What is a Morel‑Lavallée lesion, its clinical presentation, diagnostic approach, and recommended management?

Morel-Lavallée Lesion: Definition, Clinical Presentation, Diagnosis, and Management

Definition and Pathophysiology

A Morel-Lavallée lesion is a closed degloving injury caused by violent shearing forces that separate the subcutaneous tissue from the underlying fascia, creating a potential space that fills with hemolymph (blood and lymphatic fluid mixed with liquefied fat). 1

• The injury occurs when tangential or shearing trauma forcibly separates the hypodermis from the deep fascia, disrupting perforating blood vessels and lymphatics 1, 2
• The resulting cavity becomes filled with hematoma and liquefied fat, creating a hemolymphatic collection 3, 4
• These lesions have a high rate of acute bacterial colonization and chronic recurrence if not properly managed 1

Clinical Presentation

The most common location is the peritrochanteric region (over the greater trochanter), though lesions can occur in the flank, buttocks, lumbodorsal regions, and medial thigh/knee. 1, 2

Key Clinical Features to Identify:

• Mechanism of injury: High-velocity trauma (motor vehicle accidents, pedestrian struck by vehicle) or sports-related falls, even at low speed 5, 3, 4
• Physical examination findings: Large area of soft tissue swelling, ecchymosis, and fluctuance that persists beyond expected timeframe for simple contusion 5, 3
• Timing: Presentation may be acute (immediately post-trauma) or significantly delayed—cases have been reported presenting 2.5 years after initial injury 4
• Associated injuries: Patients frequently have concomitant polytrauma, which can lead to the Morel-Lavallée lesion being overlooked initially 1

Common Pitfall:

Morel-Lavallée lesions are frequently misdiagnosed as simple contusions or hematomas, leading to delayed treatment and increased risk of complications including recurrence, infection, and chronic pain. 5, 3

Diagnostic Approach

Magnetic resonance imaging (MRI) is the modality of choice for identification and characterization of Morel-Lavallée lesions. 4, 2

Imaging Characteristics:

• MRI findings: Fluid collection between subcutaneous tissue and fascia, with variable signal intensity depending on age of lesion and composition (acute blood vs. chronic hemosiderin vs. fat) 4, 2
• Point-of-care ultrasound (POCUS): Can identify the inter-fascial fluid collection and guide interventional drainage in the primary care or emergency setting 3
• Alternative modalities: CT and plain radiographs can visualize lesions but are inferior to MRI for characterization 4

Diagnostic Algorithm:

1. Maintain high index of suspicion in any patient with persistent soft tissue swelling/ecchymosis after shearing trauma
2. Perform POCUS at bedside if available to identify fluid collection 3
3. Order MRI for definitive diagnosis and characterization if POCUS positive or clinical suspicion remains high 4, 2
4. Do not dismiss the diagnosis based on low-velocity mechanism—even bicycle falls can cause Morel-Lavallée lesions 3

Management Recommendations

Early intervention with drainage and/or debridement provides the best outcomes and prevents recurrence, infection, and chronic complications. 1, 5

Treatment Algorithm Based on Timing:

Acute/Subacute Presentation (< 4 weeks):

• First-line: Ultrasound-guided percutaneous drainage of the fluid collection 3
• Rationale: Conservative treatment outcomes are best when managed acutely, before organization and capsule formation occur 1
• Technique: Use POCUS to guide needle aspiration, evacuate hemolymph completely 3

Delayed/Chronic Presentation (> 4 weeks):

• Surgical debridement and drainage is typically required due to organization of the lesion and capsule formation 5
• Rationale: Chronic lesions have higher recurrence rates with aspiration alone and often require open surgical management 1, 5

Critical Management Principles:

• Do not treat as simple contusion with conservative management alone—this leads to recurrence and prolonged clinical course 5
• Early drainage/debridement prevents: Re-accumulation of fluid, bacterial colonization/infection, chronic pain, and significantly shortens recovery time 5
• Monitor for recurrence: Even with appropriate initial treatment, these lesions can recur and require repeat intervention 1

Specific Contraindication to Conservative Management:

If a Morel-Lavallée lesion is diagnosed (not just suspected), observation alone is inappropriate—active intervention with drainage is required to prevent complications. 1, 5