Imaging Features of Morel-Lavallée Lesions

Abstract

Objectives: To review the imaging characteristics of Morel-Lavallée lesions with both ultrasound and magnetic resonance imaging (MRI).

Materials and methods: We retrospectively analyzed 31 patients (mean age = 46 years), diagnosed with a Morel-Lavallée lesion, on ultrasound (n = 15) or MRI (n = 16). On ultrasound the echogenicity, internal septations, hyperechoic fat globules, compressibility and Doppler signal were evaluated. On MRI, T1- and T2-signal intensity, capsule presence, internal septations, enhancement, mass-effect and fluid-fluid levels were assessed. The MR images were classified according to the classification of Mellado and Bencardino.

Results: Most of the lesions were situated peritrochanteric, around the knee or the lower leg. The majority of the lesions had a heterogeneous hypoechoic appearance with septations and intralesional fat globules. On MRI, most of the collections were hypointense on T1-weighted images and hyperintense on T2-weighted images. Half of the collections were encapsulated, and most collections demonstrated septations. The collections were classified as seroma (n = 10), subacute hematoma (n = 2) and chronic organizing hematoma (n = 5).

Conclusion: Ultrasound is the imaging method of choice to diagnose Morel-Lavallée lesions. MRI can be of use in selected cases (extension in different compartments, large collections, superinfection). Characteristic imaging features include a fusiform fluid collection between the subcutaneous fat and the underlying fascia with internal septations and fat globules. On MRI, six types of ML lesion can be differentiated, with the seroma, the subacute hematoma, and the chronic organizing hematoma being the most frequently observed lesions.

Keywords: Hematoma; MRI; Morel-Lavallée; Seroma; Ultrasound.

Figure 1

Mechanism of injury. Cross-sectional schematics of: (A) Normal layers of tissue from dermis to bone. (B) Tangential shearing force cause the relatively mobile dermis and subcutaneous fat to move relative to the fixed underlying fascia, causing disruption of perforating arteries (red), veins (blue), and lymphatics (green). (C) Formation of a hemolymphatic collection in the potential space between subcutaneous fat and fascia. Case courtesy of Dr Matt Skalski.

Figure 2

Mellado and Bencardino classification of Morel-Lavallée lesions. Case courtesy of Dr Matt Skalski. (A) Type I = seroma, (B) Type II = subcatue hematoma, (C) Type III = chronic organizing hematoma, (D) Type IV = perifascial dissection with closed fatty laceration, (E) Type V = perifascial pseudonodular lesion, (F) Type VI = infected lesion with or without sinus tract formation, internal septations, and thick enhancing capsule.

Figure 3

Ultrasound images of a hypoechoic heterogeneous collection in the lower leg/calf (A) with internal septations (white arrow) and fat globules (asterisk). The collection is not compressible (B–C).

Figure 4

A 42-year-old man with a marked swelling of the lower leg after direct impact to the calf due to a motor vehicle accident. Type I lesion: seroma. Sagittal T1 (A), sagittal PD FS (B) and axial T2 (C) MR images demonstrate an oval smooth collection (white arrows) between the subcutaneous fat and the fascia of the calf muscle, demonstrating low SI on T1- and high SI on T2-WI. A small focal area of isointense signal compared to subcutaneous fat was seen within the lesion (white arrowheads), corresponding with an internal fat globule.

Figure 5

A 51-year-old man with low back swelling status post trauma. Type II lesion: subacute hematoma of the lumbar region. Sagittal T1 (A), sagittal T2 (B) and axial T2 (C) MR images of the lumbar region demonstrate a collection between the thoracolumbar fascia (white arrowheads) and the overlying subcutaneous fat and superficial fascia (black arrowheads). This subacute hematoma has a homogeneously high SI on T1-WI relative to muscle, consistent with methemoglobin.

Figure 6

A 58-year-old man presenting with a left hip mass. Type III Morel-Lavallée lesion: chronic organizing hematoma. Coronal T1 (A), coronal PD FS (B), and axial PD FS (C) MR images of the left hip show a complex mass between the fascia lata (white arrowheads) and the iliotibial tract (black arrowheads). The mass has an intermediate SI on T1-WI and high SI on T2-WI. The inhomogeneity of the collection represents the separation of blood products and debris (black arrow). A peripheral, thickened, low SI capsule is seen.