Adolescent Morel-Lavallée Lesions: A Case Report of Challenges in Diagnosis and Management in Atypical Locations

Introduction

MLLs are an uncommon type of closed soft-tissue degloving injury caused by significant shearing forces secondary to high-energy trauma [1]. The phenomenon of degloving occurs as the skin and subcutaneous fatty tissue abruptly separate from the underlying deep fascia, and disrupted subdermal blood and lymphatic vessels extravasate in the resulting potential space to produce a fluid collection of blood, lymph, and fatty debris [1,2]. Local inflammatory mediators promote further vessel leakage as the lesion enlarges, replacing the fluid contents with a serosanguinous mixture of serous watery plasma and blood [1,3]. If left untreated, chronic inflammation arranges granulation tissue into a fibrous capsule enclosing the fluid collection, leaving the MLL to mature into a chronic encapsulated state that limits fluid reabsorption [2–4]. Bacterial colonization is common and occurs in nearly half of MLL cases [5].

While reported to be associated with pelvic fractures and most common in adults ages 30–40 with a roughly 2:1 male-to-female predominance, MLLs can occur across all age groups and have been historically underdiagnosed and underreported [1,6–9]. Given the infrequency and clinical heterogeneity of MLLs, the lesion’s true prevalence is indeterminate and likely underestimated [1]. One study reported 79 adult patients over 8 years at a Level I trauma center, while another study reported 38 pediatric and adolescent patients over 7 years at a tertiary children’s hospital [10,11]. MLLs often are not diagnosed in the acute-to-subacute window due to rarity of the lesion, delayed lesion presentation following the initial trauma, and clinicians’ unfamiliarity with the clinical presentation and imaging features, including atypical lesion sites outside the most common regions in the pelvis and proximal lower extremity [7–9]. Consequently, 33–44% of cases have been reported as missed on initial diagnosis [6,7,9,12].

Early recognition of MLLs is critical to prevent complications, including capsule formation, infection, skin necrosis, chronic pain, recurrence, and permanent deformity [1,4,13]. Pediatric and adolescent patients are particularly at risk for MLLs and associated complications because their subcutaneous fat and musculoskeletal systems are insufficiently developed to absorb high-energy impacts, with adverse sequelae including multi-organ damage, bleeding, and denervation [6,7,14]. Unfortunately, MLLs among children and adolescents have been notably understudied, resulting in the absence of established age-specific treatment guidelines for this particular patient population [1,7,14,15]. Failed recognition results in delayed care and more invasive management, including extensive and staged debridement [7,13].

Here, we describe an adolescent MLL secondary to a sports injury that presented in an unusual location at the calf and required extensive multidisciplinary consultation. As such, we highlight how MLLs in younger patients can present differently from the more classic presentations reported in adults, with important distinctions including mechanism of injury and lesion site. We emphasize the challenging diagnosis associated with this atypical presentation, importance of early identification and intervention to minimize complications, and consequent necessity for up-to-date standardized treatment guidelines specific to pediatric and adolescent patients.

Case Report

A previously healthy 18-year-old male presented with a right lower-extremity injury after sliding into a wall while playing basketball. He had significant swelling and associated cramping pain over the next several days. He denied any bleeding, decreased sensation, temperature differences between extremities, fevers, rashes, night sweats, bone pain, or unexpected weight changes. He had applied ice, with minimal improvement and worsening swelling.

On initial presentation to the Emergency Department, vital signs were normal. Examination noted a large well-circumscribed soft-tissue swelling overlying the right lateral calf, measuring approximately 5×4 cm (Figure 1). The overlying skin was intact with no overlying erythema. The lesion was non-tender and fluctuant. Resistance to ankle eversion and dorsiflexion were observed, with no crepitus or pain on passive stretching; range of motion was otherwise intact. The patient was able to bear weight on his right leg.

Complete blood count was normal. An X-ray of the right tibia-fibula noted soft-tissue swelling but found unremarkable bony structures without evidence of fracture, subluxation, dislocation, or lytic or blastic lesions (Figure 2). MRI of the right tibia-fibula found a large subcutaneous fluid collection at the lateral aspect of the leg, measuring 3.8×1.5×3.9 cm, spanning 15 cm in the craniocaudal dimension, with large displacement of the fatty subcutaneous tissue (Figure 3). No Baker’s cyst, muscle strain, soft-tissue mass, bone contusion, cortical fracture, or osteomyelitis were detected.

With concern for compartment syndrome ruled out, several differential diagnoses were considered, including hematoma, seroma, and fat necrosis, while abscess, soft-tissue tumor, and deep vein thrombosis were ruled out. The patient was referred by his primary pediatrician to orthopedic surgery for evaluation, and an initial diagnosis of subcutaneous hematoma was determined. Due to the patient’s pain improving and the lesion’s swelling becoming stable in size, initial conservative management was attempted with warm compresses, compression banding, and modified physical activity for 8 weeks. Reevaluation by a second orthopedic surgeon advised against procedural intervention with concern regarding aging of the hematoma that would limit drainage.

As the patient’s swelling still did not improve, he was referred to a tertiary children’s hospital. Sequential evaluations by orthopedic surgery, sports medicine, general surgery, plastic surgery, and interventional radiology determined the injury to be consistent with a MLL of the anterior subcutaneous tissues. Ultrasound-guided needle aspiration was performed at 4 months after the time of injury, draining 30 mL of serosanguinous fluid (Figure 4).

The patient’s pain resolved, and the swelling rapidly improved (Figure 5). The lower leg was placed in a controlled ankle motion boot for 2 weeks, and he underwent 14 weeks of physical therapy. No antibiotics were indicated. Repeat MRIs of the right tibia-fibula at 1 and 2 months after drainage showed decreased size but persistence of the MLL (Figure 6). His residual swelling measuring 5×1 cm was attributed to chronic bursitis. Sclerodesis was offered as an option to ensure cosmetic correction and minimize risk of recurrence, but the patient declined due to personal preference. He was cleared to resume physical activity without restrictions, reporting resolution of all symptoms and restoration of his baseline physical function at 7 months after drainage, with no plans to pursue further intervention.

Discussion

In our case, this MLL presented as a diagnostic challenge given the rarity of the lesion and our patient’s age group, with an associated nontraditional location at the lateral calf [1]. The current literature on MLLs is limited, and most studies and reviews do not distinguish between adult and pediatric presentations and management [8,13,16].

Clinically, MLLs present immediately after injury or develop days to months later, secondary to high-velocity trauma [6,13,15]. Within the adult literature, MLLs are traditionally expected to occur most frequently at the greater trochanter and hip (30%), thigh (20%), pelvis (19%), or knee (16%), often combined with polytrauma and fractures given the mechanism of injury required [1,17]. A case series in 2020 observed that pediatric and adolescent MLLs can occur more commonly in the lower leg (76%) than in the hip or thigh (24%), with the mechanism of injury more likely due to sports injuries rather than motor vehicle accidents more commonly seen with adults [11]. While these findings in this case series are consistent with our patient’s presentation, the knee was cited as the predominant site of injury in the lower leg, with the number of cases in the calf unspecified [11]. There have been other examples of pediatric MLLs located in the calf, similar to our case, as reported by Kim et al in 2018 and Remien et al in 2023 [18,19]. However, the calf site remains uncommon, as Vanhegan et al in 2012 observed only 3 out of 204 adolescent and adult MLLs reported across 14 countries to occur in the lower leg [17]. Other rare lesion sites that have also been reported include the gluteal region (6%), lumbosacral region (3%), abdomen (1%), and head (0.5%) [1,17].

Clinicians should expect to observe soft fluctuant swelling with or without pain over the affected area, often accompanied by bruising and abrasions [1,6]. Skin hypermobility, subcutaneous fluctuation, and friction burns are notable examination findings that can help distinguish MLLs from other conditions, such as simple contusions [1,2]. However, as our case demonstrates, MLLs can be difficult to distinguish within a broad differential diagnosis [10,20]. Imaging is a crucial adjunct to confirming diagnosis and determining management [8]. Initial ultrasound can reveal a hyperechoic or anechoic fluid collection, depending on the lesion’s age and predominant contents, while contrast-enhanced CT classically demonstrates hematoma or more hypodense fluid [2,6,13]. However, MRI remains the modality of choice for identifying and characterizing MLLs [2,14].

Our differential diagnosis was generated based on a noninfectious traumatic presentation devoid of systemic symptoms [2,13]. Based on the fluid collection and unremarkable bony structures on imaging, an initial diagnosis of hematoma was determined to be more likely. Due to a lack of recognition in an adolescent patient with a sports injury to the calf, there was no initial orthopedic suspicion for a MLL based on the less common patient demographic, mechanism of injury, and lesion site. There is currently no uniform consensus pertaining to an ideal time or specific lesion size on imaging for drainage of a calf hematoma; instead, drainage is considered when the lesion reaches a size causing significant symptoms [21,22].

Consequently, initial conservative management was attempted based on the non-tender nature, large but stable size, and benign appearance of the lesion at 4 weeks since the initial time of injury, with the expectation for the hematoma to resolve in 6–8 weeks [20]. Moreover, there was orthopedic concern regarding the limited fluid volume available for aspiration with the developing age of the hematoma. The amount of drainable fluid can progressively decrease as weeks elapse since the time of injury, with additional consideration of the risk of infection and recurrence in incompletely aspirated collections of blood [21,22]. Calf hematoma management can therefore be clinician- and institution-dependent, with our initial orthopedic referrals advising against drainage.

However, due to failure of the lesion to resolve within the expected time window for hematoma resorption, further multidisciplinary evaluation was conducted at a pediatric tertiary care center. The diagnosis of MLL was determined based on the patient’s recent trauma resulting in separation of the superficial and deep fascia on MRI, with fluid accumulation visible on short-tau inversion recovery (STIR) and significant fat displacement confirmed with proton-density fat saturation [2]. Furthermore, the lesion was noted to be more irregular and fusiform in shape, with associated fat globules, compared to a hematoma [8,11,20,23]. Mellado and Bencardino in 2005 classified MLLs based on MRI patterns of the lesion contents, extent, and chronicity [2]. Given the low-to-intermediate signal on T1-weighted imaging seen in Figure 3, our patient’s MLL included an acute seroma consistent with the description of a type I lesion [2].

There are currently no standardized guidelines for MLL management in adult and pediatric patients, as Mellado and Bencardino’s framework for MRI classification does not provide guidance on correlating management or outcome [8,16]. In children and adolescents, both conservative management and percutaneous aspiration have generated successful outcomes with a return to previous activity varying between 8 weeks to 6 months, with conservative approaches reportedly more common with MLLs of the lower leg, and minimally invasive approaches more common with the hip and thigh where the lesion size is typically larger [11,19,24–27]. These approaches and outcomes are consistent with our case. Other examples involving lesion recurrence, necrosis, or encapsulation have required more aggressive surgical intervention and longer periods of recovery [6,11,14,18]. However, the studies utilizing these methods have mostly been limited to single case reports or case series involving a small number of cases [11]. The MLL literature currently lacks the high-quality evidence available from a large sample size, comparisons in treatments and outcomes, and longitudinal follow-up [8,16].

While conflicting recommendations exist regarding lesions with overlying viable skin and subcutaneous tissue, a review by Molina et al in 2021 expanded upon a Mayo Clinic practice management guideline, compiling 56 case reports, case series, and review articles to propose an algorithm for management of MLLs based on lesion age characteristics [10,13]. Notably, Molina et al did not differentiate their algorithm based on patient age but did include pediatric literature in their discussion [13]. For smaller lesions less than 50 cm3, contemporary management has included conservative approaches through measures including compression banding and observation; however, Molina et al suggest that initial minimally invasive percutaneous drainage should be performed [7,11,13,16]. In acute lesions less than 3 weeks old, standard imaging has been known to miss or underrepresent the extent of injury, with reported difficulty in distinguishing MLLs from hematomas that will spontaneously resolve [10]. Therefore, an aspirate volume of less than 30–50 mL increases the likelihood of successful subsequent compression and observation for management, whereas an aspirate volume over 50 mL should be followed by placement of a drainage catheter until producing an output less than 30 mL [13].

Any lesion with devitalized tissue requires debridement, open drainage, and delayed primary closure or advanced suture techniques [13]. In subacute lesions older than 3 weeks, chronic lesions older than 3 months, or larger lesions greater than 50 cm3 with overlying viable tissue, initial aspiration should be attempted with drain placement and cavity closure, but surgical intervention would be indicated based on recurrence and the presence of a capsule [13,14]. Available techniques such as negative-pressure wound therapy may enhance healing and reduce complications [9,13]. In lesions of any age, recurrence can occur if the cavity is not adequately addressed [13,14]. Sclerodesis can help prevent recurrence with pharmacologic agents that induce local inflammation and increase apposition of the cavity walls, and liposuction and fibrin sealant have also been reported as options to close cavity dead space [1,13].

Our patient initially presented with an acute MLL that became chronic as his clinical presentation and the absence of standardized treatment guidelines contributed to diagnostic uncertainty and delayed intervention at 4 months after initial presentation. Prolonged conservative management towards an expected hematoma diagnosis likely had a counterproductive effect. While our case demonstrates a positive outcome with reduction of the patient’s swelling and restoration of his normal physical function, earlier identification and follow-up may have expedited aspiration and reduced the risk of the patient’s persistent post-drainage contour deformity [13]. Furthermore, the patient declined sclerodesis within this 7-month follow-up period, which also limited our ability to ascertain the long-term success of aspiration, given that fluid re-accumulation and recurrence are common [8,14].

This case demonstrates that a high index of suspicion for MLL is indicated in pediatric and adolescent patients with sports injuries, who will more frequently present first to their pediatricians and primary care providers [11]. Awareness of this diagnosis on initial assessment is critical to providing rapid direct referrals to tertiary care centers with specialized multidisciplinary pediatric care [20,28].

While clinicians tend to avoid procedural intervention in younger patients due to concern for complications, the recent adult literature has trended to encourage early minimally invasive aspiration to guide provider decision-making, reporting little infectious, hemorrhagic, or neurovascular risk with adequate expertise [10,13,16,22]. Given the limited literature specific to pediatric and adolescent MLLs, additional observational studies involving younger age groups with longitudinal follow-up are necessary to better ascertain the benefits of early aspiration. We suggest the need for collaboration across multiple pediatric tertiary care and trauma centers to increase sample size and standardize methodology in conservative versus aspiration strategies for subsequent comparisons in treatment outcomes. Serial imaging with ultrasound or MRI may also assist with narrowing the differential diagnosis to monitor the size and aging of the lesion’s contents during the time window for expected resorption [10,21,23]. Most importantly, although previous algorithms have been proposed regarding MLL management, our case highlights the critical need for standardized guidelines on MLL workup and treatment with consideration of patient age, lesion age, and lesion characteristics to increase diagnosis awareness and achieve consensus on care.

Conclusions

MLLs in pediatric and adolescent patients pose unique diagnostic challenges due to their rarity and varied presentations, often initially missed as hematomas. Our case demonstrates that a combination of appropriate clinical suspicion, imaging, and regular frequent surveillance are necessary to identify MLL development and progression and determine early corresponding treatment. Initial minimally invasive aspiration may be key to guiding subsequent management, but additional research on long-term outcomes in younger age groups is necessary. We underscore the importance of maintaining a high index of suspicion for MLLs in pediatric and adolescent trauma patients with sports injuries, highlighting the need for multidisciplinary collaboration and supporting the establishment of up-to-date age-specific guidelines to help achieve uniform consensus on management, ensure timely and effective treatment, and minimize risk of complications.