Angular pregnancy

Angular pregnancies are those in which implantation occurs eccentrically along the fundus of the endometrial cavity, along with the lateral upper angle or cornua of the uterus.

In contrast to interstitial tubal pregnancy, angular pregnancies have a more medial location and are considered an intrauterine implantation.

Terminology

The term "angular pregnancy" is sometimes used interchangeably with "cornual pregnancy". This causes some ambiguity and the latter is best reserved for a pregnancy within a congenitally-anomalous uterus, such as one of the horns of a bicornuate, or the rudimentary horn of a unicornuate uterus.

Epidemiology

It is a rare type of pregnancy, associated with high rates of spontaneous abortion, uterine rupture, and placenta accreta.

Clinical presentation

Given the intrauterine location of angular pregnancies and the enveloping myometrium, these patients are likely to present with symptoms later than patients with ectopic pregnancies.

Pathology

Angular pregnancy occurs when the blastocyst is implanted in the lateral angle of the endometrial cavity, medial to the uterotubal junction and round ligament ¹. 

In contrast, an interstitial ectopic pregnancy is located more laterally within the interstitial segment of the Fallopian tube which courses within the myometrial wall.

The distinction is important because the developing embryo ovum of an interstitial pregnancy develops in the uterine wall, whereas in angular pregnancy it develops eccentrically within the endometrial cavity and may be constrained within the cornua ¹.

Radiographic features

Ultrasound

• 3D ultrasound can be helpful in the precise location of the sac

• pregnancy is eccentrically high in location; the gestational sac is located within the endometrial cavity at the lateral upper angle on the spectrum between normal pregnancy and interstitial cornual pregnancies

• should always have normal myometrial coverage, which is thick and usually more than 5 mm

• grows towards the endometrial cavity and requires close follow-up to document the gestational sac growing into the cavity

Treatment and prognosis

Many of these pregnancies result in live birth but have an increased complication rate.

Complications

The true complication rate not known as cases reported as angular may have actually been interstitial but complications include:

• spontaneous abortion (~40%)

• uterine rupture (~15%)

Differential Diagnosis

• interstitial ectopic pregnancy

  • located in the intramural portion of Fallopian tube

  • also eccentrically located with respect to endometrial cavity but seen separately >1 cm from the endometrial cavity

  • interstitial line sign: an echogenic line in continuity from the ectopic to the endometrial echo complex

  • covered by myometrium but thinned to <5 mm

  • can grow to a larger size than the tubal ectopic pregnancy

• cornual pregnancy

  • presents in settings of a uterine anomaly such as unicornuate, bicornuate, or septate uterus with a rudimentary horn

  • gestational sac is located medial to the Fallopian tube including the anomalous part