Ectopic Thymic Tissue as a Rare and Confusing Entity

Abstract

A 16-year-old girl with intrathyroidal ectopic thymic tissue, which was diagnosed incidentally after surgery for thyroid nodule, is reported to emphasise the possible clinical and surgical presentations of this rare entity.

Intrathyroidal ectopic thymus in children: a sonographic survey

“…It has been reported that 6% of ectopic cervical thymus can cause dysphagia, dyspnea or stridor; however, to our knowledge no such symptoms have been reported in cases with IET [8]. There have been rare cases of thymoma, thymic carcinoma and lymphocyte-predominant lymphoma arising from the ectopic thymic tissue [10,22,23]. Ectopic thymus can also undergo thymic hyperplasia and may potentially play a role in myasthenia gravis [10,24].…”

Ectopic Thymus Presenting as a Thyroid Nodule in a Patient with the Carney Complex

“…Thymus is derived from both ectoderm and endoderm of the third and often the fourth branchial clefts and pharyngeal pouches along with the thyroid and parathyroid glands (16,17). During the sixth week of gestation, the epithelium of the third pharyngeal pouch differentiates into the inferior parathyroid and the thymus; the epithelium of the elongated ventral parts of the third pair of pouches proliferates and forms cavities (17).…”

“…During the sixth week of gestation, the epithelium of the third pharyngeal pouch differentiates into the inferior parathyroid and the thymus; the epithelium of the elongated ventral parts of the third pair of pouches proliferates and forms cavities (17). The bilateral primordia of thymic tissue migrate to the median plane, form the definitive thymus which then descends into the superior mediastinum (16,17). Ectopic thymic tissue may be located along this pathway from the angle of mouth or base of the skull to the superior mediastinum (18)(19)(20)(21).…”

“…Ectopic thymic tissue may be located along this pathway from the angle of mouth or base of the skull to the superior mediastinum (18)(19)(20)(21). Aberrant thymic tissue may be found in the neck of up to 20% of the general population (16,17) but intrathyroid ectopic thymic tissue is exceedingly rare and is usually found incidentally (18). Interestingly, in pediatric necropsies, ectopic thymic tissue is quite often associated with congenital heart disease (18).…”

“…Intrathyroidal ectopic thymic tissue is rarely symptomatic and is often interpreted as Hashimoto's thyroiditis or lymphoma of the thyroid when evaluated by fine-needle aspiration (16,(18)(19)(20)(21). Differential diagnosis of intrathyroidal and=or cervical thymomas should include related tumors of thymic or branchial pouch origin, such as hamartomatous thymomas, spindle epithelial tumors with thymus-like differentiation, and carcinoma showing thymus-like differentiation (20).…”