MOST LIKELY DIAGNOSIS: Lipofibromatous Hamartoma
This 33-year-old female presents with a mass in the palmar area associated with index finger stiffness.
Q1 – Based on the short-axis T1 fat-weighted images 1 and 2, what is your diagnosis?
Q2 – What are the small dots highlighted by pink arrows in image 1?
Q3 (Advanced) – The blue arrow in image 2 is pointing to what structure in the index finger?
Q4 – What is the signal characteristic, and proper description, of the tissue indicated by the orange arrow on image 2?
A1 – Lipofibromatous hamartoma of the median nerve.
A2 – Bundles of the median nerve.
A3 – Digital nerve surrounded by perineural fat and fibrosis.
A4 – Fat and fatty hypertrophy. Lipofibromatous hamartoma is a rare tumor of peripheral nerves which is characterized by excessive infiltration of the epineurium and perineurium by fiber adipose tissue. Since it is considered a hamartoma, some categorize it as a dysplasia. The median nerve is the most common nerve affected in the body, and often, the abnormality arises in the carpal tunnel. Average age of presentation is often the mid-20s. Lipofibromatous hamartoma of the median nerve has been described rarely in the sciatic, ulnar, and radial nerves.
Because the architecture of the tumor is so infiltrative and intertwined with the nerves, excision is almost never possible. On magnetic resonance imaging, long-axis views have described a spaghetti or cable-like appearance. This is displayed on image 3 (purple arrow).
The disorder is congenital in origin, and is commonly associated with macrodactyly and other conditions at birth.
Several cases of lipofibromatous hamartoma have been associated with exostoses and ectopic calcification. This patient demonstrates an ectopic calcification or ossification (image 4, red arrow). Several references have suggested an association with dysgenetic disorder such as neurofibromatosis. This author and observer has collected over 20 cases of lipofibromatous hamartoma of the median nerve, and none have been associated with neurofibromatosis.
Finally, lipomas and vascular tumors have been associated with this entity. A lipoma or lipomatous hypertrophy is present and was highlighted on image 2 (orange arrow).
Dysplasia’s with macrodactyly and / or extremity enlargement, may be seen in neurofibromatosis type I, Beckwith-Wiedemann syndrome, Proteus syndrome, Klippel-Trenaunay-Weber syndrome, and macrodystrophia lipomatosa.
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Content reviewed: September 8, 2021