Inaccuracy of MRI imaging in early rectal cancer

Kolorektal
Poster
Roberto Rosén¹ , Emelie Nilsson¹, Milladur Rahman¹, Carl-Fredrik Rönnow^1
1 Department of Clinical Sciences, Malmö, Section of Surgery, Skåne University Hospital, Lund University, Malmö, Sweden

Introduktion/Introduction
Adequate staging of early rectal cancer (RC) is important for allocating patients to surgery or local resection. The aim of this study was to investigate the staging accuracy of magnetic resonance imaging (MRI) in early RC.
Metod/Method
RC patients, staged by MRI as cT1-2 (cT1-2 cohort) and all pT1 (pT1 cohort) RC, without prior neoadjuvant treatment, undergoing surgery 2009-2018, were included from the Swedish colorectal cancer registry. MRI-based stages were compared with final histopathology. Uni- and multivariate logistic regression were used to identify factors potentially influencing staging accuracy.
Resultat/Result
The cT1-2 cohort consisted of 1888 cases staged by MRI as cT1-2, whereof 566 (30%) were pT3 and 41 (2%) were pT4. Accuracy of MRI for cT1-2 stage was 68%. The pT1 cohort consisted of 549 pathologically verified T1 RC, whereof 123 (22%) were overstaged with MRI (cT3 n=67, cT4 n=3, cTx n=53). MRI incorrectly staged the majority of pN+ cases in the cT1-2 cohort as cN0 (354 of 477, 73%) and the majority of cN+ cases were pN0 (131 of 233, 56%). Accuracy, sensitivity and specificity of MRI based nodal staging were 71%, 22% and 87% respectively. Out of 1586 patients staged cT1-2N0 (eligible to local resection), 653 (41%) were understaged. Conversely, 142 (29%) of patients potentially curable with local resection were overstaged as either >cT2 or cN+.
Diskussion/Discussion
MRI alone is inadequate for selecting patients with early RC for organ sparing treatment with a substantial risk of understaging pT3 lesions and overstaging pT1 lesions in addition to poor nodal accuracy.