MR Enterography : Crohn's Disease

Case Report : Young adult male   known case of crohns disease on  chemotherapy , suggests on  MR enterogram (on oral mannitol and  Intravenous Gadolinium) ,subtle narrowing (less than 5 cms) , increased wall thickness (5-7mm) , ulceration, hypoperistalsis, irregularity of terminal ileum including ileocecal junction & mesentric vessels prominence, sub centimeter lymph nodes  with similar findings in distal colon including descending colon, rectum (prominent vasa recta), with no obstructed loops or  creeping fat sign or pericolic abscess/ fistula  etc

Teaching points

By Dr MGK Murthy,   Dr Pritham and MR technologist Mr Narasimhulu 

1. Crohn's Disease is defined as Inflammtory disease of  unknown aetiology in young adults with symptoms akin to infections . No definite cure, hence immune suppression to halt progress and minimise complications (fistulae, stenosis, obstructions & abscesses) . Terminal ileum and colon commonest to be involved . 90% may require Ileocaecal region surgery sometime 

2. Radiology 

Initial work up highlight the anatomical lesions , quantify including differentiating from others including Mycobacterial  infection 

Later  role  =  for grading the severity of tissue diagnosis / evaluate the progress  on the therapy 

Though initially CT enteroclysis may be preferred, MR is now accepted as gold standard for repeat testing(No need for regular  radiation exposure  in young adults)

MR enterography = with oral contrast (preferred) and uses Mannitol (from 2-20%) for differentiation between  bowel lumen and wall (enhanced by post contrast seq) 

MR enteroclysis  = with nasojejunal tube 

(a)  Bowel wall thickness   normal 1-3 mm, mild 3-5 mm, moderate 5-7 mm and severe >7mm. (T1 post contrast or T2 Fat sat preferred) 

(b) Abnormal bowel wall enhancement (post contrast T1) . Normal , Mild (subtly>normal bowel in the vicinity), moderate ( >normal bowel , but some what less than vessel in the neighbourhood) ,   severe (some thing like vascular pattern )  = sign of both inflammation and fibrosis 

(c) Type of enhancement( role controversial)  homogenous  ----- Mucosal  ---- Layered   types  are claimed to  represent increasing severity 

(d)  Mural  signal intensity  (ref psoas muscle)  (T2 fatsat)   Milld (dark grey color) , moderate light grey), severe (white like mucosal contents) 

(e) Ulcerations (difficult to appreciate) , if  appreciated and accompanied by wall enhancement  - sign of active disease

(f) Loss of haustrations   - no grading , only length to be measured

(g) comb sign= increased   mesenteric enhancement

(h) Creeping fat sign- sign of long standing , and may rep healing 

(I ) Skip lesins - to  differentiate from others like TB/ ulcerative colitis

(J) complications-stenosis (pre stenotic dilatation, and mural signal increased must) / infiltrates (in to fat) / fistula/ abscesses

Role of Diffusion weighted images (not definitive right now, somewhat like contrast  enhancement  and may replace it in future)  diffusion bright with reduced ADC value imply  active inflammation