Imaging description

Morel–Lavallée lesions of the thigh and hip region are most commonly diagnosed by MR imaging. Their shape and location are helpful in their diagnosis. A Morel–Lavallée lesion should be located in the deep subcutaneous and perifascial space superficial to the tensor fascia lata (Figure 55.1). They should have well-defined margins and have an oval or fusiform shape. Their signal intensity is non-specific on T1-weighted images since they can be hypo-, iso-, or hyperintense on this sequence. However, they should be hyperintense on T2-weighted images. Their signal intensity can be hetero- or homogeneous. These lesions can demonstrate patchy internal enhancement with contrast and rim enhancement. Ultrasound can demonstrate a fluid collection in the typical locations that may contain hyperechoic nodules, which represent remnants of fat within the lesion.

Importance

Morel–Lavallée lesions can be pathognomonically diagnosed on MRI; therefore, one should be knowledgeable of their appearance so that unnecessary work-up for a neoplasm doesn’t occur. They may also require treatment with sclerosing agents or with surgical resection as they can repeatedly accumulate after aspiration alone. The Morel–Lavallée lesion is an internal degloving injury from trauma caused by separation of the hypodermis from the underlying deep fascia. This results in disruption of the rich vascular and lymphatic plexus that pierces the tensor fascia lata. This disruption of capillaries and lymphatics may lead to continuous fluid and lymphatic drainage into this perifascial virtual cavity filling it with blood, lymph, and debris.