The Morel-Lavallée lesion (MLL) is a post-traumatic closed degloving injury where the subcutaneous tissue is traumatically separated from the underlying deep fascial layer, creating a potential space that is progressively occupied by blood, lymph, and/or liquified fat. [1,2]
MLL is an uncommon lesion. The literature describes an 8.3% prevalence in the context of pelvic trauma, with a 2:1 male to female ratio. [3]
MLL may appear as a result of blunt force trauma or crush injuries where high‐intensity shearing forces are applied tangential to the fascial plane. Most frequently it involves the peritrochanteric region and the proximal thigh. [3]
Clinically there is often a painful focal area of swelling. Physical examination reveals a compressible, fluctuant lesion. [4]
Diagnosis is based on medical history, clinical examination, and imaging techniques, including ultrasound, CT, and MRI. MRI is the gold standard for the description and diagnosis of MLL. [5]
Ultrasound is a rapid and non-expensive method, but highly non-specific, demonstrating a variable appearance of MLL, depending on the age of the lesion. It often shows a heterogeneous hypoechoic collection with intralesional septations and/or hyperechoic fat globules, or rarely, a homogeneous anechoic lesion. The most important features demonstrated by the ultrasound examination are the absence of internal vascular flow and the lesion's location superficial to the muscle fascia and deep to the hypodermis. Sometimes a chronic lesion may be surrounded by a vascularized capsule. [2,6]
CT usually is the initial modality of investigation in acute trauma cases. It depicts the presence of a fluid collection (relatively high density, within 15-40 Hounsfield units, but sometimes with various internal densities, like that of fluid, fat, or blood), with the typical localization. In an acute presentation, MLL is ill-defined, with surrounding fat-stranding, while chronic lesions are encapsulated. [1,3]
The MRI appearance varies depending on the content (the concentration of hemolymphatic fluid) and chronicity of the lesion: homogenous signal intensity and smooth margins (sometimes an enhancing capsule) if chronic, or heterogeneous signal and irregular limits, with surrounding soft-tissue oedema if acute. These characteristics are reunited in the Mellado-Bencardino classification, which describes the appearance on T1 and T2-WI, as well as other features like the shape and enhancement characteristics. The demonstration of adipose signal intensity within the lesion, and also GRE/T2* sequences, which are useful for revealing the internal presence of blood degradation products through the blooming artefact are valuable clues towards the diagnosis. [1,3,7]
The treatment is different depending on the chronicity of the lesion and the presence of associated conditions (superinfections, bone fractures). Acute MLL is conservatively treated with compression, while chronic lesions are reserved for percutaneous aspiration and sclerotherapy. Complicated cases (superinfected, with skin necrosis), associated with a late diagnosis are surgically addressed. [3,5]
In conclusion, MLL is an uncommon posttraumatic lesion with an imaging-based diagnosis, which radiologists should be aware of because early diagnosis permits an easier, conservative treatment.
Written informed patient consent for publication has been obtained.
