Introduction
Struma ovarii is a variant of the dermoid tumors found in the ovary. A dermoid tumor is a cyst that contains tissues usually found in the outer layers of the skin, including the sweat and oil glands. Struma ovarii is a rare histological finding. It is a tumor where thyroid tissues form a predominant part of the tissue component. More than fifty percent of the tissues in the tumor are thyroid cells. It was first described by Boettilin in 1889.
What Is Struma Ovarii?
Struma ovarii comprises one percent of all ovarian tumors and two to five percent of all ovarian teratomas. A teratoma is a germ cell tumor containing different types of cells. Struma ovarii is a rare type of ovarian tumor defined by the presence of thyroid tissue comprising more than fifty percent of the tumor mass. It is also called mono-dermal ovarian teratoma. It is a benign tumor. However, it shows progression to malignancy in five percent of cases. Ascites may be seen in three percent of cases. The thyroid cells in the tumor rarely produce thyroid hormones. Hence the probability of hyperthyroidism is significantly lower. It rarely becomes malignant to be treated as thyroid cancer.
What Are the Signs and Symptoms of Struma Ovarii?
Most cases of struma ovarii may not show any signs or symptoms. Most of the patients are of reproductive age, though it can occur at any age in females. The symptoms of the conditions may resemble the symptoms of an ovarian tumor. They can include:
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Pain in the abdomen.
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A mass in the abdomen that is palpable.
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Abnormal vaginal bleeding.
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Ascites (fluid build-up in the abdomen).
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Pseudo Meigs Syndrome: It is the secondary formation of ascites and hydrothorax (a non-inflammatory condition where fluid accumulates in the pleural cavities) associated with pelvic tumors. They usually resolve after the tumor is removed.
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Hyperfunctioning of the thyroid in five to eight percent of cases.
What Are the Differential Diagnoses of Struma Ovarii?
The differential diagnoses of struma ovarii can include:
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All benign and malignant tumors of the ovary.
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Ectopic pregnancy (Occurs when the fertilized egg grows outside the uterus).
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Endometrioma (Common type of endometriosis).
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Hydrosalpinx (A condition where fluid gets collected in one or both the fallopian tubules).
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Hyperthyroidism (Increased production of thyroid hormones).
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Thyrotoxicosis ( Increase in thyroid levels with or without hormone production).
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Metastasis of thyroid cancer to the ovary.
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Physiological ovarian cyst.
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A tubo-ovarian abscess (A pocket of pus formed due to an infection in the fallopian tube or ovary).
How Is Struma Ovarii Diagnosed?
Initial tumor diagnosis can be by imaging techniques, though it can be confirmed only by histopathological studies.
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Laboratory Studies: Laboratory studies can include complete blood count (CBC), blood type, and thyroid function tests in patients who show symptoms of hyperthyroidism.
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Cancer Antigen 125: It is a non-specific marker that is elevated in some benign clinical conditions like menstruation, pregnancy, and endometriosis. It remains elevated in epithelial tumors like ovarian, endometrial, bowel, breast, and lung cancer. Studies show that this marker is seen elevated only in eight percent of cases of struma ovarii.
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Imaging Studies: Studies by Shen et al. show that CT (computed tomography) scans and MRI (magnetic resonance imaging) appearances of these tumors can help diagnose the condition. Triple contrast CT scan of the abdomen and the pelvis helps to know the extent of the disease and involvement of the lymph nodes and the adjacent structures. The appearance of struma ovarii is typically a multicystic mass with no or moderate enhancement of the cystic wall. Pelvic ultrasound becomes an optional imaging modality if a CT scan has already been done. In some cases, a pelvic ultrasound is done initially. If the patient has masses in the pelvic region whose source is unknown, mammography is advisable. If the patient shows any associated respiratory symptoms, a chest X-ray can be done to assess lung metastasis.
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Iodide I-123 Scanning: An evaluation of the uptake of sodium iodide I-123 is done to demonstrate the thyroid uptake in masses in the pelvic region.
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Histologic Studies: The struma appears to be a brown or green-brown solid, partly or fully cystic, filled with gelatinous fluid on gross observation. It is rarely bilateral. Although the cells or tissues in the struma are not active, it can rarely show thyrotoxicosis due to increased thyroid hormones. This could be due to the autoimmune stimulation of the normal thyroid gland. Pathological studies reveal that the majority of the cells in the struma are thyroid cells. They can be in papillary, follicular, or mixed patterns.
How Is Struma Ovarii Treated?
In most cases, surgical resection of the ovary is sufficient to manage the benign unilateral condition. On the other hand, there is a lack of evidence regarding conservative management in cases of malignancy. In such cases, serum thyroglobulin is used as a marker for recurrence after fertility-sparing unilateral salpingo-oophorectomy. In fertility-sparing unilateral salpingo-oophorectomy, the organ's function is preserved by sparing resection of the malignant cells. Surgical staging for ovarian cancer along with pelvic washing, total abdominal hysterectomy (total removal of the ovary and uterus), bilateral salpingo-oophorectomy (removal of the ovary and fallopian tube in both sides), lymph node sampling (lymph nodes are removed and examined under a microscope for malignancy), total thyroidectomy (complete removal of the thyroid gland), and radioactive I-131 ablation is done in patients who do not consider future fertility. In radioactive I-131 ablation, all functioning thyroid cells are destroyed.
Conclusion
Since the condition is rare, a standard modality for diagnosis and treatment is not feasible. Based on clinical presentation or imaging studies, the condition can be challenging to diagnose, as they present with diverse symptoms. In the case of a benign tumor, it can be managed as a dermoid tumor with surgical management. This helps to manage the condition even if secondary conditions like hyperfunctioning thyroid gland, ascites, or hydrothorax are present, as they usually resolve by removing the primary tumor.
