Diagnosis
Macrodystrophia lipomatosa
Discussion
Macrodystrophia lipomatosa is a rare developmental anomaly leading to localised gigantism due to overgrowth of all mesenchymal elements, but predominantly adipose tissue interspersed in a mesh of fibrous tissue [1]. Originally described in the lower extremity, the definition now applies to the upper extremity as well. True macrodactyly is in fact very rare and is a congenital anomaly characterised by an increase in the size of all elements of a digit or digits [1]. Neurofibromatosis, Proteus syndrome and macrodystrophia lipomatosa are included in this category.
Macrodystrophia lipomatosa may involve the bone marrow, periosteum, muscle, nerve sheaths and subcutaneous tissues [1]. The condition is not hereditary and is usually recognisable during the neonatal period. Unilateral involvement is the norm, although one or more adjacent digits in the same extremity may be involved [2]. The lower extremity is more commonly involved than the upper and it often occurs in the distribution of the plantar or median nerves respectively. Neural enlargement, when present, is due to infiltration of the nerve sheath by fibroadipose tissue and not due to an increase in the number of axons [1].
Surgical correction may be motivated by cosmetic concerns. Complications due to compression of neurovascular structures or secondary osteoarthritis mostly present later. Digital overgrowth ceases at puberty [1].
On plain radiographs, prominent volar soft tissue overgrowth leads to dorsal deviation of the digit. Adipose overgrowth may be visible as lucencies in the soft tissues. The phalanges can be long and broad with distal splaying, as was the case in this patient. Slanting articular surfaces and secondary osteodegenerative changes may be evident [1]. As MRI can accurately depict adipose tissue it is of great value in confirming the diagnosis. It demonstrates excessive adipose tissue with normal subcutaneous fat signal intensity and fibrous strands as linear areas of low signal intensity on T1-weighted images. The adipose tissue suppresses homogeneously when a STIR sequence is applied. Muscular infiltration by adipose tissue, thickening of peripheral nerves, as well as osseous hypertrophy and cortical thickening, can also be detected [2, 3].
The differential diagnosis includes plexifom neurofibromatosis, Klippel-Trenaunay-Weber syndrome (macrodactyly with haemangiomas), lymphangiomatosis, haemangiomatosis, Proteus syndrome and fibrolipomatous hamartoma of the nerve [2, 3]. Neurofibromas show marked hyperintensity on T2-weighted images. Proteus syndrome can be distinguished by other associations such as skull anomalies, pigmented naevi, lung cysts and intra-abdominal lipomas. Fibrolipomatous hamartoma displays fat deposits within the nerve sheath—mostly involving the median nerve. When associated with macrodactyly it is actually the same as macrodystrophia lipomatosa [2, 3]. Clinical examination in conjunction with imaging should easily discriminate between the rest of the differential diagnoses.
The MRI findings of redundant adipose tissue and proportional enlargement of other mesenchymal tissues (i.e. macrodactyly) is characteristic and should lead to a confident diagnosis of macrodystrophia lipomatosa.
We would like to thank Professor Savvas Andronikou for the case.
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