Despite the many different conditions that can affect the jaws, they can present radiographically only as areas of relative radiolucency or radiopacity compared to the surrounding bone. Even this division based on radiodensity is not clearcut – some lesions fall into both categories, but at different stages in their development.
As a result, many of these pathological conditions resemble one another closely. This often creates considerable confusion. Fortunately, the sites where the lesions develop, how they grow and the effects they have on adjacent structures tend to follow recognizable patterns. As mentioned in Chapter 19, it is the recognition of these particular patterns that provides the key to interpretation and the formation of a radiological differential diagnosis.
A detailed description helps to identify these patterns and determine the lesion’s basic characteristics. For example, it may reveal whether the lesion is a cyst or a tumour, whether it is composed of hard or soft tissue and whether, in the case of a tumour, it is benign or malignant. The resultant list of possible diagnoses in turn often determines the patient management and mode of treatment. The final definitive diagnosis is almost always based on histological examination.
In the mandible, so-called odontogenic lesions develop above the inferior dental canal, while non-odontogenic lesions develop above, within or below the canal. Thus some conditions have a predilection for certain areas whilst others develop in one site only. For example, radicular dental cysts develop at the apices of non-vital teeth, while so-called fissural bone cysts develop only in the midline. The site or anatomical position of a lesion may therefore provide the initial clue as to its identity.