What is the best initial imaging modality for visualizing bone infections in pediatric patients?

Best Imaging Modality for Pediatric Bone Infections

Start with plain radiographs first, then proceed directly to MRI for definitive diagnosis and treatment planning of suspected osteomyelitis in children. 1

Initial Imaging: Plain Radiographs

Always obtain plain radiographs as the first imaging test, despite their limited sensitivity for acute infection. 1 This approach is recommended by the American College of Radiology because radiographs are:

• Safe, inexpensive, quickly obtained, and widely available 1, 2
• Essential for excluding alternative diagnoses such as fractures, tumors, degenerative changes, or neuropathic arthropathy 1, 2
• Useful for detecting radiodense foreign bodies and soft tissue gas 1, 2
• Necessary for establishing baseline anatomic detail 1

Critical Limitation to Understand

Normal radiographs do NOT exclude osteomyelitis in children. 1, 2 The sensitivity of early radiographs is extremely low (only 16%) because:

• Bone destruction typically requires 7-10 days to appear 2
• Radiographic changes are not visible until >30% of osseous matrix has been destroyed 2
• Detection of bone destruction may take up to 3 weeks after symptom onset 1

Definitive Imaging: MRI

MRI is the modality of choice for suspected bone infections in pediatric patients, particularly given radiation dose concerns in children. 1

Why MRI is Superior

• 100% negative predictive value for excluding osteomyelitis - a normal marrow signal reliably excludes infection 1, 2
• Highest sensitivity (81%) and specificity among all imaging modalities for detecting acute osteomyelitis 3, 4
• Detects early bone marrow changes before radiographic abnormalities appear 5, 6
• Shows decreased T1-weighted bone marrow signal with increased signal on fluid-sensitive sequences (T2-weighted fat-saturated and STIR) 1
• Provides superb soft-tissue contrast and anatomic detail 1, 7

Critical Additional Information MRI Provides

MRI reveals clinically important findings that directly impact treatment decisions in 45% of pediatric cases. 3 Specifically, MRI:

• Detects osteomyelitis in approximately 50% of children with clinically suspected septic arthritis alone 1
• Shows that 70% of pediatric septic arthritis cases have associated osteomyelitis 1
• Identifies soft-tissue abscesses in 28% of pelvic osteomyelitis cases 1
• Demonstrates extension into the epiphysis and subperiosteal involvement not visible on radiographs 5
• Distinguishes isolated soft tissue infection from true bone infection 5

Contrast Administration Considerations

Contrast administration increases reader confidence and better delineates abscesses but does not increase sensitivity or specificity for osteomyelitis itself. 1 However:

• Use IV contrast in infants and younger children with abundant non-ossified cartilage, as infection limited to the intrinsically hyperintense cartilaginous growth plate and epiphyses/apophyses can be occult on unenhanced sequences 1
• Contrast helps with surgical planning by clearly defining abscess boundaries 1

Alternative Imaging When MRI is Unavailable or Contraindicated

Ultrasound (Limited Role)

Ultrasound is useful as a complementary modality but cannot diagnose osteomyelitis directly. 1 Use ultrasound for:

• Detecting subperiosteal collections associated with osteomyelitis 1
• Identifying soft-tissue abscesses and joint effusions 1
• Guiding aspiration procedures 1
• Limitation: Cannot penetrate cortex to evaluate bone marrow 1
• Yields treatment-modifying information in 30% of pediatric cases 3

Nuclear Medicine (Bone Scintigraphy)

Reserve bone scintigraphy for multifocal disease or when MRI is contraindicated. 1

• High sensitivity (81%) but lower specificity (84%) compared to MRI 4
• Can become positive as early as 1-2 days after symptom onset 1, 8
• Most useful when symptoms cannot be localized or multifocal osteomyelitis is suspected 1
• Main limitation: lower spatial resolution and inability to detect soft-tissue abscesses 1

CT Scan (Not Recommended for Acute Infection)

Do not use CT for suspected acute osteomyelitis in children. 1 CT has:

• Decreased sensitivity for bone marrow pathology compared to MRI 1
• Decreased soft-tissue contrast 1
• Radiation exposure concerns in pediatric patients 1
• Only consider CT when MRI is contraindicated or for evaluating chronic osteomyelitis with sequestra 1, 2

Common Pitfalls to Avoid

• Never rely solely on normal radiographs to exclude infection - early osteomyelitis frequently has completely normal radiographic appearance 2, 8
• Do not skip MRI in favor of CT for acute suspected osteomyelitis 2, 8
• Do not assume isolated septic arthritis - obtain MRI to evaluate for associated osteomyelitis, which occurs in 70% of pediatric cases 1
• Do not perform ultrasound alone expecting to diagnose osteomyelitis - it cannot evaluate bone marrow 1
• Do not delay MRI waiting for radiographic changes - bone destruction takes weeks to appear on plain films 1, 2

Practical Algorithm for Pediatric Bone Infection

1. Obtain plain radiographs immediately in all cases 1
2. Proceed directly to MRI if clinical suspicion remains despite normal radiographs 1
3. Use IV contrast in infants and young children with non-ossified cartilage 1
4. Add ultrasound if concerned about subperiosteal abscess or to guide aspiration 1, 3
5. Consider whole-body MRI or bone scan if multifocal disease is suspected 1