How Can We Identify Nodal Involvement and Extramural Vascular Invasion?
With the shift from postoperative to preoperative (chemo) radiotherapy (CRT) for rectal cancer patients, tumour risk profile assessment, previously based on histology of the resection specimen, is now based on preoperative imaging. Imaging provides inform
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Monique Maas and Regina G.H. Beets-Tan
11.1 Introduction With the shift from postoperative to preoperative (chemo) radiotherapy (CRT) for rectal cancer patients, tumour risk profile assessment, previously based on histology of the resection specimen, is now based on preoperative imaging. Imaging provides information on the T-stage, N-stage and involvement of the mesorectal fascia. Nodal disease is one of the most important risk factors both for local and distant recurrence and is generally considered an indication for neoadjuvant and adjuvant therapy. This chapter will discuss whether we can accurately identify nodal involvement with imaging in patients with rectal cancer.
11.2 H ow Accurate Is Imaging for Identification of Nodal Metastases? For a long time, nodal staging has been performed with endorectal ultrasonography (EUS) and computed tomography (CT). Nodal staging was mainly based on nodal size measurements. A node that was larger than 8 mm on imaging was often considered as malignant. For a part this is correct M. Maas, MD PhD (*) • R.G.H. Beets-Tan, MD, PhD Department of Radiology, The Netherlands Cancer Insititute, Amsterdam, The Netherlands e-mail: [email protected]
because in rectal cancer, the vast majority of lymph nodes with a diameter of 8 mm or larger is malignant. However, around 60% of the metastatic rectal cancer nodes are smaller than 6 mm [1]. The pooled sensitivity and specificity of EUS in a meta-analysis based on 35 studies was about 75% [2]. A comparative meta-analysis of CT, EUS and MRI showed that diagnostic performance derived from the receiver operating characteristic (ROC) curves for all three modalities was only moderate [3]. The sensitivity of EUS, CT and first-generation MRI for primary nodal staging in rectal cancer varies between 55 and 70% and specificity between 75 and 80%. EUS performed slightly better than MRI and CT due to the possibility to assess morphological features of nodes other than size. During the last decade, MRI has become the main modality of rectal cancer imaging. EUS is still used for staging of small rectal cancers, and CT is now used for distant staging only. Therefore, the largest body of evidence has been published for nodal staging with MRI. Highresolution MRI has made it possible to assess the other nodal features, such as border, shape and heterogeneity of the node signal with MRI as well. These morphological features are well visualized in nodes larger than 6 mm, but a reliable delineation of the nodal feature can be difficult if not impossible in the smaller nodes. Several studies have reported improvement of nodal staging with these additional morphologi-
© 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_11
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M. Maas and R.G.H. Beets-Tan
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Fig. 11.1 Axial T2-weighted MR image of two patients with rectal cancer. In (A) a small (9 mm) and a smaller node (5–9 mm). Both nodes show morphological features strongly indicative
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