MRI seems more useful in knowing depth of invasion whereas EUS seems to be more useful for local wall invasion.
Magnetic resonance imaging (MRI)is a useful modality for the evaluation of rectal cancer, providing superior anatomical and pathologic visualization as compared with endorectal ultrasound (EUS).
High resolution MRI is needed for stagging. And is excellent. But MRI can't distinguish early cancer( T1/T2 ) or not so good at.. here EUS comes into play which is excellent in telling the layer of involvement. MRI can accurately tell the involvement of mesorectal fascia and about circumferential resection margin during TME. It tells the lymph involvement also.. MRI with the help of DWI/ADC sequence can accurately tell the post chemotherapy status also..
T staging of carcinoma rectum before surgery with EUS is more helpful as it has greater accuracy than CT or MRI.
Studies have shown than use of TRUS leads to upstaging of tumor leading to use of neoadjuvant chemotherapy
# EUS is superior to MRI for T staging (accuracy of about 80-95% vs 70-85%).So it would be benificial in early rectal Ca especially for deciding about Sphincter saving procedures.
Plus advantage of doing EUS guided FNA of some suspicious nodes.
# For N staging they are almost comparable.
# Then advantage of MRI would be in restaging of rectal Ca after Neoadjuvant after which the accuracy of EUS is significantly decreased.
Agree with whatever has been mentioned already.
Few additions :
1. Role of EUS in primary evaluation of luminal malignancies- esophagus and rectum - especially T1/T2 has been to rule out local lymphadenopathy. T3 and beyond is invariably N +ve.
In case of rectal pathology this has an impact on qualification of the patient towards an appropriate NAT protocol - Long vs Short term RT +/- CT.
2. Limited utility in differentiating T2 and T3.
3. No role in high rectal > 12 cm lesions.
4. No role in obstructing lesions.
5. No role in evaluation of CRM and EMVI ( vs MRI ) - MERCURY trials .
6. No role in evaluation of non local nodes.
7. No role in evaluation after NAT.
8. ? utility in circumferential lesions.
9. Availability, cost, operator dependance, invasive nature, patient discomfort and under staging.
10. Declining role now as refined PA -MRI machines provide good information and are non invasive.
Regards
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