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.
METHODS: 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).
CONCLUSIONS: 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.

Macrodystrophia Lipomatosa (MDL) of the toe is a rare, congenital, disproportionate overgrowth involving one or more digits in the lower limb. Despite being a benign condition, when left untreated, it may cause physical impairment and interfere with daily activities. This form of localised gigantism is the result of excessive proliferation of fibroadipose tissue within the nerve along with associated macrodactyly. The mainstay of treatment is debulking or amputation to accommodate the patient\'s daily activities, as well as for cosmesis. In this case report, the clinical and radiographic findings, anatomical descriptions, and histopathological findings are presented. The difference between MDL, fibrolipomatous hamartoma (FLH) and lipomatosis of the nerve (LON) are also discussed.

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Adipose lesions of nerve primarily include intra- and extraneural lipomas and lipomatosis of nerve (LN). This paper will summarize the advances that have been made in the past decade, particularly related to LN and nerve territory overgrowth that have improved our understanding of the natural history, genetic background, diagnosis, imaging features, and clinical management.
Articles about adipose lesions of nerve were reviewed from 2011, when the last comprehensive review on this topic was published. Papers reporting advances on natural history, genetic background, diagnosis, imaging features, and clinical management were screened using PubMed and Google Scholar databases and then analyzed. Case reports and small case series were included only if they reported model examples of discussed pathologies, as these types of articles were summarized in recent systematic reviews on intraneural lipomas and LN. All eligible papers were assessed by the authors, who are subject matter experts.
The first screen revealed 404 articles. After careful evaluation, a total of 53 articles were analyzed which includes advances in diagnosis (especially imaging), classification of the lesions, the role of somatic mutations in PIK3CA in LN, and treatment approaches for all adipose lesions of the peripheral nerve.
Many advances have been made in the understanding of adipose lesions of nerve in the past decade. These pathologic entities are more readily recognized as a spectrum of lesions that share common phenotypic features.

Lipomatosis of nerve (LN) is a complex peripheral nerve disorder characterized by fibrofatty nerve enlargement. MRI of this pathology is pathognomonic and obviates a diagnostic biopsy. Mutation in PIK3CA has been associated with LN cases with nerve-territory overgrowth which may occur in some cases. We evaluate an association of LN of the sciatic nerve and early-onset colonic diverticular disease and discuss the potential pathogenesis.
Our institutional database was searched for LN cases. Available information of identified cases was reviewed, and cases with a confirmed diagnosis of LN affecting the lumbosacral plexus and/or sciatic nerve; available MRI of the affected nerve(s); and diverticular disease occurring in the area supplied by the nerve(s) affected by LN were further analyzed. PIK3CA mutation testing was performed on available tissue samples.
We identified 10 LN cases of lumbosacral plexus and/or sciatic nerve. Of these, three fulfilled our inclusion criteria. All three patients had concomitant colonic diverticular disease, diagnosed at a relatively young age. MRI studies of these cases showed LN involvement of the sacral nerves innervating the sigmoid colon. All three also had abnormal diagnostic workup including various GI tests and evidence of associated nerve-territory overgrowth. Colonic tissue samples for PIK3CA mutation were negative.
While the pathogenesis of the colonic diverticular disease is increasingly recognized as being multifactorial, our observations are consistent with the potential role of autonomic nervous system dysfunction affecting either the pelvic floor musculature, or the colon itself (or both) in a subset of patients with early-onset diverticular disease.

OBJECTIVE: To describe differences between lipomatosis of nerve (LN) and neuromuscular choristoma (NMC) evaluated with MR spectroscopy (MRS).
METHODS: Eight patients were included in this prospective pilot study: three patients with LNs and five with NMCs. Single voxel PRESS MRS of the tumors were acquired with 3 T MRI. MRS data were processed with LCModel version 6.3-1J using the internal \"lipid-8\" basis set. From individual lipid peak and water content measurements, total fatty acid molecules (TFAM), unsaturated fatty acid molecules (UFAM), and glycerol molecules (GM) were computed and analyzed, as well as ratios of UFAM/TFAM, TFAM/GM, and a fatty-acid chain-length index (CLI).
RESULTS: The LN group included two men and one woman (average age 58.3 years); the NMC group included two men and three women (average age 20.4 years). Lipid composition analysis showed that LN had considerably more fat than NMC: TFAM: LN = 15.29 vs NMC = 7.14; UFAM: LN = 4.48 vs NMC = 2.63; GM: LN = 5.20 vs NMC = 1.02. Both tumors had a similar fraction of unsaturated fatty acids: UFAM/TFAM: LN = 0.29 vs NMC = 0.37. LN had the usual number of FA molecules/glycerol molecule, while NMC had considerably more: TFAM/GM: LN = 2.94 vs NMC = 6.98. Finally, average FA chains were longer in NMC: CLI: LN = 17.39 vs NMC = 22.55.
CONCLUSIONS: Our analysis suggests measurable differences in the amount and composition of lipid in LN and NMC. While a larger, statistically powered study is needed, these initial findings may be helpful to properly diagnose ambiguous cases and thereby avoid surgical intervention such as biopsy.

BACKGROUND: Diverse adipose lesions can affect peripheral nerves, including an intrinsic disorder known as lipomatosis of nerve (LN). This condition leads to massive nerve enlargement and has often been associated with nerve territory overgrowth. Although LN has been well documented as a peripheral lesion, it is uncertain whether LN can occur or extend intradurally.
METHODS: In the present 2-part study, we searched our institutional database and the world literature to identify any case of LN occurring or extending intradurally. Strict pathognomonic imaging and histopathologic features of LN were required to be present.
RESULTS: We did not identify any case of LN that had occurred or extended intradurally in our institution. Specifically, in our database, we found no case of intradural LN, and an evaluation of the imaging studies of proximal examples of LN did not show any extension proximal to the spinal foramen. Our literature search identified 208 reports of potential interest, of which only 3 had reported on spinal LN. Although 2 of the 3 cases showed some similarities to LN, none had demonstrated features diagnostic for LN and none had demonstrated nerve territory overgrowth. A review of 16 cases of LN in proximal locations summarized in a recently reported systematic review did not reveal any cases with LN proximal to the foramen or in an intradural location.
CONCLUSIONS: A review of our institutional cases and reported cases did not show any example of LN extending or occurring intradurally. It appears that LN is a benign tumor-like nerve lesion that is without a central location, unlike more well-known tumors such as schwannomas.

OBJECTIVE: Lipomatosis of nerve (LN) is a massive enlargement of a nerve due to abundant proliferation of adipose and fibrotic tissue within the epineurium-part of the spectrum of adipose lesions of nerves, including intra- and extraneural lipomas. LN has been frequently associated with soft-tissue and/or osseous overgrowth. Unfortunately, much confusion exists since many names have been used for LN (e.g., fibrolipomatous hamartoma, macrodystrophia lipomatosa, and so on). To better understand this condition and to evaluate its association with nerve-territory overgrowth, the authors attempted to compile the world\'s literature on published LN cases.
METHODS: PubMed and Google Scholar databases were searched to identify published articles on LN cases, using a variety of terms. Publications in all languages were assessed. All publications with cases determined likely to be LN were read. Cases that provided clear clinicopathological and/or radiological evidence of LN were labeled as \"definite\" and cases that demonstrated features of LN (e.g., nerve-territory overgrowth) but lacked definite proof of nerve involvement were labeled as \"probable.\"
RESULTS: Initial screening revealed a total of 2465 papers. After exclusions, 281 publications reported cases with a definite diagnosis of LN and 120 articles reported cases with a probable diagnosis of LN. The authors identified 618 definite and 407 probable cases of LN. Sex distribution was balanced (51% female). Early diagnosis was common, with two-thirds of patients having symptoms in the 1st decade of life. The most commonly affected nerve was the median nerve (n = 391). Nerve-territory overgrowth was common (62% definite LN; 78% combined cases); overgrowth was exclusive to the territory of the affected nerve in all cases but 5.
CONCLUSIONS: The authors present a comprehensive review and analysis of the literature of LN cases. One of the main findings was the nerve-territory overgrowth was associated with LN, especially when present earlier in life. The authors believe that all cases of LN associated with overgrowth can be explained on anatomical grounds, even in the few reported cases in which this is not immediately obvious.

Lipomatosis of nerve (LN) is a peripheral nerve disorder characterized by fibroadipose proliferation within the epineurium. It has been associated with nerve-territory overgrowth affecting soft tissue and/or bony structures. We sought to understand if there is an anatomical relationship associated with nerve-territory overgrowth.
A review of the literature and our institutional LN cases was performed to determine the prevalence of nerve-territory overgrowth. Only cases with sufficient clinical and/or imaging data were selected. The cases were then subdivided into two groups and analyzed: (1) motor (mixed) nerve and (2) predominant sensory nerve, based on the anatomical location of the LN lesion. Subgroup analysis was performed on median nerves affected by LN, for a more homogenous population.
We identified 329 LN cases with sufficient information for analysis. Motor (mixed) nerve group (M) consisted of 287 cases (155 with overgrowth and 132 without overgrowth). Sensory nerve group (S) revealed group of 42 cases (4 cases with overgrowth and 38 without overgrowth). Statistical analysis comparing overgrowth status in the M and S nerve groups showed a statistically significant difference in overgrowth, favoring the M group for overgrowth (p < 0.0001). The analysis of median nerve group consisted of 225 cases in the M group (106 with overgrowth and 119 without overgrowth) and 20 cases in the S group (3 with overgrowth and 17 cases without overgrowth). A statistically significant difference in nerve-territory overgrowth status was present in the M vs. the S group, again favoring the M group for overgrowth. (p = 0.0083). Cases from our institution included 44 cases for this analysis. Forty-two cases in the M group (28 with overgrowth and 14 without overgrowth) and 2 cases in the S group (all 2 without overgrowth).
We believe the association of LN and nerve-territory overgrowth might be explained by involvement of mixed motor nerves; however, the exact underlying mechanism is not known.