<prompt> Struma ovaril is composed entirely ofMature thyroid tissueImmature thyroid tissuePimary ovarian carcinoid tissueNone of the above  <response>: Struma ovarii is a monodermal or specialised teratoma. They are germ cell tumours of ovary. Struma ovarii is composed entirely of mature thyroid tissue ,which may be functional and causes hypehyroidism. Struma ovarii is a rare ovarian tumor that was first described in 1899. It is defined by the presence of thyroid tissue comprising more than 50 of the overall mass. It most commonly occurs as pa of a teratoma, but may occasionally be encountered with serous or mucinous cystadenomas Ref : ROBBINS Text book of pathology REF IMG 