Figure 1: Axial T2-weighted image demonstrates a mass in the anterior abdominal wall with heterogeneous signal characteristics.

Figure 2: Sagittal T2-weighted image shows heterogeneous mass within anterior abdominal wall.

Figure 3: Axial pre-contrast VIBE image shows the lesion to be isointense to skeletal muscle.

Figure 4: Axial post-contrast VIBE image demonstrates the lesion with diffuse enhancement.

Endometrioma. (See companion case Desmoid tumor)

Endometriosis is defined as the presence of endometrial glandular tissue outside of the uterus. Clinical presentations of endometriosis often consist of chronic pelvic pain and infertility; however, many patients are asymptomatic . The most frequent site of endometriosis is the ovary. Other locations include the uterine ligaments, pelvic cul-de-sac, pelvic peritoneum, fallopian tubes, rectosigmoid colon, and bladder. Following surgery, especially cesarean section, endometrial implants may be seen within the anterior abdominal wall. Treatment for symptomatic endometriosis can be medical or surgical.

The appearance of endometriomas on MRI is variable and depends on the concentration of iron and protein in the fluid from blood products and degradation. Therefore, endometriotic implants or tissue masses may appear as hypointense areas and/or hyperintense foci on T1- or T2-weighted MR images. Other appearances include cystic masses with very high signal on T1-weighted images and very low signal on T2-weighted images. This low signal intensity on the T2-weighted images is termed "shading" and occasionally occurs in a gradient from higher to lower signal intensity. Multiple high-signal lesions, usually in the ovaries, on T1-weighted images also are highly suggestive of endometriosis. Although this is the typical appearance of endometriomas, MRI is not sensitive for superficial implants; therefore, is not completely reliable to rule out endometriosis and tissue diagnosis may be necessary.

References:

1. Daly S. and E. Outwater. Endometrioma/Endometriosis (2001). eMedicine. (7/22/04)
2. Bazot M, Darai E, Hourani R, et al. Deep Pelvic Endometriosis: MR Imaging for Diagnosis and Prediction of Extension of Disease. Radiology . 2004; 232(2): 379-89.
3. Weissleder, R., Rieumont, Mark J., and J. Wittenberg. Primer of Diagnostic Imaging 2 nd edition. St. Louis : Mosby, c1997.