Endoscopic ultrasound and endorectal magnetic resonance imaging: a prospective, comparative study for preoperative staging and follow-up of rectal cancer.

BACKGROUND AND STUDY AIMS: Endoscopic ultrasound has become the best available method for local staging of primary rectal cancer and diagnosing recurrent local disease. The aim of this study is to compare the value of endoscopic ultrasound (EUS) to magnetic resonance imaging with an endorectal coil (EMRI).

PATIENTS AND METHODS: Twenty-one patients (11 women, 10 men, mean age 63 years, range 31-79) with primary rectal cancer (n = 6) or follow-up examinations for recurrent local disease (n = 15) were investigated by EUS using an echo colonoscope (CF-UM 20, Olympus Optical) and by endorectal coil MRI on a 1.5 tesla MR system (General Electric). T2-weighted and contrast-enhanced T1-weighted images were obtained. The results of preoperative examinations were compared to histopathological findings regarding the T staging, with special focus on the transmural tumor infiltration.

RESULTS: EUS identified all tumors, whereas one tumor was missed by EMRI. EUS was superior to EMRI in T staging (accuracy 83%/40%), due to the better differentiation between T1 and T2 tumors, as the endorectal coil could not differentiate between stage T1 and stage T2. The accuracy of EMRI in assessing perirectal infiltration was 80%, compared to EUS with 100%. Local tumor recurrence was found in six of 15 patients, without endoscopic signs of recurrent disease in four of them. All were detected by EUS. Only one recurrence was missed by EMRI. Accuracy and positive and negative predictive values in follow-up examinations for recurrent disease for EUS were 93%, 86%, and 100%, and for both the T2-weighted and T1-weighted contrast-enhanced sequences of endorectal coil MRI, they were 93%, 100%, and 90%, respectively.

CONCLUSIONS: Endoscopic ultrasound and endorectal coil MRI are comparable methods in the preoperative staging and early diagnosis of recurrent rectal cancer. The advantages of EUS are the small diameter of the instrument, availability, and lower costs. In contrast, EMRI is operator-independent, and may become important for combined local and distant staging and follow-up examination in rectal cancer, if contrast-enhanced imaging can improve the sensitivity for liver metastases.