Mechanism of development and pathomorphology
A follicular jaw cyst may begin its formation at the stage when the crown part of the future tooth is already fully formed, and the root has not yet begun to develop. However, most often the pathology occurs after the completion of tooth development. In such cases, the cystic cavity contains a fully formed tooth.
On macroscopic examination, the cyst presents as a single-chambered cavity. Its characteristic anatomical feature is that the connective tissue capsule attaches strictly at the neck of the causative tooth. As a result, the crown of the unerupted tooth faces directly into the lumen of the cavity. The cyst contents are represented by a transparent yellowish fluid with cholesterol crystals.
Microscopically, the structure of the follicular cyst wall is completely identical to a radicular one: a dense connective tissue capsule is located on the outside, and the cavity is lined on the inside with stratified squamous epithelium.
Clinical and radiographic presentation
The clinical course of the disease is largely similar to radicular cysts. A prolonged and completely asymptomatic growth is characteristic. Lesions rarely suppurate, so inflammatory symptoms are usually absent. During an oral cavity examination, the dentist most often detects a retained deciduous tooth in the dental arch and, accordingly, the absence of a permanent tooth in that spot.
Radiographic signs of a follicular cyst:
- Homogeneous bone radiolucency of regular round or oval shape.
- Borders of the defect are clear and even.
- The crown part of the unerupted tooth is clearly visualized inside the cyst cavity.
- The root of the causative tooth is always located outside the lesion.
Differential diagnosis must be carried out with other jaw cysts, as well as with cystic forms of odontogenic tumors.
Subperiosteal and residual cysts
As part of the differential diagnosis, it is important to consider the features of other cystic lesions.
Subperiosteal cyst Develops if the root of the causative tooth is located close to the outer surface of the jaw. The growing cystogranuloma perforates the cortical bone plate and continues to grow under the periosteum. Clinically: presents as a painless protrusion covered by unchanged mucosa. Palpation reveals the characteristic sign of fluctuation. Radiographically: a specific picture cannot be detected. Most often, only changes in the root apex area are visible (sometimes with a rim of sclerotic bone along the cyst borders, which is typical for chronic granulomatous periodontitis). The relationship of the roots with the cyst can vary.
Residual cyst This is a cyst that remained unrecognized in the jaw after the removal of the causative tooth and continued to grow. Found in both jaws. Complications: the lesion is capable of reaching giant proportions, which critically reduces bone tissue strength and contributes to the development of a pathological fracture. Diagnostic sign: the roots of adjacent intact teeth projecting onto the defect area retain an intact periodontal ligament space.
Keratocyst (primordial cyst)
A keratocyst is a rare lesion named for the ability of its lining epithelium to undergo keratinization. It develops predominantly in the mandible and is capable of spreading along its body, angles, and rami.
Growth characteristics and clinic: Due to the high density of the outer and inner cortical plates of the mandible, the cyst spreads between them, destroying the cancellous bone. The disease is capable of causing resorption of the walls of the mandibular canal. The onset is insidious, growth is asymptomatic, and a minor painless swelling appears later. There is no history of a connection between the pathology and diseased teeth. The cyst is often found accidentally or upon the onset of secondary inflammation. Danger: the keratocyst is prone to recurrence and is capable of undergoing malignant transformation (malignancy).
Diagnostics:
- X-ray: extensive radiolucency with clear polycyclic contours. Uneven resorption creates the illusion of multilocularity. The cortical plate is thinned or absent. The periodontal ligament space of the projecting roots is preserved.
- Morphology: to establish a definitive diagnosis, an open biopsy is indicated (mandatory excision of bone and lining). Macroscopically, it is a single cavity with bay-like indentations, filled with a grey amorphous mass with an unpleasant odor. Microscopically, it is a thin fibrous capsule with keratinizing epithelium.
- Differential diagnosis: performed with ameloblastoma (symptoms are similar, but ameloblastoma causes more pronounced jaw expansion).
Epithelial non-odontogenic cysts
This group includes aneurysmal and solitary bone cysts. These are rare tumor-like lesions affecting predominantly young individuals.
Unlike odontogenic cysts, they are characterized by fairly rapid growth: in just a few months, a patient may develop a painful swelling of the affected jaw area.
The radiograph shows an eccentrically located, localized focus of bone radiolucency, expanding in the form of a swelling towards the periosteum. During diagnostic puncture, the syringe fills freely with blood, which can lead the clinician to a mistaken thought of hemangioma. Microscopic examination reveals an osteoclastic lesion.
Briefly: answers to topical questions
What surgical treatment methods are used for a follicular jaw cyst?
Two main surgical interventions are used for a follicular jaw cyst: cystectomy and cystotomy. The choice of method depends on the size of the lesion.
- Cystectomy — complete enucleation of the cyst lining with primary closure (suturing). Used for small cysts (up to 3 cm).
- Cystotomy — used for large cysts.
For small sizes, outpatient removal of the cyst together with the causative tooth is possible (for example, the lower third molar). For extensive lesions extending to the body and ramus of the jaw, surgery is performed strictly in an inpatient setting. In case of suppuration, radical intervention is postponed until the inflammation is completely eliminated, having previously established outflow for the exudate.
Which tooth groups most often cause the formation of a follicular cyst?
The formation of a follicular cyst is most commonly caused by unerupted permanent or supernumerary teeth. Typical localization depends on the patient's age:
- In children, the region of the lower molars and upper canines is affected.
- In adults, the pathology most often occurs in the region of the lower wisdom teeth (third molars), lower second premolars, as well as upper canines and upper third molars.
Additionally, supernumerary teeth can act as the cause of a tooth-containing cyst development.
How to differentiate a keratocyst and an ameloblastoma on a radiograph?
Differential diagnosis of a keratocyst and ameloblastoma based on the radiographic picture is based on the following signs:
| Sign | Keratocyst | Ameloblastoma |
|---|---|---|
| Nature of the lesion | Extensive bone radiolucency with clear polycyclic contours | Polycystic or single-chambered cystic lesion |
| Multilocularity | Uneven bone resorption creates a false impression of multilocularity | May appear as a polycystic or single-chambered lesion |
| Bone changes | Cortical plate is thinned or locally absent | Causes more pronounced jaw expansion |
| Teeth in the lesion area | Periodontal ligament space of tooth roots projecting onto the cyst area is usually detected | An unerupted wisdom tooth may be present in the cavity |
Which specific cystic forms of odontogenic tumors must a follicular cyst be differentiated from?
Follicular cysts must be differentiated from ameloblastoma. Ameloblastoma may present as a polycystic or unilocular cystic lesion; an impacted wisdom tooth may be located within its cavity.
The follicular cyst radiograph rule: "Crown inside, root outside." The cyst lining always attaches to the tooth neck, leaving the root outside the cystic cavity.
Class and exam questions
On the radiograph of a follicular cyst, the coronal portion of an unerupted tooth is always identified within its lumen, while the root is located strictly outside the radiolucency zone.
On the radiograph of a follicular cyst, the coronal portion of an unerupted tooth is always identified within its lumen, while the root is located strictly outside the radiolucency zone.
Why is a residual cyst left in the jaw dangerous?
Residual cysts are capable of continuous growth, reaching large sizes. This leads to a significant decrease in bone strength and a high risk of pathological jaw fracture.
Why is an open biopsy mandatory when a keratocyst is suspected?
Keratocysts tend to have an aggressive clinical course, frequent recurrences, and are capable of malignant transformation. Definitive diagnosis and differentiation from ameloblastoma can only be made based on the results of a biopsy morphological examination.
What else to study on this topic
- Clinical presentation and surgical treatment of ameloblastoma
- Histological structure of osteoclastic lesions of the jawbones
- Open biopsy technique for jaw tumor-like lesions
- Mechanisms of keratocyst malignant transformation
- Differential diagnosis of vascular malformations (hemangiomas) and bone cysts
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