Atypical lipomatous tumour

An atypical lipomatous tumour is a locally aggressive mesenchymal neoplasm in which the adipocytes show significant variation in cell size and have some nuclear atypia. These tumours are at risk of local recurrence. In the extremities or trunk the term atypical lipomatous tumour is justified as complete excision is usually curative and local recurrence manageable. In the retroperitoneum or mediastinum however, tumours with the same biological composition are difficult to completely remove and can recur with disastrous consequences for the patient. In these locations, the term “well-differentiated liposarcoma” may therefore be more appropriate.

Atypical lipomatous tumours account for 40-45% of all liposarcomas and occur predominantly in middle aged adults, peaking in the sixth decade. They most frequently occur in the deep soft tissues of the limbs, especially the thigh, but may also occur in the retroperitoneum or paratesticular area. Tumours often grow slowly, are painless and can achieve significant sizes.

Anatomical location is the most important prognostic factor. Lesions in surgically resectable sites tend not to recur after complete excision. In more difficult anatomic sites, incomplete excision is associated with local recurrence, which in turn can lead to loss of local control, or be associated with dedifferentiation and death. The risk of dedifferentiation is said to be over 20% in the retroperitoneum, but <2% in the limbs.

1. WHO Classification of Tumours of Soft Tissue and Bone. 4th Edition, 2013.

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Lipoma

Lipomas are benign soft tissue tumours composed of mature adipocytes. Lipomas are the most common mesenchymal tumour in adults and are most common between the ages of 40 and 60 years. 5% of patients have multiple lipomas.

Lipomas typically occur in the subcutaneous soft tissues, but can also present in deeper locations, for example within or between muscles, or on the surface of bones.

Lipomas usually present as a painless soft tissue mass. On histological examination they can contain bone (osteolipoma), cartilage (chondrolipoma) or fibrous tissue (fibrolipoma). Deep intramuscular lipomas often encase muscle fibres – this can be seen on MRI scanning and these tumours have a higher rate of local recurrence.

Angiolipoma is a lipoma variant containing small capillary walled vessels. 5% of cases are inherited as an autosomal dominant. These usually present as tender subcutaneous masses. Angiolipomas are always benign and show no tendency to recur.

A large lipoma with stranding of muscle fibres

A large intramuscular lipoma of thigh with stranding caused by muscle fibres

1. WHO Classification of Tumours of Soft Tissue and Bone, 4th Edition.

 

Information for patients:

A good summary from NHS Choices.