Systemic methotrexate treatment of interstitial pregnancy--magnetic resonance imaging (MRI) as a valuable tool for monitoring treatment.

OBJECTIVE

Interstitial pregnancy occurs in 2-4% of ectopic pregnancies and is defined as implantation of the trophoblast in the interstitial part of the tuba uterina. Therefore the term intramural pregnancy can also be found in the literature. In 20% of the cases that progress beyond 12 weeks of amenorrhea a potentially life-threatening rupture of the uterus occurs, leading to a maternal mortality rate of 2.5%. According to the literature until a few years ago diagnosis was mainly made intraoperatively, and resulted in cornual resection or hysterectomy per laparotomy. Better methods of diagnosis and treatment of interstitial pregnancy can help to decrease morbidity and mortality associated with this condition.

PATIENTS

We describe two cases of interstitial pregnancies that were eventually diagnosed and also monitored by magnetic resonance imaging (MRI) after systemic methotrexate treatment. Both patients were uniparous and experienced their second spontaneous pregnancy.

METHODS

Treatment consisted of four doses (50 mg/m2 body surface area) of systemic intramuscular methotrexate alternating with four doses (6 mg) of intramuscular folic acid. When beta-hCG levels were undetectable, MRI results were compared with pre-therapeutic MRI findings.

RESULTS

In patients A and B, beta-hCG levels were undetectable 64 and 88 days after initiation of methotrexate treatment, while magnetic resonance imaging revealed nearly equally persisting interstitial pregnancies. They initially presented as hyperintense lesions with hypointense zones and changed into a hypointense lesion with a central hyperintense area for patient A, and a completely hyperintense lesion for patient B at the time of negative beta-hCG levels in follow-up MRI.

CONCLUSION

Systemic methotrexate treatment with an intramuscular regimen is effective in the treatment of interstitial pregnancy. MRI has the ability of correct tissue differentiation and objective three-dimensional measuring of interstitial pregnancy. We therefore propose this imaging modality as a valuable tool for monitoring systemic methotrexate treatment of interstitial pregnancy that should be used additionally to beta-hCG clearance curves.