A 46-year-old female patient was referred to the Orthopedics Department due to the presence of a sizeable left gluteal mass. The patient reported a considerable injury to her left gluteal region 1 year previously, after a traffic accident. Following the accident, the patient noticed a persisting sensation of fullness in the gluteal region with no accompanying complaints such as pain or discharge of fluid. Following a fall directly onto the left gluteal area, the patient felt that the mass was enlarging and interfering with daily activities making activities like dressing and sitting on chairs particularly challenging. The patient was otherwise asymptomatic and reported no history of malignancy, fever, night sweats or use of medication. Upon examination, the swelling of the left gluteal region showed no changes to the overlying skin or signs of infection and plain X-ray of the pelvis demonstrated left gluteal swelling (Fig. 1). Contrast enhanced computed tomography (CT) scan of the pelvic region showed a large and sharply marginated cystic mass located in the fascial plane that was deep into the subcutaneous tissue and superficial to the musculature showing no contrast enhancement (Fig. 2). The anatomic detail of the mass was more precisely revealed with magnetic resonance imaging (MRI), displaying homogenous high T2 signal and low T1 signal, consistent with a cystic nature without any solid component (Fig 3).

Morel-Lavallée lesion, also known as closed degloving injury, results from the sudden, traumatic separation of the superficial tissue including skin and subcutaneous tissue from the subjacent fascia creating a potential space that can be filled with serosanguinous fluid due to the perforation of vessels and lymphatics [1]. The lesion is most commonly encountered in the trochanteric region and the proximal parts of the thigh owing to the potential of the mobility of the soft tissues in these regions, and the strength of the fascia [2,3]. The presence of abundant vascular channels in the dermal tissue piercing the fascia lata in the trochanteric region may be implicated in the continuous draining into the perifascial plane. This can create a distending cavity filled with fluid after trauma and an inflammatory reaction in the walls, creating a pseudocapsule [1,4]. Images of a classic Morel-Lavallée lesion displays homogenous fluid collection that shows high signal in T2W images and low signal in T1W images. However, when the collection is further complicated with hemorrhages, then it may show high signal intensity in one or both of the sequences according to the stage of the hemorrhage [3]. The lesion usually abuts the fascial plane enabling firm diagnosis and manifests a mass effect causing compressive changes on the adjacent musculature [3,5]. The differential diagnosis should include abscess, hematoma, fat necrosis, and soft tissue masses; however, the presence of a history of remote trauma along with the classical imaging findings can help with a definitive diagnosis.

Treatment options include conservative therapy, percutaneous aspiration, sclerodesis, and surgical resection based on the symptoms and the size of the lesion [6]. Nonoperative conservative management which involves the application of compression via bandaging to the swelling may be suitable for patients with a small and acute Morel-Lavallée lesion. Nevertheless, sizeable and chronic cases require surgical intervention. The final step that should be reached in the treatment of the lesion is the closure of the potential space within the lesion that may be achieved via sclerosing agents, sutures, and drainage, however, when these approaches have failed then en masse resection have to be considered as the last option [7–9]. Open debridement including the excision of the pseudocapsule is required in most of the chronic cases. Percutaneous aspiration, although its high recurrence rates necessitating multiple interventions, is another treatment option. Sclerodesis may be considered in cases when percutaneous aspiration failed and mostly applied agents include ethanol, doxycycline, bleomycin, vancomycin, ethanol, and talc. The agents trigger the fibrosis by destructing the peripheric part of the lesion. The prognosis of the Morel-Lavallée lesions largely depends on the size and the chronicity of the lesion. The smaller the lesion, the higher chance to resolve the lesion spontaneously, however, the sizeable and chronic lesions that involve pseudocapsule result in the failure of the reabsorption of the contents giving rise to a poor prognosis [10].

The complications of the Morel-Lavallée lesions stem from missed diagnosis or delayed presentation. If the lesion is not treated accordingly, it may result in progressive expansion, giving rise to the necrosis of the overlying skin due to the gradually increased pressure and resulting in inevitable infection [8].

Morel-Lavallée lesions resulting from the separation of the subcutaneous tissue from the subjacent fascia following trauma may mimic soft tissue masses; however, the location and characteristic imaging findings should direct the diagnosis. This can mitigate any morbidity coming from misdiagnosis.