Morel-Lavallée lesion

Morel-Lavallée lesions are closed degloving injuries associated with severe trauma which then present as hemolymphatic masses. MRI and ultrasound are useful modalities for evaluation.

Terminology

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 can result in identical lesions and these are often also called Morel-Lavallée lesions  ^1,3.

Pathology

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. The initial potential space created superficial to the fascia is filled by various types of fluid, ranging from serous fluid to frank blood.

The collection may then spontaneously resolve or become encapsulated and persistent.

Classification

• Mellado-Bencardino classification

Radiographic features

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.

Plain radiograph

The Morel-Lavellée lesion will not be demonstrated on a plain radiograph but an underlying fracture may be present. Injuries which are associated with these lesions include femoral and pelvic fractures.

Ultrasound

Typically these lesions are anechoic or hypoechoic; however, 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.

MRI

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 then conservative management is rarely successful (e.g. compression bandages). Surgical drainage may be sufficient, although in some instances the capsule needs to be resected to prevent re-accumulation.

History and etymology

It was first described in 1848 by Victor-Auguste-François Morel-Lavallée (1811-1865), a French surgeon ⁴. 

Differential diagnosis

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:

• hemangioma
• sarcoma
• fat necrosis
• subcutaneous hematoma