Sudden Onset Pelvic pain Discussion
Sudden onset pelvic pain in a female has a wide differential from ovarian to intestinal,
Using US to help with diagnosis, the first thing to determine is the presence or absence of free fluid. US evidence of free fluid increases the risk of patient instability and increases the urgency of definitive management.
In the pregnant female, the presumptive diagnosis is a ruptured ectopic. However, there are several other possible causes such as a ruptured CL or ovarian cyst, ovarian torsion or appendicitis. So the next step is to see whether a viable pregnancy is seen in the uterus. Presence of a gestational sac with an embryo decreases the risk of ectopic pregnancy. However, keep in mind that 1/10,000 - 1/30,000 (1) could have a heterotopic pregnancy (ie intrauterine + ectopic).
In a non pregnant female, the DDx includes appendicitis, ruptured ovarian cyst and ovarian torsion.
The two main diagnoses you don't ever want to miss are: ovarian torsion and ruptured ectopic pregnancy.
OVARIAN TORSION:
The key features of the torted ovary on US are:
1. enlarged >5cm with a heterogenous echotexture, peripherally located follicles (because they have been squeezed out to the periphery due to stromal oedema)
2. absent venous flow
3. Absent diastolic arterial flow
4. Absent systolic arterial flow
However, flow may still be present in the torted ovary. The only two consistent features are an enlarged ovary and sudden onset severe pelvic pain.
normal low resistance flow showing flow in diastole and systole
high resistance arterial flow showing flow only during systole
ECTOPIC
An ectopic pregnancy may not be seen on transabdominal US. If seen, it is usually a heterogenous or cystic adnexal mass with vascularity. It is usually seperate from the ovary. A corpus luteum can sometimes look like an ectopic (2). Similarly a peripherally located intrauterine pregnancy near the cornua may look like an ectopic (3).
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REFERENCES
1. Reece E.A. Petrie R.H, Sirmans M.F., Finster M., Todd W.D.Combined intrauterine and extrauterine gestations: a review.Am J Obstet Gynecol. 1983; 146: 323-330
2. Yun JH, Horrow MM, Goykhman I, Rodgers SK. The Confounding Ultrasound Diagnosis of Ectopic Pregnancy: Lessons From Peer Learning. Ultrasound Q. 2022 Dec 1;38(4):272-283.
3. Jurkovic D, Mavrelos D. Catch me if you scan: ultrasound diagnosis of ectopic pregnancy. Ultrasound Obstet Gynecol. 2007 Jul;30(1):1-7.