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A Morel-Lavallée lesion (MLL) is a closed internal degloving injury characterized by separation of subcutaneous fat from the underlying deep fascia due to blunt trauma or shearing forces. This creates a potential space that fills with hemolymphatic fluid, necrotic fat, and blood, forming a fluctuating soft tissue mass.

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• It was first described by the French physician Maurice Morel-Lavallée in 1853.

Etiopathogenesis

• Mechanism: High-energy trauma, often in road traffic accidents, sports injuries, or crush injuries, produces a tangential shearing force.

Pathology:

• Separation between superficial fascia and underlying fascia leads to rupture of capillaries and lymphatic vessels.
• Accumulation of sero-hemorrhagic fluid, blood products, and necrotic fat.
• With time, a fibrous pseudocapsule may form, especially in chronic untreated lesions, preventing spontaneous resolution.

Common sites:

• Over the greater trochanter (most common).
• Thigh, knee, pelvis, lumbosacral region.

Clinical Features

• History of trauma with soft, fluctuant swelling.
• May present acutely (painful, tense, ecchymotic swelling) or chronically (painless, compressible, fluctuant mass).
• Can be confused with soft tissue tumors or bursitis.
• May predispose to infection if untreated.

![A 36-year-old man presented with a large mass on his back after he slipped on the stairs and slid down on his back. Magnetic resonance imaging showed a large, encapsulated, subcutaneous, suprafascial lesion consistent with a Morel–Lavallée lesion.

Kim YH, Park HY. Morel–Lavallée Lesion. New England Journal of Medicine. 2021;385(23):2179. doi:10.1056/nejmicm2111332](attachment:8ff80243-c16e-4a19-b33b-365a87b3c5c5:nejmicm2111332_f1.jpg)

A 36-year-old man presented with a large mass on his back after he slipped on the stairs and slid down on his back. Magnetic resonance imaging showed a large, encapsulated, subcutaneous, suprafascial lesion consistent with a Morel–Lavallée lesion.

Kim YH, Park HY. Morel–Lavallée Lesion. New England Journal of Medicine. 2021;385(23):2179. doi:10.1056/nejmicm2111332

Radiology