bHCG negative
A negative bHCG takes the stress out of the situation, however, there are rare cases where an ectopic pregnancy may have such low bHCG levels that the urine pregnancy test can be falsely negative (1).
You look at the uterus and confirm an empty uterus.
Next you look at the adnexa and find the right ovary:
An enlarged ovary with a dominant cyst increases the chances that this patient's pelvic pain is due to ovarian torsion. An ovarian mass or cyst increases the risk of torsion (3). US features of torsion are (4):
1. an enlarged heterogenous ovary >5cm with peripheral displacement of follicles
From Bottomley C, Bourne T. Diagnosis and management of ovarian cyst accidents. Best Pract Res Clin Obstet Gynaecol. 2009 Oct;23(5):711-24
2. pelvic free fluid
3. abnormal vascularity (venous flow obstructed first, then arterial flow is impairied during diastole, then absent arterial flow)
Pulsed doppler showing only systolic flow
The most consistent US feature is an enlarged ovary. The presence of vascularity does not exclude a torsion. This can only be done at laparoscopy.
Normally ovary size is measured in volume (0.52x WxLxD) but an easy measurement to remember is that it is normally about 2-4cm (5) with scattered follicles and vascularity showing a low pressure waveform (ie flow during systole AND diastole)
Normal Ovary
: from: https://radiologykey.com/the-normal-ovary-changes-in-the-menstrual-cycle/
Pulsed doppler showing systolic and diastolic flow
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REFERENCES
1. Dunphy L, Rey CA, Arshad I, Hapangama DK. Ruptured chronic ectopic pregnancy presenting with a negative urine pregnancy test. BMJ Case Rep. 2022 Aug 12;15(8):e245742.
2. Aboud E. A five-year review of ectopic pregnancy. Clin Exp Obstet Gynecol. 1997;24(3):127-9.
3. Bridwell RE, Koyfman A, Long B. High risk and low prevalence diseases: Ovarian torsion. Am J Emerg Med. 2022 Jun;56:145-150.
4. Bottomley C, Bourne T. Diagnosis and management of ovarian cyst accidents. Best Pract Res Clin Obstet Gynaecol. 2009 Oct;23(5):711-24.
5. Moro F, Scavello I, Maseroli E, Rastrelli G, Baima Poma C, Bonin C, Dassie F, Federici S, Fiengo S, Guccione L, Villani M, Gambineri A, Mioni R, Moghetti P, Moretti C, Persani L, Scambia G, Giorgino F, Vignozzi L; Women's Endocrinology Group of the Italian Society of Endocrinology. The physiological sonographic features of the ovary in healthy subjects: a joint systematic review and meta-analysis by the Italian Society of Gynecology and Obstetrics (SIGO) and the Italian Society of Endocrinology (SIE). J Endocrinol Invest. 2023 Mar;46(3):439-456