What is the annual risk of infection in congenital midline neck cysts in children? Thyroglossal duct cysts versus dermoid cysts.

INTRODUCTION: Midline neck lumps in children are mostly found to be thyroglossal duct cysts or dermoid cysts. Thyroglossal duct cysts often have an associated sinus tract which may connect all the way to the foramen caecum on the tongue, while dermoids have no such connection. This study aims to estimate the annual infection risk for midline neck cysts based on our patient series, and to see if this differs between thyroglossal duct cysts and dermoid cysts. METHODS: All children seen at the Royal Hospital for Children, Glasgow who underwent surgical excision of a midline neck cyst between 1st January 2017 and 31st December 2021 were identified. In those whose cyst had been infected prior to surgical excision, the age at which the first episode of infection occurred was recorded and used to calculate a survival curve. RESULTS: We identified 53 children (29 male, 24 female) aged 1-16 years (median 4) at the time of surgical excision. There were 26 thyroglossal and 24 dermoid cysts, plus 2 with indeterminate histology and 1 lymph node. Of the 24 dermoids, 4 suffered infection prior to surgery (17%), and 2 of these recurred after surgery (8%). Of the 26 thyroglossal cysts, 16 suffered infection prior to surgery (62%) and 5 of these recurred (19%). 78% of thyroglossal and dermoid cysts had at least 1 episode of infection by age 10 years. DISCUSSION: In a child with a congenital midline neck cyst that has never been infected, deferring surgery for a year comes with a 7.8% risk that the cyst will get infected.

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

BACKGROUND: Thyroglossal duct cysts and dermoid cysts both commonly present as midline neck lumps in children. They are treated as separate entities with different embryological origins. There are isolated reports of thyroid gland tissue in a dermoid cyst, concurrent thyroglossal and dermoid cysts, and cysts with mixed histology. It is not known if these are rare or common. METHODS: All children undergoing excision of a congenital midline neck cyst between January 2017 and December 2022 were identified. Histopathology slides were reviewed in detail. RESULTS: In 53 children, there were 26 thyroglossal duct cysts, 24 dermoids, 1 lymph node and 2 with no diagnostic material identified. Five dermoids (28 per cent) had associated thyroid gland tissue, and 1 (4 per cent) had hybrid histology with keratinising and respiratory epithelium. Infection occurred in 17 per cent of dermoids prior to excision and 8 per cent of dermoids recurred after excision. CONCLUSION: Hybrid histology, infection and recurrence are all common in midline neck dermoids. A new theory for their embryological origin is proposed, with the suggestion that some may need more extensive surgery.