While there are many studies comparing the sensitivity, specificity and accuracy of Endosonology and MRI, as far as I understand the issue, EUS is better for T1-T2 lesions and MRI is better for more advanced T stages.

i think the ability for both in order to determine the N stage is comparable..

however, MRI can better inform about the circumferential margin and guide the use of neoadjuvant therapy for a threatened margin before TME..

certain situations where MR is better than EUS would be a stricturing tumor, post radiation tumor and recurrent tumor..

regards, raza

Agree with Dr Raza,

Would like to add--

MRI is the first line investigation for local staging in rectal cancer. 

It gives information on T staging , CRM and N stage.

However it cannot differentiate accurately between T1 and T2.

Endorectal ultrasound  can differentiate between T1 and T2 and so it is added to MRI when this needs to be known , particularly  if you are planning endo-anal excision ( to confirm T1 N0 status) .

Incidentally the Bipat meta-analysis showed---

Sensitivity 94% ; specificity of  86% for T staging with  ERUS in rectal cancer 

Sensitivity 94% ; specificity of 69% for T staging with MRI in rectal cancer

Puli meta-analysis showed a higher sensitivity and specificity for T1 lesions with ERUS as compared to T2-- so the main role of ERUS to confirm suspected T1 lesions.

ERUS though  cannot show the CRM and pelvic sidewall nodes due to small field of view  and hence high resolution phased array external MRI ( not endorectal MRI) is mandatory for  locally advanced rectal cancer to show lateral spread.

Regarding N staging ERUS and MRI are comparable. 

Bipat meta-analysis - 

Sensitivity 67% ; specificity of 78%  with ERUS

Sensitivity 66% ; specificity of 76%  with MRI 

In summary MRI is done in all cases for local staging and ERUS is added when available only to confirm T1N0 lesions to plan endoanal excision.

Dear Dr. Chi, EUS is much more operator dependent as MRI. Especially in questionable locally recurrent disease and its´ restaging, EUS and MRI both may be blind. PET may detect local as well as distant metastasis.

Kind regards,

Dietrich Doll