Dermoid cyst or thyroglossal duct cyst? A histopathological complexity

Prevalence of thyroid gland tissue in midline neck dermoid cysts in children and a proposed new ‘thyroglossal entrainment’ hypothesis for their formation

“…Previous authors 8 have suggested an alternative hypothesis, in which mixed thyroglossal-dermoid histology occurs because of areas of squamous metaplasia in thyroglossal duct cysts. We believe that our ‘thyroglossal entrainment’ hypothesis provides a better, more complete explanation for all the unusual combinations of histology identified by reports, including the presence of ectopic thyroid tissue in dermoid cysts, 3 the presence of mixed thyroglossal-dermoid histology in some lesions, 8–10 and the presence of thyroglossal and dermoid cysts within the same patient. 4–7

Midline neck lumps are common in children; these are usually thyroglossal duct or dermoid cysts, considered clinically and pathologically separate, with different embryological origins There have been isolated reports of hybrid pathologies, suggesting some degree of overlap between these entities; it is not known if these are rare or common findings In 50 children with congenital midline neck cysts, there were 24 dermoids, of which 5 had associated thyroid gland tissue, and 1 had hybrid histology with both keratinising and respiratory epithelium Infection occurred in 17 per cent of dermoids prior to excision, and 8 per cent of dermoids recurred after excision A novel ‘thyroglossal entrainment’ hypothesis is proposed for the formation of some midline neck dermoids It is suggested that patients with prior dermoid infection or recurrence after simple excision be considered for more extensive surgery to remove any associated thyroglossal tract

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“…Chandiok and colleagues 3 reported a single case of ectopic thyroid gland tissue found in close association with a midline cervical dermoid cyst; however, ours is the first attempt to identify whether such findings are rare or common. We found thyroid tissue to be present in 28 per cent of our series, so it cannot be considered uncommon.…”

“…A recent paper from Australia 3 reported thyroid gland tissue in the wall of a midline neck dermoid cyst. The authors suggested that dermoid and thyroglossal duct cysts may not be so completely pathologically distinct, although they stopped short of suggesting how they might be linked.…”