verified colonic cancer. The accuracy for the two radiologist in staging early versus advanced tumours were 94% and 89%. The Inter-observer agreement on tumour staging was very good, Κ = 0,86 (95% CI:0,67-1,00). For lymph node staging a good agreement was found, Κ = 0,64 (95% CI:0,39- 0,90). ADC measurement could be performed in all patients with a good inter-observer agreement. All malignant ADC values were < 1.0 x 10-3 mm2/s. Conclusion: Preoperative MRI can identify locally advanced sigmoid colon cancer (T3cd-T4 tumors) and has potential as the imaging of choice to select patients for neoadjuvant chemotherapy. ADC measurement could be performed in all colonic cancer patients with a good inter-observer agreement.