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Struma Ovarii with Malignancy

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Question

I would appreciate your opinion on a very unusual case I encountered in my practice recently. My patient is a 63 year old, WF, PMH of ovarian cyst removed 30 years ago. 10-12 years ago, she began growing a mass/cyst on her incision line.She saw her Physician who recommended she not do anything until earlier this year when they noticed the mass continued growing. It was then removed. Final path came back benign Thyroid tissue. Ultra sound of the thyroid resulted in MNG. FNA is benign. PET CT – 3 cm tumor posterior aspect of liver. 1.3 cm tumor under incision and 2 peritoneal nodes. FNA liver was + incisional mass benign thyroid tissue. TGB level is 7700. I advised patient to have throidectomy, liver and incisional mass removed so that we can do I131. I think in this way we can have a better chance of having peritoneal nodes pick up I131. Again, I would appreciate your impressions. ?Excise abdominal mass or not?

Respectfully,

Ana Priscu, MD

Response

Assuming that the PET scan was positive for uptake of FDG (and not just a mass seen on CT), this tumor sounds like malignant struma ovarii, in which case you should have the mass removed followed by RAI scanning and potential 131-I therapy. It is generally not possible to tell benign from malignant struma on histology alone but presence of this kind of growth with nodal or intraperitoneal metastases indicates malignancy.

Benign cystic teratomata comprise approximately 10% of all ovarian tumors. Boettlin in 1889 (1) first described the presence of thyroid tissue in a teratoma of the ovary and the amount of thyroid tissue found will vary from small, clinically insignificant quantities to a mass of thyroid tissue sufficient to cause thyrotoxicosis. Historically, the expression “struma ovarii” has been variously applied to either those teratomas associated with thyrotoxicosis or those comprised of a significant quantity of thyroid tissue. Thyroid tissue is either the major constituent or is the cause of thyrotoxicosis in 2‑4% of teratomata (2). Thus, 10% of ovarian tumors are teratomas and 2-4% of them may be called “struma ovarii”, but those with associated thyrotoxicosis are extremely rare.

The first clinical presentation of struma ovarii is typically in the 4 or 5 decade (2 – 4) but may present at any age after age 20 (3 – 5). While most patients are asymptomatic, about half will come to attention because of symptoms of abdominal pain (5, 6). Often, the diagnosis is made incidentally during abdominal surgery for another problem. In a series of 30 patients by Szyfelbein (5) three presented with ascites, two of whom also had a hydrothorax (a Meig’s or pseudo-Meig’s syndrome) (6, 7). The presence of ascites or hydrothorax is not necessarily indicative of malignancy. Tumor weight averaged 726 Gms in 8 patients reported by Alfie-Cohen (8). Most tumors are unilateral, occurring equally on the left or right side, and range in size from a diameter of 2‑36 cm (average 12 cm) (3, 5). On occasion, thyroid tissue is found in other ovarian masses which then requires histologic differentiation from ovarian cancer or other malignancy (9 – 11).

Malignant struma ovarii, like other well differentiated thyroid carcinomas, will make and secrete thyroglobulin which serves as a tumor marker for remission or recurrence (12, 13), and 131-I scanning is useful to detect residual disease. Treatment of struma ovarii involves bilateral oophorectomy because of the frequency of bilateral teratoma. In addition to oophorectomy, the treatment of malignant struma ovarii is similar to that of papillary or follicular thyroid carcinoma of the thyroid, in that thyroidectomy followed by radioiodine ablation is required to eradicate residual disease (13, 14) and facilitate follow-up for recurrence.

Computed tomography (CT), magnetic resonance imaging (MRI), or FDG-PET findings can help in the differentiation of benign from malignant tumors. On CT imaging, struma ovarii is characteristically a complex mass with well‑defined cystic components and smooth surfaces. The solid components of the tumor are heterogeneous and enhance following intravenous contrast administration, and contain scattered calcifications. On MR imaging, the mass appears complex, and is composed of multiple cystic and solid components with multilobulated surfaces and thickened septa. Cystic areas have variable size and signal intensity within the tumor (15 – 17). Solid components will enhance with Gadolinium‑DTPA because of their rich vascular supply and fibrous components. (16, 18).

Histologic sections of a struma ovarii may appear indistinguishable from those of normal thyroid tissue. Immunohistochemical staining for thyroglobulin will confirm the presence of thyroid tissue (5). There is also a report of unique uptake of a technetium-99m-labeled monoclonal antibody (Tc-99m-MAB170H.82) in two patients with struma ovarii (19). The label is directed against a panadenocarcinoma epitope (CA 170) and was picked up by very large tumors in these two patients which proved to be benign, although one had an elevation in CA125 levels. Approximately 3-10% (2, 20, 21) of struma ovarii appear to have malignant potential, but few of these will actually metastasize (20), with perhaps a score of such cases reported to date in the literature. The cytopathologic features of malignant struma ovarii are identical to the characteristic features of well differentiated carcinoma of the thyroid gland (6).

Leonard Warofsky, MD

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