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.
Signs and symptoms
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[2]
Pseudo-Meigs syndrome (ascites in the setting of hydrothorax)
See Presentation for more detail.
Diagnosis
The tumor can be characterized by imaging, but the final diagnosis is made by pathological and histological examination. Pathological examination reveals thyroid tissue as the major component of the mass and is most commonly found in a teratoma.
See Workup for more detail.
Management
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.[3]
See Treatment for more detail.
Patient education
For excellent patient education resources, visit eMedicineHealth's Thyroid and Metabolism Center. Also, see eMedicineHealth's patient education article Thyroid Problems.
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.[5]
In a retrospective study of 194 malignant struma ovarii cases, the 5-, 10-, and 15-year overall survival rates were 91.4%, 87.7%, and 83.5%, respectively. The researchers identified International Federation of Gynecology and Obstetrics (FIGO) stage IV, age 45 years or older, and poor differentiation of tumors as predictors of a worse prognosis.[6]
Morbidity/mortality
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.[4] Several other types of tumors, such as Brenner tumor or cystadenoma, may also be found with a struma. Note the following:
Malignant change seems to occur in about a third of cases[7]
Metastatic spread, which follows the pattern of ovarian cancer, occurs in approximately 5% of malignant cases[7]
Survival rates are excellent[8]
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.[9]
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.[8]
Complications
Significant changes in thyroid function may occur in the immediate perioperative period.
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.
In a review of 12 cases, Shen et al found that CT and MRI appearance of these tumors may be helpful diagnostic features.[10]
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.[11]
Pelvic sonography is optional if a CT scan has already been performed.[12] 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.
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[13] .
Currently, the pathological criteria used in diagnosing thyroid carcinoma are widely accepted as the standard in diagnosing malignant struma ovarii.[7] 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.[14]
Malignant struma ovarii is divided into the following 3 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.[13]
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.[13]
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.[15] 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,[16] 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%.[17]
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.[11]
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.[18]
What is struma ovarii?What is the prevalence of struma ovarii in the US?What is the mortality and morbidity associated with struma ovarii?What are the racial predilections of struma ovarii?What are the sexual predilections of struma ovarii?Which age groups have the highest prevalence of struma ovarii?What are the signs and symptoms of struma ovarii?Which physical findings are characteristic of struma ovarii?What are the differential diagnoses for Struma Ovarii?Which lab tests are performed in the workup of struma ovarii?What is the role of imaging studies in the workup of struma ovarii?What is the role of iodine-123 scanning in the workup of struma ovarii?What is the role of thoracentesis in the workup of struma ovarii?Which histologic findings are characteristic of struma ovarii?How is malignant struma ovarii characterized?How is struma ovarii treated?What is the role of radio-ablative iodine-131 therapy in the treatment of struma ovarii?What is included in the long-term monitoring of struma ovarii?What are the possible complications of struma ovarii?What is the prognosis of struma ovarii?
Lisa Rubinsak, MD, Fellow in Advanced Pelvic Surgery, Emory University School of Medicine
Disclosure: Nothing to disclose.
Coauthor(s)
David Chelmow, MD, Leo J Dunn Professor and Chair, Department of Obstetrics and Gynecology, Virginia Commonwealth University Medical Center
Disclosure: Nothing to disclose.
Specialty Editors
Francisco Talavera, PharmD, PhD, Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference
Disclosure: Received salary from Medscape for employment. for: Medscape.
A David Barnes, MD, MPH, PhD, FACOG, Consulting Staff, Department of Obstetrics and Gynecology, Mammoth Hospital (Mammoth Lakes, CA), Pioneer Valley Hospital (Salt Lake City, UT), Warren General Hospital (Warren, PA), and Mountain West Hospital (Tooele, UT)
Disclosure: Nothing to disclose.
Chief Editor
Michel E Rivlin, MD, Former Professor, Department of Obstetrics and Gynecology, University of Mississippi School of Medicine
Disclosure: Nothing to disclose.
Additional Contributors
Jeannie Chen Kelly, MD, Resident Physician, Department of Obstetrics and Gynecology, Tufts Medical Center
Disclosure: Nothing to disclose.
Jordan G Pritzker, MD, MBA, FACOG, Adjunct Professor of Obstetrics/Gynecology, Hofstra North Shore-LIJ School of Medicine at Hofstra University; Attending Physician, Department of Obstetrics and Gynecology, Long Island Jewish Medical Center; Medical Director, Aetna, Inc; Private Practice in Gynecology
Disclosure: Nothing to disclose.
Sarah H Hughes, MD, Assistant Professor, Department of Obstetrics and Gynecology, Division of Gynecologic Oncology, University of Massachusetts Medical School
Disclosure: Nothing to disclose.
Acknowledgements
The authors and editors of Medscape Reference gratefully acknowledge the contributions of previous author Bradford W Fenton, MD, PhD, FACOG to the development and writing of this article.
