Intersphincteric resection: MRI for staging
With the advance of surgical therapy of rectal carcinoma and improvement of adjuvant therapies the challenges for preoperative staging methods have grown over the last years. The radiologists understanding of rectal carcinoma is constantly evolving. The n
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Introduction With the advance of surgical therapy of rectal carcinoma and improvement of adjuvant therapies the challenges for preoperative staging methods have grown over the last years. The radiologists understanding of rectal carcinoma is constantly evolving. The need of precise staging before operative therapy has lead to refinements in the technique of staging examinations. The election of patients in need of neoadjuvant therapy, reevaluation after therapy, radiation therapy planning and assessment of postoperative changes and recurrence are challenges in the diagnostic workup of patients with rectal cancer. Magnetic resonance imaging (MRI) is now routinely used for preoperative staging of rectal cancer. It provides accurate assessment of the tumor and the surrounding mesorectal fascia as well as precise depiction of important anatomic structures as for example the structures of the pelvic floor and the anal sphincter in tumors of the low rectum. On the other hand evaluation of nodal metastases is still a diagnostic challenge with MRI. To take full advantage of the possibilities of the method, knowledge of operative techniques, indications for adjuvant therapy and about the typical MRI appearance of the tumor itself and its spread to adjacent structures are paramount. A standardized examination technique and description is of utmost importance to provide the surgeon with all necessary information.
Examination technique Early MRI studies used body coils which lacked the resolution to differentiate the layers of the rectal wall and therefore had no advantage over CT. The introduction of endorectal coils improved image resolution and lead to more consistent T Staging with accuracies between 71% and 91% [1]. Endoluminal MRI proved to be as accurate as Endorectal Ultrasound (ERUS) for the staging of superficial tumors [2–4]. However, limitations in the field
of view, lack of depiction of the mesorectal fascia higher up due to signal drop and problems with positioning of the coil especially in tumors of the low rectum reaching to the anal canal, with reported failed insertion rates of up to 40% [5] have made the use of these coils questionable. The development of phased array coils and subsequent introduction of high resolution MRI showed excellent results in discrimination of the mesorectal fascia and the depth of tumor invasion. With this the prediction of a tumor free circumferential resection margin (CRM) is possible [6, 7]. These findings lead to the development of a standardized imaging protocol that proved to be accurate in the multicentre European MERCURY study [8]. Bowel preparation, filling of the rectum or the use of intravenous contrast enhancement is now no longer recommended for staging of rectal cancer [7]. A 1.5-T system with phased array coils is used A Sagittal T2 weighted turbo spin echo sequence from one pelvic sidewall to the other is first performed to show the extent of the tumor and to be able to plan high resolution axial imaging (Fig. 1a). Axial large-field-of-view sections of the whole pelvis fo
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