Struma Ovarii and Monodermal Teratomas
On this page
Direct answer
Struma ovarii is a monodermal teratoma in which mature thyroid tissue predominates, and it is a specialised form of ovarian teratoma. It is usually unilateral and benign, and it can cause hyperthyroidism in a minority of patients. Malignant change, most often to papillary thyroid carcinoma, is uncommon.
What you must remember
- Definition: A monodermal teratoma in which mature thyroid tissue makes up most of the tumour, usually within a mature cystic teratoma.
- Presentation: It occurs mainly in middle-aged women and is often found incidentally on imaging or at surgery.
- Thyrotoxicosis: A minority of struma ovarii cause hyperthyroidism, so thyroid function must be checked before surgery.
- Pre-operative control: Antithyroid drugs control thyrotoxicosis before surgery to prevent thyroid storm.
- Imaging: Ultrasound or MRI shows a complex or solid mass, and radioiodine uptake in the pelvis supports the diagnosis.
- Malignant change: Papillary thyroid carcinoma is the commonest malignant transformation, but it is uncommon overall.
- Strumal carcinoid: A carcinoid tumour within struma ovarii can rarely cause carcinoid syndrome.
- Treatment: Benign disease is treated by unilateral salpingo-oophorectomy or cystectomy, with thyroid follow-up as needed.
A diagnostic and management pathway for struma ovarii
Struma ovarii is recognised by combining imaging, thyroid function and histology. The pathway below runs from suspicion to long-term follow-up.
- Suspect the diagnosis: A complex or solid ovarian mass in a middle-aged woman, sometimes with features of a teratoma, raises suspicion. Imaging alone is not sufficient for a firm diagnosis.
- Check thyroid function: Measure TSH, free T4 and free T3 before any operation, since thyrotoxicosis changes perioperative care. Hyperthyroidism is found in a minority of cases.
- Control thyrotoxicosis: Antithyroid drugs are started and the patient is made euthyroid before surgery. This reduces the risk of thyroid storm under anaesthesia.
- Confirm with scintigraphy: Radioiodine uptake in the pelvis, rather than in the neck, supports ovarian thyroid tissue. Normal neck thyroid uptake does not exclude struma ovarii.
- Operate on the ovary: Unilateral salpingo-oophorectomy or cystectomy is usually adequate for benign disease, with preservation of the uterus and the other ovary where possible.
- Follow up: Thyroid function is monitored after surgery, and malignant disease is managed with further thyroid assessment and radioiodine where indicated.
Where the exam tries to catch you
Struma ovarii questions test recognition and the perioperative risk of thyrotoxicosis.
- Trap: Calling all pelvic thyroid tissue a metastasis. Correct: Struma ovarii is a primary ovarian monodermal teratoma, and metastatic thyroid cancer is a separate diagnosis.
- Trap: Operating on a thyrotoxic patient without preparation. Correct: Antithyroid drugs control thyrotoxicosis before surgery to prevent thyroid storm.
- Trap: Assuming every struma ovarii needs total thyroidectomy. Correct: Benign struma ovarii is managed by ovarian surgery, and thyroidectomy is considered only for malignancy or a thyroid indication.
Frequently asked questions
What is the commonest malignant change in struma ovarii?
Papillary thyroid carcinoma is the commonest malignant change in struma ovarii, although malignant transformation is uncommon overall. Malignancy is diagnosed on histology and may be found within a mature teratoma. Malignant struma ovarii is managed with further surgery and, when appropriate, radioiodine.
Why does struma ovarii cause hyperthyroidism?
A minority of struma ovarii produce enough thyroid hormone to cause hyperthyroidism, because ectopic ovarian thyroid tissue secretes hormone outside the normal thyroid gland. Thyrotoxicosis must be controlled with antithyroid drugs before surgery. Thyroid function tests are therefore checked in every woman with suspected struma ovarii.
Which imaging test helps diagnose struma ovarii?
Radioiodine scintigraphy showing uptake in the pelvis supports a diagnosis of struma ovarii. Ultrasound and MRI show an ovarian mass, often complex or solid, which then needs histological confirmation. Thyroid function tests help show whether the ovarian tissue is active.
What is a strumal carcinoid?
Strumal carcinoid is a monodermal teratoma in which a carcinoid tumour grows within thyroid tissue. It can rarely cause carcinoid syndrome. It is treated by surgery of the affected ovary, with follow-up of any hormonal effects.
Is struma ovarii usually bilateral?
Struma ovarii is usually unilateral, and it is often found within a mature cystic teratoma. Bilateral disease is unusual. Unilateral salpingo-oophorectomy or cystectomy is generally sufficient for benign struma ovarii.