Posttraumatic lipoma: analysis of 10 cases and explanation of possible mechanisms.

Background: Trauma and lipoma are the most frequently met occurrences in clinical routine. Although lipomas are well-known fatty tumors both clinically and pathologically, the precise etiology is still unknown. Generally, posttraumatic lipomas are known as "pseudolipoma," which describes herniation of deeper fat through Scarpa's layer secondary to trauma. Here we present 10 patients with lipoma secondary to blunt trauma in different anatomical sites.

Objectives: To correlate trauma and lipoma relationships and to discuss the possible pathogenetic mechanism by reviewing literature.

Methods: Ten patients (12 lipomas) after blunt trauma were presented, and data of patients were reviewed. Ultrasonography and/or nuclear magnetic resonance were employed for diagnosis in addition to physical examination. All tumors were verified by histopathologic examinations. Patients were followed for a minimum of 6 months.

Results: The average age was 34. Four of the lesions (12 altogether) were located on an upper extremity, 5 on a lower extremity, 2 on the trunk, and 1 on the neck. Excision of tumors and primary closure were performed in 92% of the lesions, and only one liposuction was performed. Aesthetic results were achieved in all patients. There were no complications and recurrences.

Conclusion: The effect of blunt trauma on fat tissue may be explained by different theories. We summarized possible mechanisms into two groups according to our observations and review of the literature: The first was related to mature adiposities and mainly a mechanical effect, and the second was differentiations of the preadipocytes to lipoma by the promoting factors. We speculate that only traumas that serve as a cause of fat necrosis may trigger the formation of the lipoma, and local inflammation secondary to fat necrosis may affect adipocytes and promote new formation of lipoma.