Progressive nerve territory overgrowth after subtotal resection of lipomatosis of the median nerve in the palm and wrist: a case, a review and a paradigm

A novel mechanism for the formation and propagation of neural tumors and lesions through neural highways

By recognizing anatomic and radiologic patterns of rare and often misdiagnosed peripheral nerve tumors/lesions, we have defined mechanisms for the propagation of neural diseases. The novel concept of the nervous system serving as a complex system of "highways" driving the neural and perineural spread of these lesions is described in three examples: Intraneural dissection of joint fluid in intraneural ganglion cysts, perineural spread of cancer cells, and dissemination of unknown concentrations of neurotrophic/inhibitory factors for growth in hamartomas/choristomas of nerve. Further mapping of these pathways to identify the natural history of diseases, the spectrum of disease evolution, the role of genetic mutations, and how these neural pathways interface with the lymphatic, vascular, and cerebrospinal systems may lead to advances in targeted treatments.

What's known and what's new in adipose lesions of peripheral nerves?

BACKGROUND

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.

METHODS AND MATERIALS

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.

RESULTS

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.

CONCLUSION

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.

Strengthening the association of lipomatosis of nerve and nerve-territory overgrowth: a systematic review

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 and overgrowth: is there a preference for motor (mixed) vs. sensory nerve involvement?

BACKGROUND

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.

METHODS

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.

RESULTS

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).

CONCLUSION

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.

Fibroproliferative Neuromas May Occur After Iatrogenic Injury for Lipomatosis of Nerve

BACKGROUND:

Lipomatosis of nerve (LN) is a condition associated with nerve-territory overgrowth. We have noted a unique type of neuroma at sites of LN injury; the neuroma extends beyond the epineurium, enhances, and appears to enlarge over time.

OBJECTIVE:

We sought to understand the relationship between fibroproliferative scarring and surgery performed on the nerve.

METHODS:

A review of the searchable records for LN at our institution found 52 cases, confirmed by pathology or pathognomonic appearance on magnetic resonance imaging (MRI). Clinical histories were reviewed to categorize the surgeries performed by the degree of iatrogenic injury to the nerve. Postoperative MRI was performed in 22 of the 46 patients who had surgery, which was then retrospectively reviewed for fibroproliferative neuromas.

RESULTS:

Complex and masslike neuromas were found on MRI, correlating with the degree of iatrogenic injury to the nerve. These fibrous neuromas proliferated beyond the epineurium, disrupted fascicular architecture, were contrast enhancing when contrast was administered, indicative they were unique and unlike stump or traction neuromas. Of the 8 patients who underwent surgery involving nerve decompression alone, none developed fibroproliferative neuromas. Of the 7 patients who underwent surgery involving nerve debulking, fibroproliferative neuromas developed in 4. Of the 11 patients who underwent surgery involving nerve transection, all developed fibroproliferative neuromas (P &lt; .001). There was also a high incidence of hypertrophic scarring of the skin incision (21.3%).

CONCLUSION:

Surgical injury of LN appears to be strongly associated with the development of fibroproliferative neuromas. It is possible that the pathological overgrowth stimulus associated with LN promotes exuberant scar formation.