Pediatric Orthopedic MRI
William A. Mize M.D.
University of Minnesota Hospital and Clinic
Department of Radiology
Pediatric Imaging Section
January 24, 1996
Technical Issues
- Sedation
- Coil selection
- Pulse sequences
Sedation
- Screening
- Allergies to sedation agents
- Respiratory compromise
- NPO status
- Monitoring
- Heart rate
- Oxygen saturation
- Personnel
- Radiologist
- Department nurse
- Sedation ÒteamÓ
- Program should be developed in conjunction with anesthesia department
Sedation Agents
- Drug classes
- Chloral hydrate
- Barbiturates
- Opioids
- Benzodiazepines
- Limited formulary
- Specific dose limits
Oral Chloral Hydrate
- Patients < 18 months
- 75-100 mg/kg
- 2g maximum
- Administer 20 minutes prior to exam
IV Pentobarbital Sodium
- Patients > 18 months
- 2-3mg/kg IV push
- 6-8mg/kg maximum
- Fentanyl citrate (1-2µg/kg) may be used as adjunct - useful in patients who are "close" or have reason to need analgesia
Coil Selection - Small Parts Need Small Coils
- Infant hips - knee coil
- Pediatric elbow - wrist coil
- Pediatric pelvis - head coil
Pulse Sequences - What Do You Want to See?
- T1-weighted images:
- Marrow fat
- Subcutaneous fat
- Hemorrhage
- T2-weighted images:
Contrast
- Usually not necessary in musculoskeletal work, due to the intrinsic contrast between muscle, fat, fluid, compact bone
- Good for:
- Definable collections
- Synovium vs. fluid
- Tumor response
- Subtraction imaging
Fat Suppression vs. STIR
- Fat suppression more specific
- STIR less demanding of field uniformity - works better with surface coils
- Both work for simultaneous lesion-muscle and lesion-fat differentiation
Disorders Amenable to MRI
- Congenital
- Infection
- Tumors and tumor-like conditions
- Trauma
- Marrow disorders
- Synovial disorders
- Miscellaneous
Congenital Disorders
- Developmental dysplasia of the hip
- Skeletal dysplasias - limited role for MRI
Developmental Dysplasia of the Hip (DDH)
- 1/60 newborns have unstable hip(s)
- 88% stabilize spontaneously
- 95% of those remaining respond to flexion/abduction splinting
DDH - Imaging
- Plain film
- Bony anatomy
- Overall picture
- Arthrography
- Provides some information about cartilage
- Asessment of functional coverage
- Invasive
- Ultrasound
- Dynamic exam
- Good detail of cartilagenous structures
- Established standards for acetabular development
- CT
- Reduction assessment in cast
- 3-D imaging in chronic cases
- MRI
- Imaging assessment of obstructive factors to reduction
- Acetabular dysplasia evaluation
Infant Hip Anatomy
- Femoral head
- Acetabular cartilage
- Labrum
- Transverse acetabular ligament
- Ligamentum teres
- Zona orbicularis
- Capsule
DDH - Obstructive Factors to Reduction
- Capsular invagination
- Psoas tendon invagination
- Labral inversion
- Thick ligamentum teres
- Short transverse acetabular ligament
- Fibrofatty pulvinar hypertrophy
Infection
- Osteomyelitis
- Myositis
- Septic arthritis
Osteomyelitis in Children
- Usually hematogenous
- Direct inoculation
- Staph aureus most common
- Metaphysis most often involved
- Transphyseal vessels in infants
- Growth disturbance
- Septic arthritis
Osteomyelitis - Imaging
- Plain film
- Findings in 10 days - 2 weeks
- Bone scintigraphy
- Whole skeleton imaging
- Limited anatomic detail
- MRI
- Soft tissue information
- Surgical planning
Osteomyelitis - MRI Findings
- Marrow signal abnormality
- Marrow enhancement
- Periosteal elevation
- Sinus tract formation
- Abscess
- Sequestrum
- Soft tissue inflammation
Myositis
- Nonspecific signs/symptoms
- MRI best means for detection
- MRI excellent for surgical planning
- Contrast helpful for defining collections
Septic Arthritis
- DonÕt waste time with imaging
- Get an orthopedist and/or a needle
MRI in Tumor Evaluation
- Extent of disease
- Skip areas
- Response to therapy
- Limited role in primary diagnosis
- Important anatomic structures in evaluation of extent:
- Neurovascular bundles
- Muscle group involvement
- Joint capsule
- Transphyseal extension
Tumors and Tumor-Like Conditions
- Malignant lesions
- Osteosarcoma
- Ewing sarcoma
- Lymphoma/leukemia
- Neuroblastoma
- Soft tissue sarcoma
- Benign lesions
- Hemangioma
- Lymphangioma
- Lipoma
- Synovial cyst
- Ganglion cyst
- Subcutaneous fat necrosis
- Hematoma
- Simple bone cyst
- Aneurysmal bone cyst
- Langerhans cell histiocytosis
- Fibromatosis
Trauma
- Physeal injury
- Salter-Harris injuries
- Slipped capital femoral epiphysis
- Blount disease
- Osteochondritis dissecans
The Physis
- Four layers of cartilage from epiphysis to metaphysis
- Resting
- Proliferating
- Hypertrophying
- Endochondral ossification layer
- Hypertrophying layer is weakest
Physeal Injury
- Physis is point of mechanical weakness
- Tendons, ligaments, capsule stronger
- Injuries producing sprain in adults often injure physis in children
Physeal Injury - MRI
- Demonstrates cartilaginous components of fracture
- Often changes S-H classification
- Evaluation of physeal bridge formation
- Evaluation of growth disturbance
Physeal Bridge Formation
- May be due to intermingling of metaphyseal and epiphyseal vasculature
- More common in:
- Higher S-H classes
- Fracture transverse to physis
- Fracture involving epiphyseal aspect of physis
Slipped Capital Femoral Epiphysis (SCFE)
- Older children and adolescents
- Usually boys, big in every dimension
- Insidious, nonspecific onset
- Diagnosis usually easy on plain films
SCFE - Complications
- Avascular necrosis
- Chondrolysis
- Joint incongruity - secondary osteoarthritis
SCFE - MRI
- Unnecessary most of the time
- ? Screening of asymptomatic side
- ? ÒPre-slipÓ
- Evaluation of complications (particularly AVN)
Blount Disease
- Early fusion of medial physis of proximal tibia
- Varus deformity of knee
- Medial epiphyseal narrowing
- Medial tibial beaking
- Congenital
- 1-3 years
- Usually bilateral
- Adolescent form
- > 8 years
- Usually unilateral
Blount Disease - MRI
- Limited role
- Mapping physeal fusion
- Patients are predisposed to meniscal injury
Osteochondritis Dissecans
- Separation of osteochondral fragment along articular surface
- Poorly understood
- Proposed etiologies:
- Trauma
- Avascular necrosis
- Abnormal ossification
- Sites of predilection
- Femoral condyles
- Talar dome
- Capitellum
- Fragment status
- Stable
- Loose in situ
- Free within joint space
Osteochondritis Dissecans - MRI
- Low signal on T1WI in fragment + adjacent bone
- Variable increased signal on T2WI
- Fluid between fragment and parent bone suggests loose in situ fragment
Bone Marrow Disorders
- Marrow conversion
- Anemias
- Marrow packing disorders
- Avascular necrosis
- Legg-CalvŽ-Perthes disease
- Iatrogenic marrow changes
Bone Marrow Conversion
- Red (hematopoietic) marrow converts to yellow (fatty) marrow
- Rate and pattern are predictable
- Conversion by MRI precedes conversion by gross inspection
- 10-20% fat enough to produce high signal on T1WI
Bone Marrow Conversion - MRI
- Assessment made on T1WI
- Red marrow
- Intermediate signal
- Mild enhancement with contrast
- Yellow marrow
- High signal
- No significant enhancement with contrast
Anemias
- Red marrow expansion
- Sickle cell disease
- Thalassemias
- Blackfan-Diamond syndrome (red cell aplasia)
- Yellow marrow expansion
Iron Overload
- Transfusion and/or hemolysis
- Very low marrow signal on all sequences
- Liver and spleen also involved
Marrow Packing Disorders
- Nonneoplastic
- Gaucher disease
- Niemann-Pick disease
- Neoplastic
- Leukemia
- Extensive metastatic disease
- Neuroblastoma
Avascular Necrosis in Children
- Sickle cell disease
- Gaucher disease
- Disseminated intravascular coagulation
- SCFE
- Steroid use
- Leukemia
- Bone marrow transplantation
- Trauma
Avascular Necrosis - MRI
- Various marrow signal patterns
- Low signal reactive margin with preservation of fat signal centrally
- High signal on T1WI and T2WI
- Low signal on T1WI and high signal on T2WI
- Low signal on all sequences
- Patterns often mixed
- Signs of mechanical failure
- Subchondral crescent
- Low signal on T1WI
- High signal on T2WI
- Loss of rounded contour
- Fragmentation
Legg-CalvŽ-Perthes Disease
- Idiopathic AVN of femoral head
- Children ages 3-12 years (peak 5-8 years)
- Characteristic sequence
- Condensation
- Fragmentation
- Reparation
- Changes during reparation
- Femoral head cartilage hypertrophy
- Least pronounced superiorly
- Leads to broadening and loss of rounded contour
- Femoral head coverage by acetabulum may be inadequate
Iatrogenic Marrow Changes
- Iron overload from transfusion
- Marrow suppression from chemotherapy
- Radiation - loss of cellular elements
- Marrow repopulation following BMT
Synovial Disorders
- Juvenile chronic polyarthritis
- Hemophilia
- Pigmented villonodular synovitis
Juvenile Chronic Polyarthritis
- Formerly juvenile rheumatoid arthritis
- Affects many organ systems
- Diagnosis is clinical
- Involves knees most frequently, but any joint may be affected
Juvenile Chronic Polyarthritis - Joint Involvement
- Chronic synovitis
- Synovial hypertrophy/pannus formation
- Erosions
- Ankylosis
- Hyperemia
- Bony overgrowth
- Early physeal fusion
Juvenile Chronic Polyarthritis - MRI
- No role in diagnosis
- Primary indication - map extent of synovial hypertrophy
- Contrast enhanced T1WI is best sequence
Hemophilia
X-linked recessive coagulation disorder
Factor XIII deficiency - hemophilia A
Factor IX deficiency - Hemophilia B
Hemophilia - Joint Disease
- Repeated hemarthrosis
- Synovial inflammation
- Synovial hypertrophy/pannus formation
- Hemosiderin deposition
Hemophilia - MRI
- Synovial mapping
- Synovium low signal on all sequences
- Variable signal effusion
- Intra-osseous hemorrhage
Pigmented Villonodular Synovitis
- Idiopathic
- Affects synovial joints and tendon sheaths
- Synovial proliferation with hemosiderin deposition
- Unusual in children
- Characteristic mixed signal mass
Miscellaneous Conditions
- Dermatomyositis
- Duchenne muscular mystrophy
Dermatomyositis
- Idiopathic inflammatory disorder
- Primarily affects skeletal muscle
- Proximal muscle weakness
- Characteristic rash
- Diagnosis by electromyography and/or muscle biopsy
Dermatomyositis - MRI
- High muscle signal on T2WI
- Signal abnormalities correlate with disease activity
- Involvement pattern in thighs - adductors>gluteals>quadriceps>hamstrings
- MRI useful to select muscle biopsy site
Duchenne Muscular Dystrophy
Most severe and most common form of muscular dystrophy
X-linked recessive
Progressive muscle weakness
Death from respiratory compromise
Duchenne Muscular Dystrophy - MRI
May be used to detect and monitor muscle involvement
T1WI demonstrate fatty infiltration and eventual replacement of muscle
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