This chapter is designed to simplify the process of arriving at a radiological differential diagnosis when confronted with a radiolucency of unknown cause on a plain radiograph. This process requires clinicians to follow a methodical step-by-step approach and to know the typical features of the various possibilities. Such a step-by-step guide is suggested and summarized in Fig. 26.1. Although most lesions are still detected using plain radiographs, this process can be greatly facilitated in many cases if advanced imaging modalities, described in Chapters 16 and 18, such as computed tomography (CT), cone beam CT or magnetic resonance (MR), are available.
Unfortunately, most of the lesions encountered share several similar features and often individual conditions can present in many different ways. Thus the summary of features for the more important conditions included in this chapter is an attempt to unravel some of the inevitable confusion. Also, for simplicity, the frequency with which the various lesions present has been divided arbitrarily into common, uncommon and rare. It is hoped and intended that the reader should expand on this short-notes style framework by referring to the suggested reading list.
Consider the classification and subdivision of cysts and other similar radiolucencies within each of the other main disease categories, as shown in Table 26.1. This resultant list includes most of the more likely diagnostic possibilities for the unknown radiolucent lesion.
|Odontogenic||Radicular (dental) cyst|
|Residual radicular cyst|
|Lateral periodontal cyst|
|Odontogenic keratocyst (keratocystic odontogenic tumour)|
|Non-odontogenic||Nasopalatine duct / incisive canal cyst|
|Bone cysts (see bone-related lesions)|
|Tumours and tumour-like lesions|
|(epithelial with mature, fibrous stroma without odontogenic ectomesenchyme)||Squamous odontogenic tumour
Calcifying epithelial odontogenic tumour (Pindborg tumour)
|Adenomatoid odontogenic tumour|
|Keratocystic odontogenic tumour (odontogenic keratocyst)|
|Benign odontogenic||Ameloblastic fibroma|
|(epithelial with odontogenic ectomesenchyme, with or without hard tissue formation)||Ameloblastic fibro-odontoma
Calcifying cystic odontogenic tumour (calcifying odontogenic cyst)
|Benign odontogenic||Odontogenic fibroma|
|(mesenchymal and/or odontogenic ectomesenchyme with or without odontogenic epithelium)||Odontogenic myxoma|
|Malignant odontogenic||Odontogenic carcinoma|
|Non-odontogenic intrinsic primary bone tumours||Benign – Fibroma
|– Central haemangioma|
|Malignant – Osteosarcoma|
|Extrinsic primary tumours involving bone||Squamous cell carcinoma|
|Secondary metastatic bone tumours|
|Lymphoreticular tumours of bone||Multiple myeloma|
|Large cell lymphoma|
|Langerhans cell disease||Eosinophilic granuloma|
|(Histiocystosis X)||Hand–Schüller–Christian disease|
|Giant cell lesions||Central giant cell lesion (granuloma)|
|Brown tumour in hyperparathyroidism|
|Aneurysmal bone cyst|
|Osseous dysplasias||Periapical osseous dysplasia|
|(Fibro-cemento-osseous lesions)||Focal osseous dysplasia|
|(early stages)||Florid osseous dysplasia|
|Familial gigantiform cementoma|
|Other lesions||Ossifying fibroma|
|Simple bone cyst|
|Stafne’s bone cavity|
Compare the radiological features of the unknown radiolucency with the typical radiological features of these possible conditions. Then construct a list showing, in order of likelihood, all the conditions that the lesion might be. This list forms the radiological differential diagnosis.
Infection is described elsewhere (apical, Ch. 21, spreading, Ch. 28) and trauma is described in Chapter 29. The rest of this chapter is devoted principally to differentiating between the different cysts – the most common of the remaining categories – and the other lesions that often present as very similar radiolucencies.
Note: The term buccal bifurcation cyst is used to describe an inflammatory odontogenic cyst that develops on the side of a molar tooth in relation to a buccal enamel spur or pearl.
The diagnosis of this rare developmental cyst should be reserved for a cyst in the lateral periodontal region that is not an inflammatory cyst or an atypical odontogenic keratocyst. It is thought to develop from either the cell rests of the dental lamina or from remains of the reduced enamel epithelium on the lateral surface of the root.
Note: The term eruption cyst is used to describe a dentigerous cyst when it is in the soft tissues overlying the unerupted tooth.
Somewhat controversially, in 2005 the WHO Working Group recommended that the odontogenic keratocyst be renamed the keratocystic odontogenic tumour as they felt this name better reflected its neoplastic nature. The WHO now defines this lesion as a benign uni- or multicystic intraosseous tumour of odontogenic origin with a histologically characteristic lining of parakeratinized stratified squamous epithelium with a potentially aggressive, infiltrative behaviour. It is believed to develop from the epithelium of the dental lamina – the cell rests of Serres – instead of the normal tooth which is therefore typically missing from the series. Lesions are typically solitary but multiple odontogenic keratocysts are a feature of nevoid basal cell carcinoma syndrome (Gorlin’s syndrome), which also includes multiple basal cell carcinomas, and skeletal anomalies, e.g. bifid ribs and calcification of the falx cerebri.