Exuberant circumferential fibroproliferative neuromas in lipomatosis of nerve: a unifying theory. Illustrative case

Abstract

Background: Lipomatosis of nerve (LN) is a rare disorder characterized by the massive enlargement of peripheral nerves, frequently accompanied by generalized fibroadipose proliferation and skeletal overgrowth.

Observations: The authors have been routinely following a 20-year-old male for lipomatosis of median nerve at the wrist noted shortly after birth. He had undergone resection of the lesion accompanied by sural nerve grafting at another institution. Clinically, although his neurological loss of function has been stable, he has had continued soft tissue growth. Serial magnetic resonance imaging has revealed persistent LN proximal to the repair sites with evidence of fatty proliferation in the sural grafts and continued LN and fatty proliferation distally. There has been a progressive circumferential pattern of fibrosis around the proximal and distal suture lines, which has a similar radiological pattern to desmoid type fibromatosis (a pattern recently described in neuromuscular choristoma [NMC] desmoid-type fibromatosis).

Lessons: Considering the similar reaction of nerve in both LN and NMC despite differing genetic cascades, the authors believe a unifying process occurs in both lesions. The pattern of circumferential fibroproliferation would be most consistent with neuron-mediated growth from unspecified trophic factors, supporting a previously reported a nerve-derived "inside-out mechanism." The clinical consequences of this unifying process are presented.

Keywords: desmoid; fibrolipomatous hamartoma; inside-out mechanism; lipomatosis of nerve; nerve territory; neuromuscular choristoma.

FIG. 1

A–C: Interval clinical growth of the radial side of the palm, particularly the first web space and the hypertrophic scar over the past 15 years.

FIG. 2

Artistic rendering showing that the sequelae of nerve resection and grafting of LN may include continued bony and soft tissue overgrowth and fibrous proliferation (with permission, Mayo Foundation, 2023) (A and B). Postcontrast coronal T1 spoiled gradient recalled echo (SPGR) MRI (C and D) shows the nodular enhancing mass-like lesions in the distal forearm and at the palm corresponding with the proximal suture line in the median nerve and the distal sutures in the digital nerves. Abnormal fatty proliferation can be seen around the nerve grafts between the nodular masses at the proximal and distal suture lines.

FIG. 3

Axial T1-weighted MRI (A–H) shows the circumferential encasement of fascicles in the proximal suture line in the distal forearm sequentially from proximal to distal. In the middle, there is loss of complete architecture. Just above and below, however, there is fibrosis around the fascicular bundles. Note that LN is visible proximal to the proximal suture line.

FIG. 4

Corresponding axial postcontrast T1 SGPR (spoiled gradient recalled echo) MRI (A–H) shows the enhancement.

FIG. 5

Axial T1-weighted MR images (A–C) show the progressive fatty overgrowth occurring in the distal palm. These provide 18-year postoperative follow-up studies since subtotal resection of the LN and nerve grafting. Asterisk indicates the radial digital nerve to the index finger; plus sign, the second common digital nerve; white arrow, third common digital nerve.