Cyst is known to arise in man ever since he has teeth. Although cyst can arise anywhere in the body, the bones of jaw i.e. the maxilla and mandible are the bones with the highest prevalence of cyst in the human body due to abundant amount of epithelium remnants in jaws.
The term cyst is derived from latin word cystis which means sac or bladder like cavity. Imagine a balloon,a cyst exactly looks like a balloon. Cyst of jaw is of great clinical importance as it causes significant destruction of jaw bones and disturbance in dentition.
By definition given by WHO
A cyst is a pathological cavity filled with fluid,semi-fluid or gas and is not formed by accumulation of pus. A cyst may or may not be lined by epithelium.
A cyst in which lining of lumen is derived from epithelium involved/produced during tooth development. The cyst that arises from the tissue that normally develops into teeth are called odontogenic cyst. So the remnants of epithelium right from basal layer of oral epithelium,dentallamina,enamelorgan,cell rests of mallasez and cell rests of serre can give rise to cyst and these are then called odontogenic cysts.
Appearance of Cyst
A cyst is composed of a central cavity or lumen which contains the fluid, semi fluid or gas, the epithelial lining maybe keratinized, non-keratinized, pseudo stratified or cuboidal. Outermost capsule or wall which is composed of collagen fibres,fibroblasts, blood vessels and ground substance.
Mechanism of cyst formation
Cyst formation requires the presence of epithelium in deep tissue and a proliferative stimulus.The exact mechanism of cyst formation is not known but it occurs in two phases,initiation and enlargement.
The remnants of epithelium in the jaw proliferate in response to a stimulus which can be
-inflammation, as in case of radicular cyst
-malformation of enamel organ and/or decrease in vascular supply, as in case of dentigerous cyst
-genetic factors or other unknown stimulus as in case of keratocysts
Whatever be the stimulus this leads to proliferation of epithelial cells. Epithelial mass increases in size by division of cells on the periphery.
These epithelial cells derive their nutrition from surrounding CT as the size increases the innermost cells move away from nutrition which leads to necrosis and death of innermost cells and an epithelial lined cavity filled with fluid material is formed.
There have been many theories put forward as to how the cyst enlarges which includes
- Mural growth theory
- Hydrostatic enlargement
- Bone resorbing factors
Although inflammatory and developmental cysts are initially caused by different factors,they appear to have common growth mechanism. Let’s understand each theory one by one.
- Mural growth theory
According to mural growth theory enlargement of the cyst occurs due to active division of cells at the periphery of cyst lining and this increases the surface area of the lining.
Finger like projections seen in the epithelial lining represent the zones of active division and proliferation.
- Hydrostatic theory
This mechanism of cyst enlargement is mainly proposed for radicular cyst,follicular cyst,periodontal cyst etc. Due to
-decomposition of epithelial cells and leukocytes
-and active secretion from goblet cells and mucous cells in cyst lining
The osmolality of cyst fluid becomes higher than that of serum. As a result hydrostatic internal pressure becomes greater than the capillary pressure. Therefore,the tissue fluid diffuses into the cyst and size of the cyst increases.
- Bone resorbing factors theory
Culture of the cystic tissue has been shown to release potent bone resorbing factors. The sources of tissue factors are found to be cystic capsule and leukocytes.
Classification of cyst
Classification of cyst is very important for diagnosis and proper management of patient. Various tumors mimic the C/F of cyst and thus can be confusing.
Characteristic features of the cyst
These are the general features from which we come to a conclusion that the lesion is a cyst.
- Clinical features
Majority of cysts are benign and symptoms are due to size and location
They usually present as slowly enlarging painless swelling causing displacement of adjacent teeth malocclusion and sometimes root resorption and paraesthesia if the cystic swelling is exerting pressure over the nerve.
Expansion in the bone is different for different types of cyst for example,dentigerous cyst expands buccolingually and OKC expands antero-posteriorly in the jaw.
Larger lesions can cause pathological fracture of the jaw.
- Vitality of tooth
It is very important to take a proper history including history of lamina.
If a tooth is non vital,the swelling may have an inflammatory origin and if all the adjacent tooth are vital it may developmental in origin.
- Sinus tract
We may also see through and through sinus tract formation in relation to swelling which shows that the swelling is infected.
- Position of cyst
In case of mandibular lesion it is also important to note the location of lesion w.r.t inferior alveolar canal. If the lesion is above IAC it is TBC and if it is below IAC it is stafne cyst/defect
- Involvement of tooth
It is very important to note if there is an unerupted tooth associated with the swelling.Cyst like OKC ,dentigerous cyst and COC shows the presence of unerupted teeth
- Fluid on aspiration
Fluid can be extripated from a cystic lesion using wide bore needle (18 gauge)
Different type of aspirate is obtained and the provisional diagnosis may be based on the type of aspirate
For example –
|Clear pale straw color fluid with cholesterol
If blood is obtained on aspirate it means either needle Is in blood vessel or it is a vascular lesion & if u obtain Air on aspirate it indicates maxillary antrum or TBC.
- Biochemical analysis of fluid.
If we do biochemical evaluation of this fluid and the total protein content is > 4gm/100ml it indicates radicular or dentegerouscyst And if total protein Is < 4gm/100ml it indicates OKC
- Radiographic Features
Characteristic radiographic features of cyst is a round or oval radiolucency surrounded by a sharp radiopaque line of condensed bone. This line is unseen in an infected cyst or a very large cyst of a very large cyst that is growing rapidly. Large cyst in mandible may displace inferior alveolar canal which is clearly seen in radiograph.Some cyst may even present as a multilocular radiolucency.
Ultimately the gold standard of diagnosis is biopsy to confirm the diagnosis prior to treatment planning.But what important is to differentiate cyst from a Neoplasm