Imaging in rectal cancer with emphasis on local staging with MRI.
Arya S, Das D, Engineer R, Saklani A -The Indian journal of radiology & imaging(2015 Apr-Jun)
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View Article:PubMed Central - PubMed
Affiliation:Department of Radio-Diagnosis, Tata Memorial Centre, Mumbai, Maharashtra, India.
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Bottom Line:Contrast-enhanced MRI is considered inappropriate for both primary staging and restaging.Diffusion-weighted sequence may be of value in restaging.Multidetector CT cannot replace MRI in local staging, but has an important role for evaluating distant metastases.
Abstract
Imaging in rectal cancer has a vital role in staging disease, and in selecting and optimizing treatment planning. High-resolution MRI (HR-MRI) is the recommended method of first choice for local staging of rectal cancer for both primary staging and for restaging after preoperative chemoradiation (CT-RT). HR-MRI helps decide between upfront surgery and preoperative CT-RT. It provides high accuracy for prediction of circumferential resection margin at surgery, T category, and nodal status in that order. MRI also helps assess resectability after preoperative CT-RT and decide between sphincter saving or more radical surgery. Accurate technique is crucial for obtaining high-resolution images in the appropriate planes for correct staging. The phased array external coil has replaced the endorectal coil that is no longer recommended. Non-fat suppressed 2D T2-weighted (T2W) sequences in orthogonal planes to the tumor are sufficient for primary staging. Contrast-enhanced MRI is considered inappropriate for both primary staging and restaging. Diffusion-weighted sequence may be of value in restaging. Multidetector CT cannot replace MRI in local staging, but has an important role for evaluating distant metastases. Positron emission tomography-computed tomography (PET/CT) has a limited role in the initial staging of rectal cancer and is reserved for cases with resectable metastatic disease before contemplating surgery. This article briefly reviews the comprehensive role of imaging in rectal cancer, describes the role of MRI in local staging in detail, discusses the optimal MRI technique, and provides a synoptic report for both primary staging and restaging after CT-RT in routine practice.
Mentions
Three layers of the rectum are visible on a phased array external MRI. The innermost mucosa is thin and hypointense, the middle submucosa is hyperintense, and the outer muscularis propria is darkly hypointense [Figure 2C]. The rectum has a serosal lining only above the peritoneal reflection, which is along the anterior and lateral surfaces in the upper-third and the anterior surface in the middle-third [Figure 3]. The peritoneal reflection is visible on high-resolution sagittal and axial sequences [Figure 4]. Below the peritoneal reflection, the rectum is surrounded by the mesorectal fat which is limited by a thin fascia called the MRF, which fuses with the retroprostatic or retrovaginal fascia anteriorly and the presacral fascia posteriorly [Figure 3A]. The MRF surrounds the rectum completely only in the lower third [Figure 3B]. It is best seen laterally as a thin hypointense line on T2W sequences [Figure 5]. Inferiorly, the MRF thins out as it reaches the levator ani, which forms the roof of the ischiorectal fossa [Figure 5B].
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