45: Odontogenic cysts and tumours

Odontogenic cysts and tumours

ODONTOGENIC CYSTS

A cyst is a pathological cavity having liquid, semi-liquid or gaseous contents. It is frequently, but not always, lined with epithelium.

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%).

There is an overall male predominance and the mandible is affected three times as commonly as the maxilla.

Most odontogenic cysts are benign, but occasionally tumours or squamous cell carcinomas may arise within.

AETIOLOGY AND PATHOGENESIS

The main pathogenic factors include the following:

TREATMENT (see also Chs 4 and 5)

Odontogenic cysts are managed either by enucleation or by marsupialization (Table 45.2):

Table 45.2

Regimens that might be helpful in management of patient suspected of having odontogenic cyst or tumour

Regimen Use in secondary care (severe oral involvement and/or extraoral involvement)
Likely to be beneficial Enucleation
Marsupialization

image 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.

image 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.

INFLAMMATORY CYSTS

Inflammatory cysts are by far the most common of all jaw cysts and arise in association with a non-vital tooth.

Aetiology and pathogenesis

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.

DEVELOPMENTAL CYSTS

Dentigerous (follicular) cyst

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.

KERATOCYSTIC ODONTOGENIC TUMOUR (KCOT: ODONTOGENIC KERATOCYST; OKC; PRIMORDIAL CYST)

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.

Diagnosis

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.

Follow-up

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Jan 9, 2015 | Posted by in Oral and Maxillofacial Pathology | Comments Off on 45: Odontogenic cysts and tumours
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