Solid pelvic masses caused by endometriosis: MR imaging features

OBJECTIVE: Solid fibrotic nodules of endometriosis can simulate peritoneal metastases on imaging studies. To assist with this distinction, we analyzed the MR appearance of solid masses of pelvic endometriosis. MATERIALS AND METHODS: A search of pathologic and surgical records of patients who had pelvic MR imaging with a phased-array multicoil disclosed 13 patients who had endometriosis proved at laparotomy. MR images were reviewed retrospectively by two unblinded radiologists for the signal intensity, size, and enhancement pattern of solid peritoneal masses. Eight solid masses in six patients were detected on MR images: four lesions were in the cul-de-sac, two in the bladder wall, and two in the rectal wall. Four of the masses were excised at surgery and one was sampled by surgical biopsy; microscopy showed abundant fibrosis with small clusters of endometriotic glandular tissue. Three masses were inspected at surgery and found to represent dense fibrosis caused by endometriosis. RESULTS: Solid masses of endometriosis ranged in size from 1 to 5 cm. Seven of the eight masses had similar features on MR images: intermediate signal intensity on T1-weighted spin-echo images with punctate foci of high signal intensity, low signal intensity on T2-weighted images, and enhancement after administration of contrast material. CONCLUSION: MR imaging shows enhancing solid masses in some patients with endometriosis. These masses have MR features that might be useful in the differentiation between solid foci of endometriosis and peritoneal metastases.