Most cysts of the jaws arise from odontogenic epithelium. These are relatively common lesions – most are inflammatory cysts (about 55% of all jaw cysts), dentigerous cysts (22%) or odontogenic keratocysts (keratocystic odontogenic tumours; 19%).
Epithelial proliferation – either stimulated by inflammation in the case of radicular cysts, or occurring with genetic stimulation in the case of keratocystic odontogenic tumours and probably the glandular odontogenic cysts.
Cytokines: IL-1-alpha, TNF-alpha, MCP-1 (Monocyte chemotactic protein-1), and RANTES (regulated upon activation, normal T-cell expressed, and secreted (also known as CCL5)), levels are significantly higher in radicular cyst fluids than those in the residual cysts.
Odontogenic cysts are often discovered as an incidental finding on imaging (Fig. 45.1). They are generally symptomless, slow-growing and may reach a large size before they give rise to symptoms, such as:
swelling: cysts in bone initially produce a smooth bony hard lump with normal overlying mucosa but, as the bone thins, it may crackle on palpation rather like an egg shell (termed ‘egg shell cracking’). When the overlying bone is resorbed, the cyst may show through as a bluish fluctuant swelling (Fig. 45.2)
The diagnosis of an odontogenic cyst is based on an adequate history, clinical examination and appropriate investigations, such as pulp vitality testing and radiographs (both intraoral and extraoral) of associated teeth, together with aspiration and analysis of cyst fluids, and histopathology (Table 45.1).
|In most cases||In some cases|
TREATMENT (see also Chs 4 and 5)
|Regimen||Use in secondary care (severe oral involvement and/or extraoral involvement)|
|Likely to be beneficial||Enucleation
Enucleation is the complete removal of the cyst: the benefit is that all the cyst tissue is available for histological examination and the cyst cavity will usually heal uneventfully with minimal aftercare. Enucleation is potentially problematic however, if the cyst involves the apices of adjacent vital teeth, as the surgery may deprive the teeth of their blood supply and render them non-vital.
Marsupialization is the partial removal of the cyst: the benefit is that it is somewhat less invasive than enucleation and tooth vitality is retained but it requires considerable aftercare and good patient cooperation in keeping the cavity clean whilst it resolves. In order to keep the cavity open, a ‘bung’ or acrylic plug is usually inserted in the opening, often attached to a denture or acrylic splint. The bung stops most food collecting in the cavity, but the cavity must still be syringed by the patient after each meal. Healing is slower than after enucleation: marsupialized cyst cavities may take up to 6 months to close down to the extent of becoming ‘self-cleansing’. The other disadvantage of marsupialization is that not all the cyst lining is available to histopathological examination, and this could lead to misdiagnosis.
The epithelial lining of inflammatory cysts is derived from the rests of Malassez, which proliferate to produce thick, irregular, often incomplete squamous epithelium, with granulation tissue forming the cyst wall in the denuded areas (Fig. 45.3). Depending on the nature of the inflammatory response, there may be areas of chronic inflammation, or acute inflammation with abscess formation. Cholesterol crystal clefts are often present and mucous cells may be found. The cyst fluid is usually watery, but may be thick and viscid with cholesterol crystal clefts giving it a shimmering appearance. The cysts have capsules of collagenous fibrous connective tissue and cause bone resorption and may become quite large.
Bacterial endotoxins may initiate epithelial proliferation together with complement activation and T lymphocyte infiltration, T cells releasing contributory inflammatory cytokines-interleukins, IL-1 and IL-6, in particular. Osmosis plays a role in cyst expansion. Prostaglandins, collagenases and matrix metalloproteinases plus gene products NF-κB ligand (RANKL) and osteoprotegerin (OPG) appear to be associated with the bone destruction both in periapical cysts and periapical granulomas. The Runx2 (core-binding protein (cbfa)1/polyoma enhancer-binding protein (pebp)2alphaA) a DNA-binding transcriptional molecule expressed in osteoprogenitor cells, and transforming growth factor (TGF-β2) are involved in the new bone formation.
Radicular cyst (dental or periapical cyst): where the cyst is associated with the apex of a non-vital tooth. Occasionally, a radicular cyst may develop on the lateral aspect of a root, where the stimulus has been an inflammatory reaction arising from necrotic pulp in a lateral root canal. Radicular cysts are seen especially where:
The diagnosis is based on history, clinical examination and appropriate investigations, such as pulp vitality testing and radiographs (both intraoral and extraoral) of associated teeth, aspiration and analysis of cyst fluids, and histopathology. Protein p63 expression may be useful to identify cyst types with a more aggressive and invasive phenotype.
Treatment (see also Chs 4 and 5)
The treatment of inflammatory cysts depends on whether or not the involved non-vital tooth is to be retained. Conventional intra-canal endodontic treatment will often lead to the resolution of very small radicular cysts, but regular radiographic review is necessary until there has been complete resolution of the cyst. If, when the tooth has been root-filled, the cyst does not resolve, or if the cyst is of such a size that it is unlikely to resolve with endodontic treatment alone, surgery is indicated – either enucleation or marsupialization.
Dentigerous cyst is the second most common odontogenic cyst. This develops within the normal dental follicle that surrounds an unerupted tooth, or from degeneration of the stellate reticulum, or an accumulation of fluid between the layers of the reduced enamel epithelium. The lining typically consists of flattened stratified epithelium.
The dentigerous cyst is most frequently found in areas where unerupted teeth are found – mandibular third molars, maxillary third molars and maxillary canines, in decreasing order of frequency. These cysts may grow to a large size, displace the tooth with which they are associated, or rarely cause resorption of adjacent tooth roots
Diagnosis is usually made by clinical and radiographic assessment – when the follicular space exceeds 5 mm from the crown it is likely that a cyst is present. However, odontogenic keratocysts and ameloblastomas may occasionally mimic the radiological appearances of follicular cysts. Aspiration may be helpful in differentiating the lesions
Eruption cysts are considered as minor soft tissue forms of dentigerous cysts. In these cases, the involved teeth are usually prevented from eruption by dense fibrous tissue overlying them. They often burst spontaneously before eruption of the associated tooth, and only require excision if impeding normal eruption. Then, a narrow window can be excised over the erupting tooth.
The KCOT is the least common, but most dangerous odontogenic cyst. KCOT can be associated with the naevoid basal cell carcinoma syndrome (NBCCS: Gorlin syndrome) (see Ch. 56). By definition, most KCOTs develop instead of a tooth, arising from the dental lamina or remnants, while some, particularly in the posterior mandible, may develop from basal cell off-shoots or hamartomas from the overlying gingival epithelium. They may be associated with the PTCH gene on chromosome 9 and the epithelium may harbour patched (PTCH) mutations, leading to constitutive activity of the embryonic Hedgehog (Hh) signalling pathway.
KCOT growth has been attributed to osmolality of the cyst fluid, and to various bone-resorbing factors, including collagenases, IL-1, matrix metalloproteinases and parathyroid-hormone-related protein.
The KCOT is a great mimic; it may have many clinical appearances, and may be seen over a wide age range. Most involve the mandibular angle and may expand to occupy the major part of the ramus as a radiolucent lesion. They may sometimes be multilocular. They may resorb the cortical plates and expand into the soft tissues, envelop unerupted teeth giving a dentigerous appearance or displace teeth but not resorb them. KCOTs are generally painless, and often grow to a large size before giving rise to symptoms, unless they become secondarily infected.
Diagnosis may be suggested by clinical features supported by imaging, and aspiration and estimation of soluble protein level in aspirated cyst fluid may be an aid to the diagnosis, since a protein level of <4 g/100 mL suggests KCOT, whereas a value >5 g/100 mL suggests a radicular or dentigerous cyst, or rarely a cystic ameloblastoma. The demonstration of keratin squames in an aspirate is virtually diagnostic of a KCOT. The diagnosis of KCOT is confirmed on histological grounds.
The cyst lining usually has a characteristic appearance of a regular keratinized stratified squamous epithelium, commonly five to eight cell layers thick and without rete pegs (Figs 45.4 and 45.5). There is a well-defined basal layer predominantly of columnar, but occasionally cuboidal, cells. Desquamated keratin is often present within the cyst lumen and the fibrous wall is usually thin.
Treatment (see also Chs 4 and 5)
Gorlin syndrome should be excluded – especially if the lesions are bilateral and/or in young people. Although there is some dispute over the most appropriate treatment for keratocysts, all authors agree that the cyst lining should be meticulously removed. Small unilocular lesions should be thoroughly enucleated. Large or multiloculated cysts should be excised with a margin of surrounding bone. KCOTs tend to recur following removal; recurrence rates can be as high as 60%.