How Can We Better Identify Mesorectal Fascia Involvement?
The mesorectal fascia (MRF), or visceral layer of the endopelvic fascia, encircles the rectum and the mesorectal fat, nodes, and lymphatic vessels to form a distinct anatomic unit, called the mesorectum. The MRF runs along the anterior aspect of the sacru
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Brunella Barbaro
10.1 Anatomy The mesorectal fascia (MRF), or visceral layer of the endopelvic fascia, encircles the rectum and the mesorectal fat, nodes, and lymphatic vessels to form a distinct anatomic unit, called the mesorectum. The MRF runs along the anterior aspect of the sacrum, where it fuses with the presacral fascia, and then laterally on either side of the rectum. Anteriorly in males, it forms a dense band of connective tissue posterior to the seminal vesicle and prostate gland called the Denonvilliers’ fascia [1]. Magnetic resonance (MR) imaging can evidence with a clear delineation the MRF. High-resolution T2-weighted imaging is the key sequence for evaluation of primary rectal cancer. On T2-weighted imaging, the mesorectum is visualized by high intensity, and the mesorectal fascia as thin hypointense line (Fig. 10.1). The use of fat-suppressed sequences is considered inappropriate and not recommended because the MRF is not well visualized. This information determines the circumferential resection margin (CRM) for a total mesorectal excision. Total mesorectal excision is currently the standard surgical treatment of rectal cancer and involves resection of the rectum and mesorectum with an intact mesorectal fascia. B. Barbaro, MD Catholic University - School of Medicine Fondazione Policlinico Universitario A. Gemelli, Rome, Italy e-mail: [email protected]
Fig. 10.1 Axial high-resolution T2-weighted MR image in a patient with rectal cancer shows mesorectal fascia as a thin hypointense line (arrows) which encircles the hyperintense mesorectal fat
10.2 Why Is MRF So Important? It was shown that involvement of CRM was the most important factor for predicting the risk of local recurrence after rectal cancer surgery [2] but also systemic failure [3]. Because several studies have shown that preoperative radiotherapy-chemoradiotherapy is more efficient and less toxic than postoperative therapy [4], it has become increasingly important to evaluate the risk of positive CRM before the operation. Local rectal cancer staging basically
© Springer-Verlag Berlin Heidelberg 2018 V. Valentini et al. (eds.), Multidisciplinary Management of Rectal Cancer, https://doi.org/10.1007/978-3-319-43217-5_10
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focuses on the following issues: whether preoperative therapy is needed to achieve sufficiently low local recurrence rates and whether there is a need for an interval between the preoperative therapy and surgery. The relationship of the pelvic floor and anal canal and the proximity of the tumor or pathologic lymph nodes to the MRF or actual infiltration into the MRF are central in this evaluation. Although it has been shown that 5 × 5 Gy is very efficient to prevent local recurrences in many patients, it is much less effective when the tumor comes close to or invades the MRF. These tumors should be identified and treated with a long course of chemoradiation and a long interval to provide downsizing.
10.3 W hy MRF Instead of CRM in Preoperative Rectal Cancer Staging? The term positive CRM has r
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