This type of anomaly occurs in about 10 % of cases [3, 13], and encompasses all types of unilaterally formed uterus (formly “unicornuate” uterus) [10]. There is an asymmetric failure of development of one of the Müllerian ducts, with the formation of an elongated uterus uterine horn, generally shifted to one side of the pelvis, which communicates with a normal vaginal canal. MR imaging typically shows a “banana”-shaped uterus in one side of the pelvis, with or without an associated rudimentary horn (Fig. 8.5) [7, 13]. In about 65 % of cases, there is an associated rudimentary horn which may contain functional endometrial tissue or not. The cavity of the rudimentary horn can communicate with the contralateral endometrial cavity in about 10 % of cases [3]. The diagnosis is usually made incidentally during the investigation of infertility. If a rudimentary functioning, non-communicating horn is present, there is retrograde menstrual flow and the diagnosis usually occurs at menarche with the clinical picture of dysmenorrhea and hematometrium [13, 14]. If functional endometrium is present within a non-communicating rudimentary horn, MR will show a distented uterine remnant filled with hemorrhagic material consistent with hematometra (Fig. 8.6). These patients have a greater risk of developing endometriosis, ectopic pregnancies, and obstetric complications [13, 14]. In about 40 % of the cases, associated renal anomalies occur, the most common of which is renal agenesis [14], ipsilateral to the rudimentary horn [11].

In this anomaly there is complete failure of fusion of the Mullerian ducts, with formation of two separate uteri with distinct endometrial cavities and cervices, which characterizes the complete bicorporeal uterus (ESHRE/ESGE U3b/C2), the formerly “Didelphys uterus” [10]. In 75 % of cases, there is a complete or partial longitudinal vaginal septum associated. The presence of vaginal septum may lead to the development of hematometrocolpos, increasing the risk of endometriosis [13, 14]. In patients with transverse vaginal septum and obstruction of one hemi-vagina, the association with ipsilateral renal agenesis is very common [13, 15]. When there is no vaginal obstruction, the patient is usually asymptomatic. If there is obstruction, the diagnosis is often made at menarche, with cyclic pelvic pain and enlarging abdominal girth. On speculum examination, a blocked hemivagina can be identified. MRI shows two separate uteri with normal endometrial-myometrial interface and preserved zonal anatomy (Fig. 8.7). The diagnosis of longitudinal vaginal septa is easily made with the use of vaginal gel or when there is an obstructed hemivagina distended by hematocolpos (Figs. 8.8 and 8.9).

In this anomaly, there is incomplete fusion of the Mullerian ducts, forming two symmetrical horns, which merge caudally usually in the isthmus, forming a bicorporeal uterus with normal cervix (ESHRE/ESGE U3), the formerly “Bicornuate” uterus. The bicorporeal uterus may be partial (class U3a) or complete (class U3b), depending on the degree of separation of the uterine corpus by the external fundal indentation [10]. It occurs in approximately 10 % of cases [12, 13]. Both uterine horns are divergent (intercornual distance greater than 4.0 cm) and there is a deep cleft between the horns (exceeding 50 % of the uterine wall thickness) (10). Patients are usually asymptomatic; however, there is a high rate of associated obstetric complications [3, 12]. MR demonstrates noninvasively the outer contour of the uterine fundus, with two divergent uterine horns, and a large fundal indentation (exceeding 50 % of the uterine wall thickness) between them (Fig. 8.10). The zonal anatomy is preserved in both horns. Associated pathologies such as leiomyoma and adenomyosis are also easily identified. In a bicornuate-bicoli uterus there is some communication between the horns, unlike didelphic uterus where the uteri are completely separate.