By:Nour-Eldin A. Nour-Eldin Mohammed

Normal Anatomy

Mandibular condyle (head)

Glenoid fossa

Articular tubercle (eminence)

Lateral pterygoid muscle raphe

Lower head of lateral pterygoid muscle

Anterior band of articular disc

Mandibular condyle (head)

Posterior band of articular disc

Posterior disc attachment

Mandibular condyle (head)

Articular disc

MRI and autopsy sections: upper row oblique sagittal MRI, asymptomatic volunteer: left lateral, middle medial, rightopened mouth

Internal Derangements

General orthopedic term implying a mechanical fault that interferes with the smooth action of a joint

The most common internal derangement is disc displacement

Clinical Features Clicking sounds from joint(s) Restricted or normal mouth opening capacity Deviation on opening Pain

Imaging Features Anterior disc displacement: posterior

band of the disc located anterior to the superior portion of the condyle at closed mouth on oblique sagittal images

Disc may have normal (biconcave) or deformed morphology

In opened mouth position disc may be in a normal position (“with reduction”) or continue to be displaced (“without reduction”)

Internal Derangements

lateral sections central sections open-mouth

Partial anterior disc displacement at baseline

Complete anterior disc displacement

Open-mouth MRI

medial section Autopsy

Lateral disc displacement and normal bone

Medial disc displacement

Oblique coronal MRIcoronal MRI

Posterior disc displacement

OsteoarthritisDefinition Non-inflammatory focal degenerative disorder

of synovial joints, primarily affecting articular cartilage and sub-condylar bone; initiated by deterioration of articular soft-tissue cover and exposure of bone.

Clinical Features Crepitation sounds from joint(s) Restricted or normal mouth opening capacity Pain or no pain from joint areas and/or of

mastication muscles Occasionally, joints may show inflammatory

signs Women more frequent than men

anteriorly displaced and deformed, degenerated disc and irregular cortical outline with osteophytosis and sclerosis of condyle .

Advanced osteoarthritis and anterior disc displacement, with joint effusion

Bone Marrow AbnormalitiesDefinition Bone marrow edema: serum proteins

within marrow interstitium surrounded by normal hematopoietic marrow.

Osteonecrosis: complete loss of hematopoietic marrow.

Imaging Features•Abnormal signal on T2-weighted image fromcondyle marrow: increased signal indicates marrow edema; reduced signal indicates marrow sclerosis or fibrosis

•Combination of marrow edema signal and marrow sclerosis signal in condyle most reliable sign for histologic diagnosis of osteonecrosis

•Marrow sclerosis signal may indicate advancedosteoarthritis without osteonecrosis, or osteonecrosis

ArthritidesDefinition Inflammation of synovial membrane

characterized by edema, cellular accumulation, and synovial proliferation (villous formation).

Clinical Features Swelling of joint area, not frequently seen in TMJ Pain (in active disease) from joints Restricted mouth opening capacity Morning stiffness, in particular stiff neck Dental occlusion problems; “my bite doesn’t fit” Crepitation due to secondary osteoarthritis

Rheumatoid arthritis.

After 1 year

Rheumatoid arthritis. A MRI shows completely destroyed disc, replaced by fibrous or vascular pannus and cortical punched-out erosion (arrow) with sclerosis in condyle.

Psoriatic arthropathy. Oblique coronal and oblique sagittal CT images show punched-out erosion in lateral part of condyle (arrow).

Psoriatic arthropathy. MRI shows contrast enhancementwithin bone erosion and in joint space, consistent with thickened synovium/pannus formation. OpenmouthMRI shows reduced condylar translation but normallylocated disc (and normal bone in this section)

Inflammatory arthritis

AnkylosesDefinitionFibrous or bony union between joint components.

Growth Disturbances (Anomalies)Definition

Abnormal growth of mandibular condyle; overgrowth, undergrowth, or bifid appearance.

Normal TMJ

Condylar Hypoplasia

Condylar hypoplasia and facial asymmetry

Bifid condyle.

Inflammatory or Tumor-like ConditionsCalcium Pyrophosphate

Dehydrate CrystalDeposition Disease (Pseudogout)

Benign TumorsSynovial Chondromatosis Benign tumor characterized by cartilaginous

metaplasia of synovial membrane, usually in knee, producing small nodules of cartilage, which essentially separate from membrane to become loose bodies that may ossify.

Synovial Chondromatosis

OsteochondromaDefinitionBenign tumor characterized by normal bone and cartilage, near growth zones.

Osteoma

Malignant Tumors

Osteosarcoma mandible; 18-yearold female

Malignant tumor, mandible; 70- year-old male with metastasis from lung cancer

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