Struma ovarii tumor is a subtype of an ovarian teratoma and is composed entirely or predominantly of thyroid tissue and containing variable-sized follicles with colloid material.
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Epidemiology
It accounts for 0.3-1% of all ovarian tumors and ~3% of all mature cystic teratomas 1.
Clinical presentation
Approximately 5-8% of cases can show symptoms or signs of thyrotoxicosis.
Pathology
To qualify as a struma ovarii tumors more than 50% of the tumor should be composed of thyroid tissue 7.
The gross pathologic appearance of struma ovarii differs from that of mature cystic teratomas where struma ovarii consist of amber-colored thyroid tissue, with hemorrhage, necrosis, and fibrosis.
Radiographic features
While imaging features can be non-specific and overlap with other ovarian neoplasms, ultrasound and CT usually demonstrate a complex adnexal lesion with multiple cystic and solid areas, reflecting the gross pathologic appearance of the tumor 1. Ascites may be present in up to a third of cases 7.
Ultrasound
No specific feature from other teratomas. They may appear solid, cystic or of mixed echogenicity. A characteristic feature that has been described is the presence of a solid echogenic component with a smooth surface and internal vascularity called “struma pearls” 9.
CT
On CT they are most often seen as smooth, marginated multicystic masses with high attenuation on non-contrast CT and no or moderate cyst wall enhancement 4.
MRI
May be seen as a multiloculated cystic mass, with solid parts. The cystic spaces can demonstrate both high and low (from gelatinous colloid 3) signal intensity on T1 and T2 weighted images.
The presence of areas of very low signal intensity on T2 weighted images, due to the viscous colloid material is sometimes considered as suggestive for the presence of struma ovarii tumor.
T1 C+ (Gd): the solid portions may show enhancement 2
Treatment and prognosis
Treatment is with surgical resection. The vast majority of struma ovarii tumors (90-95% 1,5) tend to be benign and therefore carry a good prognosis.
History and etymology
First described by R Boettin in 1889 7,8.
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