Presentation
Left leg pain and swelling second day after falling from the bike.
Patient Data
A heterogenously hypoechoic almost fusiform shaped lesion/collection is seen deep to the subcutaneous plane at the site of maximum tenderness at the anterolateral aspect of the left upper leg. The collection is likely representing a hematoma. A thin echogenic capsule can be seen surrounding the collection. Comparison with the asymptomatic leg further clarifies the lesion location. No fracture was seen in leg X-rays (not shown here).
Case Discussion
The above mentioned ultrasound findings and history of trauma are most likely suggestive of Morel-Lavallée lesion.
Morel-Lavallée lesions occur as a result of shearing force in trauma settings which results in the separation of the subcutaneous fat from the deep fascia and the accumulation of blood, lymph, and/ or fat globules between superficial fascia and deep fascia. The most common site for this kind of lesion is superficial tissues over the greater trochanter. Other locations include the upper arm, lumbosacral region, gluteal region, and anterolateral leg compartment as in our case 2.
Ultrasound shows variable features depending upon the age of the hemorrhagic products from hyperechoic in case of acute hemorrhage to completely anechoic when blood products are absorbed leaving behind clear fluid. No internal vasculairty is seen on color doppler.
An important differential for this kind of lesion especially in patients presenting late for imaging after trauma can be a soft tissue sarcoma in which contrast-enhanced MRI will be helpful in showing intralesional homogenous enhancement. Other differentials include hematoma due to coagulopathy, fat necrosis, and bursitis (depending upon lesion location).