[Morel-Lavallée syndrome and post-traumatic nodular fat necrosis: Two post-traumatic complications mimicking cellulitis]

Dermal and subcutaneous inflammation following direct trauma is initially evocative of soft-tissue infection. However, two differential diagnoses must be considered: Morel-Lavallée syndrome and post-traumatic nodular fat necrosis.Case 1: a 51-year-old woman fell off her motorbike and had dermabrasions on her right and left tibial ridges that rapidly developed into dermo-hypodermitis of the entire limb. There was no improvement after 3 weeks of antibiotics. The patient was apyretic. She had a soft, non-inflammatory tumefaction on the inner aspect of her left knee. Ultrasound revealed subcutaneous collection in both legs. The surgeons confirmed a diagnosis of Morel-Lavallée syndrome and drained the two collections. Progress was good and the patient healed without major consequences. Case 2: following a fall on her stairs, a 40-year-old woman presented dermabrasions and haematomas on her left leg. Antibiotic therapy failed to prevent the progression of dermo-hypodermitis. The patient remained apyretic and there was no inflammatory syndrome. A CT scan showed thickening of a subcutaneous fat and fluid collection, resulting in diagnosis of post-traumatic nodular fat necrosis. Management was surgical and the outcome was good.These two cases show two post-traumatic cutaneous complications: Morel-Lavallée syndrome and post-traumatic nodular fat necrosis. Morel-Lavallée syndrome occurs after tangential trauma next to richly vascularized tissue. Post-traumatic nodular fat necrosis is defined as necrosis of adipocytes. In both cases, diagnosis is confirmed by imagery (Ultrasonography, tomography).Our two case reports show that inflammatory presentation of both Morel-Lavallée syndrome and post-traumatic nodular fat necrosis can lead to diagnostic and therapeutic errors while a surgical procedure is necessary since tissue necrosis can occur.