Oral medicine:16. radiolucencies and radio-opacities. c. odontogenic tumours

Odontogenic tumours

Odontogenic tumours are rare, are often asymptomatic, and discovered incidentally on imaging (Table 1). They are generally slow-growing and may reach a large size before becoming symptomatic, eg:

They usually appear as well-defined corticated unilocular or multilocular radiolucencies but, unlike cysts, they are more likely to cause root resorption and buccal and lingual cortical expansion.

The majority of odontogenic tumours are benign. Management is surgical and is dependent upon the type of tumour and varies from enucleation to resection.

Benign odontogenic tumours

Benign odontogenic tumours are 100 times more common than malignant ones: most (>50%) are odontomas, or ameloblastomas (around 10%).

Ameloblastomas are significant since they may recur or metastasize. Composed of ameloblast-like epithelial cells arranged as a peripheral layer around a central area resembling stellate reticulum, two main histological types exist. The follicular type contains discrete islands (follicles) of epithelial cells: the plexiform type consists of anastomosing strands. Ameloblastomas predominate in the posterior mandible, presenting typically in third to fifth decades as a slow-growing, painless, uni-or multi-locular mass (‘soap-bubble’ appearance on imaging) (Figures 1 and 2) usually replacing a tooth and producing more buccolingual expansion and knife edge root resorption than does KCOT (but differentiation is difficult by plain radiography or CT). MRI may then help.

Squamous odontogenic tumour is rare and usually presents as a painless swelling and radiolucency between teeth which become mobile. It may mimic periodontal disease.

Calcifying epithelial odontogenic tumour (CEOT: Pindborg tumour) – rare, benign but aggressive. Three distinct histological features are:

Usually seen in mandibular premolar or molar region associated with the crown of an impacted tooth, CEOT is radiolucent with scattered calcified components.

Adenomatoid Odontogenic Tumour – is the ‘two-thirds tumour’ – most commonly noted in the second and third decades of life and two-thirds of cases:

Sheets and strands of epithelial cells are arranged as convoluted bands and tubular structures, in which ameloblast-like cells are arranged radially around a homogeneous eosinophilic material. It presents as a well-demarcated unilocular radiolucent lesion, often with punctate calcifications. It rarely recurs after excision.

Keratocystic odontogenic tumour (KCOT) has a propensity for destruction and recurrence locally. Radiologically, KCOT usually presents as a well-defined corticated unilocular or multilocular radiolucency which enlarges through cancellous bone, giving rise to late cortical expansion, and for its size the amount of bucco-lingual expansion is small compared to other odontogenic tumours (Figures 3 and 4). The lining has a regular keratinized stratified squamous epithelium, five to eight cell layers thick and without rete pegs. Desquamated keratin is often present within the lumen and the fibrous wall is usually thin. KCOT are often multilocular, well-defined, radiolucent, usually without an associated tooth. The keratin-rich debris shows a characteristic central signal drop on MRI T2-weighted images.

KCOT is associated with chromosome 9 patch gene mutations. Multiple KCOTs in young patients should suggest the basal cell naevus (Gorlin-Goltz) syndrome – an autosomal dominant disorder also with midface hypoplasia, frontal bossing and prognathism, falx cerebri calcification and skeletal anomalies.

Ameloblastic fibroma consists of islands, elongated strands, or terminal buds of ameloblast-like cells and central stellate reticulum cells, surrounded by a cellular hyaline material. It is usually well-defined, pericoronal multiloculated radiolucent and associated with an impacted tooth, often in the posterior mandible.

Odontogenic myxoma is clinically and radiographically indistinguishable from ameloblastoma.

Odontoma (odontome) – a ‘hamartoma’ consisting of dentine and enamel, is often associated with an impacted tooth, classified as follows:

Odontomes typically present during the second decade, are more common in females than males, and often in the mandibular premolar–molar region. Typically, they can behave like teeth: they can grow and tend to erupt, or may displace adjacent teeth. Failure of a tooth to erupt is usually the justifying reason for radiographic exposure which identifies the odontome.

Cementoblastoma is a neoplasm of cementum typically seen in patients under 25 years. Usually fused to a root (typically mandibular premolar or first molar), it is a well-defined radio-opacity with a radiolucent margin. It may cause pain which responds to NSAIDs. Hypercementosis, in contrast, is smoother, less nodular, and has a thin radiolucent margin continuous with the periodontal ligament space.

Malignant odontogenic tumours

These are generally considered as the malignant counterparts of the benign categories (Table 2).

Some useful points with regard to odontogenic tumours are given in Table 3.