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Morel-Lavallée lesions are closed degloving injuries associated with severe trauma which then present as hemolymphatic collections or masses. MRI and ultrasound are useful modalities for evaluation.
The lesions classically occur over the greater trochanter of the femur 1. Morel-Lavallée lesions, strictly speaking, occur in the thigh. However, similar biomechanical forces to the lumbar region, over the scapula, or over the knee 13 can result in identical lesions and these are often also called Morel-Lavallée lesions 1,3.
Morel-Lavallée lesions typically occur when the skin and subcutaneous fatty tissue traumatically and abruptly separate from the underlying fascia.
The initial injury represents a shearing of subcutaneous tissues away from underlying fascia/muscles along interfascial planes.
The initial potential space created superficial to the fascia is filled with various types of fluid, ranging from serous fluid to frank blood.
The collection may then spontaneously resolve or become encapsulated and persistent.
Some authors have suggested a classification system mainly based on MR assessment 12.
The size of these lesions is variable, ranging from small thin slivers of fluid to thickly encapsulated lesions many centimeters in diameter. When chronic they are typically oval or fusiform in shape and adherent to the underlying fascia.
The Morel-Lavellée lesion will not be demonstrated on a plain radiograph but an underlying fracture may be present. Injuries that are associated with these lesions include femoral and pelvic fractures.
Typically these lesions are anechoic or hypoechoic. As with a standard hematoma, it can be predominantly echogenic in the acute phase, becoming more hypoechoic as blood products liquefy over time 11. Internal debris, including fat globules, can give rise to echogenic foci or even fluid-fluid levels 1. A capsule of variable thickness may be seen. The shape may range from flat to mass-like.
MRI is able to clearly determine the relationship of the collection with the underlying fascia. The fluid is of variable signal intensity depending on makeup and may even show a fluid-fluid level 1.
Treatment and prognosis
Once these lesions become established and encapsulated, conservative management (e.g. compression bandages) is rarely successful. Surgical drainage may be sufficient, although in some instances the capsule needs to be resected to prevent reaccumulation.
History and etymology
It was first described in 1848 by Victor-Auguste-François Morel-Lavallée (1811-1865), a French surgeon 4.
If in a classic location and with a characteristic appearance then little differential exists. In cases where the lesion is heterogeneous in morphology or fluid-fluid levels are present, the possibilities include 1,2: