Ectopic Pregnancies in Unusual Locations

Thomas A Molinaro, M.D.; Kurt T Barnhart,M.D.,M.S.C.E.


Semin Reprod Med. 2007;25(2):123-130. 

In This Article

Interstitial (Cornual) Ectopic Pregnancy

The interstitial segment of the fallopian tube is the segment that lies within the muscular wall of the uterus.[35] Interstitial pregnancy accounts for up to 1 to 3% of all ectopic pregnancies.[36,37] The term cornual pregnancy is used interchangeably in the United States as a synonym for interstitial pregnancies. However, it refers to a pregnancy in the interstitial segment of a unicornuate or bicornuate uterus.[35] As the pregnancy grows in the area of the fallopian tube that enters the uterus, surrounding myometrial tissue allows for further development of the pregnancy into the second trimester. Rupture of such an advanced gestation may result in catastrophic hemorrhage, with a mortality rate of up to 2%.[35,38,39] Diagnosis of interstitial pregnancies relies heavily on ultrasound and potentially on laparoscopic evaluation.[40] Ultrasound frequently shows a thin rim of myometrial tissue surrounding the ectopic pregnancy sac.[41] The interstitial line has been described as an echogenic line extending into the corneal region and abuting the gestational sac, and is highly specific for interstitial pregnancy.[39] Risk factors for development of interstitial pregnancy include previous ectopic pregnancy, previous salpingectomy, uterine anomalies, ipsilateral salpingectomy, IVF, ovulation induction, and sexually transmitted infections.[35,39]

The traditional treatment of interstitial pregnancy has been corneal resection or hysterectomy in the cases with severely damaged uteri.[40] These surgical treatments have required laparotomy. However, there are successful case reports of laparoscopic resection of corneal pregnancies.[42,43,44] In a survey of 32 cases of interstitial pregnancy, nine required laparotomy for uterine rupture and hemoperitoneum.[35] Laparoscopic resection may be assisted by direct injection of vasoconstrictive agents such as vasopressin.[39,44] In addition, Katz et al[40] and Meyer et al[45] reported hysteroscopic resection of interstitial pregnancies under laparoscopic visualization and ultrasound guidance, respectively, with success in three patients. Zhang et al[46] have also reported two successful hysteroscopic cases.

Although surgical management of interstitial pregnancy has remained most common, methotrexate has been used as first-line treatment. In an analysis of 13 case series of a total of 47 total cases treated with methotrexate, Fisch et al[47] concluded that methotrexate is a safe option. However, there are reports of high failure rates, and there is a need for proper patient selection and extended monitoring. Because of the later presentation of these pregnancies, interstitial pregnancies are often associated which high serum β-hCG levels and the presence of fetal cardiac activity. There is no consensus on the dose or number of methotrexate injections that should be used in the treatment of interstitial pregnancies. There are reports of successful treatment with single-dose methotrexate injection; however, there are also reports of failures.[37,48] It has been theorized that interstitial pregnancies are less susceptible to methotrexate because of their increased blood supply, although size of the gestation may also be a factor. It has been recorded that interstitial pregnancies with hCG levels >1000 mlU/mL should be treated with multidose methotrexate.[48]

Fisch et al[47] reported the use of local intra-amniotic methotrexate injection in combination with multiple-dose systemic methotrexate for successful conservative management of ectopic pregnancy. In a review of reported cases of interstitial pregnancy treated with all forms of methotrexate, Lau et al[39] found an overall success rate of 83% for all protocols and that local methotrexate had a three times shorter average time to resolution of serum β-hCG. Al-Kahn et al[49] report the use of intravenous methotrexate in the successful management of interstitial pregnancy. Although the most effective methotrexate protocol for conservative treatment of ectopic pregnancy is unknown, all of the above-mentioned authors agree that close monitoring (and even hospital admission) should be considered because rupture is possible even after treatment has begun.

There are reports of other novel attempts at conservative management of interstitial ectopic pregnancy. In a case of a 12-week interstitial gestation that failed systemic methotrexate, Cheng et al[50] reported success with intra-amniotic injection of etoposide, a topoisomerase II inhibitor used in the treatment of gestational trophoblastic disease. Similarly, there is a report of an interstitial pregnancy that failed a two-dose protocol of systemic methotrexate and was treated successfully with selective uterine artery embolization.[51]

In conclusion, the diagnosis of interstitial pregnancy can be quite difficult to make, requires accurate ultrasound interpretation, and may require laparoscopic evaluation. Ruptured interstitial pregnancy may present with hypovolemic shock necessitating emergent laparotomy.[52] In the stable patient, conservative measures may be attempted, including laparoscopy or medical management.[53] Future fertility is possible for interstitial pregnancy treated conservatively, although there is a concern for uterine rupture secondary to the weakened myometrial wall. This concern is both for interstitial pregnancies treated surgically or with chemotherapeutic measures.[35,51]


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