Thyroid tissue outside the thyroid gland: Differential diagnosis and associated diagnostic challenges

Area of Science:

• Pathology
• Endocrinology
• Surgical Pathology

Background:

• Ectopic thyroid tissue, found outside the normal thyroid gland location, can manifest in diverse anatomical sites.
• These ectopic thyroid tissues encompass a spectrum of conditions, ranging from benign cysts to malignant neoplasms.
• Recognizing these entities is crucial as they can mimic other pathologies, posing diagnostic difficulties.

Purpose of the Study:

• To comprehensively review and elucidate various conditions involving thyroid tissue located outside the thyroid gland.
• To discuss the differential diagnostic considerations for both benign and malignant entities of ectopic thyroid tissue.
• To highlight the diagnostic challenges encountered by pathologists in identifying these uncommon thyroid tissue presentations.

Main Methods:

• Literature review of established and emerging entities of ectopic thyroid tissue.
• Analysis of histological features and anatomical locations pertinent to differential diagnosis.
• Discussion of diagnostic criteria and evolving knowledge, particularly for incidentally found thyroid tissue.

Main Results:

• Identified key entities such as thyroglossal duct cysts, lingual thyroid, parasitic nodules, lymph node thyroid tissue, and struma ovarii.
• Emphasized that differential diagnosis relies heavily on lesion location and specific histological characteristics.
• Acknowledged that definitive diagnosis can be challenging, especially in cases of incidentally discovered thyroid follicles in lymph nodes.

Conclusions:

• Ectopic thyroid tissue presents a wide range of benign and malignant possibilities requiring careful pathological evaluation.
• Understanding the anatomical context and histological nuances is paramount for accurate diagnosis of these ectopic thyroid tissues.
• Continued research and evolving diagnostic criteria are necessary for challenging cases of extrathyroidal thyroid tissue.