How do I interpret my foot MRI results?

How to Interpret a Foot MRI

MRI is the recommended imaging modality for evaluating most complex foot conditions, offering excellent soft tissue contrast, multiplanar capabilities, and bone marrow visualization without radiation exposure.

Initial Approach to Foot MRI Interpretation

Standard MRI Sequences to Expect

• T1-weighted images: Excellent for anatomy and bone marrow fat
• T2-weighted images: Highlight fluid/edema
• STIR (Short Tau Inversion Recovery): Fat suppression to detect bone marrow edema
• Proton density sequences: Good for ligament and tendon evaluation

Systematic Review Method

1. Osseous structures: Evaluate for fractures, bone marrow edema, osteomyelitis
2. Joints: Assess alignment, cartilage integrity, effusions
3. Soft tissues: Examine tendons, ligaments, plantar fascia, neurovascular structures
4. Fat pads and bursae: Look for inflammation or atrophy

Key Pathologies to Identify on Foot MRI

Bone Pathology

• Stress fractures: Appear as linear low signal on T1 with surrounding edema on T2/STIR
• Osteomyelitis: Shows bone marrow edema with adjacent soft tissue inflammation 1
• Bone tumors: Evaluate for signal characteristics, margins, and extension

Joint Conditions

• Arthritis: Look for joint space narrowing, subchondral cysts, osteophytes
• Charcot arthropathy: Shows bone fragmentation, joint effusion, and disorganization 1
• Synovitis: Appears as thickened synovium with enhancement if contrast is used

Soft Tissue Pathology

• Tendon injuries: Assess for thickening, signal changes, or discontinuity
• Plantar fasciitis: Appears as thickening and increased signal in the plantar fascia 1
• Morton's neuroma: Appears as a well-defined mass between metatarsal heads
• Foreign bodies: May appear as low signal intensity structures with surrounding inflammation 2

Special Considerations for Diabetic Foot

When evaluating diabetic foot conditions, pay particular attention to:

• Osteomyelitis vs. Charcot arthropathy: MRI is the recommended imaging modality when diagnosis remains in doubt after clinical assessment and plain radiographs 1
• Infection patterns: Look for bone marrow edema with "secondary signs" such as adjacent skin ulceration, cellulitis, soft tissue abscess or sinus tract 1
• Distribution patterns: Osteomyelitis typically affects toes, metatarsal heads, calcaneus, and malleoli, while neuropathic arthropathy is most common in the midfoot 1

Common Pitfalls in Foot MRI Interpretation

• Overdiagnosis of plantar fasciitis: Some MRI findings can be seen in asymptomatic patients 1
• Magic angle artifact: Can mimic tendon pathology, particularly in the posterior tibial tendon
• Bone marrow edema interpretation: Can be difficult to differentiate between infection, trauma, and Charcot changes 1
• Anatomical complexity: The foot's intricate structure requires careful correlation with clinical findings 3, 4

When Additional Imaging Is Needed

• For suspected foreign bodies: If radiographs are negative but clinical suspicion remains high, ultrasound is recommended as a second-line imaging modality 2
• For diabetic foot with equivocal MRI findings: Consider WBC imaging or FDG-PET/CT for differentiating osteomyelitis from Charcot arthropathy 1
• For chronic plantar heel pain: When radiographs are negative, MRI is considered the most sensitive imaging study 1

Practical Tips for Optimal Interpretation

• Review images in all available planes (axial, sagittal, coronal)
• Compare with the contralateral foot when available
• Correlate imaging findings with clinical symptoms to avoid overdiagnosis 1
• Communicate with the referring physician about specific clinical concerns to focus your interpretation 4

Remember that MRI interpretation should always be performed in the context of clinical findings, as even the most sophisticated imaging cannot replace a thorough clinical assessment.