Colon Cancer Awareness Month


Anorectal cancer is approximately 1/3 of all colorectal cancer cases.

Anatomy: The rectum is typically divided into low, mid and high segments of 5cm each above the anorectal
angle. It is surrounded by the mesorectal fascia.










The treatment and prognosis of an anorectal cancer
depends on:

  • The location: (low, mid, high)
  • The presence of lymphadenopathy
  • The presence of metastases.
  • The relationship of the cancer to the mesorectal fascia
  • The depth of invasion of the rectal wall and surrounding Structures.


Recommended Imaging modality
MRI is regarded as the best modality to diagnose local anorectal dis-ease (compared to CT and ultrasound). It provides superior depiction of anatomical structures, and accurately distinguishes between tumor and healthy tissue. It is similar to CT in assessment of distal


Imaging strategy
T2-weighted images in all planes are the mainstay. Diffusion weighted images are useful in highlighting areas of tumor, especially in evaluat-ing treatment response. Most of the time, IV gadolinium contrast is not necessary. (IV contrast is required for CT.)

T1 and T2 tumors are confined to the rectal wall. They have the best prognosis.
T3 tumors extend into the mesorectal fat.
T4 tumors extend beyond the mesorectal fascia.


N0: no abnormal nodes.
N1: 3 abnormal nodes.
N2: > 4 abnormal nodes

M0: no mets.
M1: metastases are present.




The following are recent cases from NorthCoast Imaging.

Low rectal T3N2 tumor (nodes in the mesorectal fascia).

Axial T2
Sagittal T2



High Rectal T3 tumor

Sagittal T2
Axial Diffusion (DWI)
Coronal T2


Large anal cancer with invasion of sphincter complex and extensive lymphadenopathy.

Sagittal T2
Axial DWI
Axial T2


Contributor: Dr. Konrad Kirlew – Consultant Radiologist