Parosteal lipoma
characteristic of this lesion is its relationship to an adjacent bone and the presence of bony excrescences extending from the cortex into the lesion. There maybe an associated reaction in the underlying bone including a periosteal reaction, cortical thickening or cortical erosion. compression on adjacent nerve structures is well reported.
Fibrolipoma
contains benign streaks of fibrous tissue. If other tissue types are present including cartilage and bone the term benign mesenchymoma is used
Lipoblastoma
soft tissue tumour of infancy which usually matures to lipoma. Although benign, recurrence is well described following surgical excision. Males are more commonly affected.
Hibernoma
Hibernoma is a rare tumour of brown fat. The most common locations are in the thigh, shoulder, back and neck. Malignant transformation does not occur. On MRI the lesions resemble lipoma but show more prominent internal septations and failure to completely suppress on STIR imaging. The lesion has been described as a dirty looking lipoma.
Angiolipoma
contains thin walled blood vessels and can be encapsulated or non encapsulated. The encapsulated ones tend to be superficial cutaneous lesions calcification may also be present. The infiltrating non encapsulated form is deeper and rarer.
Spindle Cell
a lesion occurring almost exclusively in men aged over 45 and is a predilection for the subcutaneous tissue of the back and shoulders. If the lipoma contains smooth muscle the term myolipoma is used in contrast to spindle cell lipoma these predominate in females and also occurs in adulthood.
Misc others
Lipomatosis of the nerve is an unusual lesion where fatty tissue interspaces with the neural fibres of a peripheral nerve. The median nerve is the most frequently described and associated with macrodactyly which can involve single or multiple digits. Other fatty variants include lipoma of the tendon sheath, joint involvent including lipoma arborescens which most characteristically occurs in the knee. Diffuse lipomatosis is characterised by widespread fatty infiltration, usually from the first decade, which may be associated with bony hypertrophy and gigantism. The shoulders and upper trunk are frequently involved and the condition is sometimes referred to as the Michelin Man Syndrome. A similar condition called multiple symmetric lipomatosis occurs in adult males in whom there is a history of excessive alcohol intake. Occasionally a family history is present. It is postulated that a mitochondrial disorder underlies the disease. A further variant is shoulder girdle lipomatosis where layers of fatty tissue are laid down between the muscle groups of the shoulder girdle. Adiposistolorosa occurs in post menopausal women and is associated with multiple painful fatty masses generalised obesity weakness and psychiatric disturbance.