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MRI Web Clinic - January 2024

Lipomatosis of Nerve

 

 

Clinical History:  A 25-year-old male presents with wrist pain. Axial T1- (1a) and axial fat-suppressed T2- (1b) weighted MRI images of the wrist are provided.  What are your findings?   What is your diagnosis?

Findings

 

Diagnosis

Lipomatosis of the median nerve.  

Introduction

Originally described by Mason in 19531, lipomatosis of nerve (LN) has undertaken several names including fibrolipomatous hamartoma, lipofibromatous hamartoma, neural fibrolipoma, lipofibroma, and fatty infiltration of the nerve2,3.  The World Health Organization adopted the designation of lipomatosis of nerve in 2002, which remains the current preferred designation4.  This uncommon condition results in tumorlike enlargement of a peripheral nerve (most commonly the median nerve5,6), potentially with involvement of distal branches, territorial bones, and adjacent soft tissues.  This Web Clinic reviews the entity, clinical background, and provides multiple imaging examples.  

Discussion

70% of patients with LN present before the age of 303.  The majority in children present before age 10 and have no family history of the disease.  Males and females are equally affected6.  Patients often present with a non-painful soft tissue mass, following the distribution of the affected nerve.   Patients can experience progressive pain, numbness, weakness, and parathesias, particularly in cases of neural compression or entrapment7,8.  Macrodactyly is seen in 27-67% of cases, particularly when digital branches of the affected nerve are involved, and is termed macrodystrophia lipomatosa (figures 3, 6)2,6.  When macrodactyly occurs, it typically involves the second and third digits of the hand or foot, but multiple digits may be affected6.

 

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Figure 3: Lipomatosis of the median nerve with macrodystrophia lipomatosa - INTERACTIVE IMAGE. Artist rendering of the wrist and hand demonstrates lipomatosis of the median nerve with enlargement and extension into the first, second, and third digit digital nerves. Associated boney macrodactyly of the thumb, index, and middle finger is present, with fibrofatty enlargement of the thenar musculature. (To view the interactive image, use the left mouse button to click on an area at the right side of the image, then hold the button while dragging to the left.)

 

LN most commonly involves the upper extremity, with most (59.9%) cases involving the median nerve3.  In median nerve cases, the LN is typically located within the carpal tunnel and may follow a branching pattern extending into the hand and fingers.   Involvement proximal to the wrist is rare.  Additional reported areas include the plantar (11.2%), ulnar (7%), radial, sciatic, femoral, obturator, tibial, superficial peroneal, and sural nerves3.  Brachial plexus, lumbosacral plexus, and even cranial involvement have been reported3,9,10.  LN does not seem to occur intradurally3.

The exact etiology of LN is not yet understood.   Some believe the etiology is congenital or developmental abnormal growth of fibrofatty tissue, with possible genetic associations involving PIK3CA or other genes3,11.  The entity has been found in some patients at birth, supporting a congenital origin12. Associations with Proteus syndrome and Klippel-Trenaunay-Weber syndrome have been discussed13.  Others believe LN is an acquired or reactive process due to prior trauma, repetitive microtrauma or nerve irritation (such as in carpal tunnel syndrome patients).  Some authors propose a combination of both congenital and microtrauma are responsible for the entity11.

On gross examination, LN demonstrates diffuse enlargement of the affected nerve, appearing as a tan-yellow fibrofatty mass within the nerve sheath2,6.  Histologically, LN demonstrates a hamartomatous proliferation of mature fat and fibroblasts within the epineurium, interspersed among nerve bundles, resulting in marked expansion of the nerve.  The proportion of the components may vary.  The surrounding tissue shows no involvement or inflammation11.  The infiltrative pattern of fat allows distinction from a soft-tissue lipoma adjacent to a nerve2.   The nerve fibers are typically intrinsically normal but may show atrophy in cases of late disease2.  In cases of macrodystrophia lipomatosa, patients have a diffuse disproportionate increase in fibroadipose tissue along the affected digit2,6.  Bony enlargement results from endosteal and periosteal deposition of bone.  The periosteum is studded with millimetric nodules containing chondroblasts, osteoblasts, and osteoclasts; these become larger and more numerous towards the distal ends of the phalanges14.

 

 

Imaging Findings

On radiography, LN patients without macrodactyly are often demonstrate normal x-rays, but may show a soft tissue mass with radiolucent fatty tissue14.  If macrodactyly is present, osseous and soft tissue overgrowth is common, which occurs both longitudinally and axially (figure 6d), usually ceasing after puberty2,6,14.  Bony overgrowth is more prominent volarly and distally, resulting in distal splaying and bowing2,6,14. On MRI, LN characteristically demonstrates serpentine longitudinally oriented low to intermediate signal nerve fascicles surrounded by adipose tissue, within a diffusely enlarged nerve2,6.  The resultant morphology has been likened to a “spaghetti-like” appearance on longitudinal images3 and “coaxial cable-like” appearance on axial images. The latter finding has been described as pathognomonic for LN5,15, subsequently allowing a confident MRI diagnosis12.  MRI is also useful preoperatively, as LN cannot be excised without sacrificing the pathologic nerve, distinguishing itself from other tumors such as an intraneural lipoma12.  The neural branching pattern of LN is evident with MRI, which can be used to map out the extent of the disease.  In patients with macrodactyly, increased fat is also noted within the affected digits2,6.

 

 

 

 

 

 

 

 

Treatment

LN treatment options vary and are usually determined on a case-by-case basis and can range from observation to complete nerve resection.  Asymptomatic patients are typically treated with observation8.  In symptomatic LN cases involving the median nerve at the carpal tunnel, carpal tunnel release is often performed (figure 13) and can decrease pain and improve oppositional strength10.   Carpal tunnel release may be performed in conjunction with external neurolysis8.  More invasive procedures such as debulking and microsurgical interfascicular dissection are typically reserved for patients with more progressive symptoms and/or nerve compression.  Due to the involvement of intraneural elements, these procedures carry a high complication risk as postoperative fibrosis may impair nerve conduction and result in long-term functional deficits8,11.  Complete excision of the lesion is rarely recommended for LN due to the benign nature of the lesion, risk of functional impairment, and possible formation of painful postoperative neuromas8 .  Macrodactyly cases with deformity may be treated with debulking procedures and/or amputation, with the intent of reducing symptoms, cosmetics, or improving function2,3.  Recurrent overgrowth can also occur after debulking procedures, requiring additional operations3.

 

 

 

Summary

Lipomatosis of nerve has been known by several eponyms, is a benign overgrowth of mature fat and fibrous tissue contained within the epineurium of a nerve, and results in expansile masslike neural enlargement.   The most common location is within the median nerve at the carpal tunnel.   The etiology is uncertain and may be related to prior nerve injury and/or an underlying genetic abnormality.  The MRI imaging appearance is pathognomonic, demonstrating a “coaxial cable-like” appearance on axial images.  Treatment options vary, with conservative measures often preferred to maintain nerve function.  

 

References

  1. Mason M. AMERICAN Society for Surgery of the hand. J Bone Joint Surg Am. 1953;35-A(1):257-275.
  2. Murphey MD, Carroll JF, Flemming DJ, Pope TL, Gannon FH, Kransdorf MJ. Benign musculoskeletal lipomatous lesions. Radiographics. 2004;24(5):1433-1466. doi:10.1148/rg.245045120
  3. Marek T, Mahan MA, Carter JM, et al. What’s known and what’s new in adipose lesions of peripheral nerves? Acta Neurochir (Wien). 2021;163(3):835-842. doi:10.1007/s00701-020-04620-2
  4. Folpe A, Giannini C. Soft Tissue and Bone Tumours WHO Classification of Tumours. Vol 3. 5th ed. IARC Publications; 2020.
  5. Toms AP, Anastakis D, Bleakney RR, Marshall TJ. Lipofibromatous hamartoma of the upper extremity: A review of the radiologic findings for 15 patients. American Journal of Roentgenology. 2006;186(3):805-811. doi:10.2214/AJR.04.1717
  6. Murphey MD, Smith WS, Stacy, Smith E, Kransdorf MJ, Thomas Temple H. From the Archives of the AFIP Imaging of Musculoskeletal Neurogenic Tumors: Radiologic-Pathologic Correlation. Vol 19.; 1999.
  7. Oleaga L, Florencio MR, Erefio C, et al. Skeletal Radiology Fibrolipomatous Hamartoma of the Radial Nerve: MR Imaging Findings Clinical Information. Vol 24.; 1995.
  8. Roh YT, Song SW, Jeong C, Kang Y, Park IJ. Carpal tunnel syndrome caused by lipofibromatous hamartoma of the median nerve. J Korean Neurosurg Soc. 2020;63(5):664-670. doi:10.3340/jkns.2020.0082
  9. Azeemuddin M, Waheed AA, Khan N, Sayani R, Ahmed A. Fibrolipomatous Hamartoma of the Median Nerve with Macrodystrophia Lipomatosa. Cureus. Published online March 9, 2018. doi:10.7759/cureus.2293
  10. Barraza-Silva J, Berebichez-Fridman R, Corona-Cobian LE, Bernal-López LM, Álvarez-San Martín R. Lipofibromatous hamartoma of a digital branch of the median nerve: A case report and review of literature. Clin Case Rep. 2021;9(9). doi:10.1002/ccr3.4728
  11. Soffar MM, Fadali G, Ghalab MA, Abouzaid AM. Lipofibromatous hamartoma of digital nerve: A case report. Plast Reconstr Surg Glob Open. 2021;9(12). doi:10.1097/GOX.0000000000003981
  12. De Maeseneer Jaovisidha L Lenchik D Witte ME Schweitzer DJ Sartoris D Resnick MS, De Maeseneer M, Jaovisidha S, et al. Fibrolipomatous Hamartoma: MR Imaging Findings. Vol 26.; 1997.
  13. Kuo YL, Wu YH, Hsiao PF, Hsieh YJ. Lipofibromatous hamartoma of the superficial peroneal nerve: Two case reports. Dermatologica Sinica. 2012;30(1):21-24. doi:10.1016/j.dsi.2011.09.007
  14. Goldman’ And AB, Kaye’ JJ. Macrodystrophia Lipomatosa : Radiographic Diagnosis. Vol 128.; 1977. www.ajronline.org
  15. Bordalo-Rodrigues M, Amin P, Rosenberg ZS. MR imaging of common entrapment neuropathies at the wrist. Magn Reson Imaging Clin N Am. 2004;12(2):265-279. doi:10.1016/j.mric.2004.02.008

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