Which of the following is the investigation of choice for assessment of depth of penetration and perirectal node involvement in rectal cancer?

Investigations for rectal carcinoma: For Diagnosis: Best diagnosed by sigmoidoscopy (rigid not flexible) and biopsy of tumour Barium enema For Staging: TRUS (transrectal ultrasonography) CT MRI TRUS (Transrectal Ultrasonography) The depth of the tumour invasion can be accurately determined by TRUS, but it cannot detect cancer metastasis in lymph nodes (though it can detect enlarged lymph nodes, but it cannot predict if- cancer infiltration is present or not). CT Scan CT scan is also helpful for cancer extension, but again CT scan also cannot tell clearly about node invasion by cancer cell. MRI Scan It has become the most useful investigation tool (specially with the use of transrectal coils) for rectal carcinoma. It can very well predict the invasion of tumour in rectum as well as lymph node invasion with high accuracy. Ref: Maingot's 11/e, Page 701.