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.

Circumferential Adipose Lesion of the Sciatic Nerve.

BACKGROUND: Adipose lesions of nerve are generally distinguished as either extraneural or intraneural lipomas or, alternatively, lipomatosis of nerve. We present a patient with an unusual circumferential lipoma that completely encircles the right sciatic nerve and discuss a possible pathogenesis. CASE DESCRIPTION: A 44-year-old woman presented with progressive symptoms and signs of sciatic neuropathy for 1 year. Magnetic resonance imaging revealed a large lipomatous mass extending from the level of the lesser trochanter to the distal third of the femur. The sciatic nerve was completely enveloped by the lipoma in the proximal segment, partially enveloped in the mid-segment and was separate from the nerve in the distal segment. The lipoma was not covered by the epineurium. The tumor was completely resected and the patient's neurologic symptoms improved. CONCLUSIONS: The pathogenetic mechanism of the reported circumferential lipoma of the sciatic nerve is not known. Two possible mechanisms considered included 1) envelopment by an extraneural lipoma over time and 2) occurrence of a lipoma in the paraneurial compartment (and in this case, extension into an extraneural one). Based on the available literature, lipomas that circumferentially envelop the entire nerve seem to be underrecognized and poorly understood. Analogous cases of lipomas enveloping nerves or other structures than nerves have been reported in the literature. Our reported case highlights the complexity of adipose lesions affecting nerves.