3T MRI accurately stages rectal cancer, identifies candidates for sphincter-sparing surgery

Patients examined at the Qilu Hospital of Shandong University in China for rectal cancer benefit from the added diagnostic power of 3T MRI for staging and identifying candidates for sphincter-sparing surgery.

Dr. Xiaoming Zhang, a radiologist at Qilu Hospital, reported Monday that her single-site prospective trial involving 38 patients with primary rectal cancer showed that 3T MRI was 92% accurate for grading T-stage rectal cancer and 97% accurate at successfully identifying patients for sphincter-sparing surgery. The system did not perform as well for diagnosing lymph node metastases. For that measure, the accuracy rate for the protocol was 79%.

MRI diagnosis and staging were correlated with surgical results and histopathology. The distance from the lower margin of rectal cancer to the point where the levator ani muscle attached to the rectum was measured to predict a possible approach for sphincter-sparing surgery.

Twenty-three men and 15 women, with a mean age of 60, were examined. The patients were administered a laxative and underwent sodium chloride enema to thoroughly cleanse the bowel before imaging. Lumenal distension of the rectum was also performed before MRI, Zhang said.

Studies were acquired on a 3T scanner equipped with an eight-channel surface coil. Axial, coronal, and sagittal T2, axial T1, FSE, and spoiled gradient echo sequences were performed. Two-D MR hydrography used an SSFSE sequence and 3D DCE-MRI with fat saturation.

Three radiologists, who were blinded to the patients' clinical information, rated the scans' imaging quality on a five-point scale. They rendered a diagnosis and predicted the possibility of sphincter-sparing surgery based on data from 11 pulse sequences. Tumor node metastasis grading was combined with T1- and T2-stage tumors into a single grade. All detected nodes were more than 1 cm in diameter.

Among case examples, Zhang described her group's experience with a 57-year-old man with well-differentiated T1 rectal adenocarcinoma. A polyp was identified with T2 sequence. On DCE-MR, the tumor was well discriminated from the normal wall. The distance from the lower margin of the rectal tumor to the upper margins of the external sphincter was greater than 5 cm, making the patient eligible for sphincter-sparing surgery, she said.

The readers preferred the dynamic contrast-enhanced sequence because it produced the best depiction of tumor margins, Zhang said. The T2 sequences, including coronal, sagittal, and axial views, were preferred to the 2T presentation with fat saturation. The DCE sequence's advantage over the fat saturation method may have stemmed from its bright depiction of fatty tissue around the rectum.

MR hydrography demonstrated the rectal lumen showing endoluminal features, such as filling defects. The imaging quality is similar to that obtainable with barium enema, Zhang said.

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