Atypical lipomatous tumours (ALT) are rare semi-malignant adipose tissue tumours with the potential to transform into sarcomas. They may occur throughout the body, although the hands are very rarely involved. We present the case of a 49-year-old man with a lipomatous tumour measuring 8×4 cm at the dorsum of the right thumb. MRI demonstrated an inhomogeneous signal after contrast medium application. The tumour was excised in its entirety. Since histology confirmed the diagnosis of an ALT, the thumb was irradiated. The patient remained free of recurrence. An ALT has to be suspected if a lipomatous tumour is very large. We recommend an MRI prior to surgery in tumours larger than 5 cm. Excision should follow oncologic principles.
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