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Journal of the New Zealand Medical Association, 17-December-2004, Vol 117 No 1207

Thyroid papillary carcinoma in subhyoid ectopic thyroid tissue

Hsin-Yu Lee, Mei-Hsiu Chen, Chih-Yuan Wang

Abstract

Ectopic thyroid tissue is a rare entity in thyroidology; however, the occurrence of thyroid carcinoma in such aberrant thyroid tissue has been reported. Carcinoma arising in subhyoid thyroid is especially unusual, with even fewer reports published. Usually, surgical excision is considered to be therapeutic strategy for managing possible malignancy in ectopic thyroid. Thyroid ultrasonography, radioactive iodine scanning, and fine-needle aspiration cytology are rapid, safe, and minimally invasive diagnostic procedures. We report one case of papillary carcinoma in subhyoid ectopic thyroid to emphasise the importance to evaluate all ectopic thyroid tissues.

Thyroid tissue may develop in unusually anatomical location, i.e. ectopic thyroid. An ectopic thyroid can occur anywhere along the course followed by thyroglossal duct during its embryonic descent from the tongue—resulting in a lingual, suprahyoid, subhyoid, or even an intratracheal thyroid.1 A thyroglossal duct cyst is commonly associated with the clinical ectopic thyroid. Since ectopic thyroid tissue always raises the possibility of metastatic thyroid cancer, it is pivotal to identify the possible malignancy when an ectopic thyroid or thyroglossal duct cyst is noted.2 However, the absence of a normal thyroid gland may occur in the patients with clinically evident ectopic thyroid.

Removal of such ectopic tissue can lead to permanent hypothyroidism.2 Therefore, delicate investigations for ectopic thyroid should be carried out to decide therapeutic intervention before operation. Here, we report a case of subhyoid ectopic thyroid to emphasise the importance for evaluating such patients.

Case report

A 50-year-old Chinese woman presented to her local practitioner with a 5-year history of a painless and elastic mass in the midline of neck, moving up and down with swallowing in the region of hyoid bone. Under the impression of thyroglossal duct cyst, she was referred by the local practitioner to our hospital for surgical intervention.

A thyroid function test revealed a euthyroid state, and anti-thyroglobulin or anti-microsomal antibody could not be detected. A thyroid I-131 scan revealed heterogenous and multinodular goitre, with ectopic I-131 uptake in the subhyoid area. Neck ultrasonography showed a bilateral fine multinodular goitre, and a 1.66 x 1.64 x 1.58 cm solid, hypoechoic, heterogenous tissue just below the hyoid bone.

Perinodular vascularisation was noted via colour Doppler ultrasound (Figure 1). Fine-needle aspiration cytology of this mass showed clusters of follicular cells with larger cellular nuclei by rapid staining.3 Ectopic thyroid was favoured with potential neoplastic change, and an operation was suggested. Pathological examination showed papillary carcinoma arranged in papillae with ground-glass nuclei in ectopic thyroid; and adenomatous goitre without primary carcinoma was found in thyroid parenchyma. No lymph nodes metastasis was recognised. Postoperative I-131 ablation (30 mCi) was carried out, and cancer work-up revealed residual thyroid tissue without metastasis.

Figure 1. Thyroid ultrasonography of ectopic thyroid showed a hypoechoic, heterogenous nodule with perinodular vascularisation (arrowed)

Discussion

The thyroid gland is formed during embryonic stage as epithelial proliferation of the primitive alimentary tract. The median anlage of thyroid parenchyma migrates from the pharyngeal floor in the foramen caecum of the tongue (during the third to fourth week of development) and forms a shield in front of thyroid cartilage and trachea. Ectopic thyroid formation usually, represents an arrest of thyroid anlage in the descent along the normal pathway. These anatomically correctly positioned thyroid tissues are subject to nodular hyperplasia, and rarely neoplastic formation.

Several decades ago, lateral aberrant thyroid tissue was usually concluded to be metastatic cancer.4 Surgical excision of ectopic thyroid seemed to be the best policy to identify possible malignancy in the past experience.5 However, the old dictum was modified, because absence of the normal thyroid gland may occur in 70% of patients with ectopic thyroid.2,6 Indeed, if the ectopic thyroid is benign and is the only thyroid tissue present, surgical excision of ectopic thyroid will result in permanent hypothyroidism.2,7,8

Therefore, to decide the correct therapeutic strategy between benign and malignant lesions, delicate investigations are indicated for such ectopic thyroid tissue. Thyroid ultrasonography, radioactive iodine scanning, and fine-needle aspiration cytology are safe, rapid, and minimally invasive methods for preliminary diagnosis in ectopic thyroid.

Author information: Hsin-Yu Lee, Senior Lecturer, Division of Endocrinology; Mei-Hsiu Chen, Senior Lecturer, Division of Endocrinology; Chih-Yuan Wang, Assistant Professor and Chief of Division of Endocrinology, Department of Internal Medicine, Far-Eastern Memorial Hospital and National Taiwan University, Taipei, Taiwan

Correspondence: Dr Chih-Yuan Wang, Division of Endocrinology, Department of Internal Medicine, Far-Eastern Memorial Hospital and National Taiwan University, 4F-4, No.121, Sec. 1, Ho-Ping East Road, Da-An District, Taipei, 106, Taiwan. Fax: +886 2 23414262; email: thyroid@ms28.hinet.net

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