Radiolucencies Flashcards
Why do radiolucencies occur on radiographs
Thinning of hard tissue relative to adjacent area
Reduced hard tissue mineral (which reduces the density of a tissue e.g. caries)
A less dense area will allow X-ray photons to pass through them much more readily. As more photons hit the X-ray beam detector, we get a more radiolucent appearance
List some radiolucencies that represent normal anatomy
Maxillary antrum/sinus (aerated, radiolucent sinus present above the apices of upper posterior teeth. Not filled with bone but air which has very low density, therefore appears radiolucent)
Mental foramen
Submandibular fossa (an area where the mandible is thinner. This fossa should be relatively symmetrical but can mimic a lesion in the mandible sometimes)
What is the maxillary antrum?
Also known as the maxillary sinus
A cavity that is not filled with bone but air which has very low density therefore presents as an aerated radiolucent sinus located above the apices of upper posterior teeth.
What is the submandibular fossa
An area where the mandible is thinner.
This fossa should be relatively symmetrical but can mimic a lesion in the mandible sometimes.
Won’t be as well defined or have corticated margins whereas most pathologies will have these features
List some artefacts that can result in a radiolucency
Overexposure-
May result in more photons reaching the detector to give a more radiolucent appearance on the radiograph
Superimposition of an air shadow-
E.g., if a patient hasn’t pressed their tongue to the roof of their mouth on an OPT, we would get a more radiolucent area (which represents the air shadow of the oral cavity)
When describing a radiolucency, what features do we have to consider
Site-
Mandible or maxilla?
Above or below ID canal (above = more likely to be odontogenic/from tooth forming tissues, below = less likely to be odontogenic
Relation to dentition or a tooth (periapical = at the apex of a tooth, peri-coronal = around the crown of a tooth, peri-radicular = related to the root of a tooth)
Size (important for surgical planning)
Shape (informs differential diagnoses and planning access and removal)
Margin (informs differential diagnoses and planning access and removal)
Locularity (informs differential diagnoses and planning access and removal)
Effect on adjacent structures (teeth, floor of the antrum/sinus, ID canal)
What does a well defined, corticated radiolucency with smooth margins suggest about the pathology causing it?
If a lesion has corticated, well defined, smooth margins, it suggests the lesion is growing quite slowly and is more likely to be a benign pathology
What does an ill-defined radiolucency with moth eaten or punched out margins with no cortication suggest about the pathology causing it?
If a lesion’s margins are moth eaten or ill defined, cannot be distinguished from other areas of a structure very well, or there’s a punched out margin with no cortication, it suggests the lesion is growing rapidly. More likely to be seen where there’s infection or malignancy
List the effects a radiolucency may have on adjacent structures
Damage to teeth-
Resorption
Displacement
Delayed eruption (if a lesion arises in a peri-coronal position, it may delay the eruption of the tooth, impeding its eruption pathway into the mouth)
Loss of associated lamina dura (a thin line of dense bone found around the root of a tooth adjacent to the PDL)
ID canal-
Displacement
Erosion of its cortices
Maxillary antrum-
Upwards displacement of maxillary antrum floor
List some pathological causes of radiolucencies
Cysts-
Odontogenic (inflammatory or non-inflammatory/developmental)
Non-odontogenic
Tumours-
Benign
Malignant (primary or secondary)
Bone related lesions-
Giant cell lesions
Cemento-osseous dysplasias (in its early stages)
Bone diseases-
Osteoporosis
Sickle cell disease
Hyperparathyroidism
What is a cyst?
Pathological epithelial lined cavity within the tissues, filled with fluid, semi fluid or gas that is not derived from the accumulation of pus.
However can become secondarily infected if it becomes large enough (in which case, it will become pus filled)
Radiographically a PA granuloma and and a PA cyst are impossible to differentiate. Apart from a biopsy sent to histopathology, what could be used to differentiate between the 2?
Size may give a hint or an indication of what pathology the radiolucency is likely to be, from the 2.
The larger the lesion, the more likely it is to be a radicular cyst.
Once radiolucencies are above 1.5cm, about 1/3rd of them will be radicular cysts, whereas about 1/3rd of radiolucencies under 1cm will be PA granulomas
(However we can get large granulomas or small cysts)
What are the radiographic features of a radicular cyst?
Well-defined, uni-locular, corticated radiolucency associated with the apex of a tooth that is almost always non-vital.
No cortication evident at the apex of the tooth as this is where the infection causing the cyst originates.
There may also be some loss of cortication if the cyst is infected.
Adjacent teeth may be displaced but they are rarely resorbed as a result of a radicular cyst
Some buccal expansion may be evident
What are some indications of non-vitality, where the tooth has a suspected radicular cyst
Indications of the tooth’s non-vitality may include large restorations, deep caries, RCT, previous history of trauma to the tooth, dense in dente (which can form a pathway to the pulp causing non-vitality)
Upper 2’s are frequently affected by radicular cysts. What is one explanation for this?
Very common to get a dens-in-dente in these teeth (tooth within a tooth).
A dense-in-dente forms a pathway to the pulp which allows the tooth to lose vitality due to infection
What are the radiographic features of a residual cyst?
Essentially a radicular cyst that has persisted following XLA of the associated tooth.
Well-defined, uni-locular, corticated radiolucency, located where there is a missing tooth (any denture bearing area, underneath a bridge etc.)
There may also be some loss of cortication if the cyst is infected.
Occurs where the cyst has not been enucleated / the socket hasn’t been cleaned out or undergone curettage, as a result the epithelium lining of the cyst remains. This can seal back off and start to produce fluid again, continuing to grow as a residual cyst
What are the radiographic features of a dentigerous cyst?
Well defined, corticated, unilocular radiolucency (>4mm) associated with the crown of an unerupted, often displaced tooth.
Radiolucency tends to stop at the ACJ encompassing the entirety of the crown. But if it’s more extensive, it can encompass more of the tooth or even be displaced to one side of the crown.
Associated tooth, adjacent teeth may be displaced.
Damage to the adjacent teeth (resorption, although this is not very common)
Displacement of adjacent structures (antrum floor, ID canal)
Buccal expansion
Most common site for a dentigerous cyst to form includes:
Lower 8s
Lower premolars
Upper 3s
Upper 8s?
Upper premolars
Supernumeraries
What issue may arise when trying to diagnose a dentigerous cyst?
A dentigerous cyst occurs as a result of fluid accumulation between the enamel follicle and the enamel.
Radiographically, the cyst therefore presents as an expansion of the follicular space.
Up to 4mm from the crown to the edge of the follicle is considered a normal follicular space. If it is greater than this, we should consider cystic degeneration of the follicle
But when a tooth is close to eruption, there may be some natural widening of the follicular space. This is just a physiological response to age and eruption. As a result, the follicle may be a little more prominent just before a tooth erupts.
Up to 4mm from the crown to the edge of the follicle (ACJ) is considered a normal follicular space. If it is greater than this, we would consider cystic degeneration of the follicle
Describe the radiographic features of an odontogenic keratocyst
Well defined, corticated, multilocular radiolucency, often with a scalloped margin
Can be pseudolocular (lobulated outline with the impression of multiple locules or separate areas within the cyst but no bony septa dividing the cavity) instead of multilocular (separate cysts adjacent to each other (cyst within cysts))
Can appear in a dentigerous relation (e.g. peri-coronal radiolucency around an unerupted tooth, particularly around a L8, can mimic a dentigerous cyst therefore)
Commonly located in the angle of the mandible/posterior body of the mandible. Can be seen in the maxilla (most commonly anteriorly, where the canines are)
Can displace associated teeth or structures (ID canal)
Can damage adjacent teeth (external root resorption)
These cysts tend to take the path of least resistance when growing. As a result, they tend to grow quite long or quite lengthy through the mandible e.g., through the ramus all the way to body of the mandible, without any or very little expansion
Can be an incidental finding, very clinical few symptoms despite a very large lesion being present
Why do odontogenic keratocysts have a high recurrence rate?
If these lesions are large or multilocular, there’s a high chance of recurrence.
There are 2 reasons for this-
The epithelial cyst lining for keratocysts is very thin and friable. Some cysts like radicular cysts have quite a tough lining that can be removed quite easily but keratocysts have a more friable lining which sheds much more easily and therefore it is possible to leave cells of the lining behind. These can persist and grow to form another cyst
The chances of leaving behind cystic material also increases if it’s a lesion is multilocular with daughter cysts around the edge. Need to remove all the smaller locules within a cyst, otherwise the largest cavities can be cleared out leaving smaller daughter cysts behind, to persist and grow
Why is follow-up imaging indicated following the treatment of odontogenic keratocysts. What technique is used to take follow up images for these lesions?
Due to recurrence rate being high for these lesions.
The technique used to image the lesions will depend on lesion location e.g., a mandibular lesion will likely be followed up using a sectional OPT whereas something in the upper maxilla may be much harder to view in a 2D plane and therefore a CBCT may be better to follow the lesion up
