Fact-sheet: Neural lipomatosis
Updated on 09/17/2021 at 12:16 PM
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Definition
- Benign proliferation of adipose tissue within the epineurium, separating nerve fibers.
- Unknown cause, several hypotheses such as: trauma, chronic irritation, abnormal development of the flexor retinaculum (median nerve), congenital
- Rare condition
- Sex ratio 1:1
Clinical features
- Early involvement with progressive neurologic deficit (generally before age 30), or late presentation
- Pain, discomfort, entrapment syndrome (carpal tunnel, Guyon's canal), swelling
- Involvement usually affects a single nerve and most often involves the median nerve (85% of cases), at the level of the forearm, carpal tunnel or even its digital branches
- In a number of cases, mesenchymal hypertrophy (adipose tissue, bone) is observed within the nerve territory leading to macrodactyly (macrodystrophia lipomatosa)
- Other reported involvements: ulnar nerve, radial nerve, sciatic nerve, plantar nerves, superficial fibular nerve, brachial plexus, lumbosacral plexus..
Radiography
- macrodactyly
Ultrasound
- Same appearance as on MRI, namely hypoechoic tubular nerve fibers and hyperechoic fatty proliferation at their periphery
- non-visualization of the normal nerve
- the topography of the lesion allows suggesting the nerve origin of the detected mass
MRI
- Reference examination
- Fusiform enlargement of a nerve with tubular structures giving a "spaghetti" appearance on coronal or sagittal images and a "coaxial cable" appearance on axial images.
- Nerve fibers with T1 and T2 hyperintensity, separated by adipose tissue of variable abundance with T1, T2 hyperintensity, T1 FatSat hypointensity
- No contrast enhancement after gadolinium injection
- Late, possible signs of denervation in the territory of the affected nerve (amyotrophy, muscular fatty infiltration)
- The MRI appearance is pathognomonic and allows avoiding biopsy
Management
- No biopsy (pathognomonic MRI)
- Surgical treatment difficult without sacrificing the nerve
- In case of entrapment syndrome, surgical decompression possible
Classification
- Several terms exist but the retained term is "neural lipomatosis" (WHO 2000 classification), and encompasses several subtypes
Differential diagnosis
Differential diagnosis of peripheral nerve enlargement:
- Tumors of nerve origin; benign nerve sheath tumors (schwannomas, neurofibromas), malignant nerve sheath tumors
- Pseudo-tumors: intraneural ganglion cyst, post-traumatic neuroma, Morton neuroma (common plantar digital nerve), neural lipomatosis
- CIDP: chronic inflammatory demyelinating polyradiculoneuropathy