First described by French physician Maurice Morel-Lavallée in 1863, Morel-Lavallée lesions (MLLs) are trauma-induced soft tissue injuries that result when shear forces separate subcutaneous tissue from underlying fascia, allowing fat and fluid to accumulate [[1], [2], [3], [4]]. These lesions are most common in the pelvis and lower extremities, often with concomitant fractures, and are secondary to motor vehicle accidents or blunt trauma [4,5]. They clinically present as painful, fluctuant swellings that contain blood and fat debris, and magnetic resonance imaging (MRI) is the preferred diagnostic modality [1,2,4,6]. Definitive management is dictated by the size, location, and age of the injury, with treatment ranging from observation and aspiration to surgical debridement and excision.

MLLs are well represented in surgical and radiologic literature, though their histopathologic representation is limited as only four cases have been described in existing literature. The reactive changes in these lesions can be worrisome for a neoplastic process, leading to unwarranted workup, delayed diagnosis, and misdiagnosis. Incorrect diagnoses at the initial assessment can make later presentations increasingly difficult to manage and lead to long-term morbidity due to wound expansion, infection, capsule formation, and recurrence [2,5]. In this paper, the pathologic characteristics of six additional cases are reported.