Morel-Lavallée lesion in lower back, an uncommon location: A case report with detailed literature review

INTRODUCTION

Morel-Lavallée lesion is an uncommon closed degloving soft-tissue injury. This condition was first described by Maurice Morel-Lavallée in 1863.^[1] This lesion occurs due to separation of skin and subcutaneous tissue from the deep fascia by the shearing forces, thereby creating a potential space. Injury to blood vessels and lymphatics leads to the accumulation of blood and lymph in this potential space.^[2]

The most common location for this lesion is over the greater trochanter, which accounts for more than 60% cases of Morel-Lavallée lesions.^[3] The other common locations are the thigh and pelvis. This has also been described in a few uncommon locations such as calf, arm, lumbosacral region, and abdomen.^[4] In this case report, we describe a classical Morel-Lavallée lesion in an uncommon location, i.e., in the lower back.

CASE REPORT

A 25-year-old male patient with a history of a road traffic accident, 2 weeks ago, due to a fall from a motorcycle presented with a large swelling over the lower back, in the lumbar region. He noticed a small swelling immediately after trauma, which had gradually increased in size and was associated with mild pain. On examination, there were multiple bruises over the swelling [Figure 1]. The swelling was soft, fluctuant, and mildly tender on palpation.

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Figure 1: Photograph of the patient showing abrasions over the posterior lumbar swelling.

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High-resolution ultrasonography (USG) revealed a large anechoic fluid collection between the subcutaneous fat planes and the underlying fascia in the posterior lumbar region. The collection extended on both sides of midline, measuring 16 × 6 × 18 cm (Transverse × Anteroposterior × Craniocaudal). There were a few thin incomplete peripheral septations and few echogenic nodular foci, representing fat globules within the collection [Figures 2 and 3]. There was no solid component or vascularity in the collection.

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Figure 2: High-resolution ultrasonography showing a large oval-shaped fluid collection between the subcutaneous fat plane (white arrow) and deep fascia (black arrow) with thin septations (white arrow head).

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Figure 3: High-resolution ultrasonography showing a large oval-shaped fluid collection in the posterior lumbar region with fat globules (white arrow).

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Non-contrast computed tomography (CT) confirmed the shape, extent, and location of the collection between deep fascia and subcutaneous fat plane [Figures 4 and 5]. The collection showed low attenuation (HU of 20–30). There was no evidence of underlying bone injury. This collection was diagnosed as Morel-Lavallée lesion. As the appearance was typical, magnetic resonance imaging (MRI) was not done. Incision and drainage of the collection were done for complete evaluation.

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Figure 4: Axial computed tomography image showing posterior lumbar fluid collection (black arrow). Fat globules indicated by the white arrows.

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Figure 5: Sagittal computed tomography image showing posterior lumbar fluid collection (black arrow).

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Approximately 300–350 mL of serosanguinous fluid was drained and sent for laboratory analysis. Pathological examination revealed reactive fibroadipose tissue with areas of fat necrosis and hemorrhagic products. It was reported to be sterile. After drainage, the patient was relieved of swelling and symptoms.

DISCUSSION

Morel-Lavallée lesion is a closed degloving injury due to shearing forces caused by high-energy trauma. The classical location of this Morel-Lavallée lesion is the peritrochanteric region.^[3] The predisposing factors in this region are strong fascia lata, relative mobility of subdermal soft tissues, and superficial location of femoral cortex.^[1] Although this condition was classically described in the thigh region, other uncommon locations such as the knee, calf, lower back, and abdominal wall, can also be affected.^[4]

This condition usually presents as a soft and fluctuant swelling. The useful clues for clinical diagnosis are the presence of skin mobility, compressibility, and fluctuation of swelling, presence of friction marks on skin, and loss of skin sensation due to cutaneous nerve fiber damage.^[1] Diagnosis is often delayed as they are overlooked or may take time to develop.

Delay in diagnosis can lead to chronic inflammatory reaction and fibrous encapsulation, resulting in the formation of a chronic cystic lesion. Infection can be another rare complication of untreated lesions.^[5]

Imaging is crucial in early diagnosis by depicting the classical location of collection between the subcutaneous fat planes and deep fascia. USG is the first line of investigation which can clearly demonstrate a well-defined fluid collection in a classical location and distribution.^[4] There can be internal echoes, small incomplete septations, or fat globules in some cases. The presence of fat globules, although not specific, is a feature in favor of Morel-Lavallée lesion.^[6] Chronic cases may demonstrate a surrounding thick capsule. USG can also help to rule out other possibilities such as abscess or mass lesion. It is useful to guide percutaneous aspiration.

CT can show the location, extent of collection, and can rule out associated fractures, however, it has limited ability to differentiate various stages of Morel-Lavallée lesions.

MRI, with its excellent soft-tissue resolution, is the gold standard investigation for characterization of Morel-Lavallée lesions.^[5] MRI can clearly demonstrate the well defined oval shaped or fusiform fluid collection and the location of the collection between the subcutaneous fat and the deep fascia, which is crucial for the diagnosis. It helps in accurate assessment of the extent of the collection. The signal intensity of the collection may vary depending on the age of the blood degradation products. Few lesions may show a fluid-fluid level or a surrounding capsule. Presence or absence of capsule, capsular or internal enhancement varies depending on the chronicity of the lesions.^[2]

Mellado and Bencardino proposed a classification system for Morel-Lavallée lesions, based on MRI findings, in correspondence with histopathological findings.^[7] There are six types of Morel-Lavallée lesion based on this classification [Table 1].

Differential diagnosis for Morel-Lavallée lesion includes post-traumatic hematoma (especially in patients with coagulopathy), abscess, fat necrosis, bursitis, and, rarely soft-tissue neoplasms like sarcoma.^[5] Hematomas are more likely to occur in subcutaneous, intramuscular, or intermuscular planes. Associated coagulopathies can be detected by abnormal levels of clotting factors. Abscesses are often associated with systemic symptoms like fever, altered laboratory parameters, and a thick, enhancing wall on imaging. Post-traumatic fat necrosis usually results in heterogeneous lesions predominantly composed of fat or lesions with spiculated margins. Collections related to bursitis are confined to the normal anatomical boundaries of bursae, whereas Morel-Lavallée lesions extend beyond these boundaries. Soft-tissue sarcomas present as slowly progressive, painful masses, unlikely to be associated with high-energy trauma, and they produce more intense and heterogeneous enhancement.

Treatment options depend on the stage of collection and include a conservative approach with a compression bandage in early stages and a limited size of collection. Larger lesions need aspiration with compressive bandage, percutaneous incision and drainage, or open debridement and drainage. Sclerosing agents can be used in selective cases. Chronic encapsulated collections may require resection of the capsule.^[2]

CONCLUSION

Imaging is crucial for early diagnosis and treatment of Morel-Lavallée lesions. USG is the first line of imaging and may provide a definitive diagnosis in cases with a classical shape and location of collection between the subcutaneous fat plane and deep fascia. MRI is needed to delineate the extent of larger lesions, to characterize collections in various stages, and to differentiate Morel-Lavallée lesion from other mimics. Knowledge of pathophysiology, imaging features, and common and uncommon locations of Morel-Lavallée lesions is essential for prompt diagnosis and to prevent complications.