Submucosal Enhancing Stripe as a Contrast Material–enhanced MRI-based Imaging Feature or the Differentiation of Stage T0–T1 from Early T2 Rectal Cancers
Li-Juan Wan, MM* • Yuan Liu, MM* • Wen-Jing Peng, MM • Shuang-Mei Zou, MD • Feng Ye, MD •Han Ouyang, MD • Xin-Ming Zhao, MD • Chun-Wu Zhou, MD • Hong-Mei Zhang, MD
Radiology 2020; 00:1–9
Screening programmes have led to increased detection of early rectal cancers. Patients with early-stage rectal cancers can now be treated with chemo-radiotherapy or transanal endoscopic mucosal surgery (TEMS) rather than a total mesorectal excision which can carry significant morbidity. The treatment decision is often guided by local staging using MRI. Currently T0-T1 and T2 tumours are differentiated by assessing the status of the muscularis propria (SMP) on high resolution T2 weighted imaging.
This paper introduces a novel and interesting radiological sign to differentiate T0-T1 from T2 rectal tumours - the submucosal enhancing stripe (SES). The submucosa of the rectum contains an abundance of vessels, which enhances on administering intravenous contrast, forming a continuous enhancing stripe. This stripe is lost or interrupted by a rectal tumour which crosses through the submucosa into the muscularis propria (i.e a T2 tumour). The main aim of the study was to assess how good the SES is at differentiating T0-T1 from T2 tumours and to compare which is better at differentiating T0-T1 and T2 rectal tumours; the conventional method of assessing the SMP or the novel SES.
The authors performed a retrospective study of rectal MRI scans performed at their institute from 2012 to 2019. Only T0-T1 and T2 tumours with no prior chemo-radiotherapy which then underwent surgical resection within 3 weeks of the MRI were included. To further increase the validity of the findings only early T2 tumours were included, as the authors felt larger T2 tumours that infiltrated into the outer layer of muscularis propria could be easily distinguished from T1 tumours.
The authors provide a thorough description of the inclusion and exclusion criteria, their MRI imaging protocol and the methodology of how the scans were reviewed. 431 patients met the inclusion criteria and their scans were reviewed independently by two GI radiologists with 38 years of rectal MRI experience between them. The imaging features which were assessed included tumour location, length, circumference, shape, distance from the anal verge, if the SES was present or absent and if the SMP was regular or irregular.
249 patients had T0, Tis, T1 tumours and 182 T2 rectal tumours. In the T0-T1 group 84% had an intact SES whereas in the T2 group 92% had a disrupted SES.
The diagnostic accuracy, sensitivity and specificity for the SES was 87% (95% CI: 84, 90), 84% (95% CI: 79, 88) and 92% (95% CI: 87, 95) respectively. For the SMP the diagnostic accuracy, sensitivity and specificity was 67% (95% CI: 63, 72), 63% (95% CI: 57, 69) and 73% (95% CI: 66, 79) respectively. Cohens Kappa Coefficient was used to calculate inter observer agreement. There was excellent inter observer agreement with the SES (indicating that it is a reproducible sign) whilst with SMP it was only moderate.
Multivariate analysis performed on different imaging features showed that the SES, SMP and tumour shape are independent factors which allows the differentiation of T0–T1 from T2 tumours. Lesions with a SES, a regular SMP and carpetlike shape or a combination of the three features has a greater likelihood of being T0–T1 tumour. These key features from the multivariable model yielded an area under the receiver operating characteristic curve of 0.92 (95% CI: 0.90, 0.95).
This paper introduces a promising fresh new sign to aid local staging of rectal cancer, backed by an extensive retrospective review of a large volume of rectal MRIs. The SES is a reproducible sign with a high diagnostic accuracy. The paper clearly describes the underlying principles of this novel sign with good, clear accompanying images and histological correlation.
The study did have some limitations as it was performed at a single centre and it was retrospective so did not influence treatment decisions and no data were provided on outcomes. Gadolinium enhanced MRI is not routinely recommended in the most recent ESGAR Rectal Cancer guidelines from 2016 and the investigators used rectal gel to distend the lumen which is also not used routinely.2 Nevertheless this paper describes and investigates a new and interesting sign in rectal MRI staging which may have a role in the future.
References:
- Wan LJ, Liu Y, Peng WJ, et al. Submucosal Enhancing Stripe as a Contrast enhanced MRI-based Imaging Feature for the Differentiation of Stage T0-1 from Early T2 Rectal Cancers. Radiology 2020. https://doi.org/10.1148/ radiol.2020201416. Published online November 10, 2020.
- Beets-Tan, R.G.H., Lambregts, D.M.J., Maas, M. et al. Magnetic resonance imaging for clinical management of rectal cancer: Updated recommendations from the 2016 European Society of Gastrointestinal and Abdominal Radiology (ESGAR) consensus meeting. Eur Radiol 28, 1465–1475 (2018). doi.org/10.1007/s00330-017-5026-2
Dr Varun Chillal is currently completing a fellowship in Gastrointestinal Imaging at St James Hospital, Leeds, UK. He studied Medicine at the University of Leicester and undertook an intercalated BSc in Medical Management at Imperial Business School. As part of his foundation training, he worked as clinical demonstrator at the University of Leicester. He completed his specialist radiology training in West Midlands Deanery within the Birmingham rotations. He intends to take up a Consultant Gastrointestinal Radiologist post in the NHS next year.
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