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Thornwaldt cyst

Thornwaldt cyst (also spelled as a Tornwaldt cyst or Thornwald cyst) is a common incidental benign midline nasopharyngeal mucosal cyst.

Epidemiology

The lesion is developmental and usually asymptomatic. In most cases it is found incidentally and as such age of diagnosis represents age of imaging of the nasopharynx. Peak incidence has been variably reported between the ages of 15 and 60 years of age 1,3, presumably due to gradual accumulation of fluid following obliteration of the neck.

A Thornwaldt cyst has an autopsy prevalence of approximately 4%, with no gender predilection 3. These incidence found at autopsy studies in 1950´s and 60´s differs from findings in a recent incidence study using CT and/or MR, demonstrating incidence of only 0,06 % 7, the reason for this discrepancy remaining unclear.

Clinical presentation

Thornwaldt cysts are almost always asymptomatic. However, if they become infected they can cause halitosis or periodic discharge of foul tasting fluid into the mouth. Some may present with otitis media due to obstruction of the eustachian tube. A symptomatic cyst is also called Thornwaldt´s disease 7,8.

Pathology

Thornwaldt's cysts are classified as crusting and cystic 8. They form as a result of retraction of the notochord where it contacts with the endoderm of the primitive pharynx.
This is believed to happen at about the 10th week of embryonic development. Closure at the orifice results in so called cystic type, while crusts adhering to the orifice without closing result in crust type 8. The cyst is lined by respiratory epithelium and accumulates with fluid with variable proteinaceous content, inflammation can occur due to obstruction.

Rarity section contains a report of Thornwaldt cyst formation following concurrent chemoradiotherapy for nasopharyngeal carcinoma 6.

Radiographic features

These lesions have a characteristic appearance and should usually not be confused with more sinister pathology. Typically they are well circumscribed rounded lesions immediately deep to the mucosa. They are usually nestled between and anterior to the longus colli muscles they elevate the mucosa forming a convex surface into the nasopharynx. They are variable in size, ranging from a few millimetres to a few centimetres in diameter, but are typically 2 - 10mm in size1,3

CT 

On CT they appear as well circumscribed low density (fluid density centrally) and are non enhancing. If the fluid is protein rich, then it may be hyper-attenuating and even mimic a solid lesion.

MRI

Similarly, MRI demonstrates these cysts as being well circumscribed with a thin wall.

  • T1 - signal is variable depending of protein content
  • T2 - high signal 
  • T1 C+ (Gd) - no enhancement

Treatment

Asymptomatic lesions require no treatment. If treatment is required then de-roofing the cyst (marsupialisation) is usually sufficient, and can be performed via a transnasal approach 4.

Differential diagnosis

There is usually no real differential, however adenoidal / mucosal masses can sometimes have cystic components, and therefore the differential includes:

Etymology

It is named after Gustav Ludwig Thornwaldt, German physician, 1843-1910 5

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