MRI in Accurate Staging of Rectal Cancer

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Introduction
Rectal cancer is one of the major causes of cancer mortality in the world[1]. MRI is considered as the best modality for rectal cancer staging as it facilitates assessment of the mesorectal fascia with high accuracy[2],[3],[4],[5]. MRI is capable of diagnosing rectal cancer very accurately. T stage (tumor stage) stands for depth of rectal wall invasion by the tumor. In preoperative T staging of rectal cancer, the reported overall accuracy is 71–91%[2]. Prognosis of rectal cancer is determined by extramural venous invasion (EMVI), the distance of mesorectal extension (DME), the number of lymph nodes involved, perineural invasion and involvement of CRM[6]. Due to the selection of accurate treatment methods such as neo-adjuvant/adjuvant …show more content…

T3 tumors penetrate the muscularis propria and invade into the subserosa. T3 rectal cancer is sub-classified as T3a, T3b, T3c and T3d if DME is < 1 mm, 1–5 mm, > 5–15 mm and > 15 mm respectively. The extramural depth of tumor invasion for T3a (< 1 mm) on MRI is too small for measurement and can vary from person to person. Because the distance is very narrow, therefore, the diagnosis might frequently differ from person to person that finally result in the different treatment method. One of the studies suggested that with respect to 5-year disease free survival rate, there was no significant difference between T3a and T3b or T3c and T3d, but was statistically significant when re-categorized as T3ab and T3cd using 5mm as cutoff point[10]. Many previous studies investigated the prognosis of T3 subdivision using various cutoff points (4mm, 5mm, 6mm) and came to conclusion that deeper the tumor invasion, worst the prognosis [11][12]. Recently, using 5mm as a cutoff point to differentiate early and advanced T3 rectal cancer is highly acceptable. According to recent studies, patients with DME more than 5 mm should be identified properly because they have the worse prognosis compared to patients with DME less than 5

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