Sonographic Mimic of Ovarian Ectopic Pregnancy by Point-of-Care Ultrasound.

A 34-year-old woman presented to the emergency department following a low-energy mechanism motor vehicle collision for which she was the restrained driver. Her primary complaint was mild diffuse lower abdominal discomfort. Her past medical history was unremarkable and she was not on any systemic anticoagulation. On physical examination, she was noted to be tachycardic on arrival with some tenderness to palpation in the suprapubic region of the abdomen. The FAST examination was conducted as part of her secondary survey. In the suprapubic window, free fluid was demonstrated in the pelvis. An incidental cystic lesion was identified within the left ovary (Figure 1 ). The patient endorsed having no menstrual period for many months since she last gave birth and denied any contraceptive use in the interim. A subsequent endovaginal ultrasound exam was performed by the emergency physician while awaiting urine hCG results to evaluate for clinical suspicion of ruptured ovarian EP. The endovaginal ultrasound characterized small free pelvic fluid in the pouch of Douglas with trace fluid anterior to the uterus (Figure 2 ) and fluid in the left adnexa adjacent to the ovary (Figure 3 ). Within the left ovary, an anechoic cyst within a cyst was visualized. This was initially suspected to represent a yolk sac within a gestational sac by the emergency medicine physician. However, urine hCG and quantitative serum hCG were undetectable. The remainder of her diagnostic evaluation was unremarkable. There were no identified traumatic injuries requiring intervention. The patient was ultimately discharged home from the ED in good condition.

Ectopic pregnancy (EP) is defined as the extra-uterine implantation of a fertilized embryo and occurs in up to 1.4-2% of all natural conceptions [ 1 ]. However, the incidence may be as high as 7.5% in the population of all women presenting to United States emergency departments with a positive pregnancy test [ 2 ]. Risk factors for EP include prior infections such as pelvic inflammatory disease, previous EP, endometriosis, and previous abdominal or pelvic surgeries. While the vast majority of EPs occur in the fallopian tubes, up to 3.2% have been observed in an ovarian location [ 3 ]. Ovarian EP can be particularly challenging as patients with rupture are much more likely to present in hemodynamic shock at the time of diagnosis, experience larger volume intraoperative blood loss, and require prolonged hospitalization [ 4 ]. Although a high index of suspicion and prompt evaluation can reduce poor outcomes, a lack of definitive management can lead to devastating results. Up to 9% of all maternal deaths are due to EP [ 5 ].

The sonographic mimic of EP detailed in the figures above represents a mature Graafian (tertiary) follicle. The mature ovarian follicle appears in the pre-ovulatory phase, just prior to oocyte expulsion from the follicle. The follicle was mistaken for an intraovarian gestational sac and the cumulus oophorus was mistaken for a yolk sac. These factors misled the emergency medicine physician to the incorrect postulation of primary ovarian EP. As quantitative serum beta-hCG was undetectable, the diagnosis of EP was subsequently excluded. Primary ovarian EP is an exceedingly rare phenomenon, representing up to 3.2% of all EPs [ 3 ]. There are sonographic features that can help distinguish a true EP from a normal ovarian follicle. The border of the ovarian cyst in this patient is thin-walled. In addition, the cumulus oophorus, which is a layer of thickened zona granulosa cells, will always be located on the periphery of the mature follicle. The appearance of a true gestational sac, by comparison, is that of a wide hyperechoic wall surrounding an internal anechoic space [ 6 ]. An example showing the typical appearance of a true gestational sac (from a different patient) is shown in Figure 4 . Oftentimes, the ovarian EP will appear like a complex and heterogeneous cystic structure and cannot be differentiated from a hemorrhagic ovarian cyst on ultrasound [ 7 - 8 ]. Rarely, fetal tissue or cardiac activity may be visualized in an ovarian EP [ 2 ]. Other signs that should raise suspicion for a true EP include large volume or heterogeneous free fluid. White arrows: bound gestational sac with thick hyperechoic walls. Red arrow: yolk sac. Asterisk: incidental small subchorionic hemorrhage. The FAST examination has become the standard of care in the evaluation of patients with blunt abdominal trauma and has excellent test characteristics for the detection of free peritoneal fluid including a sensitivity between 73% and 88%, specificity between 98% and 100%, and accuracy of 96-98% [ 9 ]. However, the observation of free pelvic fluid in women of reproductive age should be interpreted in the appropriate clinical context and correlated with other physical findings and index of suspicion. Physiologic free fluid may be observed commonly in the posterior cul-de-sac on ultrasound as a normal finding, independent of trauma or other pathological processes [ 10 ].

Physiologic-free pelvic fluid is commonly observed in women of ovulatory age and is seldom of clinical consequence. Ovarian EP is rare but is more likely to present with hemorrhagic shock and worsened clinical outcomes. An astute emergency medicine provider should retain a high index of suspicion for conditions including blunt abdominal trauma and ruptured EP, as they represent pathologies associated with high morbidity and mortality. However, patients must also be evaluated in the appropriate clinical context, with careful consideration given to sonographic mimics and incidental findings that may inappropriately guide therapy.