Honsoul Kim MD, PhD, Abstract Co-Author: Nothing to Disclose

Jieun Koh MD, Presenter: Nothing to Disclose

Hyuk Hur, Abstract Co-Author: Nothing to Disclose

Woong Sub Koom, Abstract Co-Author: Nothing to Disclose

Myeong-Jin Kim MD, PhD, Abstract Co-Author: Nothing to Disclose

Joonseok Lim MD, Abstract Co-Author: Nothing to Disclose

To depict the MRI characteristics of rectal cancer of which pathological complete remission (PCR: Mandard grade 1) has been achieved by neoadjuvant concurrent chemoradiation therapy (CRT).

We retrospectively analyzed 88 (Male/femal=55/33, age of 58.62±11.24 years) rectal cancer patients who underwent pre-/post-CRT MRI, CRT and surgery between January 1998 and December 2012 and were found to have achieved PCR. Post-CRT MR was obtained 8~54 (23.4±9.9) days before surgery. Tumor distal margin reached lower, middle and upper rectum (n=49/38/1, 6.0±2.3cm to anal verge). We analyzed pre-/post-CRT MRIs to assess tumor circumferential resection margin (CRM), MR T stage (gross perirectal infiltration), volume (volumetry), MR tumor regression grade (TRG), T2 signal intensity (SI) grade (comparing with muscle), residual morphology, diffusion restriction and nodal status. Paired t-test was used to compare pre-/post-CRT tumor volume.  

Pre-CRT (24.34±24.37cm3) and post-CRT (7.67±8.99cm3) MR revealed a tendency of marked volume decrease (P<0.001, reduction rate: 70.6±19.3%). MR TRG G1(PCR)/G2/G3/G4/G5(marked progression) were 3/23/61/1/0. MR T stage (T1&2/T3a/T3b/T3c/T4) were 14/6/26/35/7(pre-CRT) and 19/13/28/21/7(post-CRT). CRM results (negative/threatening/invasion) were 37/34/17(pre-CRT) and 44/33/11(post-CRT). SI grade (not visible/lower-than-muscle/iso-to-muscle/intermediate high/edema-SI) were 0/0/8/80/0(pre-CRT) and 3/14/50/15/6(post-CRT). Morphologic grade of post-CRT MR (not visible/scanty remnant/subtle soft tissue/gross nodule) were (3/13/25/47). DWI was performed in 68 post-CRT MRIs, of which 10 showed diffusion restriction. The post-CRT MR LN grade were (negative/borderline/suspicious=39/44/5), but pathology review identified metastatic LNs in only 2 negative and 2 borderline graded cases. Six patients (6.8%) later developed tumor recurrence.

MRI of rectal cancer which achieved PCR after CRT demonstrates highly variable and confusing imaging characteristics. A tendency of marked volume reduction and decreased T2 SI after CRT does exist, but remaining mass and/or enlarged LNs of soft tissue SI are not infrequently encountered.

Post-CRT rectal cancer can show highly variable MRI features. Striking remnant mass and/or LNs with bulk showing soft tissue SI does not necessarily neglect the possibility of having achieved PCR

Kim, H, Koh, J, Hur, H, Koom, W, Kim, M, Lim, J, The MRI Features of Rectal Cancer Which Achieved Pathological Complete Remission after Neoadjuvant Concurrent Chemoradiation Therapy.  Radiological Society of North America 2014 Scientific Assembly and Annual Meeting, - ,Chicago IL. http://archive.rsna.org/2014/14011779.html