TMJ- Imaging Flashcards
What are the advantages of using plain films
- Low radiation dose
- Easily accessible
What are the disadvantages of plain films
- Cannot assess soft tissues of joint
- Diagnostic yield os limited to projection & geometry & superimposition
- low sensitivity for bone patholofy
- Low- moderate value in assessment of “
- TMJ osseous components
- facial skeletal asymmetry
- internal jaw anatomy/ pathology
What are the plain radiography film techniques used to assess TMJ
- Reverse Townes
- Panormaic
What are the advantages and disadvantages of panormaic
ADV:
-Quick & readily available
- comfortable
- section to just condyles
DISADV:
- difficult to reproduce due to inconsistent magnification & geometric distortion
- sensitive to positioning errors
- superimposition & ghost images
- no soft tisssues
- cannot exclude bony pathology
Indications for OPG for TMJ
- Change in occlusion
- mndibular shift
- change in movements range
- altered sensory/ motor
- recent trauma
Contrainidications for OPG TMJ
Joint noises
myofascial pain
Why are PA mandibles not used for TMJ
- condyles not visible as superimposed
Good for fractures at posture-anterior views
How it is conducted:
forehead & nose against image detector. X-ray beam posterior & perpendicular to film
How are reverse townes taken
pt opens mouth & condyles move and translate down articular emincence
- beam angled change (dropped 30 degrees upward angle)
What are the advantages of reverse townes plain film?
Beam angle changed→ no longer condyles superimposed by base of skull
What is a trauma dislocation
condyle is displaced out of the glenoid fossa but still within the joint
What is the most common type of trauma dislocation
Anterior dislocation
What is an anterior dislocation & its presentations
Condyle displaces anteriorly to articular eminence
presentations: cannot close mouth
What is a superior dislocation & its presentations
Roof of glenoid fossa fractures & condyle displaced superiorly into middle cranial fossa
What is subluxation of joint?
condyle doesn;t get stuck infront of articular eminence- condyle has an increased range of movmeemnts
What conditions are associated with recurrent dislocations
Ehlers Danloas and Marfans
How does Multi-detector Computed Tomography work?
- fan shaped x-ray beam
- patient moves horizontally through scnner
- beam and detectors rotate around gantry
- images are generated as slices to view bone and soft tissues
How can soft tissue differenation be improved in CT
Use of contrast agents to improve soft tissue differentiation
Agent is taken up by tissues that are well vascularised
Increases density & therefore attenuation of x-ray beams where more areas of x-ray accumulation
How do Cone beam CT work
xray beam is coned shape
- single rotation around patient
Lower dose of ioning radiation compared with MDCT
Cannot view soft tissues
What are the advantages of CBCT
- see bony structures without superimposition
- assess osseous and ankylosis
what are the indicaitons for multidetector CT
- when a neoplasm is suspected to extend beyond the osseous structures
- TMJ replacement
How does MRI work
Mangetic field (1.5-3 tesla) and radiofrquency
- no ionising radiaiton
- soft tissues: good differentations
what are the disadvantages of MRI
- long scan tme
- close to pt
Contraindications for MRI
- Claustrophobia
- pacemaker
- Metabollic foreign body
What is the MRI sequence
T1: FAT is bright e.g bone marrow & salivary glands
T2: Water- white CFS around brain. and. ucosa surface
Using T2, How is pathology presented on MRI
More Water & is less dense
How is the disc imaged
- MRI: cross sectional
- disc positioning & startus
what is the disc normal anatomy
disc is bioconcave
- convex anteroposteriorly
What is the discs normal position
posterior band 12
Intermediate zone 10
Indications for MRI
- Assess disc status/ position
- Assess synovitis in inflammation
- bony changes for diagnosis of arthritisi
- Allow to see deep structures
What is myofascial pain
most common TMJ diagnosis
- joint often normal
- Pain is caused by muscle tension, fatigue ot spasm
- related to parafunctional habits
history & exam used for diagnosis
- pain and tender in MOM on palpation
-
What is meant by internal derangement
Displacement of disc from normal position
What is meant by reduction on opening?
& associated symptoms
As disc returns from anterior position to normal position→ clicks into place
clicking, pain, trismus/ locking
What is a normal position of the disc
disc between condyle head, glenoid fossa & eminence
What is the position of the disc (open and closed) in anterior displacement with reduction
closed: disc is anterior to condylar head
Open: condylar head translates down articular eminence
- disc moves posteriorly reducing to a normal position (located between condyle head, in glenoid fossa and articular eminence
What is Anteriorly disc displacement without reduction
disc anterior to condylar head- does not return to normal position between temporal bone & mandibular condyle
What is degenerative joint disease
- non-inflammatory processes
- causes wear and tear to sustained microtrauma over a long period of time
-Deterioration of articular cartilage, exposing bone and causing flattening of the condylar head & bone defects
What are the symptoms of degenerative joint disease
painful crepitus & trismus
What are the imaging features of degenerative joint disease
- erosions
- flattening of articulating surface
- osetophytes
- subchondral cysts
- sclerosis
- decreased joint space
+/- disc displacement
Where and when does osteophyte accumulation occur
Occur in degenerative joint disease
- occur at muscle attachments
- usually seen anteriorly on condylar head
- fracture & form loose bodies
How does sclerosis present in degernative joint disease
Increased density in condylar head- whiter on plain film
What is a subchondral cyst
Formation of fluid filled cavity beneath the articular surface
How does a diseased condylar head present
more dense
little distinction between cortical & cancellapus bone
- flattening of articulating surface, anterior osteophycte becomes deformed due to microtrauma
what is internal deranagement associated with
osteoarthritis- RA
- occurs due to microtraumas in the joint
How does rheumatoid arthritis affect the TMJ
Synovial inflammation associated with bony erosison
- pannus (granulatomous tissue ) grow in synovium
- replacing normal joint space
- more likley to have derangement
How does Juvenile arthritis affect the TMJ
onset less than 9- 16 years
- chronic/ intermittent synovial inflammation- swollen and painful joints
- tmj Involved in 20-90
if more than 1 joint affected- more likely to be TMJ
- If younger- TMJ is likely to be affected
How does inflammatory arthritic conditions present ion imaging?
erosions
joint effusion
marrow oedema
synovial enhancement on MRI
How does RA present on MRI
Sharpened pencil condylar head
- loss of convexity
How does JIA (juevenile idiopathic arthtitis) present on an MRI
- Toadstool
- wide shallow gelnoid fossa
What is joint effusion associated with and how does it present
Can be seen in both arthritis conditions & following a trauma
- Collection of fluid in the joint space
-Increase in joint space on plain film/ CT
- High T2W signal in the joint space on MRI
Strong relationship between effusion and joint pain
What is meant by ankylosis & its causes
Fusion of elements of the joint causing trismus
occurs due to: trauma/ infection/ severe juvenile inflammatory arthritis
What are the 2 types of ankylosis
fiboroius
bony
How does ankylosis present
reduced/ no joint space
Bony anklyosis: Bony bridge/
Fibrous: jigsaw puzzle interlocking articular surface (temporal bone to condylar head)
What is meant by condylar hyperplasia & how does it present
larger condyle with normal morhopology
- associated with ipsilateral hemimandible
- glenoid fossa remodel to accommodate
- facial assymmetry
self limiting in 3rd decade
Where do tumours arise in the TMJ
Condylar head
- alter shape
How does osteochondroma differ to condylar hyperplasia
osteochondroma is a tumour & does not enlarge ipsilateral half of mandible
- mixture of bone & cartilage present
What might present with an oesteochondroma on a CT
- Remodelling of temporal component to accommodate larger head
-pushing of bone around
What is an osteoma
Benign
Extra projection of dense Bone
What is chondorosarcoma
Malignancy
Mass eroding the bone
What are the features of chondoromasarcoma
Infiltrative
Less well defined
CT: More soft tissue mix with normal bone filling the area of where condyle should be
Indications for imaging
Suspected osseous abnormality / infections
Failure of conservative treatments
Worsening symptoms
History of trauma
Significant dysfunction
Alterations in range of motion
Sensory or motor abnormalities
Significant changes in occlusion
