Background: Soft tissue trauma and lipomas are common occurrences in surgical practice. Lipomas are defined as benign tumours of adipose tissue with so far unexplained pathogenesis and aetiology. A link between preceding blunt soft tissue trauma at the site of the tumour and the formation of lipomas has been described earlier. These soft tissue tumours have been named 'post-traumatic lipomas'.
Objectives: In a retrospective review, to analyse all patients with benign adipose tissue tumours treated at our institution between August 2001 and January 2007.
Methods: All cases were reviewed regarding medical history, magnetic resonance imaging findings, intraoperative findings, clinical chemistry and histology.
Results: In 170 patients presenting with lipomas, 34 lipomas in 31 patients were identified as post-traumatic. The mean +/- SD age of the patients with post-traumatic lipomas was 52 +/- 14.5 years. The mean time elapsed between soft tissue trauma and lipoma formation was 2.0 years (range 0.5-5). Twenty-five of the 31 patients reported an extensive and slowly resolving haematoma after blunt tissue trauma at the site of lipoma formation. The mean +/- SD body mass index was 29.0 +/- 7.6 kg m(-2). Fourteen of 31 patients presented with an elevated partial thromboplastin time. Eleven of 34 lipomas were found on the upper extremities, five on the lower extremities, 13 on the trunk, and two on the face. All tumours were located subcutaneously, superficial to the musculofascial system. Thirty-three lipomas were removed by surgical excision and one by liposuction following an incisional biopsy. Histological examination revealed capsulated and noncapsulated benign adipose tissue in all 34 tumours.
Conclusions: The existence of a pathogenic link between blunt soft tissue trauma and the formation of post-traumatic lipomas is still controversial. Two potential mechanisms are discussed. Firstly, the formation of so-called post-traumatic 'pseudolipomas' may result from a prolapse of adipose tissue through fascia induced by direct impact. Alternatively, lipoma formation may be explained as a result of preadipocyte differentiation and proliferation mediated by cytokine release following soft tissue damage after blunt trauma and haematoma formation.