Pagonis et al. Journal of Medical Case Reports 2011, 5:552 http://www.jmedicalcasereports.com/content/5/1/552 range of motion of the wrist (extension 40°, flexion 60°). She was also unable to flex the distal phalanx of the thumb. The mass was apparent on plain X-rays and an MRI examination showed a well-orientated tumor, mea- suring 8.0 × 4.0 × 3.75 cm. It extended from the deep palmar space, between the tendons and the metacarpals leaving the periosteum intact (Figures 1 and 2). The mass was hyper intense in T1 and had low signal in fat suppression, which was suggestive of an inter-intra mus- cular lipoma, the so-called infiltrating lipoma which was confirmed by biopsy. A nerve conduction study per- formed on the anatomically involved nerves showed alteration of the normal values due to pressure on both the median and ulnar nerves. Surgery was performed under axillary block and by tourniquet controlled hemostasis. A palmar zig-zag inci- sion was made. The tumor was identified and found to compress all the surrounding tissues. Intra-operatively, the median and ulnar nerves were carefully identified and protected. Marginal excision of the tumor was per- formed which decreased inter-compartmental pressure which had previously affected all relevant anatomic structures (Figures 3 and 4). Intra-operatively, we dis- covered that the flexor pollicis longus tendon had been severed in one of the previous carpal tunnel release operations. We decided to reconstruct the tendon in a second phase operation, four months later with an inter- calated palmaris longus autograft (Figure 5). Histopatho- logical analysis of the resected tumor revealed a mature adipose tissue consistent with a lipoma, and no evidence of any malignancy. Page 2 of 5 At the final follow-up thirty months postoperatively, the hand was pain-free without neurological deficit and exhibiting full range of motion. Thumb motion exhib- ited no deficits. Discussion Lipomas consist of mature fat cells, which may occur in subcutaneous, inter-muscular or intra-muscular loca- tions. They generally progress slowly and painfully which explains their often large size at diagnosis, parti- cularly if located deeply. The differential diagnosis between lipomas and well-differentiated liposarcomas is extremely important and allows appropriate monitoring and treatment planning. Recently, many cytogenetic stu- dies have dealt with tumors originating from adipocytes, including benign lipomas, as well as malignant well-dif- ferentiated liposarcomas (WDLPS). The majority of these tumors present genetic mutations in regions 12q13-15 and 6p13q [4]. Any soft tissue mass larger than 5 cm should be regarded as malignant until proved otherwise [5]. The term well-differentiated liposarcoma has been used to describe low-grade lipomatous neo- plasms with a propensity for local recurrence [6]. Well- differentiated lipoma-like liposarcomas are one of the more common subtypes of the well differentiated lipo- sarcomas. It is doubtful whether liposarcomas ever dif- ferentiate from pre-existing lipomas [2]. Adipose tissue is so widely distributed throughout the human body that one would expect these tumors to be one of the most frequently encountered benign neo- plasms. The small numbers of cases being treated for Figure 1 MRI showing the recesses of the lipoma, invading the web spaces between the metacarpals.