Morel-Lavallée lesion (MLL) is a unique form of post-traumatic alopecia that results in mechanical rupture of the scalp, which can cause scalp pain and loss of hair (test).In its most common form, MLL occurs after trauma, often following a motor vehicle accident or a fall from a height, when the scalp receives a deep, penetrating wound that damages the dermis and/or subcutaneous tissue at the point of impact. The deep muscular layer of the scalp may be damaged as well, resulting in extrusion of fat and fluid-filled cysts, which appear at the site of the wound beneath the scalp. This can cause pain and hair loss in the area, usually directly beside the wound.
MLL is an entity that is known to include both inflammatory and non-inflammatory components. The inflammatory component includes a mixture of inflammatory cells, serum, and a large amount of edema fluid. This edema fluid provides the main environment for the growth of bacteria, which can increase in number leading to chronic or recurrent inflammatory conditions of the scalp. The non-inflammatory component of MLL is due to the damage caused to the hair follicles, which results in the permanent scarring and subsequent loss of hair in the area.
The diagnosis of MLL depends on clinical symptoms as well as imaging tests, such as magnetic resonance imaging (MRI) and computerized tomography (CT) scans, to ascertain that the injury is a deep penetrating wound of the scalp, and not caused by a surface skin wound. The diagnosis can be further confirmed with histopathology.
Histopathological examination of a Morel-Lavallée lesion reveals a continuous dermis, filled with a mixture of inflammatory cells, fat, necrotic debris, edema fluid, and serum. In some cases, hemorrhagic areas may be seen. Hair follicles are also present, but often show changes such as transection, disruption of the bulb, or fragmentation.
Once the diagnosis of Morel-Lavallée lesion is made, the mainstay of treatment is wound care, and antibiotics are prescribed for the secondary bacterial infection. Surgery may occasionally be required in cases where the lesion causes pain, or if the wound causes partial or total loss of scalp cover.
The prognosis for Morel-Lavallée lesion is mainly determined by the length of time the lesion has been present. Lesions that are older than 6 months are generally harder to treat and are more likely to result in permanent hair loss to some extent. On the other hand, lesions that are less than 6 months and heal without surgical intervention may not cause permanent hair loss.
Overall, the prognosis for Morel-Lavallée lesions is usually good, with most lesions healing without significant sequelae, and a fairly satisfactory outcome. With proper treatment, most patients can expect to resume their usual activities within a couple of months. With appropriate wound care, the risk of recurrence is decreased, and the prognosis is favourable in the long run.
