Note:
Anteriorly displaced disc is shown in 34% asymptomatic people
Normal disc position is seen in 23% symptomatic people
Normal MR appearance:
Closed mouth: The junction of posterior band and bilaminar zone should lie at 12 O clock position (+- 10 degrees)
Abnormal morphology:
Biconvex or rounded disk: due to deformed thickened posterior band and decrease in anterior band size
Crumpled disk
Flat disk
Perforated disk
Abnormal signal:
Completely low signal disk
Disc perforation
Heterogenous abnormal signal
Disk displacement:
Include anterior, anterolateral, anteromedial, lateral, medial and posterior
Between 10 and 11 O clock: partial anterior displacement
Less than 10 O clock: anterior displacement
Anterior displacement with recapture (reduction): Posterior band is displaced but returns to normal
Anterior displacement without recapture (reduction): Disk may remain anteriorly displaced
Anterior displacement with disc perforation or disruption of posterior attachment:
Stuck disk: disk remains in fixed position relative to glenoid fossa and articular eminence in both closed and open mouth positions, due to adhesions
Posterior disk displacement: rare (0.01% of TMJ disorders); posterior band displaced beyond the one o’clock position
Additional signs:
Joint effusion
Retrodiskal layer rupture: rupture of superior retrodiskal layer may produce disk instability
Changes in lateral pterygoid attachments
Double disc sign: thick lateral pterygoid
OA: flattening, osteophytes, sclerosis, erosion
Complications:
OA
Avascular necrosis
What to comment on MR?
Disc position: normal, displacement (anterior, partial anterior, posterior)
Disc morphology: normal bow-tie, thin, thick, crumpled, perforated
Condylar translation: normal or adequate, limited, no movement
Joint effusion: present, absent
Bone: Flattening of conylar process, erosion, cysts, osteophytes. abnormal marrow signal
Masticator space: muscles
Other conditions to look at:
RA, gout, CPPD, PVNS, infection, AVN, idiopathic condylar resorption (Cheerleaders disease!), synovial osteochondromatosis
References:
1. Tomas X et al. MR Imaging of Temporomandibular Joint Dysfunction: A Pictorial Review. RadioGraphics 2006;26:765-781
2. Aiken A et al. MR imaging of temporomandibular joint. MRICNA 20 92012) 397-412
