Thyroid teratoma is an exceptionally rare neoplasia that can mimic multinodular disease of the thyroid. Due to its rarity, the clinical features and natural history of the disease are largely unknown.
Most are diagnosed in newborns and infants and display benign features, while the majority of the cases reported in adults are malignant [1-3].
Teratomas are congenital tumours arising from ectopic primordial germ cells that fail to migrate to the gonads during the first weeks of embryogenesis. Accordingly, they occur along the midline and paramidline in both gonadal and extragonadal sites [4]. By definition, they contain elements of all three germ-cell layers [1, 3, 5].
Cervical teratomas are considered to be of thyroid origin if at least one of the following criteria are met: the teratoma occupies part of the gland, it is in direct continuity with the gland, or there is a complete absence of the thyroid. The latter hypothesises that there might have been total replacement of the thyroid by the tumour or, alternatively, that the teratoma originated from a thyroid precursor that failed to develop into a mature gland [1, 5].
Fine-needle aspiration cytology is often indeterminate and diagnostic imaging tests are not enough to differentiate malignant tumours from benign, therefore surgical resection is required for final diagnosis and treatment [1-3, 5, 6].
Presentation is as a neck nodule. Depending on the size of the lesion, they can cause airway or oesophageal compression, much like multinodular goitre [1, 3].
By definition teratomas are heterogeneous, thus may contain a wide range of tissues with different imaging characteristics. US may show a predominantly solid nodule with cystic components, typically with a well-defined hypoechoic margin. Coarse calcifications and hyperechogenic components related to the presence of fat can be identified. The CT features are similar to those described in other locations. In general CT depicts a well-demarcated heterogeneous solid lesion with varied attenuations of fluid, soft-tissue, fat and calcium [3, 5]. Like their mediastinal counterparts, large lesions tend to displace other structures.
Our patient underwent surgical resection via right hemithyroidectomy and a diagnosis of benign cystic teratoma of the thyroid was made based on the surgical specimen evaluation.
TEACHING POINTS
A thyroid teratoma is an exceedingly rare lesion in adults and its preoperative diagnosis by FNAC is challenging.
Cross-sectional imaging may help when fat and calcifications are detected.
The majority of cases in adults are malignant and definitive diagnosis is only possible after pathologic analysis. As such, surgical resection is required.
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