Struma ovarii is a rare variant of mature cystic teratoma (dermoid cyst) where >50% of tumor content consists of thyroid tissue, classified as a monodermal teratoma. Comprises 2-5% of all ovarian teratomas and <1% of all ovarian neoplasms. As it contains functional thyroid tissue, hyperthyroidism (thyrotoxicosis) may develop in 5-8%. Distinguishing imaging feature is high-density content on CT (iodine content of thyroid colloid) and variable T1/T2 signal on MRI (depending on colloid viscosity). Malignant transformation (struma ovarii carcinoma) occurs in 5-10%.
Age Range
30-60
Peak Age
45
Gender
Female predominant
Prevalence
Rare
Struma ovarii is a monodermal teratoma originating from ovarian germ cells — during embryonal development, ectodermal germ cells differentiate into thyroid tissue becoming the dominant tissue (>50%). Thyroid follicles are filled with colloid (thyroglobulin, iodine-rich protein) — physical properties of this colloid directly determine imaging: (1) High density on CT — high iodine content of thyroid colloid strongly absorbs X-rays (due to high atomic number of iodine); (2) MRI T1/T2 signal — variable depending on colloid protein concentration and viscosity: high concentration ('gel-like') gives high T1/low T2, low concentration ('watery') gives low T1/high T2; (3) Dark cystic content on US — thick colloid produces low-level internal echoes. In multilocular structure, loculations with different viscosity show different signal/density — this 'mosaic' or 'stained glass' pattern is the diagnostic clue for struma ovarii.
High density of 70-110 HU in cystic components of ovarian mass on non-contrast CT. This finding is due to natural iodine concentration of thyroid colloid and is specific for struma ovarii among ovarian lesions. Simple ovarian cysts show 0-20 HU, hemorrhagic cysts 40-70 HU, fat component of dermoid cysts negative HU, while thyroid colloid component of struma ovarii is 70-110 HU higher than all of these. Different loculations showing different densities in multilocular structure ('mosaic' pattern) strengthens diagnosis. This finding is critical in preoperative diagnosis because it is rarely considered clinically due to rarity.
High density (70-110 HU) in cystic content on non-contrast CT. Distinctly different from simple fluid (0-20 HU). This high density is due to iodine content of thyroid colloid. Different loculations in multilocular structure may show different densities.
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High density (>70 HU) attributed to thyroid colloid is seen in cystic components of the ovarian mass on non-contrast CT, and struma ovarii should be considered.
Variable signal intensity in different loculations on T1-weighted images. Dense viscous colloid shows high T1 signal, watery colloid shows low T1 signal. This variability creates 'mosaic' pattern.
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Variable signal intensity is seen in the mass loculations on T1-weighted sequences, consistent with colloid content of varying viscosity.
Variable signal in different loculations on multilocular structure in T2-weighted images. Viscous colloid shows low T2 signal ('dark colloid'), watery colloid shows high T2 signal. 'Stained glass'-like pattern is created.
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Loculations of varying signal intensities are seen in a multilocular structure on T2-weighted sequences, demonstrating 'stained glass' pattern consistent with struma ovarii.
Multilocular cystic or solid-cystic ovarian mass. Different echogenicity in different loculations — some hypoechoic (watery colloid), some hyperechoic (viscous colloid). Dermoid component (hair, fat, calcification) may accompany.
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A multilocular cystic mass of ovarian origin is seen with variable echogenicity in loculations, consistent with struma ovarii.
Thyroid uptake in pelvic region on Tc-99m pertechnetate or I-123 scintigraphy. Direct evidence of functional thyroid tissue. In hyperthyroidism, cervical thyroid uptake may be suppressed.
Report Sentence
Uptake attributed to functional thyroid tissue is seen in the pelvic region on thyroid scintigraphy, confirming the diagnosis of struma ovarii.
Criteria
Normal mature thyroid tissue. Follicular architecture preserved, no atypia. 90-95% of cases.
Distinct Features
Smooth-contoured, encapsulated, no or minimal prominent solid component. Multilocular cystic structure. Benign prognosis — cystectomy is curative.
Criteria
Functional thyroid tissue producing thyroid hormone. Hyperthyroidism signs (tachycardia, tremor, weight loss, TSH suppression). 5-8% of cases.
Distinct Features
TSH suppressed, fT4/fT3 elevated. Cervical thyroid uptake suppressed on scintigraphy, pelvic uptake prominent. Symptoms resolve with surgery. Preoperative antithyroid treatment may be needed.
Criteria
Malignant transformation within thyroid tissue. Papillary thyroid carcinoma most common (70%), follicular carcinoma (20%). 5-10% of cases.
Distinct Features
Prominent solid enhancing component, irregular border, surrounding invasion. Elevated thyroglobulin as tumor marker. Postoperative I-131 ablation therapy may be needed. Prognosis generally good (differentiated thyroid carcinoma).
Distinguishing Feature
Dermoid cyst shows fat density (-20 to -120 HU), calcification/teeth, fat-fluid level. Struma ovarii is distinguished by high-density cystic content (70-110 HU — iodine-containing colloid). Both are from teratoma family and may coexist — dermoid component + struma ovarii combination is possible.
Distinguishing Feature
Mucinous carcinoma may show 'stained glass' pattern in multilocular cystic structure (loculations of different signal intensity) — may be confused with struma ovarii. However, mucinous carcinoma does not show high density on non-contrast CT (mucin 10-30 HU), very large (>10 cm), CA-125/CA-19.9 elevated. Struma ovarii is distinguished by high CT density (70-110 HU — iodine), smaller size, and thyroid function tests.
Distinguishing Feature
Endometrioma shows homogeneous high T1 signal (methemoglobin), 'shading' on T2 (homogeneous signal decrease), signal preserved on fat suppression. Struma ovarii has multilocular and variable T1/T2 signal (different signal in different loculations), high density on non-contrast CT (70+ HU — endometrioma 20-45 HU). Clinical: endometrioma with cyclical pain + endometriosis, struma ovarii with hyperthyroidism.
Urgency
routineManagement
surgicalBiopsy
Not NeededFollow-up
annualStruma ovarii treatment is surgical — laparoscopic cystectomy or unilateral oophorectomy is sufficient in benign cases. If hyperthyroidism is present, preoperative antithyroid treatment (methimazole) should be given and euthyroid status ensured before surgery. Malignant struma ovarii (<10%) requires total hysterectomy + bilateral salpingo-oophorectomy + thyroidectomy — followed by I-131 radioactive iodine ablation therapy (differentiated thyroid carcinoma protocol). Postoperative follow-up: thyroglobulin level monitored as tumor marker (in malignant cases), annual thyroid function tests. Prognosis is excellent — curative in benign cases, even in malignant cases 90%+ 10-year survival (differentiated thyroid carcinoma prognosis). Due to rarity, preoperative diagnosis is usually not made — reported as histopathological surprise.
Struma ovarii is generally benign. Malignant struma ovarii (thyroid carcinoma arising within struma ovarii) occurs in 5-10% of cases. Hyperthyroidism is seen in 5-8% of cases and can be treated without thyroidectomy. Treatment is surgical resection (cystectomy or oophorectomy). Malignant cases may require thyroidectomy and RAI therapy.