Gina Brown MBBS, Presenter: Nothing to Disclose

Ian Daniels MBBS, Abstract Co-Author: Nothing to Disclose

Andrew R Norman PhD, Abstract Co-Author: Nothing to Disclose

In rectal cancer, accurate preoperative assessment of local tumour spread is critical,as this allows prognostic stratification and targeting of pre-operative therapy.High-spatial-resolution (HSR) MRI in rectal cancer staging has been investigated in small series,but neither the reproducibility of the technique nor its accuracy in comparison with histopathology assessment of local tumour spread have been established.A multicentre European collaboration (MERCURY) was initiated to prospectively evaluate HSR MRI in determining extent of local tumour spread in rectal cancer.

The primary endpoint of the study was equivalence between prospective measurement of tumour invasion beyond the bowel wall on HSR MRI and histopathology measurement of the same.The two techniques were to be considered equivalent if the difference between the two methods was within +/- 0.5mm. Based on an expected standard deviation of this difference of 2.121mm, 277 patients were required to demonstrate equivalence with an alpha of 0.05 and a beta of 0.025 (alpha = 2 beta).The primary hypothesis was that the 95% confidence interval of the difference between HSR MRI assessment and histopathology assessment should lie within -0.5 and 0.5mm. HSR MRI of the primary tumour using T2 Fast spin-echo following defined protocols for image acquisition and reporting was undertaken in consecutive patients with rectal cancer.A total of 715 consecutive patients from 11 European centres were registered in the study between January 2002 and October 2003, 295 were eligible for the primary end-point assessment of depth of invasion beyond the bowel wall following primary surgery.

Mean depth of tumour invasion beyond the bowel wall was 2.77mm (sd 4.60) and 2.81mm (sd 4.28) for HSR MRI and histopathology respectively.The difference between HSR MRI and histopathology assessment of the depth of tumour invasion beyond the bowel wall was -0.046mm and the 95% confidence interval was -0.487 to 0.395.Therefore, HSR MRI and histopathology assessment of extramural depth showed equivalence.

The study confirms that HSR MRI accurately measures tumour depth in the multicentre setting allowing accurate pre-operative prognostication.

Brown, G, Daniels, I, Norman, A, High Spatial Resolution MRI Predicts Tumour Spread in Patients with Rectal Cancer: Results from the MERCURY Study Group.  Radiological Society of North America 2004 Scientific Assembly and Annual Meeting, November 28 - December 3, 2004 ,Chicago IL. http://archive.rsna.org/2004/4414510.html