Fibrolipomatous Hamartoma of the Median Nerve

Olya Polishchuk

Mary Wyers, M.D.

Children's Memorial Hospital

Abstract

4 year old male with painless swelling of the mid-palm

Keywords

hamartoma, fibrolipomatous hamartoma, MRI, plain film

Publication Date: 2004-07-15

History

4 year old male with painless swelling of the mid-palm

Findings

Plain film: There is normal alignment of osseous structures. No bony abnormalities are identified. There is palmar soft tissue mass in the region of thenar eminence.

MRI: (T1, T2 and post gadolinium sequences) There is a well-defined mass involving the volar surface of the wrist. The mass begins at the level of the distal radial growth plate, extends through the wrist to the level of the distal metacarpals. The mass displaces the flexor tendons dorsally. The mass enlarges the median nerve and is composed of fatty and fibrous components. There is no significant enhancement.

Diagnosis

Fibrolipomatous hamartoma of the median nerve

Differential

Neurofibroma, traumatic neuroma, perineuroma, hemangioma. However, these lesions are T2 bright or enhance, allowing radiologic differentiation of these lesions from fibrolipomatous hamartoma.

Discussion

Fibrolipomatous hamartoma of the nerve is a benign tumor-like mass of fibrofatty tissue that inflitrates and encases involved nerves and its branches, but does not involve the surrounding tissues. Pathologically, the mass consists of benign fibrous and fatty elements around and inbetween affected nerves, but with no axonal proliferation. Most cases have been reported as occurring in the median nerve, involving the volar aspects of the hands, wrist, and distal forearms, but uncommon locations involve the ulnar nerve, the radial nerve, the nerves of either side of the toes, cranial nerves, and the brachial plexus. The lesion may be asymptomatic, or may present with nerve compression symptoms causing pain, diminished sensation, paresthesia, and thenar motor weakness. Carpel tunnel syndrome may be a late complication. Focal macrodactyly has been associated with this lesion, which is referrred to as macrodystrophia lipomatosa.

Plain radiographs of involved areas often are negative or show non-specific soft tissue swelling. MRI best characterizes this lesion, which is low on T1WI with high-intensity fat signal around and in betweeen the low-intensity nerve axons. It remains low-to-intemediate on T2-fat-sat-WI, and does not demonstrate enhancement with gadolinium. On axial images the lesion has a very characteristic co-axial cable appearance of low-intensity axons surrounded and interdigitated by fibrofatty signal.

Treatment is controversial as excision can sometimes leave the patient with debilitating nerve deficits. Furthermore, an intense healing response after resection has beeen reported, leaving the patient with worse pain than prior to the surgery. Therefore the decision to resect is on a case by case basis.

References

1. Sone et al, "Macrodystrophia Lipomatosa: CT and MR Findings", Radiation Medicine: Vol 18. No. 2, 129-13, 2000.