Age / Sex : 65 / F

C.C.: progressive enlargement of the right ring and middle fingers that was noticed at childhood

Macrodystrophia lipomatosa

Discussion

Findings:
1) Plain radiograph of the hand shows bone proliferation arising from the ulnar side of the distal and middle phalanges of the ring and middle fingers. There is enlargement and mottled lucency in the soft tissues of these fingers.
2) The coronal T1-weighted SE and fat suppression T2-weighted FSE MR images reveal asymmetric thickening of the subcutaneous fatty tissue of the ulnar aspect of the ring and middle fingers. On the axial PD FSE MR image at the level of the proximal phalanx, low signal intensity enlarged palmar digital nerves and fibrous strands are embedded within the mainly fatty tissue of these fingers. There is fatty infiltration of the lumbrical muscles at the metacarpal level.

Differential Diagnosis:
- Macrodystrophia lipomatosa, Neurofibromatosis, Klippel-Trenaunay-Weber syndrome, Lymphangiomatosis, Hemangiomatosis, Fibrolipomatous hamartoma, Proteus syndrome

Diagnosis: Macrodystrophia lipomatosa

Discussion:
- Macrodystrophia lipomatosa (MDL) is a rare form of localized gigantism that is characterized by the congenital, not hereditary, and progressive overgrowth of the all mesenchymal elements, particularly the fibroadipose tissue. This entity is classically described as involving a distal extremity in the median or plantar nerve distribution, though whole extremity involvement can also occur. The lower extremity is more commonly involved than the upper extremity. Involvement is usually unilateral. However, there may be enlargement of one or more adjacent digits in the same extremity. Digital overgrowth ceases at puberty and the usual reason for the surgical correction is for the cosmetic appearance but mechanical problems can be encountered when secondary degenerative joint disease reduces the function and large osteophytes cause compression of the neurovascular structure. Our patient had difficulty in flexing the ring and middle fingers, and had undergone reconstructive surgery.
- Radiographically, distal involvement, phalangeal overgrowth, and lucency within the soft tissue, which is characteristic of fatty hypertrophy, are highly suggestive of MDL. The CT and MR imaging can help confirm the diagnosis of MDL by demonstrating the increased fat tissue. The main differential considerations for localized gigantism include MDL, neurofibromatosis, Klippel-Trenaunay-Weber syndrome, lymphangiomatosis, hemangiomatosis, fibrolipomatous hamartoma of the nerve with macrodactyly, and Proteus syndrome. In neurofibromatosis, the enlarged digits may be bilateral. However, the involvement of one extremity does not necessarily involve contiguous digits. Based on the MR findings, the differential diagnosis of localized gigantism is limited to a malformation with the fatty proliferations and bone overgrowth such as fibrolipomatous hamartoma and Proteus syndrome. A fibrolipomatous hamartoma can occasionally be observed in association with macrodactyly and displays fat deposits within the nerve sheath. On the other hand, MDL shows the deposits of fat within the nerve sheath, bone marrow, periosteum, muscles, and subcutaneous tissue.

References:
1. Wang YC, Jeng CM, Marcantonio DR, Resnick D. Macrodystrophia lipomatosa: MR imaging in three patients. Clin Imaging 1997;21:323-327
2. Soler RA, Rodriguez E, Bargiela A, Martinez C. MR findings of macrodystrophia lipomatosa. Clin Imaging 1997;21:135-137
3. Ly JQ, Beall DP. Quiz case. Macrodystrophia lipomatosa. Eur J Radiol 2003;47:16-18 4. Blacksin M, Barnes FJ, Lyons MM. MR diagnosis of macrodystrophia lipomatosa. AJR 1992;158:1295 -1297