Morel Lavallée lesion
A Morel Lavallée lesion occurs over the greater trochanter of the femur and represents a closed degloving injury typically associated with significant trauma 1. Although strictly speaking a Morel Lavallée lesion is only over the greater trochanter, similar biomechanical forces to the lumbar region, over the scapula or the knee can result in identical lesions 1,3.
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 fluid of variable make up ranging from serous fluid to frank blood.
The collection may then spontaneously resolve, or become encapsulated and persistent.
Radiographic features
The size of these lesions is variable, ranging from small thin slivers of fluid to thickly encapsulated lesions many centimetres in diameter. When chronic they are typically oval or fusiform in shape adherent to the underlying fascia.
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 make up and may even show a fluid fluid level 1.
Treatment
Once these lesions become established and encapsulated then 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.
Etymology
First described in 1848 by Morel-Lavallée 4.
Differential diagnoses
If in a classic location and 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:
- aneurysmal bone cyst (ABC)
- haemangioma
- sarcoma
- fat necrosis
- subcutaneous haematoma
