Welcome to another ultrasound-based case, part of the “Ultrasound For The Win!” (#US4TW) Case Series. In this peer-reviewed case series, we focus on real clinical cases where bedside ultrasound changed management or aided in diagnoses. In this case, a 38-year-old pregnant woman presents with acute right-sided abdominal pain radiating to her flank.

Case Presentation

A 38-year-old G3P2 woman presents to your ED with right sided abdominal pain with acute worsening of pain. She denies a prior history of similar symptoms. Pain is located on the right lower quadrant radiating to the right flank. She denies dysuria, hematuria, vaginal discharge, or bleeding. She tells you that her last menstrual period was about six weeks ago, and had a recent positive home pregnancy test. She has not yet had an obstetrics visit for this pregnancy. On physical exam she appears diaphoretic, writhing in pain, and dry heaving. Her abdomen is soft, with exquisite tenderness to palpation on the right lower quadrant and suprapubic region with no palpable masses. There are no overt peritoneal findings on your examination.

Vitals

Differential Diagnosis

• Appendicitis
• Ectopic pregnancy
• Nephrolithiasis
• Ovarian cyst
• Ovarian torsion
• Tubo-ovarian abscess

The wide differential diagnosis of acute severe lower abdominal pain in a pregnant patient provides a difficult predicament for the emergency physician. The diagnostic imaging modality of choice (e.g. computed tomography (CT), magnetic resonance imaging (MRI), or ultrasound) vastly differs depending on which diagnosis is most suspected. The added complication of a first-trimester pregnancy and risks with radiation also affects which studies should be performed.

Fortunately, the emergency physician was able to perform point-of-care ultrasound at the patient’s bedside to help rule out several of the most likely diagnoses.

Point-of-care Ultrasound

Figure 1. Visualized intrauterine yolk sac consistent with intrauterine pregnancy, ruling out ectopic pregnancy

Figure 2. Yolk sac (arrow) appears as a “cheerio” within a gestational sac (G) within the uterus (U)

Figure 3. Right kidney with no evidence of hydronephrosis, making renal colic unlikely

Figure 4. Enlarged right ovary with cystic structures

Figure 5. Color Doppler revealing absence of flow within the ovary and flow peripherally

Figure 6. Free fluid in Morison’s Pouch, presumably from a ruptured hemorrhagic ovarian cyst

Figure 7. Free fluid (arrow) in Morison’s Pouch, between the liver (L) and kidney (K)

The images obtained on the point-of-care ultrasound was able to significantly narrow down the differential diagnosis within minutes, allowing for the ordering of the appropriate radiological studies and consultation for definitive management.

Based on the concerning findings on bedside ultrasound together with the clinical suspicion for ovarian torsion, gynecology was emergently consulted and a radiology-performed comprehensive ultrasound was ordered.

Ultrasound Image Quality Assurance (QA)

When assessing for ovarian pathology, the use of transvaginal ultrasound is typically required in order to fully evaluate the uterus and adnexae. In this case, however, the right ovary was so enlarged that it could be easily seen transabdominally.

Pelvic ultrasonography for first-trimester pregnancy is considered a core emergency ultrasound application by the American College of Emergency Physicians (ACEP). Ectopic pregnancy should be considered in every woman who presents with abdominal pain or vaginal bleeding with a positive pregnancy test. Emergency physicians can confirm an intrauterine pregnancy (IUP) with 100% specificity when using the criteria of the appearance of a yolk sac, which appears as a “cheerio” (Figure 2), or fetal pole within a gestational sac.^1,2 With a confirmed IUP, the risk of a combined (i.e. heterotopic) pregnancy is extremely rare, with an estimated incidence of 1:4,000-1:8,000³, and can essentially be ruled out. A caveat to this is the patient who is undergoing assisted reproductive technology (ART) which increases the incidence of heterotopic pregnancy to an estimated 1:100!³

While ultrasound is the diagnostic imaging modality of choice for ovarian torsion, the diagnosis is confirmed in the operating room. Unfortunately, the ultrasonographic findings of ovarian torsion are variable, representing the spectrum of disease that encompasses torsion. An enlarged (typically greater than 2×3 cm) or cystic ovary with multiple peripheral follicles has been described.⁴ The use of Color Doppler can be helpful in supporting the diagnosis of ovarian torsion; the absence of flow within the ovary is highly suggestive of ovarian torsion. The added, albeit more advanced, use of Spectral Doppler can additionally distinguish between venous and arterial waveforms, and can be used to calculate a Resistive Index*. Torsion is highly unlikely if venous flow is present (PPV 94%).⁵ While venous flow to the ovary is the first to be affected, arterial flow, especially peripherally, can still be present⁵, as was seen in the images in this patient (Figure 8). However, it is important to note that the use of Color Doppler alone cannot be used to rule out torsion.⁶

Figure 8. Spectral (Pulsed Wave) Doppler reveals arterial flow peripherally with increased resistive index

For further discussion on Color Doppler, Spectral Doppler, and Resistive Index, hydronephrosis in evaluation of nephrolithiasis, and free fluid on a FAST, please see prior Ultrasound for the Win! Cases.

Disposition and Case Conclusion

The radiology-performed ultrasound report:

Single live intrauterine pregnancy with an approximate gestational age of 6 weeks 5 days. Right ovary is enlarged, with multiple cysts, with mild high resistance peripheral flow. Patient was exquisitely tender over the right ovary. Appearances are concerning for torsion/detorsion. Clinical correlation is recommended. Left ovary is unremarkable.

Given the prompt consultation, the gynecology team met the patient while she was obtaining her comprehensive ultrasound. The patient was consented and taken emergently to the OR, where right ovarian torsion (twisted 720 degrees) was confirmed, with 200 cc of hemoperitoneum from a ruptured hemorrhagic cyst. The ovary was successfully salvaged, and she remains pregnant with no complications.

Ovarian torsion is a rare but serious surgical emergency that is difficult to diagnose. It is the fifth most common gynecologic emergency with a prevalence of 2.7%.⁶ Ovarian torsion is a spectrum of disease that involves twisting of the ovary at its pedicle. Risk factors for torsion are listed in Table 1.

The clinical presentation of ovarian torsion is variable and non-specific, but classically involves a sudden-onset of sharp or stabbing unilateral lower quadrant pain with nausea or vomiting.⁷ Unfortunately, as these non-specific symptoms overlap with other acute pathologic processes such as renal colic, it is often misdiagnosed. A 15-year review of confirmed cases of ovarian torsion showed high rates of initial misdiagnoses, with torsion considered in less than half of all cases. It is important to maintain a high level of clinical suspicion of torsion, as a timely diagnosis and surgical consultation is necessary to maximize the likelihood of salvaging the ovary. The estimated ovarian salvage rates remain low (>10%).⁷

The most common abnormality seen is an enlarged ovary with or without cysts, which act as a fulcrum from which the ovary can twist at its pedicle. A torsed ovary begins with compromise of venous and lymphatic drainage, leading to an edematous and enlarged ovary. As the disease progresses, arterial flow may be compromised. However, given the dual blood supply to the ovaries (from the ovarian and uterine arteries), it is not uncommon to see arterial flow especially in the periphery, with absence of flow within the ovary itself in cases of ovarian torsion.

Given the non-specific presentation and rare prevalence of ovarian torsion, the use of computed tomography (CT) is often used to rule out other acute disease processes when the clinical picture is unclear. A 20-year retrospective review by Moore et al. sought to determine if CT could be used to rule out ovarian torsion. They found that all surgically-confirmed cases of ovarian torsion in the study revealed an abnormal ovary (i.e. enlarged, ovarian cyst, or adnexal mass) on CT.⁸ It was concluded that a CT with normal, well-visualized ovaries is sufficient to rule out torsion.⁸ However, despite this, if the clinical suspicion is high for ovarian torsion, and bedside ultrasound can be used to expediently rule out other acute pathologies (e.g. renal colic, ectopic pregnancy), a radiology-performed comprehensive ultrasound still remains the diagnostic study of choice.

Ovarian torsion is a rare surgical emergency that is often misdiagnosed and presents with non-specific symptoms that overlap with other acute pathologic diseases. The ability to quickly diagnose the condition and obtain prompt surgical consultation is necessary to maximize ovarian salvage rates.

Take Home Points

1. Ovarian torsion is a rare surgical emergency that presents with non-specific symptoms and requires early diagnosis and surgical consultation to maximize the chance of salvaging the ovary.
2. Ultrasonographic findings of ovarian torsion include an enlarged (greater than 2×3 cm) or cystic ovary, absence of Color Doppler flow, or lack of venous flow with Spectral Doppler.
3. Point-of-care ultrasound can be used to rule out other acute conditions that present similarly, thus narrowing down your differential diagnosis.
4. While not considered the imaging modality of choice, CT can be used to essentially rule out ovarian torsion, if unremarkable, well-visualized ovaries are seen.⁸

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