What does patchy bone marrow edema typically indicate?

Patchy Bone Marrow Edema: Clinical Significance

Patchy bone marrow edema is a nonspecific MRI finding that indicates increased interstitial fluid within bone and requires correlation with clinical context to identify the underlying cause, which ranges from benign self-limited conditions to serious pathology including osteonecrosis, insufficiency fractures, inflammatory arthritis, infection, or malignancy. 1, 2

Key Differential Diagnoses to Consider

Osteonecrosis

• Bone marrow edema surrounding a focus of necrosis is a hallmark finding, particularly when combined with joint effusion, which increases risk for femoral head collapse 3, 2
• MRI with dynamic contrast enhancement differentiates osteonecrosis from other causes: osteonecrosis shows a rim of high plasma flow surrounding a subchondral area without flow (representing granulation tissue), whereas transient bone marrow edema syndrome shows subchondral hyperperfusion 3
• Osteonecrosis demonstrates overall decreased maximal enhancement compared to transient bone marrow edema or subchondral insufficiency fracture 3

Transient Bone Marrow Edema Syndrome (BMES)

• This is an idiopathic, self-limiting condition (lasting 3-9 months) that shows diffuse bone marrow edema throughout the femoral head and neck without the characteristic rim sign of osteonecrosis 3
• Most commonly affects middle-aged men and younger women, originally described in pregnant women during third trimester 3, 4
• Treated conservatively with protected weight-bearing 1, 4

Subchondral Insufficiency Fractures

• These fractures most commonly affect the medial femoral condyle in middle-aged to elderly females and can progress to articular collapse requiring arthroplasty if untreated 1, 5
• MRI identifies these fractures before radiographs become abnormal, showing bone marrow edema with associated fracture lines 3, 1
• Deep edema extending >1 cm from the articular surface with geographic patterns suggests insufficiency fracture 1

Inflammatory Arthritis

• Bone marrow edema combined with synovitis and joint effusion indicates inflammatory disease requiring disease-modifying therapy rather than symptomatic treatment 1, 5
• In rheumatoid arthritis, subchondral bone marrow edema is associated with inflammatory cell infiltrate and osteoclasts, predicting future erosion development 6
• In spondyloarthritis, bone marrow edema of sacroiliac joints identifies active sacroiliitis and correlates with radiographic progression 6

Infection (Osteomyelitis)

• Osteomyelitis causes bone marrow edema with increased signal on T2 and STIR sequences 2
• In diabetic patients with Charcot arthropathy, bone marrow edema can be difficult to distinguish from superimposed osteomyelitis 3, 2

Malignancy

• Bone marrow edema can be a premonitory sign in malignant hemopathies including multiple myeloma, leukemia, and lymphoma 7
• Malignant bone tumors present with bone marrow edema, particularly with cortical destruction or rapid growth 2
• In neoplasm, the lesion is typically more obvious on T1-weighted sequences compared to stress fractures where edema is more pronounced on T2-weighted sequences 3

Trauma and Mechanical Causes

• Acute trauma and fractures produce bone marrow edema that typically resolves within 1-3 months 2
• Stress fractures show pronounced linear edema on T2-weighted sequences, much more than on T1-weighted sequences 3

Diagnostic Approach

Initial Imaging Strategy

• MRI with T2-weighted and STIR sequences is the preferred imaging modality to demonstrate bone marrow edema and assess for associated findings 1, 2
• Correlate imaging patterns with clinical context: deep edema >1 cm from articular surface, associated fracture lines, or geographic patterns with surrounding reactive edema help identify the underlying cause 1

Advanced Imaging When Needed

• MRI with dynamic contrast enhancement differentiates osteonecrosis (rim of high plasma flow around area without flow) from transient bone marrow edema syndrome (subchondral hyperperfusion) and subchondral insufficiency fracture 3
• In-phase and out-of-phase MRI sequences reliably differentiate benign stress fractures from pathologic fractures: normal marrow shows signal suppression on opposed-phase images, while tumor-replaced marrow lacks suppression 3

Critical Clinical Pitfalls

Do Not Assume Benignity

• New or increasing bone marrow edema correlates with pain progression and can lead to joint destruction if the underlying cause is not addressed 1, 5
• Bone marrow edema lacks specificity because it occurs in multiple conditions and can even be seen in healthy individuals 2

Do Not Delay Diagnosis

• Particularly in diabetic patients with Charcot arthropathy, delayed multidisciplinary referral leads to significant clinical deterioration 3, 1
• Rule out subchondral insufficiency fracture early, as MRI identifies these before radiographs become abnormal 1, 5

Context Matters

• Bone marrow edema in healthy athletes or postpartum patients may be physiologic, whereas the same finding in an elderly patient with acute pain suggests insufficiency fracture 1
• Do not ignore clinical context when interpreting bone marrow edema patterns 1, 2

Monitor for Progression

• Subchondral insufficiency fractures can progress to articular fragmentation and collapse, particularly in the medial femoral condyle 1, 5
• In osteoarthritis, new or increasing bone marrow edema is associated with increased knee pain and progression of cartilage damage 5, 6