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Case Report |
Address correspondence to Maria D. Navarro, M.D., Department of Pathology, North Shore University Hospital, Manhasset, New York, 11030, USA; te1 516 562 4184; fax 516 562 4591.
Abstract
Struma ovarii are specialized teratomas consisting of thyroid tissue with various microscopic features, ranging from benign to malignant. We report a rare form of malignant struma ovarii, composed exclusively of a follicular variant of papillary thyroid carcinoma with capsular invasion, which occurred in a 65-yr-old woman.
(received 2 July 2003; accepted 3 October 2003)
Keywords: malignant struma ovarii, malignant ovarian tumor, follicular variant of papillary thyroid carcinoma
Introduction
Struma ovarii is a neoplasm characterized by thyroid tissue in the ovary as the predominant component in a benign cystic teratoma, or a benign teratoma in which only thyroid tissue has developed [1]. It has a peak incidence in the fifth decade of life and often involves the left ovary [1,2]. Although 5 – 15 % of benign ovarian teratomas contain some thyroid tissue, only 2% are composed exclusively of struma ovarii [3]. Malignant transformation of struma ovarii is uncommon, with reported rates ranging from 5–37% [2]. The rarity of the tumor, lack of universally accepted histologic criteria for malignancy, and protracted clinical course contribute to discrepancies in the reported cases. Presented here is a case in which an unusual malignant transformation with capsular invasion occurred in a pure struma ovarii.
Case Report
A 65-yr-old woman was found to have a pelvic mass that was discovered during an evaluation of post-menopausal bleeding. She was admitted to the hospital for an exploratory laparotomy, total abdominal hysterectomy, bilateral salpingo-oophorectomy, and possible staging. Her medical history included essential hypertension for 10 yr, diverticulosis, repair of recto-vaginal fistula post-delivery, cholelithiasis, tonsillectomy, and adenoidectomy as a child. There was no history of smoking or alcohol consumption. Pre-operative studies included an abdominal computed tomographic scan, performed 2 weeks before admission, which showed a complex left adnexal mass, 7 cm in diameter. A pelvic sonogram showed an enlarged left ovary, 7 x 6 x 5 cm, with cystic components, septations, and no calcification or free fluid. The uterus and right ovary appeared to be normal. Laboratory studies included a normal complete blood count. The serum potassium was slightly low, 3.0 mmoI/L, and for this she received supplemental potassium. The electrocardiogram showed a sinus rhythm with a nonspecific ST and T wave abnormality. She underwent an exploratory laparotomy, and a total abdominal hysterectomy with bilateral salpingo-oophorectomy.
The intraoperative pathologic diagnosis was "favor struma ovarii," based on frozen section examination of the left ovary. Grossly, the left ovary weighed 106 g and measured 7 x 6 x 4 cm; cut sections of the ovary showed multiple cysts, which contained clear brown fluid, with a multilobated, soft, brown, solid, inner lining. The fallopian tube measured 6 x 0.5 cm; cut surfaces of the fallopian tube were unremarkable.
The histologic sections showed a partly encapsulated neoplasm composed of small to mostly medium or rarely larger follicles, filled with homogenous, pale to strongly eosinophilic colloid with focally scalloped configuration. Follicular lining cells of approximately 50–70% of the tumor had characteristic vesicular nuclei with occasional grooves. A follicular variant of papillary carcinoma of thyroid with capsular invasion was favored.
The whole tumor was embedded for microscopic examination. Practically the entire tumor was composed of carcinoma without identifiable benign thyroid tissue (struma ovarii) or other teratoid elements (Figs. 1
–3). Vascular invasion was not evident. The diagnosis was subsequently confirmed by examination at Memorial Sloan Kettering Cancer Center (Reuter, V, personal communication). The right ovary measured 2.0 x 1.5 cm and showed simple cysts and corpora albicantia; the right fallopian tube was unremarkable. The uterus weighed 43 g and showed an inactive endometrium, but was otherwise unremarkable.
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Discussion
The presence of thyroid tissue in the ovary was first described by Böttlin in 1889 and the term "struma ovarii colloides" was coined by Meyer in 1903 [4]. Since then the entire spectrum of thyroid pathology, including nontoxic nodular goiter, toxic goiter, Hashimoto’s thyroiditis, nonspecific thyroiditis, adenomas, and carcinomas has been described [1]. Struma ovarii, as in our case, is more often found to involve the left ovary. Malignant transformation of struma ovarii is very rare. Malignancy arises more often in a nest of benign thyroid tissue within a benign cystic teratoma than in struma ovarii [5]. As listed in Table 1, our review of the literature has identified reports of 16 papillary carcinomas [1,5–9], 10 follicular carcinomas [8,10–14], 5 combined papillary and follicular carcinomas [11,13,15–17], and 4 follicular variants of papillary carcinoma [2,18,19].
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There is disagreement about the criteria for the diagnosis of malignant transformation within a struma ovarii. Pardo-Mindan et al [16] noted that nuclear alterations alone are insufficient diagnostic criteria, since atypical cells are frequent in noncancerous lesions. In addition, for the diagnosis of malignancy, Pardo-Mindan et al required the presence of invasion of the capsule or a peritoneal implant. The presence or absence of capsular or vascular invasion is difficult to evaluate in the ovary, since the thyroid tissue microscopically often does not form a discrete nodule, is not encapsulated in the usual fashion, and is sometimes associated with thick connective tissue septa into which the struma is embedded. These features make the evaluation of capsular invasion in struma ovarii difficult and capsular invasion cannot be used as a criterion for separating benign from malignant lesions.
Many authors believe that the diagnosis of malignancy can be made on the basis of cellularity, cellular atypia, and mitotic activity, although blood vessel invasion has been mentioned as the most reliable criterion [1]. As quoted by deGraaf et al [10], Fox and Langley opined that a sufficient degree of cellular pleomorphism, cytologic atypia, and mitotic activity are acceptable as signs of malignancy. From our institution, Vadmal et al [20] reported a case of benign struma ovarii without evidence of malignant features at oophorectomy. Six years after the oophorectomy, there were pelvic recurrences and metastases to the liver and retroperitoneum. Microscopically, the neoplastic nodules in the tumor ranged from benign appearing thyroid tissue to low-grade complex papillary and follicular carcinoma. Recurrences reported in the literature have occurred in the omentum, peritoneum, contralateral ovary, liver, spleen, lungs, pleura, inguinal lymph nodes, skin, and, in one instance, the cranial vault [23]. It is notable that, even with recurrences and metastases, only 1 patient is reported to have died; the death 3 yr post-diagnosis and was attributed to pneumonia and cardiovascular insufficiency [16]. Follow-up in reported cases has ranged from a few mo to 27 yr.
The prognosis of malignant struma ovarii is difficult to predict, because of the scarcity of cases and the long intervals before recurrences and metastases occur [5]. Thus, patients with malignant struma ovarii should be managed with caution; they require long-term follow-up with a "wait and see" attitude.
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