OSTEOMYELITIS

What is the earliest imaging sign of acute hematogenous osteomyelitis?

Soft tissue swelling and decreased marrow signal on X-ray.

When does X-ray become positive in acute osteomyelitis?

After 10\text{–}14 days from onset of infection.

Which imaging modality detects osteomyelitis earlier than X-ray?

MRI.

What MRI findings are seen in early osteomyelitis?

T2 hyperintensity and contrast enhancement in bone marrow.

What is the role of radionuclide scans in diagnosing osteomyelitis?

Show increased uptake early but are non-specific.

How can you differentiate osteomyelitis from cellulitis using imaging?

MRI or scintigraphy shows bone involvement only in osteomyelitis.

What is a Brodie abscess on X-ray?

Well-defined radiolucent area surrounded by sclerotic bone.

What imaging confirms subacute osteomyelitis when labs are negative?

X-ray or radionuclide scan.

What X-ray findings suggest chronic osteomyelitis?

Bone destruction, sequestra, sclerosis, and cortical thickening.

What MRI finding suggests bone necrosis in osteomyelitis?

Areas with no contrast enhancement and hypointensity on T1.

Which imaging is best for visualizing subperiosteal abscesses?

Ultrasound or MRI.

What does cortical destruction on X-ray indicate in osteomyelitis?

Likely chronic or complicated infection.

How does MRI influence treatment decisions in osteomyelitis?

Identifies need for surgical drainage if large abscesses are present.

What X-ray finding is typical in early post-traumatic osteomyelitis?

Normal initially, later shows periosteal reaction.

What imaging helps distinguish between osteomyelitis and bone infarction?

MRI with contrast: active inflammation enhances in osteomyelitis.

What is the hallmark MRI feature of acute osteomyelitis?

Diffuse bone marrow edema with contrast enhancement.

What imaging differentiates vertebral osteomyelitis from degenerative disease?

MRI showing disc space involvement and endplate changes in osteomyelitis.

What is the “railroad track” sign seen in?

Chronic osteomyelitis with marked cortical thickening.

What imaging helps identify intraosseous abscesses?

MRI.

What CT finding may be seen in chronic osteomyelitis?

Sequestra, involucrum, and cortical irregularity.

What imaging is used to guide aspiration in suspected osteomyelitis?

Ultrasound or CT.

What is the role of PET-CT in osteomyelitis?

Detects metabolic activity; useful in complex or recurrent cases.

What is the key difference between sequestrum and involucrum on imaging?

Sequestrum is dead bone without blood supply; involucrum is new bone around it.

What imaging feature distinguishes spinal tuberculosis from pyogenic osteomyelitis?

Paraspinal abscess and relative preservation of intervertebral discs in TB.

What imaging helps differentiate osteoid osteoma from osteomyelitis?

CT shows nidus in osteoid osteoma; MRI shows surrounding inflammation.

What is the "double line sign" on MRI?

Seen in avascular necrosis, not in osteomyelitis.

What imaging is most sensitive for early vertebral osteomyelitis?

MRI with gadolinium contrast.

What MRI finding supports a diagnosis of discitis rather than osteomyelitis?

Disc signal changes without enhancing bone marrow lesions.

What imaging feature helps differentiate Ewing sarcoma from osteomyelitis?

Onion-skin periosteal reaction and soft tissue mass in Ewing sarcoma.

What is the role of ultrasound in pediatric osteomyelitis?

Useful for detecting subperiosteal fluid collections.

What X-ray sign indicates aggressive bone lesion vs. infection?

Sunburst pattern or Codman triangle seen more often in tumors.

What is the preferred imaging for suspected prosthetic joint infection?

Labeled WBC scan or combined MRI and nuclear medicine studies.

What imaging finding supports fungal osteomyelitis over bacterial?

Often more focal lytic lesions with less reactive bone formation.

What is the “abscess rim sign” on MRI?

Indicates presence of pus within bone or soft tissue abscess.

What imaging differentiates stress fracture from osteomyelitis?

MRI shows linear marrow edema along cortex in stress fractures without ring-enhancing abscess.

What is the role of diffusion-weighted MRI in osteomyelitis?

Helps detect restricted diffusion in acute abscesses.

What imaging helps diagnose vertebral osteomyelitis in IV drug users?

MRI of the spine showing infection at C1-C2 or thoracic levels.

What is the “penumbra sign” in musculoskeletal imaging?

Suggests aneurysmal bone cyst, not osteomyelitis.

What imaging finding differentiates sarcoidosis from osteomyelitis?

Multiple small lytic lesions with preserved architecture in sarcoidosis.

What is the role of FDG-PET in chronic osteomyelitis?

Can localize metabolically active infection for biopsy guidance.

What imaging helps differentiate Lyme arthritis from septic arthritis?

MRI or ultrasound for synovial fluid analysis; no bone involvement in Lyme.

What is the appearance of cloacae in chronic osteomyelitis on imaging?

Tract connecting sequestrum to skin surface on fistulography or MRI.

What imaging differentiates mycobacterial osteomyelitis from pyogenic?

Slower progression and less aggressive periosteal reaction in mycobacterial.

What is the imaging hallmark of vertebral osteomyelitis?

Endplate erosion and disc space narrowing on MRI.

What imaging helps rule out metastatic disease mimicking osteomyelitis?

Whole-body MRI or bone scan with correlation to clinical history.

What imaging modality is best for evaluating implant-associated osteomyelitis?

MRI with metal artifact reduction or labeled WBC scan.

What imaging feature supports actinomycosis instead of pyogenic osteomyelitis?

Sinus tracts and sulfur granules clinically, imaging may show diffuse sclerosis.

What imaging is used to assess healing after osteomyelitis treatment?

Serial MRI or CRP trends with clinical follow-up.

What imaging helps confirm relapse of osteomyelitis after treatment?

MRI showing recurrent marrow edema and contrast enhancement.

What is the significance of gas in bone on X-ray or CT?

Highly suggestive of emphysematous or mixed flora osteomyelitis.