Radiology Flashcards
Topics covered: Cysts and Cyst-like Radiolucencies, Imaging of the TMJ, Imaging of Salivary Glands, Radiology of Other Pathologies, Radiographic Appearances of Malignancy in the Oral Cavity
Why do most jaw lesions appear radiolucent?
As they have a reduced radiodensity compared to surrounding bone as a result of:
- Resorption of bone
- Decreased mineralisation of bone
- Decreased thickness of bone
What is a cyst?
A pathological cavity having fluid, semi-fluid, or gaseous contents and which is NOT created by the accumulation of pus.
Name 3 types of odontogenic developmental jaw cysts:
- Dentigerous cyst (and eruption cyst)
- Odontogenic Keratocyst
- Lateral periodontal cyst
Name 2 types of odontogenic inflammatory jaw cysts:
- Radicular cysts
- Inflammatory collateral cysts
What are the 3 types of radicular cyst?
Apical
Lateral
Residual
What are the 2 types of inflammatory collateral cyst?
Paradental cyst and Buccal bifurcation cyst
Name one type of non-odontogenic developmental jaw cyst:
Nasopalatine duct cyst
Name 2 types of non-odontogenic cyst-like jaw lesions:
- Solitary bone cyst
- Stafnes idiopathic bone lesion
How would you establish a differential diagnosis when looking at jaw cysts/cyst-like radiolucencies?
- Look at the radiograph and decide whether the radiolucency is:
- Anatomical
- Artifactual
- Pathological - If pathological nature describe the lesion:
- Site
- Size
- Shape
- Margins
- Internal structure
- Tooth involvement
- Effect on adjacent anatomy
- Number
Name one jaw cyst that can occasionally occur bilaterally:
Paradental cyst
Which syndrome might you suspect is a patient presents with multiple odontogenic keratocysts?
Multiple Basal Cell Naevoid Syndrome
When might a cyst become poorly defined on a radiolucency?
If there is infection or malignancy
What does a moth-eaten cyst-like radiolucency indicate?
Malignancy
List 8 pathological causes for periapical radiolucency:
- Periapical granuloma
- Periapical abscess
- Radicular cyst
- “Perio-endo” lesion
- Cemento-osseous dysplasia (in early stages)
- Surgical defect (following peri-radicular surgery)
- Fibrous healing defect (following resolution of lesion)
- Ameloblastoma occurring next to a tooth
How do radicular cysts form?
By chronic inflammation at the apex of the tooth due to pulp necrosis.
Is a radicular cyst associated with a vital or non-vital tooth?
Non-vital tooth
Is a radicular cyst most commonly seen in the maxilla or mandible?
Maxilla (60%)
Following pulpal necrosis of the tooth, describe the pathological journey of the tooth:
Pulp necrosis > Periapical periodontitis > Periapical granuloma > Radicular cyst
What is the clinical presentation of a radicular cyst?
- Often asymptomatic
- May become infected - resulting in pain
- Typically slow growing with limited expansion
What is the radiographic presentation of a radicular cyst?
- Site - apex of a non-vital tooth
- Size - variable
- Shape - unilocular and rounded
- Margins - well defined and corticated
- Internal structure - entirely radiolucent
- Tooth involvement - yes associated with the root, margins continuous with lamina dura
- Effects - can displace adjacent teeth/structures, long-standing lesions can cause external root resorption
- Number - single (but potentially multiple if grossly carious dentition
How do you differentiate a radicular cyst from a periapical granuloma?
- Difficult to differentiate radiographically
- Radicular cysts are typically larger
- If radiolucency diameter is >15mm - 2/3 cases will be a radicular cyst
How do dentigerous cysts arise?
Arise when there is cystic change of the dental follicle.
What are dentigerous cysts associated with?
The crown of an unerupted /impacted tooth - commonly mandibular third molars, maxillary canines
Are dentigerous cysts most commonly seen in the maxilla or mandible?
Mandible
What is the radiographic presentation of a dentigerous cyst?
- Site - around the crown of an unerupted tooth (often symmetrical encapsulation of crown but may expand unilaterally
- Size - variable (e.g. can involve entire ramus of mandible)
- Shape - unilocular and rounded but can be scalloped if large
- Margins - well-defined and corticated
- Internal structure - entirely radiolucent
- Tooth involvement - yes, continuous with CEJ (but large cysts can begin to envelope the root as well)
- Effects - displacement of the tooth, potential external root resorption of adjacent teeth, variable displacement of adjacent structures
- Number - single
How do you differentiate a dentigerous cyst from an enlarged dental follicle?
- Consider cyst if follicular space > or = 5mm
- Measure from surface of crown to edge of follicle
- Normal follicular space typically 2-3mm
- Assume cyst if >10mm - Consider cyst if radiolucency is asymmetrical
Are inflammatory collateral cysts associated with a vital tooth or a non-vital tooth?
Vital tooth
Where do buccal bifurcation cysts normally arise?
At the buccal aspect of the mandibular first molar
Where do paradental cysts normally arise?
Typically occurs at the distal aspect of a partially erupted mandibular third molar.
What is the typical radiographic presentation of an inflammatory collateral cyst?
- Site - buccal or distal to furcation area of permanent molars (mandible > maxilla)
- Size - <25mm
- Shape - unilocular and rounded
- Margins - well-defined and corticated
- Internal structure - entirely radiolucent
- Tooth involvement - yes, involves furcation
- Effects - tilting of tooth, cortical displacement - buccal bifurcation cysts tend to tilt the crown of the tooth buccally
- Number - single or bilateral
Which types of cysts/cyst like lesions tend to occur in younger patients? (1st and 2nd decades)
- Inflammatory collateral cysts (paradental, buccal bifurcation)
- Solitary bone cyst
- Odontogenic Keratocysts
What direction do OKCs grow?
Anteroposteriorly
Are OKCs most commonly found in the mandible or the maxilla?
Mandible
Are OKCs most commonly found anteriorly or posteriorly?
Posteriorly
What is the typical radiographic presentation of OKCs?
- Site - commonly posterior mandible
- Size - variable but can get very large
- Shape - pseudolocular or multilocular, scalloped
- Margins - well defined and corticated
- Internal structure - entirely radiolucent
- Tooth involvement - no but often next to one
- Effects - marked expansion with trabecular bone in contrast to limited displacement of cortices, minimal displacement of adjacent teeth, rare external root resorption
- Number - single (but can be multiple if syndromic)
If multiple keratocysts are present, what condition should you consider?
Basal Cell Naevus Syndrome
**aka Gorlin-Goltz Syndrome or Bifid Ribs Syndrome
How does Basal Cell Naevus Syndrome normally present?
multiple OKCs, multiple basal cell carcinomas (skin), palmar and plantar pitting, calcification of intracranial dura mater etc
What is an ameloblastoma?
A locally destructive but slow progressing benign epithelial tumour
What direction do ameloblastomas grow in?
All directions - anteroposteriorly and buccal-lingually
Where do most ameloblastomas grow?
Posterior mandible
What is the typical radiographic appearance of an ameloblastoma?
- Site - commonly in the posterior mandible
- Size - any size
- Shape - unilocular or multilocular (multilocular lesions are more common and may have a coarse septae and/or “soap bubble appearance”
- Margins - well-defined and corticated
- Internal structure - radiolucent (but rare radiopaque variant)
- Tooth involvement - none
- Effects - can grow in all directions (not constrained by cortices) - thinning or cortices can cause ‘knife edge’ external root resorption
- Number - single
What is an odontogenic myxoma?
A benign mesenchymal odontogenic tumour
Where are odontogenic myxomas more commonly found?
Often in the mandible premolar/molar region
What is the typical radiographic appearance of an odontogenic myxoma?
- Site - often premolar/molar region of mandible
- Size - any size
- Shape - multilocular and scalloped
- May have coarse septae and/or soap bubble appearance
- Small lesions can be unilocular
- Margins - well-defined, thin corticated margin
- Internal structure - radiolucent
- Tooth involvement - none
- Effects - initially extends to the inter-radicular spaces but larger lesions displace teeth, initial expansion within trabecular bone before displacing cortices
- Number - single
What symptoms may the patient experience if they have a nasopalatine duct cyst?
A salty taste in their mouth
May have a slight palatal swelling
What is the typical radiographic appearance of a nasopalatine duct cyst?
- Site - always anterior maxilla in midline
- Size - usually between 6mm and 30mm in diameter
- Shape - typically unilocular, rounded and symmetrical but can be pseudolocular and lop sided, may appear heart-shaped due to superimposed anterior nasal spine
- Margins - well-defined and corticated
- Internal structure - entirely radiolucent
- Tooth involvement - no, but inevitably next to incisor roots
- Effects - displacement of incisors, palatal expansion
- Number - single
How would you differentiate a nasopalatine duct cyst from an incisive fossa?
The incisive fossa may or may not be visible on radiographs (midline, oval-shaped radiolucency, typically not visibly corticated on radiographs)
In the absence of clinical issues, consider the transverse diameter
- <6mm - assume incisive fossa
- 6-10mm - consider monitoring
- >10mm - suspect cyst
What is a solitary bone cyst?
Aon-odontogenic lesion - technically NOT classed as a cyst
Also known as simple/traumatic/haemorrhagic bone cyst
What can solitary bone cysts occur in association with>
Other bone pathology (e.g. fibro-osseous lesions)
What is the typical radiographic presentation of a solitary bone cyst?
- Site - typically posterior mandible
- Size - typically <30mm approximately
- Shape - unilocular or pseudolocular, scalloped - may extend into inter-radicular spaces with finger-like projections
- Margins - variable
- Internal structure - entirely radiolucent
- Tooth involvement - none (although may occur near teeth)
- Effects - typically none, rare displacement of teeth
- Number - single
What is a Stafne defect?
A depression in the bone (cortical bone preserved)
What does stafnes defect contain?
Salivary or fatty tissue
What is the typical radiographic presentation of stafne’s defect?
- Site - mandible (often body but can be ramus)
- Size - usually <20mm
- Shape - unilocular and rounded
- Margins - well-defined and corticated
- Internal structure - entirely radiolucent
- Tooth involvement - none
- Effects - typically none, rare displacement of adjacent structures
- Number - single
How might a cyst appear differently in the presence of infection?
May lose its well-defined corticated margin
May appear malignant
How would a cyst appear radiographically in bone vs in the maxillary sinus?
The cyst would appear radiolucent in bone but radiopaque in the maxillary sinus
What anatomical structures make up the TMJ?
- Bone:
- condylar head of the mandible
- articular eminence and the glenoid fossa of the temporal bone in the middle cranial fossa. - Muscles:
- specifically the muscles of mastication - Articular disc
- Ligaments
- Neurovascular structures
Which imaging modalities ca be used to assess the TMJ?
- Plain film - OPT, PA Mandible, Reverse Townes, Lateral Obliques
- Cone Beam CT
- Computed tomography (CT)
- Magnetic Resonance Imaging (MRI)
- Nuclear Medicine
Is an OPT necessary for TMJ assessment?
Explain your answer.
FGDP states that in most cases an OPT is NOT necessary for the assessment of TMJ.
This is because most TMJ pain is myofascial in origin rather than bony or soft tissue in origin.
What view of the condylar head does an OPT give?
Lateral view
However position can vary depending on the pt positioning (e.g. large overjet - postural compensation)
What view of the condylar head does a PA mandible give?
Posteroanterior view
What view of the mandible does a Reverse Townes give?
AP view of the mandible
What view of the condylar head does a lateral oblique give?
Gives a lateral view of the condylar head
How might a CBCT be useful for assessing the the TMJ?
- Allows visualisation of the TMJ in cross-section
- Allows limitation of the FOV to just the condylar heads with the articular eminence - useful when looking for bony changes
- Can be useful when assessing the TMJ of a pt that has had recent trauma that does not require immediate surgery
What is not very defined in a CBCT?
Soft tissue
Why are conventional CT’s better for examining neoplastic masses than CBCT?
As conventional CT’s allow the visualisation of both soft tissue and bone whereas CBCTs only allow visualisation of bone.
Do conventional CT’s have better resolution than CBCTs?
It depends on the voxel size
Typically CBCTs have a smaller voxel size than CTs
However, if the CBCT has a greater voxel size then it may have better resolution.
Why is a higher resolution useful when taking xrays?
As it shows greater detail.
What is the gold standard imaging modality for visualising the TMJ and why?
MRI
- No radiation dose
- Shows soft tissue and bony pathology
- Good for assessing articular disc position
What 2 views must be taken when assessing the TMJ using MRI?
Coronal view and parasagittal view along long axis of condyle
What direction is normal disc displacement of the TMJ?
Anteriorly and medially
What 3 disc displacements of the TMJ are important to be aware of?
- Anterior disc displacement with reduction - reciprocal clicks on opening when the disc is recaptured, expect the articular disc to lie in an anterior position in the closed mouth and will sit in a normal position on mouth opening
- Anterior disc displacement without reduction - limitation of opening, pain
- Anterior disc displacement and bony arthritic changes - lose joint space
What does SPECT stand for?
Single Photon Emission CT
What is the patient injected with when using nuclear medicine (SPECT) as your imaging modality when
assessing the TMJ?
IV Technetium 99-metastable (radioisotope)
What is the half-life of IV Technetium 99-metastable (radioisotope)?
6.5 hours
What is the SPECT imaging technique useful for?
When assessing condylar hyperplasia
What is an advantage and disadvantage of SPECT?
Highly sensitive but poorly specific - good at picking up increased metabolic activity but difficult to determine cause of the uptake
In SPECT what might increased metabolic activity indicate?
Pathology, increased growth, or inflammation
When would you use arthrography for assessing TMJ?
Rarely used
Alternative to MRI - if MRI not feasible due to contraindications (claustrophobia, implanted devices etc.)
Assessment of soft tissues - specifically articular disc
Can be used for diagnostic and therapeutic purposes
In arthrography what is injected into the joint space?
Iodinated contrast
During arthrography what is used to allow you to visualise the bony anatomy?
Fluoroscopic guidance
In arthrography, if contrast leaks from the lower joint space, what does this indiacate?
That there is disc perforation.
List the 3 major pairs of salivary glands:
- Parotid
- Submandibular
- Submental
Where is the parotid gland located?
Located in the pre-auricular and retromandibular regions of the facial skeleton.
Which muscle does the parotid gland lie over anteriorly?
The masseter muscle
What muscle does the parotid duct pierce through?
The buccinator
Where does the submandibular salivary gland lie?
In the submandibular fossa deep on the lingual aspect of the body of the mandible into the submandibular space
Which 2 muscles does the submandibular duct pass between?
- Mylohyoid muscle
- Hyoglossus muscle
Where is the duct orifice of the submandibular gland located?
At the lingual frenum (shared with the sublingual gland duct)
Where does the sublingual salivary gland lie?
In the sublingual fossa anteriorly within the FOM.
Where is the duct orifice of the sublingual gland located?
At the lingual frenum (shared with the submandibular gland duct)
Where do you find minor salivary glands?
Within the mucosa overlying the hard palate, soft palate, retromolar pad, and in the FOM
In what case might minor salivary glands be present on imaging?
In cases where there is pathology
Why do we image salivary glands?
- To visualise glandular obstruction - mucous plugs, salivary stones, neoplasia
- To investigate dry mouth - exclude Sjogren’s-related changes or changes related to a history of radiotherapy
- To investigate swelling - secondary to Sjogren’s, bacterial/viral, or possibly neoplastic growths such as malignancy
What 6 imaging modalities are available when imaging salivary glands?
- Plain film radiographic techniques
- Ultrasound
- Sialography - involves injection of iodinated contrast into ductal anatomy
- CT (computed tomography)
- MRI (magnetic resonance imaging)
- Nuclear Medicine Techniques
What are the 3 main plain film radiographic views that can be taken to view salivary glands?
- Lower true occlusal
- OPT
- Lateral Oblique
What are lower true occlusal view useful for visualising in the context of salivary glands?
Submandibular salivary stones
What are OPTs useful for visualising in the context of salivary glands?
Sialoliths within the submandibular gland itself.
Also useful for visualising teeth to exclude the possibility of odontogenic pathology.
What is the issue with OPTs when visualising sialoliths within the FOM duct anterior to the genu (bend of the submandibular gland)?
Suggest a resolution to this issue:
Any sialolith within the FOM duct anterior to the genu will be superimposed over the body of the mandible making it difficult to visualise on an OPT.
Resolution: use in conjunction with a lower true occlusal view to allow better visualisation
Why are true laterals and PA mandibles not useful radiographic techniques for visualising salivary glands?
Due to superimposition of multiple anatomical structures.
What is the greatest advantage of using Ultrasound as an imaging modality when visualising salivary glands?
It does NOT use ionising radiation
How does an ultrasound imaging work?
It works by using high-frequency sound waves (at a frequency that cannot be heard audibly)
The ultrasound transducer creates sound waves when electric current is given to the crystals on the transducer surface.
The high-frequency sound waves enter the body and reflect back to the transducer when boundaries between different tissues are met.
Using the speed of sound and time to return the echo, the tissue depths are calculated and the ultrasound unit creates a 2D image respectively.
Why do ultrasounds require a coupling agent?
Sound waves have short wavelengths which are not transmittable through air - therefore must be used with a coupling agent (e.g. gel) to help sound waves get into tissues through the ultrasound transducer
What does an ultrasound transducer do?
It emits and detects sound waves/echoes
When describing an ultrasound image, what does Hypoechoic mean?
Dark
When describing an ultrasound image, what does Hyperechoic mean?
Bright
When describing an ultrasound image, what does Homogenous mean?
Uniform density
When describing an ultrasound image, what does Heterogenous mean?
Mixed density
Why is ultrasound useful for imaging salivary glands?
- Typically glands are superficially positioned
- apart from deep lobe of the parotid - Can assess the parenchymal pattern (homogenous vs heterogenous), vascularity (allows assessment of any inflammation), ductal dilatation, and the presence of salivary stones or neoplastic masses (benign or malignant).
- Can be used in conjunction with a sialogogue (ie. citric acid) to aid saliva flow/ production - will allow better visualisation of dilated ducts.
What does Sialography involve?
The injection of iodinated radiographic contrast into a salivary duct to look out for obstruction
How much iodinated contrast is injected into a salivary duct during Sialography?
Typically 0.8-1.5ml
Is LA required for Sialography to take place?
No
What are the indications for Sialography?
- To look for obstruction or stricture (narrowing) of the salivary duct which could be leading meal time symptoms
- To plan access for interventional procedures (basket retrieval of stones or balloon dilation of ductal strictures)
What are the contraindications for Sialography?
- Existing infection
- Mobile salivary stone - seen on plain film/us imaging
- Allergy to contrast (very rare)
What imaging modality should be used as an alternative to Sialography if the patient is allergic to iodinated contrast?
MRI Sialography