Rectal MR

General

• Usually get a T2 fast spin or turbo spine echo and a T2 single shot spin echo

  • The fast spin/turbo spin is the one which looks nice and can actually see shit, higher signal to noise - use this one

  • The single shot is faster but ass

• Will get an oblique-axial view which is used to look down the lumen of the rectum

• Will get an oblique coronal view which is used to look down the lumen of the distal rectum and anus

• Glucagon sometimes give to stop peristalsis in the bowel - better images

• Rectum considered distal portion of bowel and is the distal most 15 cm of bowel ending at the anal verge

  • Superior 5 cm = Upper rectum

  • Middle 5 cm = middle rectum

  • Lower 5 cm = lower rectum

• Below the peritoneal reflection (low rectum) is completely extra-peritoneal

• Superior to the peritoneal reflection the mid and superior anterior rectum is intra-peritoneal

Anal Sphincters

• External sphincter

  • Darker external line (blue)

  • Extends slightly lower than internal

• Internal sphincter

  • The brighter/white internal stuff (red)

Mesorectal Fascia

• Thin dark line surrounding the mesorectal fat

• Like a tear drop shape

• Superiorly ends at the level of the recto-sigmoid junction where it blends into the sigmoid mesentery

• Inferiorly blends into the puborectalis and levator muscles

• Wide in the center

Puborectalis

• U shaped muscle on either side

Interpretation

Staging

• Confined to the submucosa = T1

• Confined to involves muuscularis but not beyond it = T2

  • NOTE: On imaging we cannot differentiate between T1 & T2 so they are grouped together

• Extends beyond muscularis and into the mesorectal fascia = T3

  • IF you see T3 you need to state how far the tumor extends from the border of the muscularis to its fartherst part into the mesorectal fascia

    • T3a = extension < 1mm into MRF

      • Treated as a T1/T2 cancer with resection

    • T3b = extension 1-5 mm into MRF

    • T3c = extension 5-15 mm into MRF

    • T3d = extension > 15 mm into MRF

  • If extension is >5mm, 50% 5 year survival

  • If less >85% survival at 5 years

• Extends beyond muscularis into mesorectal fascia AND invades adjacent structures = T4

  • Common adjacent structures

    • Prostate

    • Sidewall muscles

• T3 is the big divide

  • Once it is T3 then they have to get neoadjuvant chemo prior to surgery

  • If T1/2 I think they can just go straight to surgery

Anatomy