follicular cyst of the mandible
Dentigerous cysts, also called follicular cysts, are slow-growing benign and non-inflammatory odontogenic cysts that are thought to be developmental in origin.
On imaging, they usually present as a well-defined and unilocular radiolucency surrounding the crown of an unerupted or impacted tooth within the mandible.
Dentigerous cysts are the second most common odontogenic cysts after those related to the roots of the teeth (periapical cysts) . They usually present in the 2 to 4 decades of life and are uncommonly seen in childhood because they almost exclusively occur in secondary dentition .
Typically, dentigerous cysts are painless and discovered during a routine radiographic examination, however, they may be large and result in a palpable mass. Additionally, as they grow, they displace adjacent teeth .
Several cases of dentigerous cysts presenting as recurrent head and neck infection or as a deep neck space abscess have been described.
A dentigerous cyst is formed by the hydrostatic force exerted by the accumulation of fluid between reduced enamel epithelium and the tooth crown of unerupted teeth . As such the cyst encloses the crown and is attached to the neck at the cementoenamel junction . They almost exclusively occur in permanent dentition. Stratified squamous nonkeratinising epithelium lines the cyst.
Over 75% of all cases are located in the mandible, with the most commonly involved teeth being :
- mandibular third molar (most common)
- maxillary third molar (2 most common)
- maxillary canine
- mandibular second premolar
Dentigerous cysts are usually solitary. However, multiple cysts are recognized to occur in association with syndromes such as:
Dentigerous cysts are frequently identified on OPGs. A cystic expansile pericoronal lesion containing the crown of an impacted tooth projecting into cystic cavity is considered pathognomonic and often no further imaging is required .
CT and MRI may give additional information and help in distinguishing this entity from other cystic lesions of the mandible and maxilla.
When small, it is difficult to differentiate a dentigerous cyst from a large but normal dental follicle. A working definition is that a dentigerous cyst exists when the distance between the crown and dental sac is greater than 2.5-3.0 mm .
Panoramic radiograph (OPG)
Radiographically, dentigerous cysts appear as unilocular well defined pericoronal radiolucencies centered on an impacted or unerupted tooth. They have a thin regular sclerotic margin and expand the overlying cortex without cortical breach (unless superimposed fracture or infection). Their size is extremely variable, ranging from only slightly greater in size than a normal follicle to very large, appearing to hollow-out the majority of the jaw .
The roots of teeth are often outside the cyst . There may also be erosion or resorption of the roots of adjacent teeth .
CT appearances mirror those of radiographs. The relationship to the unerupted tooth can often be better appreciated, and the cyst cavity is filled with water density fluid. Maxillary lesions may project superiorly into the paranasal sinuses or nasal cavity .
The main role of MRI is help distinguish these lesions from other cystic lesions of the jaw when appearances are atypical.
- T1: low signal, similar to water/CSF
- T2: high signal, similar to water/CSF
- T1 C+ (Gd): no solid component or enhancement, except for potentially a thin peripheral rim of enhancement
Treatment and prognosis
Treatment usually involves removal of the entire cyst and the associated unerupted tooth. In patients with a very large lesion or who are unfit medically, marsupialisaiton is an option .
Recurrence is uncommon but may occur if parts of the cyst lining are left in situ .
- pathological jaw fracture: if large enough
- very rarely dentigerous cysts may develop into mural ameloblastoma
- there is a potential for development of squamous cell carcinoma in the context of chronic infection
When small, it is difficult to differentiate a dentigerous cyst from a large but normal dental follicle .
When larger, the differential is essential that of lytic lesions of the jaw and includes: