Applied Radiology

Diagnosis

Shear injury

Findings

Within the subcutaneous fat overyling the greater trochanter of the femur, there is a rounded lesion, which is predominantly hyperintense on T2-weighted images and hypointense on T1-weighted images. Curvilinear hypointensities with the lesion on T2- weighted images are consistent with debris. The lesion has a thin hypointense capsule on both T1- and T2-weighted images. The grayscale ultrasound image demonstrates a nearly anechoic lesion with a small amount of layering echogenic debris. During the ultrasound examination, the lesion was fluctuant.

Discussion

A Morel Lavallee lesion occurs over the greater trochanter of the femur and results from a closed degloving injury (or shear injury), which separates the subcutaneous tissues from the underlying fascia. The lesions tend to appear within hours to days of the injury. Similar lesions can occur near the knee, the lumbar spine, and the scapula, although these classically are not designated by the eponomous term.

After a significant shearing of the subcutaneous tissues from the underlying fascia, fluid accumulates within the potential space. The fluid contains variable amounts of lymph, blood, fat, and debris. The Morel Lavellee lesion occurs within the subcutaneous tissues and may be rounded or represent a thin fluid collection tracking along the fascia. Underlying fractures are often present. Ultrasound examination reveals a fluctuant, fluid-filled lesion within the subcutaneous tissues, which is most often anechoic, although echogenic debris is often present within the nondependant portions. Occasionally a fat-fluid level may be present. Magnetic resonance imaging (MRI) is useful for delineating the underlying fascia and for determining the degree of encapsulation, an important factor in determining the proper treatment. The fluid component is most often hyperintense on T2-weighted images and hypointense on T1-weighted images, but the signal characteristics are affected by the amount of hemorrhage and fat within the collection.

Treatment is reserved for cases, which do not resolve spontaneously or with compression bandages. The presence of a capsule suggests that percutaneous or surgical drainage will be unsuccessful, although success can sometimes be achieved with drainage and sclerodesis using talc or doxycycline. Once a collection has become established, surgical excision is often necessary. Without proper treatment, these lesions are at high risk of superinfection.

1. Gilbert BC, Bui-mansfield LT, Dejong S. MRI of a Morel-Lavellée lesion. AJR Am J Roentgenol. 2004;182:1347-1348.
2. Neal C, Jacobson JA, Brandon C, et-al. Sonography of Morel-Lavallee lesions. J Ultrasound Med. 2008;27:1077-1081.
3. Mallado JM, Bencardino JT. Morel-Lavallee lesion: Review with emphasis on MR imaging. Magn Reson Imaging Clin N Am. 2005;13:775-782.
4. Hak DJ, Olson SA, Matta JM. Diagnosis and management of closed internal degloving injuries associated with pelvic and acetabular fractures: the Morel-Lavallee lesion. J Trauma. 1997;42:1046-1051.