Magnetic Resonance Imaging evaluation in neoadjuvant therapy of Locally Advanced Rectal Cancer: a systematic review
Objective: The aim of this manuscript is to present an overview and update about several imaging modalities including morphological conventional Magnetic Resonance Imaging (MRI), functional MRI such as Dynamic Contrast Enhanced-MRI (DCE-MRI) and Diffusion Weighted Imaging (DWI) in diagnosis, staging and pre-surgery treatment response assessment in locally advanced rectal cancer (LARC). A methodical review regarding the diagnostic accuracy in neoadjuvant therapy response assessment of MRI, DCE-MRI, DW-MRI and Positron Emission Tomography/Computed Tomography (PET/CT) was reported.
Methods: Several electronic database were searched including PubMed, Scopus, Web of Science, and Google Scholar. Exclusively the studies that report findings about therapy response assessment in LARC using MRI, DCE-MRI, DWI, and PET/CT with details about diagnostic accuracy, true and false negatives, true and false positives number were included. Forest plot and Receiver Operating Characteristic (ROC) curves analysis was performed. Risk of bias and the applicability at study level were calculated.
Results: 25 papers were identified for the review. ROC curves analysis demonstrated that Multimodal Imaging integrating morphological and functional MRI features has the best accuracy both in term of sensitivity and specificity to evaluate preoperative therapy response in LARC. DCE-MRI following to PET/CT showed the highest diagnostic accuracy and their results are also more reliable than conventional MRI and DWI alone.
Conclusions: MRI is the modality of choice for staging rectal cancer to assist surgeons in obtaining negative surgical margins. MRI facilitates the accurate assessment of mesorectal fascia and the sphincter complex for surgical planning. Functional MRI (DCE-MRI) may also help in the prediction and estimation of response to treatment. However, a greater number of studies should be performed in the future for each modalities to improve the reliability of any conclusion.