Retroconversion of immature teratoma of the ovary: CT appearances

We have studied seven patients presenting to the Royal Marsden Hospital between 1983 and 1989 with metastatic immature teratoma of the ovary. All patients underwent initial surgery followed by combination chemotherapy and a second laparotomy. Serial CT scans were performed at 2-3 monthly intervals from diagnosis until the second laparotomy, and the results of this were correlated with the CT appearances. In six of the seven patients CT scanning demonstrated 'retroconversion' of immature malignant tumour masses to benign mature disease during treatment. CT features of maturation included increased density of mass lesions, whose margins became better circumscribed in relation to adjacent tissues, and the onset of internal calcification, with fatty areas and cystic change. These changes on CT correlated exactly with normalization of an initially raised serum tumour marker, alpha feto-protein (AFP) in all six patients. The second laparotomy revealed only mature teratoma in all patients following chemotherapy. In three patients show continued growth of the mature deposits necessitated further surgery for local pressure symptoms, but overall, none has shown malignant relapse, and all are currently well between 1 and 6 years after diagnosis. This is the first report of the CT appearances of retroconversion of immature ovarian teratoma in a series of patients, which is an important radiological diagnosis to make in order to avoid confusion with advancing malignancy. A review of the literature is presented.