Morel-Lavallee Lesion (MLL)

Diagnosis Definition

• The Morel-Lavallee lesion (MLL) results from a closed traumatic degloving soft tissue injury that most commonly occurs in the area of the greater trochanter and knee
• The injury results in separation of the hypodermis from the underlying fascia when a shearing force is applied to the soft tissue, disrupting the perforating vascular and lymphatic structures
• A mixture of blood, lymph, and fatty debris collects in the potential space, which is replaced by serosanguinous fluid as the lesion enlarges; if left untreated, inflammation can lead to pseudocapsule formation
• Treatment options include percutaneous drainage with sclerodesis, however, once collections are encapsulated, surgical drainage and resection may be required

Imaging Findings

• On MRI, the MLLs may be of variable signal intensity depending on the age and constituents of the fluid collection
• Fibrinous and hemorrhagic debris appears hypointense on T2-weighted images and fat globules appear as dependently positioned hyperintense areas on T1-weighted images
• Fluid-fluid levels and septations may be seen
• When a pseudocapsule forms, the collections become circumscribed

KEY IMAGES

Pearls

• Fat globules are a specific feature of an MLL
• Infection, pseudocyst formation, and cosmetic deformity can result from improper or untimely diagnosis and management
• Most common location is the hip followed by the knee

References

1. Gilbert BC et al. MRI of a Morel-Lavallée Lesion. AJR 2004; 182(5):1347-1348
2. Vassalou EE et al. Morel-Lavallée Lesions of the Knee: MRI Findings Compared With Cadaveric. AJR 2018; 210(5):234-239
3. Chew FS. Imaging of Soft Tissue Lesions and Calcifications. In: Musculoskeletal Imaging: The Essentials. Wolter Kluwer; 2001:261-262