Struma Ovarii 

Updated: Mar 08, 2019
Author: Lisa Rubinsak, MD; Chief Editor: Michel E Rivlin, MD 

Overview

Background

Struma ovarii is a rare ovarian tumor that was first described in 1899. It is defined by the presence of thyroid tissue comprising more than 50% of the overall mass. It most commonly occurs as part of a teratoma, but may occasionally be encountered with serous or mucinous cystadenomas.[1] Strumae ovarii comprise 1% of all ovarian tumors and 2-5% of ovarian teratomas.

Several variants of the tumor exist. Benign strumosis is a rare version where mature thyroid tissue implants are present throughout the peritoneal cavity. Strumal carcinoid is defined by the presence of carcinoid tissue within a struma ovarii. The vast majority of strumae ovarii are benign, but malignant disease is found in a small percentage of cases, the most common being papillary thyroid carcinoma.

The symptoms of struma ovarii are similar to those of other ovarian tumors and are nonspecific in nature. The tumor can be characterized by imaging, but the final diagnosis is made by pathological and histological examination. Surgical resection remains the definitive treatment for benign disease, and surgery with adjuvant radioiodine therapy has been shown to be successful in treating metastatic and recurrent disease.[2]

Epidemiology

Frequency

United States

Struma ovarii is rare. Approximately 1% of all ovarian tumors and 2.7% of all dermoid tumors are classified as struma ovarii.[3]

Mortality/Morbidity

Malignancy is defined by various criteria in different studies, principally differing on classifying struma as either a thyroid or ovarian cancer. In the most recent World Health Organization classification, malignant struma ovarii are included in the thyroid tumor group[3] Several other types of tumors, such as Brenner tumor or cystadenoma, may also be found with a struma.

·         Malignant change seems to occur in about a third of cases.[4]

·         Metastatic spread, which follows the pattern of ovarian cancer, occurs in approximately 5% of malignant cases.[4]

·         Survival rates are excellent.[5]

Although the tumor is predominately composed of thyroid tissue, thyrotoxicosis is seen in only 5% of all cases. Only 1 case of thyrotoxicosis resulting from peritoneal strumosis has been reported.[6]

In a study of 68 patients with malignant struma ovarii, Goffredo et al found excellent disease-specific survival rates for the condition no matter which treatment—unilateral oophorectomy, bilateral oophorectomy, oophorectomy and omentectomy, or debulking surgery—was used. The report, which utilized the Surveillance, Epidemiology, and End Results (SEER) database of the National Cancer Institute, also determined that the risk of aggressive thyroid cancer in patients with malignant struma ovarii is high. The overall 5-, 10-, and 20-year survival rates in the study were 96.7%, 94.3%, and 84.9%, respectively, with only one of the deaths that occurred being attributed to malignant struma ovarii. The investigators found, however, that six patients (8.8%) were diagnosed concomitantly or subsequently with thyroid cancer, with two thirds of the thyroid cancers growing beyond the thyroid gland. All of the thyroid cancer patients were still alive at the last follow-up.[5]

 

Race

Because of its rarity, no clear racial predilection for struma ovarii has been determined.

Sex

Defined as a tumor of ovarian origin, struma ovarii occurs exclusively in genetic females.

Age

See the list below:

  • Struma ovarii typically presents between the ages of 40-60.

  • Struma ovarii rarely occurs before puberty.

 

Presentation

History

The symptoms of struma ovarii are similar to those of other ovarian tumors and are nonspecific in nature. They can include the following:

·         Abdominal pain

·         Palpable abdominal mass

·         Abnormal vaginal bleeding

·         Ascites (Reported in up to one third of cases)[7]

·         Pseudo-Meigs syndrome (ascites in the setting of hydrothorax) (Reported in fewer than 10 cases)

·         Incidental discovery on pelvic imaging or surgery

Thyroid hyperfunction is a presenting symptom in 5-8% of patients with struma ovarii.[2]

 

 

Physical

Struma ovarii is difficult to diagnose and physical examination often does not reveal any abnormalities. The tumor may present as a large abdominal mass, which can be palpable on examination depending upon size and location. Patients may also experience expanding abdominal growth and a fluid wave consistent with ascites. Rarely, dyspnea and pulmonary crackles can be indicative of Pseudo-Meigs syndrome.

 

DDx

Differential Diagnoses

  • All other forms of ovarian neoplasms, both benign and malignant

  • Ectopic Pregnancy

  • Endometrioma

  • Hydrosalpinx

  • Hyperthyroidism and Thyrotoxicosis

  • Metastatic thyroid cancer to the ovary

  • Physiological ovarian cyst

  • Tubo-ovarian abscess

 

Workup

Laboratory Studies

See the list below:

  • CBC count

  • Blood type and screen

  • Cancer antigen 125

    • Nonspecific marker elevated in a variety of benign clinical settings, including menstruation, pregnancy, endometriosis

    • Elevated in epithelial ovarian, endometrial, bowel, breast, and lung cancer

    • Elevated in only 8 cases reported in the literature in the setting of struma ovarii[7]

  • Thyroid function tests are ordered only in patients with symptomatic hyperthyroidism.

Imaging Studies

See the list below:

  • In a review of 12 cases, Shen et al found that CT and MRI appearance of these tumors may be helpful diagnostic features. [8]
  • Triple-contrast CT scan of the abdomen and pelvis should be performed to evaluate the extent of disease and the involvement of lymph nodes and other adjacent structures (eg, bowel). Typically, struma ovarii appear as a multicystic mass with no or moderate cystic wall enhancement. [9]
  • Pelvic sonography is optional if a CT scan has already been performed. [10] Frequently, this is an initial study.
  • Mammography should be performed in patients with pelvic masses of unknown origin.
  • Chest radiographs should be obtained in patients with systemic symptoms or signs of disease spread in abdomen/pelvis to assess for lung metastasis.
  • In select cases, preoperative evaluation with uptake of sodium iodide I-123 has been performed to demonstrate thyroid uptake in pelvic masses.

Other Tests

See the list below:

  • Iodine-123 scanning (In patients with suspected struma, this will evaluate active thyroid tissue in the pelvis or abdomen.)

  • Thoracentesis in patients with pleural effusion (Cytology may reveal adenocarcinoma in the pattern of malignant thyroid cells.)

Histologic Findings

On gross examination, the struma is brown or green-brown and solid, but it can also be partly or entirely cystic, filled with gelatinous fluid. The struma is rarely bilateral. Most strumal tissue is not functionally active, and cases associated with thyrotoxicosis can be due to autoimmune stimulation of the normal thyroid gland.

Pathological examination reveals thyroid tissue as the major component of the mass, and is most commonly found in a teratoma. Thyroid tissue may be papillary, follicular, or mixed pattern, and it can include elements of mucinous cystadenocarcinoma, Brenner tumor, carcinoid, or melanoma. Birefringent crystals of calcium monohydrate are present in most patients, which is considered specific for tumors of thyroid origin. Immunohistochemical staining for thyroglobulin, triiodothyronine (T3), and thyroxine (T4) can confirm the diagnosis.

Malignancy is defined by histological features of the tumor including cellular atypia and hyperplasia, nuclear pleomorphism, mitotic activity, and invasion into surrounding vessels or the ovarian capsule. In a case cohort of 118 patients with struma ovarii, Wei et al found that papillary thyroid carcinoma and stromal carcinoid were the most common well differentiated malignancies found arising in struma ovarii[11] .

Currently, the pathological criteria used in diagnosing thyroid carcinoma are widely accepted as the standard in diagnosing malignant struma ovarii.[4] However, there is still controversy over the defining characteristics of a malignant struma ovarii tumor. A blinded analysis of 19 histologic characteristics of thyroid tumors in 60 clinically benign and 26 clinically malignant struma ovarii cases found the majority of characteristics to be similar in both types of tumors. The clinical outcome of struma ovarii is unpredictable and cannot be predicted based on histologic features.[12]

Malignant struma ovarii is divided into 3 different categories by histology.

  • Papillary type is the most common and identified by “ground glass” or overlapping nuclei.
  • The follicular variant of papillary carcinoma shares the same nuclear characteristics as the papillary type, but has a follicular architecture.
  • Follicular carcinoma in struma ovarii is identified by vascular and/or capsular invasion. [11]

Strumal carcinoid has both struma ovarii and carcinoid tumor, with the carcinoid component considered by many to be a malignant transformation. Carcinoid tumor cells often have higher proliferative rate and invade into the struma. Histologically, they can grow in trabecular or insular pattern, some with glands or cysts containing goblet cells. They typically exhibit no aggressive clinical behavior and surgical excision is often curative.[11]

 

Treatment

Surgical Care

For the vast majority of cases, surgical resection of the ovary is sufficient to treat benign, unilateral disease. A paucity of evidence exists in the literature regarding conservative management in cases with evidence of malignancy.[13] In these patients, serum thyroglobulin levels can be followed as a marker for recurrence following fertility-sparing unilateral salpingo-oophorectomy. In patients who do not desire future fertility, malignant struma ovarii necessitates surgical staging for ovarian cancer with pelvic washings, total abdominal hysterectomy, bilateral salpingo-oophorectomy, lymph node sampling, total thyroidectomy,[14] and radioactive I-131 ablation. The recurrence rate in patients with malignant struma ovarii who undergo surgery without subsequent radioablation has been cited as high as 50%.[15]

 

Follow-up

Further Inpatient Care

For patients with a benign struma ovarii, standard surgical follow-up is sufficient.

For patients with malignant disease on surgical pathology, postoperative adjuvant therapy with radio-ablative iodine-131 is recommended. After surgical staging, a thyroidectomy is suggested before adjuvant treatment to potentiate the effects of radioablation. As normal thyroid cells preferentially uptake I-131, thyroidectomy would ensure delivery to the malignant cells. Additionally, a thyroidectomy would provide pathological confirmation that the struma is indeed ovarian in origin.

It is crucial for the surgeon to be aware of the intra- and postoperative complications of thyroidectomy (including hypocalcemia, damage to the recurrent laryngeal nerve, and/or need for postoperative thyroid replacement), and to be comfortable with their management. Radioactive I-131 ablation has been shown to treat malignant disease in both its initial presentation and any subsequent recurrence with excellent efficacy, although the rarity of the disease and lack of data surrounding its long-term management prove challenging to clinicians.[9]

Thyroglobulin is the preferred tumor marker followed in patients with malignant struma ovarii and should be followed sequentially after surgery and ablation. Increases in serum thyroglobulin should be followed up with total body scanning to detect recurrence, which is treated with subsequent radioablation.[16]

Complications

Significant changes in thyroid function may occur in the immediate perioperative period.

Prognosis

For the vast majority of patients, the struma is benign, and the prognosis is excellent. Even in malignant cases, adjuvant iodine-131 ablation with surgical extirpation has proven curative. Recurrences may be detected using iodine-123 scanning, and repeat iodine radioablation can lead to extended disease-free survival.

In an analysis of 88 patients with malignant struma ovarii, several factors were identified as being associated with recurrence or extraovarian spread. These include adhesions, peritoneal fluid of 1 liter or more, ovarian serosal rent, a papillary histology, or a struma component 12 cm or more. The overall survival rate for all patients is 89% at 10 years and 84% at 25 years.[17]

Patient Education

For excellent patient education resources, visit eMedicineHealth's Thyroid and Metabolism Center. Also, see eMedicineHealth's patient education article Thyroid Problems.

 

Questions & Answers