Fig. 12  Massive ovarian edema caused by infiltration from a mucinous colorectal tumor. The large pelvic mass (arrow) is of high signal intensity on axial T2wi (a) and

demonstrates peripheral and heterogeneous contrast enhancement on dynamic contrast-enhanced T1 fat-satu- rated image (b)

assist in further assessment of the adnexa. Rarely, a calcified mass may result from chronic infarction which cannot reliably be differentiated from a calcified ovarian tumor (Currarino and Rutledge 1989). Malignant massive ovarian edema may be seen when there is metastatic infiltration of the lymphatics of the ovary (Krasevic et al. 2004; Bazot et al. 2003) (Fig. 12).

2.5.3\ Diagnostic Value

Early diagnosis and treatment is crucial to prevent irreversible ovarian damage and prevent infectious complications. Most patients with suspected torsion clinically and on sonography will undergo immediate surgical untwisting. However, in patients that present with severe acute pain of uncertain diagnosis, CT may be the first line investigation and the signs of ovarian torsion may be difficult to appreciate. MRI and CT are often used in clinically atypical cases, especially in chronic torsion. In early torsion, the imaging signs may be indicative but not specific of ovarian torsion. MRI and CT are particularly useful in detecting twisted lesions displaced outside the pelvis,

where sonography may be limited. In pregnancy and in children, MRI is the modality of choice to further assess suspected ovarian torsion.

2.6\ Ectopic Pregnancy

Ectopic pregnancy describes implantation and growth of the fertilized ovum at any site other than the endometrial cavity. The fallopian tube accounts for the vast majority of all ectopic gestations (95%), with 75% found in the ampulla and the remainder occurring in the fimbrial and isthmic portions with roughly equal distribution (Bouyer et al. 2002). Rarely, ectopic pregnancy may occur within the ovary (3.2%), or within the peritoneal cavity (1.3%). Ectopic cervical pregnancy is more commonly found in pregnancies achieved through in vitro fertilization technologies (Ushakov et al. 1997). The major cause of ectopic pregnancy is disruption of normal tubal patency due to infection, surgery, müllerian anomalies, or tumors. The rise of ectopic pregnancies in the last decade is

Fig. 13  Hematosalpinx in ectopic tubal pregnancy. Transaxial T2WI (a) and contrast-enhanced T1WI with fat saturation (FS) (b). In a 27-year-old woman with a positive pregnancy test, a cystic adnexal mass (asterisk) displaces the uterus. There is widening of the endometrial cavity. The adnexal lesion is separated from the adjacent

left ovary (arrow) and displays inhomogeneous signal intensity with areas of high and low SI on T2WI (a) indicative of hemorrhage. The cystic content of the fallopian tube and distinct homogenous tubal wall enhancement is demonstrated following contrast media administration (b). Courtesy of Dr. Teresa Margarida Cunha, Lisbon

associated with the increased incidence of pelvic inflammatory disease. A history of PID with chronic salpingitis is found in 35–50% of patients with ectopic pregnancy.

2.6.1\ Imaging Findings

On MRI, tubal wall enhancement and fresh tubal hematoma are highly specific for ectopic tubal pregnancy (Kataoka et al. 1999) (Fig. 13). The gestational sac is a cystic, centrally fluid-filled structure that is surrounded by a thick-walled peripheral rim. The latter displays inhomogeneous signal intensity on T2WI and medium signal intensity on T1WI, which may contain small areas of high signal intensity suggestive of blood (Nishino et al. 2002). When such a gestational sac-like structure is found separate from the uterus without tubal structures, this finding is equivocal due to the differential diagnostic problems of cystic ovarian masses (Kataoka et al. 1999). Identification of the uterine junctional zone between the gestational sac surrounded by myometrium and the uterine cavity is highly ­suggestive of a rare type of ectopic pregnancy, interstitial pregnancy (Filhastre et al. 2005). In

suspected ectopic pregnancy, the combination of an adnexal mass and acute intraperitoneal hemorrhage is suggestive of tubal rupture.

2.6.2\ Differential Diagnosis

In women of reproductive age presenting with elevated human chorionic gonadotropin levels, demonstration of a gestational sac-like structure is highly suggestive of ectopic pregnancy. However, ovarian cancer may rarely be detected during early pregnancy and be misdiagnosed as ectopic pregnancy (Riley et al. 1996). Based on the MRI findings alone, ectopic pregnancy may be misdiagnosed as an ovarian mass, e.g., ovarian cancer or endometriosis. Interstitial ectopic pregnancy may resemble cystic adenomyomas or necrotic leiomyomas (Filhastre et al. 2005).

2.6.3\ Value of Imaging

The diagnosis of ectopic pregnancy is usually established by the combination of the clinical history, β-HCG levels, and transvaginal sonography. The role of MRI has not been defined. It may, however, provide additional information in the case of equivocal ultrasound,