Interstitial ectopic pregnancy

Interstitial ectopic pregnancy (also known as an intramural) is an important type of ectopic pregnancy with higher risks of rupture and haemorrhage compared to usual tubal ectopic pregnancies. 

The term interstitial pregnancy is sometimes interchangeably used with cornual pregnancy, but the later specifically refers to the presence of a gestational sac within a rudimentary uterine horn, a unicornuate uterus, cornua of a bicornuate uterus or septate uterus. 

It accounts for 2-4% of all ectopics (commonest site for an atypical ectopic pregnancy). The incidence is thought to be rising 7.

It occurs within the interstitial portion of the fallopian tube and therefore has the potential to grow to larger sizes than standard tubal ectopic pregnancies by the time of presentation.

The main risk factor is a history of prior intrauterine instrumentation.

Sonographic features include:

  • interstitial line sign 2
    • an echogenic line from the mass to the endometrial echo complex reportedly has high sensitivity (80%) and specificity (98%)
  • may show an eccentric gestational sac
    • the diagnosis is suggested by visualisation of an intrauterine gestational sac or decidual reaction located high in the fundus, with <5 mm of surrounding myometrium in all planes ("myometrial mantle")

3D ultrasound may be helpful for delineating a gestational sac's location.

  • gestational sac is eccentric to the junctional zone

The morbidity and mortality are higher (15x) due to a later presentation and associated complications. 

Management of an interstitial ectopic includes the use of methotrexate (either systemic or local), potassium chloride (KCl) injection, conservative laparoscopic surgery, uterine artery embolisation, cornuectomy or hysterectomy. The latter two are usually reserved for emergency situations or in case of failure of the other methods.

For an eccentric gestational sac on imaging, consider the article on differential diagnosis of an eccentric gestational sac.

Ultrasound - obstetric
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Article information

rID: 1510
Section: Pathology
Synonyms or Alternate Spellings:
  • Interstitial ectopic
  • Angular ectopic pregnancy
  • Interstitial pregnancy

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