Struma Ovarii

Fig. 7.1

Radioiodine I-123 imaging with whole body scan

Fig. 7.2

MRI of pelvic mass

She was referred to the Gynecologic Oncology Clinic, and the methimazole dose was titrated until the free T4 and total T3 were within the normal range. Five months after her presentation, she underwent exploratory laparotomy, total abdominal hysterectomy, bilateral salpingo-oophorectomy, right and left pelvic node sampling. The surgical pathology showed a 13 cm struma ovarii (Figs. 7.3 and 7.4). The lesion was proliferative, with follicular crowding and nuclear atypia, which are indeterminate microscopic features, but insufficient to establish a diagnosis of carcinoma. Three lymph nodes were negative for tumor. Postoperatively, the patient was placed on thyroxine, which was titrated to a dose of 125 mcg × 7.5 tablets per week. Her laboratory tests showed an undetectable serum thyroglobulin level while on this replacement dose. Four months after surgery, she underwent Thyrogen-stimulated testing which showed a thyroglobulin of 0.9 ng/ml, and a whole body scan showed two foci of increased radiotracer localization within the thyroid bed, compatible with residual thyroid tissue. There was no evidence of uptake in the extrathyroidal neck or at distant sites, and no evidence of uptake within the pelvis outside the bladder.

Fig. 7.3

Ovarian tumor containing thyroid tissue as the predominant cell type, which typically occurs as part of a teratoma

Fig. 7.4

Thyroid follicle filled with colloid

Background

“Struma” is the Latin term for a “swelling in the neck,” and struma ovarii was first described in 1895 by Vol Kalden [1]. It is a rare ovarian tumor defined by the presence of thyroid tissue as a major cellular component, and most commonly occurs as part of a teratoma. In a pathologic study from two major academic centers, out of 1,390 ovarian tumors, 167 were teratomas [2]. Less than 1 % contained foci of thyroid tissue or were struma ovarii. Struma ovarii is most commonly diagnosed between the ages of 40 and 60 years [3]. Pathologically, the thyroid epithelium in the teratoma may be organized in a solid, embryonal or pseudotubular pattern, rather than forming thyroid follicles, and thyroglobulin staining may be required to identify the cells as thyroidal in origin [3].

The clinical presentation may include symptoms ranging from thyrotoxic complaints, a pelvic mass, or ascites [4]. If there is autonomous production of thyroid hormone by the struma ovarii, this would lead to TSH suppression and absence of function by the normal thyroid gland [2]. The diagnosis may be suspected in a woman with hyperthyroidism who has no goiter and minimal or absent thyroidal uptake of radioiodine. In such cases, the far more likely causes remain exogenous thyroid hormone use and various forms of thyroiditis. The diagnosis is made, as in our case, by radioiodine imaging of the pelvis. Rarely, women with struma ovarii and hyperthyroidism also have a goiter, which may be due the coexistence of Graves’ disease and struma ovarii, in which thyroid-stimulating immunoglobulins stimulate the thyroid tissue in the ovary as well as the neck, or the presence of toxic nodular goiter, in which there is also radioiodine uptake over the ovary and the neck [5].

An antithyroid drug, preferably methimazole, is given for 4–6 weeks prior to surgery, depending on the severity of the thyrotoxicosis and underlying risk factors (older age, underlying cardiovascular disease, etc.). As in this case, beta blocking drugs may also be used for symptomatic relief and for heart rate control. In cases of benign struma ovarii causing hyperthyroidism, after resection, the cervical thyroid gland that was previously suppressed may resume normal function [2].

Surgical removal is the treatment for struma ovarii, even in a patient with coexisting Graves’ disease or toxic nodular goiter, due to the risk of carcinoma. The pathologic criteria for carcinoma in struma ovarii include tumor invasion, metastases, or recurrence, or the typical cytopathologic features of papillary thyroid cancer. A pathologic study evaluated 54 patients with ovarian tumors due to struma ovarii and 13 (24 %) were found to be carcinomas, 11 with features of papillary carcinoma and 2 with features of follicular carcinoma [6]. Cancer is more likely in larger tumors and was present in 75 % of tumors >16 cm, and rarely in tumors <5 cm [6].

In cases of malignant struma ovarii, there is no standard treatment protocol. Generally, treatment includes oophorectomy and total thyroidectomy. Following surgery, a radioiodine scan is performed, after Thyrogen stimulation or thyroxine withdrawal, although there has been no consensus recommendation. If there is abnormal radioiodine uptake in the abdomen or possible metastases, high-dose radioiodine is administered [3, 7–9].

The follow-up involves monitoring for recurrence, including radioiodine whole body scan and at least 10 years of surveillance with serum thyroglobulin [3, 7–9]. An increase in serum thyroglobulin may prompt a repeat radioiodine scan [3]. Aside from recurrences of malignant struma ovarii in the abdomen, there have also been reports of recurrences at distant sites, including the bones, brain, and lung [8]. After surgical resection of the struma ovarii and total thyroidectomy, patients will require lifelong thyroxine replacement. The dose should be titrated to a goal TSH in the low normal to slightly suppressed range, although no specific cutoffs have been established [7].

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