Second trimester adnexal torsion of a large ovarian mature teratoma: Diagnostic value of whirlpool sign.

Adnexal torsion is a gynecological emergency and an important cause of acute pelvic pain, occurring most frequently in women of reproductive age. In pregnancy, torsion is classically associated with ovarian stimulation and small-to-medium sized mobile adnexal masses. We report the case of a 35-year-old nulliparous woman who presented to the emergency department with acute left flank pain and vomiting at 18 weeks and 6 days of a spontaneous singleton pregnancy. Ultrasound revealed a 150 mm left adnexal mass with features suggestive of a mature cystic teratoma, including a unilocular lesion with mixed echogenicity, echogenic nodules ("cotton wool" pattern), linear echogenic interfaces ("starry sky" sign), and posterior acoustic shadowing. Importantly, a heterogeneous, vascularized nodular structure was identified adjacent to the mass, displaying the characteristic sonographic whirlpool sign, strongly suggestive of adnexal torsion. Laparoscopic left adnexectomy was performed during the second trimester, as irreversible adnexal necrosis was already established. Histopathological examination confirmed the diagnosis. Postoperative recovery was uneventful, and the pregnancy progressed to term, resulting in the delivery of a healthy newborn. This case highlights the diagnostic value of meticulous ultrasound assessment and in particular, the recognition of the whirlpool sign as a key sonographic marker of adnexal torsion. The presence of this sign enabled prompt diagnosis and timely surgical management, demonstrating that adnexal torsion should remain a diagnostic consideration even in spontaneously conceived pregnancies with large mature cystic teratomas during the second trimester.