Magnetic Resonance Imaging in Rectum Cancer Staging and Evaluation of Response to Neoadjuvan Therapy
Özet
Magnetic Resonance Imaging (MRI) plays a critical role in the primary staging and restaging of rectal cancer, guiding neoadjuvant treatment selection and surgical planning. According to ESGAR guidelines, high-resolution 2D T2-weighted and diffusion-weighted imaging are essential sequences, utilizing fields of 1.5T or higher without the strict need for endorectal coils or contrast agents. Accurate T staging requires evaluating rectal wall integrity, where extension into the mesorectum classifies the disease as T3 (subdivided from a to d based on invasion depth), and involvement of adjacent organs or the anal complex indicates higher stages. Lymph node staging relies on size and morphology, evaluating the mesorectum, iliac, and obturator regions. Prognostic indicators like the circumferential resection margin (CRM) and extramural venous invasion (EMVI) are carefully monitored. Post-neoadjuvant therapy, restaging occurs around eight weeks to determine response through tumor regression degrees (TRD) and volume changes on diffusion W images. Healing manifests as fibrosis, and mucinous response types must be evaluated to identify true regression from stable, unresponsive disease. Ultimately, though MRI accuracy decreases during post-treatment restaging, it remains the standard modality to assess residual tumor, nodal shrinkage, and sphincter involvement, which directly impact five-year survival rates and recurrence risks.
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