HPI: 22yo female with one day of abdominal pain. Initially cramping but worsening in severity, now characterized as sharp. Worse with standing and walking.
Physical Exam:
Abdominal- LLQ and suprapubic tenderness
UA- no infection
Wet mount- positive for yeast
Bedside US- large right adnexal mass
OB/Gyn Ultrasound (US) in the ED?
Abdominal pain in the female patient is often not straight forward, as there are a great number of mimickers that involve pathology in the uterus and adnexa. Any pain which is described as "low" or present in the back/flank should compel one to consider gynecologic etiologies. In the event where the history strongly suggests gynecologic pathology, US is the imaging of choice. Both transabdominal ultrasound (TAUS) and transvaginal ultrasound (TVUS) provide excellent resolution of lower abdominal structures. More broadly, US is a low-cost, low-risk (no radiation) alternative to other diagnostic imaging. Specifically, in an ED setting it has great utility to "rule out badness." TAUS offers an ample opportunity for bedside evaluation and rapid triage in the event of an unstable or highly undifferentiated patient.
How to perform:
The transabdominal (TAUS) portion of the Ob/gyn US exam should be undertaken with the patient in the supine position. A full bladder is preferred as it will provide better echogenic windows when completing a TAUS (the opposite is true for TVUS). Orienting the probe indicator towards the head, the provider will scan through the longitudinal plane from right to left with the probe placed just superior to the pubic symphysis. All relevant anatomy should be visualized including the uterus, Pouch of Douglas, and adnexal anatomy (ovaries included). Then the transducer is rotated into the transverse plane to obtain views of the uterus from cervix to fundus.
Make sure to capture images of relevant anatomy including ovaries, endometrial stripe, and IUP if present. A video that tracks through the entire uterus to prove the absence of IUP is helpful. Additionally, videos that sweep through an entire ovary can be useful in characterizing a cyst, if present.
US findings of ovarian pathology
Locating the ovaries can be challenging as they often reside in different locations throughout the pelvis for different individuals. You may have to do some ovary hunting. A normal ovary is likely to have a number of follicles present and often resembles a "chocolate chip cookie" as shown below. As always with US, fluid-filled structures such as follicles (<1cm), marked by arrowheads below or cysts (>1cm) will appear anechoic (black). The surrounding ovarian parenchyma is a brighter strip surrounding the follicles (arrow).
When evaluating cysts on US, both size and characterization matter. A simple cyst is defined as one that is less than 5cm in size. Simple cysts are characterized by circular/ovular border without irregularities. They should be anechoic (black) throughout, demonstrating no shadows or internal echoes that might be indicative of hemorrhage, debris, or loculations. The image below is an example of a hemorrhagic luteal cyst. Note the increased echogenicity (shadowing) within the asterisk-marked structure (luteal cyst) compared to the anechoic follicles (arrowheads).
Now let's apply those aforementioned principles to the patient in this case using the images below:
TVUS of RIGHT ADNEXA
What do you see that is abnormal? How would you characterize the abnormalities? Size? Features?
TVUS of RIGHT ADNEXA
This is a large (8.5 cm x 7 cm) complex cyst (blue), defined by its loculations (purple) and dependent debris (red).
Treatment
Any luteal cyst greater than 3cm requires gynecologic follow-up. Any complicated cyst, defined as >5cm of loculated with internal debris should be referred to gynecology for either consultation in the ER or outpatient follow-up depending on the patient's clinical status.
For example, a complicated appearing cyst in a febrile, hypotensive sexually active female may be a tubo-ovarian abscess. Similarly, if free fluid is seen in the pelvis in conjunction with a complex cyst in a hemodynamically unstable patient presenting with sudden onset abdominal pain, she may have had a ruptured ectopic pregnancy vs ruptured hemorrhagic cyst vs ovarian torsion. These scenarios require gynecologic consultation in the ER with possible disposition to the OR. In such cases, bedside US can be useful in painting a clearer clinical picture to a consultant.
In the stable female patient with abdominal pain, detection of a cyst or abnormal structure on bedside TAUS warrants further imaging with a formal TVUS for better characterization. Such a study will permit risk stratification of a cyst including simple vs complex, as well additional criteria to determine the likelihood of neoplastic pathology or malignancy. Specifically, a set of criteria known as the "Simple Rules" (see reference #1 below) are relied upon, because any one characteristic is not diagnostically predictive. These criteria take into account size, blood flow, loculations, borders, free fluid, acoustic shadowing, and presence/absence of papillary structures. While these rules are beyond the scope of practice of Emergency Physicians, they are often used by gynecology and oncology when evaluating adnexal cysts.
Additional resources:
1. https://www.ncbi.nlm.nih.gov/pubmed/26800772
3. Chapter 7 Pregnancy- Matthew Dawson and Mike Mallin. "Introduction to Bedside Ultrasound: Volume 1" Free iBook.
May Tape Review for CME
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