What is the best imaging modality for a sacral ulcer suspected of having osteomyelitis (infection of the bone)?

From the Guidelines

For suspected osteomyelitis in a sacral ulcer, MRI with contrast is the best initial imaging modality. This recommendation is based on the most recent and highest quality study available, which suggests that MRI offers superior soft tissue resolution and can detect early bone marrow edema, allowing for early diagnosis with sensitivity of 90-95% and specificity of 80-85% 1.

Key Points to Consider

• MRI with contrast is the modality of choice in the evaluation of osteomyelitis, as it provides detailed images of both bone and soft tissue 1.
• CT scanning is an alternative if MRI is contraindicated, though it has lower sensitivity for early osteomyelitis 1.
• Plain radiographs have limited utility as they only show bone changes after 30-50% of bone mineral is lost, which can take 10-14 days after infection onset 1.
• Nuclear medicine studies like bone scans or white blood cell scans may be considered in specific situations but generally offer less anatomic detail than MRI 1.

Clinical Considerations

When ordering the MRI, it is essential to specify "MRI sacrum with and without contrast to evaluate for osteomyelitis" to ensure proper protocol. The radiologist should be informed of the clinical suspicion for osteomyelitis to guide appropriate interpretation. While awaiting imaging, appropriate wound care and empiric antibiotics should be initiated if clinical suspicion is high.

Imaging Modalities

• MRI: Best initial imaging modality for suspected osteomyelitis in a sacral ulcer, offering superior soft tissue resolution and detection of early bone marrow edema 1.
• CT: Alternative imaging modality if MRI is contraindicated, useful for detecting cortical bone changes and soft-tissue infections 1.
• Ultrasound (US): Complementary role in evaluating osteomyelitis, primarily for detection and characterization of soft-tissue infections 1.
• Nuclear Medicine: Limited role, mainly used when MRI is contraindicated, infection is multifocal, or associated with orthopedic hardware or chronic bone alterations 1.

From the Research

Imaging Modalities for Osteomyelitis

• The initial imaging procedure for suspected osteomyelitis is radiography, but its sensitivity is low in the early stages of the disease 2, 3.
• Magnetic resonance imaging (MRI) with and without contrast material has a higher sensitivity for identifying areas of bone necrosis in later stages 2, 3.
• MRI is as sensitive as bone scintigraphy in the early detection of osteomyelitis and is often more specific in differentiating bone from soft-tissue infection 4.
• The sensitivity and specificity of MRI for diagnosing osteomyelitis are 90% and 80%, respectively, with findings including bone marrow edema, T2-weighted image hyperintensity, T1-weighted image confluent signal, and cortical erosion 5.

Best Imaging Modality for Sacral Ulcer Suspected of Having Osteomyelitis

• MRI is the preferred imaging modality for evaluating the presence and extent of osteomyelitis, particularly in cases where the infection is suspected to involve the bone 6, 4.
• MRI can facilitate differentiation of acute from chronic osteomyelitis and help detect foci of active infection in the presence of chronic inflammation or posttraumatic lesions 4.
• The use of gadolinium-enhanced MRI can be helpful in delineating the extent of the infection and demonstrating the border of any associated abscesses 4.

Risk Factors and MRI Findings

• Diabetes is an independent risk factor for osteomyelitis, and patients with diabetes should be evaluated for osteomyelitis with recommendation for bone biopsy in appropriate clinical settings 5.
• Cortical erosion and confluent signal on T1-weighted images are independent risk factors for osteomyelitis and should be considered when evaluating MRI findings 5.