Introduction: Struma ovarii are quite unusual lesions that represent less than 3% of all teratomas and its malignant transformation is very uncommon. The clinical manifestations are characteristic of pelvic tumor and the hormonal metabolism is not usually modified. Radiography, employing ultrasound procedures, is the most commonly used pre-surgical detection method but only histological examination makes the diagnosis. The malignance recognition by pathological study not always is easy; in this sense, it requires an exhaustive sampling of the lesion, being specially carefully in some aspects related with malignant transformation such as extending beyond the capsula and involving peripheral tissues. A thyroidal differentiation must be confirmed by immunohistochemical study and other local processes with similar histology should be ruled out. Given the exceptional character of malignant forms, there does not appear to be unanimous agreement on a standard therapy with a somewhat uncertain prognosis.
Case report: We show a case of a 22-year-old patient with an ovarian tumor that was discovered by ultrasound examination and surgically removed. The histologic study revealed struma ovarii with malignant transformation towards follicular carcinoma and unlike previously published cases, had a prevalence of clear cells. The patient was submitted to a second surgical staging intervention, with conservative surgery and follow-up controls being considered given that was a young woman with a desire to have children. Laparoscopy was employed as the best method capable to facilitate shorter convalescence.
Outcome: Clinical and analytical controls, measuring thyroglobulin levels, has been satisfactory up to the present.