Identifying the ligaments on imaging

The broad ligament and the mesovarium are usually not discernable by cross-sectional imaging unless they are surrounded by large amounts of ascites. Their position, however, can be identified by the structures they contain (Foshager and Walsh 1994). In ascites, the ovaries can be seen suspended from the posterior surface of the broad ligament (Fig. 9) (Saksouk and Johnson 2004). The ovarian ligament may occasionally be visualized as a short and narrow soft tissue band extending between the uterus and the ovary.

In the retroperitoneum, at the level of the inferior renal pole, the ovarian artery and vein can be identified along the psoas muscle medial to the ureter (Fig. 10) (Karaosmanoglu et al. 2009). The ovarian artery is located medial to the vein and due to its smaller size is less constantly conspicuous on CT or MRI. They cross obliquely anterior the ureter at the middle to the lower lumbar region and are then located laterally to the ureter in the lower abdomen and pelvis (Figs. 10 and 11).

Tracking these vessels continuously downwards from the retroperitoneum to the pelvis leads to the suspensory ovarian ligament (Fig. 6) (Lee et al. 2003). The latter is an excellent landmark for localizing the ovary. It is a short and narrow fan-shaped soft tissue band that widens as it approaches the ovary. Sometimes it can also be identified as a linear band that is thicker than the

a

ovarian vein. Due to its vascular landmarks, it is more commonly identifiable than the other ovarian ligaments (Saksouk and Johnson 2004). This ovarian vascular pedicle sign serves also as a useful imaging sign to differentiate between pelvic masses of ovarian from those of uterine origin.

2\ Developmental Anomalies

Developmental anomalies of the ovaries are very rare. Although ovaries have a different developmental origin from uterus and fallopian tubes, ovarian anomalies are significantly more often associated with congenital uterine anomalies (22%), particularly with unicornuate uterus (Dabirash et al. 1994). Uterus and fallopian tubes develop from the paramesonephric ducts. Defects of the paramesonephric tubes result not only in abnormalities of the uterus but also of the fallopian tubes, kidneys, and ureters.

In utero the primordial ovaries are located on the medial surface of the urogenital ridge on each side of the lower thoracic and upper lumbar spine, inside the Wolffian body. The ovaries descend during the 3rd month of fetal life with the ovaries located at the level of the iliac crest by the 3rd month of life. They take their place in the ovarian fossa at the end of the first year of life (Stevens 1992). Ovarian migration is guided by

b

Fig. 9  Broad ligament and ovary in CT. In a patient with free fluid, the ovaries (*) can be visualized posterolaterally of the broad ligament. The left round ligament (small arrow) is visualized at the anterior aspect of the broad ligament and courses anterolaterally towards the

internal inguinal canal (a). At the lateral free margin of the broad ligament, the suspensory ligament attaches to the anterior margin of the left ovary. It transmits the ovarian artery and vein (long arrow) and is contiguous to the mesovarium (a, b)

Fig. 10  Ovarian vessels in the retroperitoneum and suspensory ligament “ovarian vascular pedicle.” CT scans at level below the renal hilum (a) aortic bifurcation (b), upper pelvis (c), and mid pelvis (d). Ovarian artery and vein (arrow) course along the psoas muscle parallel to the ureter (long arrow) (a). At the lower lumbar region, they cross obliquely (arrow) and are visualized lateral to the

ureter (long arrow). The ovarian vessels (arrow) are continuous with the suspensory ligament, which is identified near the external iliac vessels (c). It demonstrates a wedging as it approaches the ovary. The latter can be identified by multiple small cystic follicles (d). Follicle cyst in the right ovary (*). U uterus

the gubernaculum which connects the lower pole of the gonad and attaches to the uterus, forming the ovarian and round ligaments of the uterus (Trinidad et al. 2004).

2.1\ Congenital Abnormalities

In phenotypic females, absence of both ovaries is usually associated with abnormal karyotypes and a syndrome of gonadal dysgenesis. These patients may have underdeveloped gonads, or unior bilateral streak gonads (Fig. 12), which carry a risk of malignancy (Clement 2002). Congenital

unilateral agenesis of an ovary in a normal female is extremely rare and usually asymptomatic. It presents more likely the result of torsion with atrophy, particularly in the prenatal period. It may be accompanied by ipsilateral renal or ureteric agenesis and/or malformation of the ipsilateral fallopian tube (Dueck et al. 2001).

Accessory or supernumerary ovaries are extremely rare, and may also be associated with other congenital genitourinary abnormalities. An accessory ovary contains ovarian tissue and is usually located in vicinity of a normal ovary (Clement 2002). Supernumerary ovaries are not attached to the ovary, but may be found at various sites within and outside

Fig. 11  Ovarian veins. Coronal CT demonstrates the ovarian veins. The left ovarian vein (arrow) can be tracked from the left ovary to the retroperitoneum

the pelvis. In most cases, they are smaller than 1 cm in size (Hahn-Pedersen and Larsen 1984). The ectopic ovarian tissue possesses the functional as well as the pathological potential of normal ovaries and may give rise to primary carcinoma of the peritoneum (Seidman et al. 2002).

Adrenal cortical rests may be observed within the wall of the fallopian tubes and broad ligament.

Congenital abnormalities of the fallopian tubes are also extremely rare. As in the ovaries, they result more likely from torsion or an inflammatory process. Isolated congenital abnormalities include aplasia, duplication, accessory ostia, and congenital diverticula of the fallopian tubes (Rezvani and Shaabab 2011). Tubes may also be partially atretic or hypoplastic and these may be

associated with uterine abnormalities such as rudimentary uterine horn or bicornuate uterus. Offspring of women exposed to diethylstilbestrol may suffer from infertility due to tubal anomalies including short sacculated or dilated fallopian tubes (Nunley et al. 1984).

2.2\ Ovarian Maldescent

Ovarian maldescent has an incidence of 0.2– 0.5% (Allen et al. 2012). It may be unior bilateral and is more common in Müllerian malformations (17%), with the highest association with didelphis and unior bicornuate uterus, and hypoplastic uterus (Allen et al. 2012). In ovarian maldescent, ovaries may be found in an ectopic position along its migration pathway from the lumbar region to the ovarian fossa. Rarely, ovaries may descend too far down until the inguinal canal (Ghattamaneni et al. 2009).

A common location of ovarian maldescent above the pelvic brim is the paracolic gutters (Fig. 13). After pregnancy, the ovaries may be hindered to return to their original position due to adhesions. Furthermore, an ectopic ovarian position may be associated with adhesions, inflammation, and surgery, or result from abnormal ovarian mobility due to elongation of the broad ligaments (Spencer et al. 2010).

Imaging findings

Identification of the upper pole of the ovary at or above the level of the iliac bifurcation defines ovarian malposition (Allen et al. 2012). In women of childbearing age, ovaries in atypical positions can be identified in the majority of patients due to the typical morphology of follicles. MRI is the preferred examination technique to diagnose maldescended or ectopic ovaries due to their excellent visualization on the T2WI (Fig. 13). An ovary not visualized in the ovarian fossa should be sought in other locations in proximity to the uterus and above the pelvic brim, rarely may it be located near the inguinal canal.