Interstitial ectopic pregnancy, also known as intramural ectopic pregnancy, is an important type of ectopic pregnancy with higher risks of rupture and hemorrhage compared to usual tubal ectopic pregnancies.
The term interstitial pregnancy is sometimes interchangeably used with cornual pregnancy, but the latter 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 and is the most common 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. Hence the risk and severity of hemorrhage are higher.
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 visualization 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 eccentric to the junctional zone.
Treatment and prognosis
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 embolization (UAE), cornuectomy or hysterectomy. The latter two are usually reserved for emergency situations or in case of failure of the other methods.
- uterine myometrial rupture: tends to occur by the 2nd trimester 5
- greater tendency for massive hemorrhage (as above)
For an eccentric gestational sac on imaging, consider the article on the differential diagnosis of an eccentric gestational sac or angular pregnancy.
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- 5. Akrivis Ch, Varras M, Kyparos J et-al. Early ultrasonographic diagnosis of unruptured interstitial pregnancy: a case report and review of the literature. Clin Exp Obstet Gynecol. 2003;30 (1): 60-4. - Pubmed citation
- 6. Lin EP, Bhatt S, Dogra VS. Diagnostic clues to ectopic pregnancy. Radiographics. 2008;28 (6): 1661-71. doi:10.1148/rg.286085506 - Pubmed citation
- 7. interstitial pregnancy. Am. J. Obstet. Gynecol. 2010;202 (1): 15-29. doi:10.1016/j.ajog.2009.07.054 - Pubmed citation
- 8. Walid MS, Heaton RL. Diagnosis and laparoscopic treatment of cornual ectopic pregnancy. Ger Med Sci. 2010;8 doi:10.3205/000105 - Free text at pubmed - Pubmed citation
- 9. Chukus A, Tirada N, Restrepo R et-al. Uncommon Implantation Sites of Ectopic Pregnancy: Thinking beyond the Complex Adnexal Mass. Radiographics. 2015;35 (3): 946-59. doi:10.1148/rg.2015140202 - Pubmed citation
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First trimester of pregnancy
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failed early pregnancy
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