Effectiveness of MRI for the Assessment of Mesorectal Fascia Involvement in Patients with Rectal Cancer: A Systematic Review and Meta-Analysis

Abstract

Aims: Defining the most appropriate definition of mesorectal fascia involvement (MRF+) by reviewing literature and using new inclusion criteria to re-evaluate the effectiveness of MRI in the assessment of MRF+ for rectal cancer. Methods: PubMed, Medline, Embase, and the Cochrane Library databases were electronically searched from 1999 to 2012. The bivariate random effects model was used to estimate the pooled outcomes of each subgroup. The definition of MRF+ in MRI and the influence of neoadjuvant chemoradiotherapy (neo-ChRT) were especially discussed. Results: Fourteen studies involving 1,600 patients were included. Different definitions of MRF+ (≤1, ≤2 and ≤5 mm) in MRI exhibited different pooled sensitivity (76, 79 and 92%), specificity (88, 66 and 48%) and diagnostic odds ratio (DOR) (22.4, 6.6 and 16.0). The definition of MRF+ at ≤1 mm showed the highest DOR. The specificity (88 vs. 93%, p = 0.026) and DOR (15.5 vs. 39.0, p = 0.001) were lower in patients who underwent neo-ChRT than those who did not while using ≤1 mm as the definition of MRF+. However, the sensitivity showed no significant difference (67 vs. 74%, p = 0.129). Conclusions: MRI is valuable for the assessment of MRF. The most appropriate definition of MRF+ in MRI is ≤1 mm. The effectiveness is higher in patients who did not undergo neo-ChRT.

Essential Items for Structured Reporting of Rectal Cancer MRI: 2016 Consensus Recommendation from the Korean Society of Abdominal Radiology

“…Several studies specifically investigated the possibility of defining a line between 1 and 5 mm as the threshold to diagnose CRM involvement on MRI. According to a recent meta-analysis (42), of three different threshold values of 1, 2, and 5 mm for the shortest tumor distance from the mesorectal fascia on MRI, the highest overall accuracy for diagnosing CRM involvement, demonstrating 76% pooled sensitivity, 88% pooled specificity, and diagnostic odd ratio of 22.4, was observed for a distance of 1 mm. Another study analyzed the risk of local recurrence according to the shortest tumor distance from the mesorectal fascia on MRI and showed that, relative to the distance > 5 mm, the risk of local recurrence was not significantly different in 1–2 mm and 2–5 mm groups, but was significantly higher in ≤ 1 mm group (hazard ratio of 3.72) (39).…”

How Should Imaging Direct/Orient Management of Rectal Cancer?

“…When CRM involvement was defined as a tumor within 1 mm of the mesorectal fascia, MRI had a specificity and sensitivity of 76 and 88%, respectively. 44 CRM involvement is a poor prognostic factor in rectal cancer. 45,46 Long-term follow-up of the MERCURY study showed that 5-year overall survival was 62.2% in the CRMnegative group compared with 42.2% in the CRM-positive group and was the only significant prognostic risk factor for overall survival (OS), DFS, and local recurrence (LR) on multivariate analysis.…”

Magnetic Resonance Imaging for Staging of Primary Rectal Cancer: Imaging Prognosticators

“…28 In a meta-analysis of thresholds of 1, 2, and 5 mm for the shortest tumour distance from mesorectal fascia on MRI, using ≤1 mm to define CRM involvement had the highest overall accuracy, with 76% pooled sensitivity, 88% pooled specificity, and diagnostic odds ratio of 22.4. 31 The European Society of Gastrointestinal and Abdominal Radiology and the Korean Society of Abdominal Radiology also recommend a cut-off of ≤1 mm to define tumour-involved CRM on MRI, 5,32 and a cut-off of ≤2 mm to define a threatened CRM on MRI. 5 Apart from direct extension from the primary tumour, other high-risk features in the mesorectum (such as extramural venous invasion, vascular / tumour deposits, and less likely metastatic nodes) can also cause tumourinvolved CRM (Figure 8).…”