Cancer of the endometrium: value of MR imaging in determining depth of invasion into the myometrium.

The depth of invasion into the myometrium correlates with the frequency of lymph node metastases in patients with cancer of the endometrium. A distinction between superficial invasion (less than 50% of the thickness of the myometrium) and deep invasion (greater than 50%) is particularly important. The ability to distinguish between these two groups on MR was studied in 33 patients with endometrial cancer who had primary hysterectomy. The overall accuracy of MR in showing deep invasion was 82%, with a sensitivity of 91% and a specificity of 64%. The main limitation of MR was four false-positive results with regard to deep invasion. In all of these, the erroneous diagnosis was found at histologic examination to be due to a large polypoid tumor that distended the uterus so that a thin rim of myometrium was stretched over it rather than being deeply infiltrated by it. Our experience shows that MR can be used to distinguish between superficial and deep invasion of the myometrium. However, degree of invasiveness may be overestimated in exophytic polypoid tumors with significant intraluminal extension.