Purpose:
To investigate the role of intravoxel incoherent motion diffusion-weighted imaging (IVIM-DWI) in the prediction of histological differentiation and local invasion (T stage) of rectal non-mucinous adenocarcinoma for appropriate treatment planning.

Material and methods:
Pre-operative magnetic resonance imaging (MRI) and IVIM-DWI examinations were prospectively performed in patients with rectal non-mucinous adenocarcinoma. A total of 36 patients with a mean age of 61 ± 8 years (range: 26-85 years) were included. Size, signal intensities and enhancement pattern of tumors, lymphadenopathy, serosal involvement, adjacent organ invasion, and metastasis were noted. IVIM-DWI parameters were estimated. Relationships between IVIM-DWI parameters and histopathological results were analyzed using Mann-Whitney U and Kruskal-Wallis tests. Receiver operating characteristic analysis was performed for optimal cut-off values.

Results:
In our study, a total of 36 patients were enrolled. There was a negative relationship between tumor differentiation and perfusion (f) (p < 0.05). A negative relationship was detected between T staging and true diffusion (D), pseudo-diffusion coefficient (D*) and apparent diffusion coefficient (ADC) values (p < 0.05). Lower D, D*, and ADC values were detected in late stage (T3-T4) rectal tumors and nodal metastasis (p < 0.05). Lower f values were achieved in higher histological grades (p < 0.05). In differentiation of poorly from well- and moderately differentiated tumors, cut-off value of < 20.89 showed 88.5% sensitivity and 85.7% specificity (area under the curve: 0.771, p < 0.05).

Conclusions:
Aggressive tumors with low histological differentiation and metastatic lymphadenopathy exhibit lower diffusion and perfusion values. As a perfusion indicator, f provides valuable information regarding tumor differentiation. IVIM-DWI can be used as an adjunctive modality to routine abdominal MRI in the local staging of rectal carcinoma.