SummaryBackground: Spontaneous ovarian hyperstimulation syndrome (sOHSS) can occur following hypothyroidism. Ultrasonography facilitates diagnosis and monitoring of this syndrome. We describe ovarian sonographic changes in a hypothyroid patient with sOHSS after treatment with levothyroxine (l-T4).Case presentation: A 15-year-old girl presented with abdominal pain and distension for a few months. On examination, she had classical features of hypothyroidism. Abdominal and pelvic ultrasound revealed enlarged ovaries with multiple thin-walled cysts and mild ascitic fluid. On follow-up, abdominal ultrasound showed significant reduction of ovary size after 6 weeks of initiation of l-T4. Normal ovary size with complete regression of ovarian cysts was seen after 4 months.Conclusion: Serial ultrasound in sOHSS associated with hypothyroidism showed regression of ovarian cysts and ovarian volume after 4 months whereas in other studies, it is reported to happen in various durations, presumably according to its etiology.Learning points OHSS can rarely occur due to hypothyroidism.This type of OHSS can be simply treated by l-T4 replacement, rather than conservative management or surgery in severe cases.Ultrasound follow-up shows significant regression of ovarian size and cysts within 6 weeks of initiation of l-T4.Ultrasound follow-up shows normal ovarian size with complete resolution of ovarian cysts 4 months after treatment.

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