Q44.B
A cystic hygroma is a congenital multiloculated lymphatic lesion that can arise anywhere, but is classically found in the left posterior triangle of the neck. This is the most common form of lymphangioma. It contains large cyst like cavities containing watery fluid. Microscopically cystic hygroma consists of multiple locules filled with lymph. In the depth the locules are quite big but they decrease in size towards the surface.
It can be associated with a nuchal lymphangioma or a fetal hydrops and Turner syndrome
http://en.wikipedia.org/wiki/File:Lymphangioma.jpg
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While a thyroglossal cyst is a fibrous cyst that forms from a persistent thyroglossal duct.
It usually presents as a midline neck lump (in the region of the hyoid bone) that is usually painless, smooth and cystic, if infected pain can occur. There may be difficulty breathing, dysphagia (difficulty swallowing), and/or dyspepsia (discomfort in the upper abdomen), especially if the lump becomes large.
The most common locations for a thyroglossal cyst is midline or slightly off midline, between the isthmus of the thyroid and the hyoid bone or just above the hyoid bone. A thyroglossal cyst can develop anywhere along a thyroglossal duct, though cysts within the tongue or in the floor of the mouth are rare.
A thyroglossal cyst will move upwards with protrusion of the tongue.
Thyroglossal cysts are associated with an increased incidence of ectopic thyroid tissue. Occasionally, a lingual thyroid can be seen as a flattened strawberry-like lump at the base of the tongue.
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BRANCHIAL CLEFT CYSTS are congenital cysts, that arise in the lateral aspect of the neck when the second branchial cleft fails to close during embryonic development.
They are bilateral in about 2-3% of the cases. Usually, they do not appear at birth, but become noticeable much later in life. If they get infected, they may form a deep neck abscess or a draining fistula.
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for more information
http://www.ghorayeb.com/branchialcleft.html