Mature Cystic Teratoma Mimics Heterotopic Pregnancy on Sonograph

Mature cystic teratomas (MCTs) present clinically with a wide host of different symptomatic manifestations. Because they are often comprised of multiple tissue types, imaging can also take on many different forms making the diagnosis of MCT difficult in certain situations. In this case, we present a patient who had a MCT that mimicked a heterotopic pregnancy on sonograph.

A 21-year-old female G1P0 at approximately six weeks gestation by last menstrual period presented to the emergency department with a chief complaint of vaginal bleeding that began the previous day. A transvaginal ultrasound demonstrated a viable intrauterine pregnancy with fetal cardiac activity and an additional structure in the left adnexa resembling a gestational sac and fetal pole absent of cardiac activity. Obstetrics was consulted, and a preliminary diagnosis of heterotopic pregnancy was made. Diagnostic laparoscopy with intraoperative ultrasound revealed a 3 cm cyst in the left ovary that appeared to contain serous fluid. Aspiration and subsequent dissection of the cyst revealed material consistent with a mature cystic teratoma confirmed by pathologic analysis.

This case highlights the importance of ultrasound in detecting adnexal masses while also exposing some of its limitations. Due to their variable presentation and potential to mimic other insidious pathologies, MCTs must always be considered when identifying adnexal structures on ultrasound.