Discussion
MLL was first reported in 1863 by the French physician Maurice Morel-Lavallee, who described it as a post-traumatic collection of fluid due to soft tissue injury [
8]. MLL was initially used to refer to injuries involving the trochanteric region and proximal thigh. In recent years, however, the term has been used to describe lesions with similar pathophysiology in various anatomical locations, including the hip and thigh [
5,
6,
9]. MLL commonly occurs as a result of peri-pelvic fracture due to high-impact trauma. However, it may also result from a low-velocity crush injury that occurs during sports activities such as football or wrestling [
6,
9,
10]. The clinical features of MLL vary depending on the amount of blood and lymphatic fluid collected at the site of injury and on the time elapsed since the injury. Moreover, MLL may also concurrently present with symptoms such as soft tissue swelling, contour deformity, palpable bulge, skin hypermobility and decreased cutaneous sensation [
6,
7]. Furthermore, the presence of a soft fluctuant area due to fluid collection is a hallmark of its physical findings [
3,
4]. The symptoms of MLL are frequently manifested within a few hours or days following the onset of trauma. In up to 1/3 of total cases, however, symptoms may occur several months or years following the onset of injury. This strongly suggests that obtaining a meticulous history of the patient is essential for making an accurate diagnosis of MLL [
2,
5‐
7].
A diagnosis of MLL can be established based on imaging studies of the suspected sites and by physical examination. On radiological examination, it is characterized by the presence of a non-specific, non-calcified soft tissue mass [
11,
12]. On ultrasonography, it is characterized by hyperechoic (blood-predominant) or anechoic (lymph-predominant) fluid collection depending on the age of the lesion and its predominant content. Acute and subacute lesions less than 1 month old show a heterogeneous appearance with irregular margins and lobular shape. In addition, both chronic lesions and lesions older than 18 months show a homogenous appearance with smooth margins and flat or fusiform shape [
12,
13]. On CT and magnetic resonance imaging (MRI) scans, MLL lesions are well visualized as well-defined encapsulated fluid collections with fluid-fluid levels. On MRI scans, however, the lesions are better visualized with soft-tissue contrast enhancement. Therefore, MRI is a better choice of imaging modality than CT in making a diagnosis of MLL [
12,
14]. Based on T1- and T2-weighted MRI scans, MLL can be classified into six types. In addition, the age of the blood within the lesion is a key factor in making an accurate diagnosis of MLL [
14‐
16].
Although various strategies for the treatment of MLL have been reported, including the application of compression bandages, percutaneous aspiration and drainage, open debridement and sclerodhesis, there are no established treatment modalities for patients with MLL [
4,
9,
12,
16‐
33]. Conservative management such as compression bandage application, NSAID medication, physiotherapy and absolute bed rest are considered the first-line treatment regimen in patients with acute, small lesions without underlying fractures. Of these, the compression bandage can be used to supplement other treatment options [
4,
9,
12,
16,
20,
22,
28]. Percutaneous drainage can be used to manage larger acute lesions that cannot be resolved with a single application of compression bandages. It may also be attempted along with sclerotherapy as a first-line therapy in patients with chronic lesions [
17,
24,
26,
31]. Talc sclerotherapy was introduced by Luria et al. [
23] in 2007. Since then, various methods of sclerodhesis, including some that involve the use of alcohol and doxycycline, have been reported. Sclerotherapy is performed by injection of sclerosant into the dead space; the sclerosant is allowed to remain for a few minutes, followed by percutaneous drainage. Sclerotherapy can be used as a first-line therapy in patients with acute lesions that are refractory to compression bandages and in patients with chronic lesions [
18,
23,
25]. In patients with chronic lesions, percutaneous drainage may result in recurrent postoperative hematoma or secondary infection [
30]. It is therefore mandatory to combine percutaneous drainage with sclerotherapy. In patients with acute lesions with underlying open fractures and in those with chronic lesions with evidence of infection or tissue necrosis due to a local mass effect, open debridement can be attempted as a first-line therapy. Open debridement may also be considered as the final therapy in patients who are refractory to percutaneous drainage with sclerotherapy [
19,
21,
27,
29,
30,
32,
33]. Surgical intervention is also indicated in patients with longstanding MLL with pseudocapsule because they are unresponsive to percutaneous drainage and therefore vulnerable to recurrence [
11,
27,
32,
33]. The use of synthetic glue and the quilting suture technique after removal of the fibrous capsule have also been reported to prevent fluid collection in the dead space [
1,
33‐
36].
Based on a review of the literature, MLL occurs predominantly in patients in their 30s-40s. To our knowledge, only rare cases of MLL occur in children (Table
1). Letts [
37] reviewed 16 pediatric cases of degloving injuries and analyzed the causes and sites of injury. This author classified degloving injuries into those involving anatomical degloving (gloving injuries with skin surface disruption) and those involving physiological degloving (degloving injuries with disruption of the underlying skin vasculature without skin surface disruption). Six of the studied patients suffered from physiologic degloving injuries due to train or motor vehicle accidents involving the leg, buttock and back; the mean age of these six patients was 11 years (range, 6–14 years). All six patients, most of whom received defatted skin grafts, had a concurrent anatomical degloving injury. Harma et al. [
22] reported five pediatric cases of MLL, of which two were due to automobile crashes. These authors treated a 6-year-old patient with conservative management and a 14-year-old patient with debridement and local flap coverage. In addition, Mukherjee et al. [
12] reported a case of MLL in a 14-year-old boy who presented with a soft tissue mass on the right greater trochanter. For this patient, no data were available regarding a possible past history of trauma or the duration of symptoms. Therefore, these authors made a diagnosis of MLL based solely on ultrasonography and MRI scans. They treated the patient with conservative management with elastic compression bandages. Carlson et al. [
19] treated 22 patients with MLL, two of whom were pediatric cases, with debridement and dead space closure. Both of the pediatric cases were caused by motor vehicle accident and were treated immediately after the onset of injury. Choudhary et al. [
38] reported a case of a 12-year-old boy who presented with thigh swelling and blistering two weeks after sustaining an injury while riding an all-terrain vehicle (ATV). Based on ultrasonography, the patient was diagnosed with MLL and treated with sotradechol foam injection and doxycycline. This patient had no traumatic lesions in the early stage of injury, but gradually presented with symptoms. An imaging study played a key role in making a diagnosis of MLL in this patient. Anakwez et al. [
17] reported a case of MLL that occurred following a knee injury caused by falling on asphalt during a football game. The patient presented with pain and bruising of the knee and thigh but had no notable orthopedic symptoms on physical and radiological examination. Two weeks later, however, the patient exhibited localized bruises and blisters and, based on the results of MRI scans, was subsequently diagnosed with MLL. Aspiration was attempted, but drainage was unsuccessful. The patient was managed conservatively with compression dressings and physical therapy. Most recently, Efrimescu et al. [
21] reported a case of MLL in a 14-year-old boy. The patient presented with pain and swelling after the onset of blunt trauma to the lower back and was diagnosed with MLL after simple radiography and MRI. This patient was managed with open drainage.
Table 1
A summary of reported cases of MLL in children
1 | 6/M | Crush under automible | Lateral lumbar | Unknown | | Pelvic fracture | Bladder neck rupture | Conservative treatments | (-) | |
2 | 14/M | Crush under automible | Lumbo-sacral | Unknown | | Pelvic, femur fracture | Perianal soft tissue injury | Debridement and local flap | Sacral decubitus ulcer | |
3 | 14/M | Unknown | R greater trochanter | Unknown | Swelling, discomfort, soft tissue mass | (-) | (-) | Elastic compression bandage | (-) | |
4 | 13/M | Motorvehicle collision | R hip | Immediate | | L ulnar fracture, R knee subluxation | L knee laceration, L hand degloving injury | Debridement and dead space closure | | |
5 | 13/M | Motorvehicle collision | Presacral | Immediate | | R iliac wing, bilateral anterior ramus, femur, R tibia, fibular fracture | L pulmonary contusion | Debridement and dead space closure | | |
6 | 12/M | ATV accident | L thigh | 2 wks | Swelling, blister | | | Aspiration and sclerodesis with Sotradechol foam injection and doxycycline | (-) | |
7 | 11/M | Football | L knee | 2 wks | Pain, bruise, open blister, nonfluctuant mass | | | Compressive dressing and physical theraphy | (-) | |
8 | 14/M | Blunt trauma | Lumbar area | 2 hrs | Voluminous swelling, bruising | | | Open drainage | (-) | |
We experienced a case of MLL occurring in a 28-month-old patient. To our knowledge, this represents the youngest case of MLL yet reported. In this patient, no data were available concerning a possible past history of shearing injury. The patient had no abrasions or bruises on initial physical examination, and MLL was therefore not considered in the initial diagnosis. For this reason, the patient initially received conservative management only for the pelvic fracture. Moreover, this patient displayed no fluid collection other than the retroperitoneal hematoma detected on CT scans on admission and on day 3. This patient therefore posed a diagnostic challenge. On day 4, the patient presented with skin color change with swelling and fluctuation. This led to the speculation that not only did fluid collection occur as a result of persistent bleeding from the pelvic fracture in the dead space caused by detachment after the onset of initial shearing injury but also that the resulting mass effect led to the occurrence of skin necrosis.
Pediatric cases of MLL are characterized by the relatively high vulnerability of young patients to trauma. It is also noteworthy that the diagnosis of MLL is often delayed in very young patients, for whom history taking regarding shearing injury and the duration of symptoms is often difficult [
12,
17,
22,
38]. It is therefore mandatory to carefully examine the patient for external wounds, bruises, swelling, fluctuation, hypermobility of skin and other clues, such as a tire mark, that may be evidence of shearing injury by exposing the patient from head to toe [
37]. Even in patients who initially present immediately after the onset of injury with no symptoms, it is necessary to perform a follow-up physical examination and imaging studies. This is essential for the identification of delayed lesion development. When children and adults are subjected to blunt trauma of the same width, children are vulnerable to higher shock per unit area. It can therefore be inferred not only that children are more vulnerable to developing multiple organ damage due to MLL but also that they are at increased risk of developing fractures or deep organ injuries due to the incomplete development of their musculoskeletal systems. Moreover, children have a relative lack of the shock-absorbing function due to the incomplete development of subcutaneous fat [
39]. It can therefore be inferred that pediatric cases of MLL might lead to severe degloving injuries. Furthermore, due to their lower volume of blood, children are vulnerable to hypovolemic shock due to bleeding as well as to skin necrosis due to an abrupt mass effect arising from the collection of internal bleeding in the dead space. Such children should be promptly treated immediately after being diagnosed with MLL.
Competing interests
The authors declare that they have no competing interests.
Authors’ contributions
All of the authors were involved in the preparation of this manuscript. EYR wrote the manuscript and reviewed the literature. DHK assisted in the surgery and contributed to the literature search. HK participated in the clinical and surgical management of the patient. S-NJ participated in the conception and design of the study and operated on the patient. All of the authors read and approved the final manuscript.