[Malignant transformation of thyroid tissue in an ovarian dermoid cyst: case report]

Mature cystic teratoma is the most common type of ovarian teratomas and also the most frequent tumor originating from germ cells. Usually unilateral, it is, by definition, composed of well-differentiated derivates which originate from all three layers. It is most frequently diagnosed in the female reproductive period; in its pure form, it is generally benign, but occasionally it may undergo malignant transformation in one of its elements.

The authors report a case of a 43-year-old woman who underwent a thyroid regulation substitutive therapy 12 years after thyroidectomy which had been performed because of Basedow's disease. On the occasion of her fourth delivery by cesarean section, bilateral cystical formations in both ovaries were found. Upon ending the delivery, the right ovary with the cyst was surgically removed, as well as part of the cystically changed left ovary. The pathohistological analysis of the samples taken from the left ovary cyst pointed to the following diagnosis: dermoid cyst of the ovary a mature cystic teratoma, whereas the samples from the cystic tumor of the right ovary were diagnosed as: ovarian teratoma malignant a papillary carcinoma of the thyroid tissue and cystadenoma papillare serosum ovarii. The histological type of the malignant thyroid tissue neoplasm in the teratoma was a papillary carcinoma consisting of papillary proliferations lined by cuboidal, cylindrical and pseudostratified epithelium with charasteristic "ground glass" nuclei, but without invasion into the blood vessels.

Malignant transformation of the ectopic thyroid tissue, which is one of the elements of the ovarian cystic teratoma, is extremely rare: it is diagnosed on basis of the histological picture and criteria which are the same as for the tumor of the thyroid gland. One should not exclude a pssibility that the identical or different pathological alterations characteristic of the thyroid gland may also be detected in the ectopic thyroid tissue of a dermoid cyst.

The reported case was chosen due to its complex and rich clinical and pathohistological picture characterized by the occurrence of a bilateral dermoid cyst with the malignant transformation of the thyroid tissue. The malignant neoplasm in the mature ovarian cystic teratoma was papillary carcinoma of the thyroid tissue with all histological properties typical for the thyroid gland carcinoma. The possibility of the malignant transformation of the endodermal thyroid tissue in the mature ovarian cystic teratoma and changes in the thyroid gland of the Basedow's disease type diagnosed before are without clear causation.