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MRI is Accurate in Diagnosing, Staging and Treatment Planning for Rectal Cancer

October 26, 2009
Written by: , Filed in: Nuclear Medicine
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A recent study was conducted to assess the accuracy of 3-T MRI in the evaluation of patients with rectal carcinoma.

Results show that 3-T MRI is accurate in the preoperative diagnosis, staging, and surgical planning of patients with rectal carcinoma.

The Study
This study was comprised of 38 patients (23 men, 15 women) who had suspected rectal carcinoma based on clinical findings that included any of the following:

  • guaiac-positive stools;
  • constipation;
  • abnormal digital rectal examination;
  • abnormal endoscopy.

MRI was performed with a 3-T scanner, and sequences included T2-weighted sequences without and with fat suppression, T1-weighted gradient echo with and without fat suppression, radial oblique 2D hydrographic single-shot fast-spin echo, and 3D fat-suppressed dynamic gadolinium-enhanced images.

Three radiologists who were unaware of the clinical information reviewed the images.

A 4-point grading scale was used to independently assess the overall image quality, the presence of artifacts, and the border between the tumor and normal rectum.

Each rectal tumor was staged with MRI, which was later correlated with surgery and pathology.

T1 and T2 lesions were not differentiated from one another, although they were characterized as having a smooth outer tumor border within the rectal wall and no perirectal fat invasion.

These were differentiated from T3 lesions, which were characterized as having irregular outer borders and perirectal fat invasion.

T4 lesions had obscured fat planes.

The feasibility of sphincter-sparing surgery was assessed by measuring the distance of the tumor from the external sphincter, demarcated by where the levator ani muscle attached to the rectum. Sphincter- and anus-sparing surgery was considered feasible if this distance was >=2 cm.

All 38 patients had rectal carcinoma on MRI, which was confirmed on histopathology. T2-weighted sequences depicted the tumor margins well and had the highest image quality scores.

Rectal carcinoma was better visualized on sequences without fat suppression.

MRI had an accuracy of 92% in estimating the T stage.

MRI also had an accuracy of 92% in differentiating between tumors with stage T3 or greater, from those with T2 or lower disease, as well as an accuracy of 100% in differentiating between stage T4 and T3.

MRI had an accuracy of 96% in determining the surgical approach for treatment.

3-T MRI is accurate in the preoperative diagnosis, staging, and surgical planning of patients with rectal carcinoma.

Reviewer’s Comments

The results of this study are useful in demonstrating the feasibility of MRI in predicting the T stage as well as assessing resectability of rectal carcinoma.

While CT can quickly evaluate the abdomen and pelvis for distant metastases, it is limited in the primary tumor evaluation due to its lower soft-tissue contrast compared to MRI.

Consequently, MRI can potentially provide a complete assessment of the primary tumor as well as evaluate for metastases. A limitation noted in this study was the small number of patients.

Author: John C. Sabatino, MD

Zhang XM, Zhang HL, et al. 3-T MRI of Rectal Carcinoma: Preoperative Diagnosis, Staging, and Planning of Sphincter-Sparing Surgery. AJR; 2008; 190 (May): 1271-1278

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