Mason (1953)
Also called fibrolipomatous hamartoma of nerve, perineural lipoma, fatty infiltration of the nerve, intraneural lipoma, lipomatosis of nerve
Due to infiltration and hypertrophy of mature fibrofatty tissue infiltrating epi and perineurium
Commonly present at birth or early childhood, and most present before 30 years of age
Non-hereditary
Median nerve is most commonly involved (more than 80%). 2nd most common ulnar nerve. Other reported nerves include brachial plexus, radial, peroneal nerves
Usually less than 30 years age
Clinical features:
Soft, slowly enlarging mass in the palmar aspect of the hand, wrist or forearm since childhood
Pain
Neurological symptoms
Associated macrodactyly = macrodystrophia lipomatosa, usually involves 2 and 3rd digits, in 27-67%
Radiography:
Soft-tissue swelling and bone overgrowth, usually of 2 and 3rd digits, may show bowing
Secondary degenerative changes may be seen
Ultrasound:
Alternating hyper and hypoechoic bands (cable appearance) due to elongated and enlarged median nerve
MRI:
Pathognomonic - longitudinally oriented cylindric foci (3 mm diameter) of low signal surrounded by fat signal (cable appearance)
Increased fat in overgrown digits
Thickened median nerve
References:
1. Murphey MD et al. Imaging of Musculoskeletal Neurogenic Tumors: Radiologic-Pathologic Correlation . Radiographics. 1999;19:1253-1280
2. Stuart RM et al. Sonography of Peripheral Nerve Pathology . AJR 2004; 182:123-129
3. Murphey MD et al. Benign Musculoskeletal Lipomatous Lesions. RadioGraphics 2004;24:1433-1466
4. Nouira K et al. Fibrolipoma of the median nerve. Joint bone spine 2007: 74: 98-99
