Nishard Abdeen MD, Presenter: Nothing to Disclose

Khaldoun Koujok MD, Abstract Co-Author: Nothing to Disclose

Pablo Caro MD, Abstract Co-Author: Nothing to Disclose

Rhys Abdeen Abdeen, Abstract Co-Author: Nothing to Disclose

Intra-abdominal abscesses in children are often imaged with contrast enhanced CT, and there are few data regarding MRI appearance. MRI offers superior contrast resolution without  ionizing radiation, which is an important consideration in children. The purpose of this study is to describe the appearance of abscesses on MRI, particularly diffusion weighted imaging, with particular reference to distinguishing abscess from bowel loops using ADC values.

Twenty five intra-abdominal abscesses in twenty two children were retrospectively evaluated with axial DWI , axial and coronal  T2 weighted SSFSE, and sagittal T2 weighted images with  fat saturation. The abscess region showing the most restricted diffusion on ADC map was measured using a circular region of interest  of 0.3 mm2. ADC in an adjacent bowel loop and in the bladder was also recorded. Four observers ( three pediatric radiologists and one pediatric radiology fellow) performed the same measurements on all abscesses. Interobserver variation was assessed using 95% Bland Altman limits and intraclass correlation coefficients.

The mean ADC was sigificantly decreased ( p<0.05, student t test) in all abscesses relative to afjacent bowel loops for all observers as follows, with mean values of 0. 715 +/-0.083, 0.727+/-0.087, 0.756+/- 0.048, and 784+/ -0.067 ( x10-3 mm2/s) compared to mean values for adjacent bowel loops  which were 3.256+/-0.079, 3.286+/-0.095, 3.131+/-0.098 and 3.185+/-0.106( x 10 -3 mm2/s) respectively. The mean ADC for  bowel loop contents was similar to that of urine ADC  for all observers  at  3.444+/-0.021, 3.327+/-0.212, 3.435+/-169, 3.386+/-0.187 ( x 10 -3 mm2/s) respectively.  There was good  interobserver agreement with 95% limits of agreement between readers varying between 17 and 22% of the mean.

Diffusion weighted imaging is effective at distinguishing abscesses which show restricted diffusion ( arrow in figure)  from bowel loops or bladder ( b in figure)  which do not. Mean ADC in abscesses is significanlty lower than in bowel loops. The ADC in bowel loops adjacent to teh abscess are similar to that of free fluid ( urine).

Diffusion weighted MRI can distinguish abscess from adjacent bowel loops in children, without ionizing radiation or  intravenous contrast.

Abdeen, N, Koujok, K, Caro, P, Abdeen, R, Effectiveness of Diffusion Weighted Imaging in Evaluation of Intra-abdominal Abscesses in Children.  Radiological Society of North America 2014 Scientific Assembly and Annual Meeting, - ,Chicago IL. http://archive.rsna.org/2014/14045768.html