Intraneural lipomas: institutional and literature review

Intraneural lipoma of the median nerve: a case report

Intraneural lipomas and lipofibromas (also called lipofibromatous hamartomas) are rare, benign tumours occurring in peripheral nerves in the forearm and wrist. They usually present as asymptomatic masses, but if they are large enough, they may cause symptoms of compression neuropathy. Intraneural lipomas and lipofibromas differ with regard to anatomy and clinical behaviour: the former tumour has a well-defined capsule and most commonly occurs within the median nerve in the forearm and wrist. It is diagnosed in the fourth and fifth decades of life and seen more frequently in women. The latter (lipofibroma) has no capsule, is infiltrative in nature, is composed of fatty and fibrous tissue and also most commonly seen in the median nerve. It occurs in a younger age group with no sexual predominance. Due to these differences, these lesions are managed differently 1 2.

[Interdisciplinary Treatment Of Tumorous And Tumour-Like Lesions Of Peripheral Nerves]

Tumorous or tumour-like lesions of peripheral nerves are generally rare, heterogeneous and challenging to diagnose and treat. They may become apparent by a palpable swelling (lump) near nerves, sensory and/or motor deficits, pain to touch or neuropathic pain. In 91% of cases, tumours are benign. The differentiation of entities and their characteristics as well as a function-preserving resection strategy are highly relevant. Misdiagnosis and inadequate treatment can lead to severe deficits and pain syndromes. Benign tumours include schwannomas and neurofibromas, which can occur sporadically but can also be associated with neurogenetic tumour disposition syndromes if they occur more frequently. Rarer benign nerve tumours include perineuriomas, lipomas, aggressive fibrosis (desmoid tumours), paragangliomas and haemangiomas. Ganglion cysts are described as tumour-like lesions. The association of nerve tumours with neurogenetic syndromes and the correct classification of potentially malignant lesions such as MPNST (malignant peripheral nerve sheath tumour) or intermediate stages such as ANNUBPs (atypical neurofibromatous neoplasms with unknown biological potential) pose particular challenges. Interdisciplinarity is highly relevant for clinical treatment and a correct diagnosis. The aim of our work is to provide an overview of the relevant entities, diagnostic evaluation and contemporary treatment strategies based on the current data situation and taking into account the recently published interdisciplinary AWMF S2k guideline "Diagnosis and Treatment of Peripheral Nerve Tumours".

Intraneural lipoma of the ulnar nerve: A rare case report and review

Intraneural lipoma of the ulnar nerve is a rare peripheral nerve tumor in an uncommon location. Although its benign course, it can cause disabling symptoms such as pain, diminished sensation or paraesthesia, tenderness, and occasionally even loss of strength. We present the case of a middle age woman with insidious paresthesias and swelling of the hypothenar eminence of the left hand for over 1 year. A hand and wrist radiograph first confirmed a focal soft tissue mass with fat density and excluded potential bone lesions. Then, an ultrasound was performed that showed a slightly hyperechoic mass with a fibrillated pattern in contiguity with the proximal aspect of the ulnar nerve. The morphological arrangement of this mass, its location along ulnar nerve distribution and the main signal characteristics in magnetic resonance imaging such as hyperintensity in T1- and T2-weighted images and hypointensity in fat saturation sequences inferred an intraneural lipoma. Due to the progressive symptoms, elective resection of the lesion was performed with full recovery of the symptoms.

Intraneural Lipoma: A Rare Cause of Median Nerve Compression

Intraneural lipomatous tumors are rare lesions that mostly affect the upper extremities. These slowly growing tumors can have a serious neurological and functional impact when they reach a significantly large size. We report herein a case of a 53-year-old female who presented with a large median nerve intraneural lipomatous tumor causing compression-related signs. She was treated with monoblock excision of the tumor that was completely residing between the median nerve fibers. At her last follow-up, no median nerve deficits were recorded, and the patient went to full resolution.

Beyond schwannomas and neurofibromas: a radiological and histopathological review of lesser-known benign lesions that arise in association with peripheral nerves

Peripheral nerve sheath tumors comprise a significant percentage of both benign and malignant soft tissue tumors. The vast majority of these lesions are schwannomas and neurofibromas, which most radiologists are familiar with including the well-described multimodality imaging features. However, numerous additional often under-recognized benign entities associated with nerves exist. These rarer entities are becoming increasingly encountered with the proliferation of cross-sectional imaging, particularly magnetic resonance imaging (MRI). It is important for the radiologist to have a basic understanding of these entities as many have near-pathognomonic MR imaging features as well as specific clinical presentations that when interpreted in concert, often allows for a limited differential or single best diagnosis. The ability to provide a prospective, pre-intervention diagnosis based solely on imaging and clinical presentation is crucial as several of these entities are "do not touch" lesions, for which even a biopsy may have deleterious consequences. To our knowledge, the majority of these benign entities associated with nerves have only been described in scattered case reports or small case series. Therefore, the aim of this article is to provide a radiopathologic comprehensive review of these benign entities that arise in association with nerves with a focus on characteristic MRI features, unique histopathologic findings, and entity specific clinical exam findings/presentation.

Occult lipomatosis of the nerve as part of macrodystrophia lipomatosa: illustrative case

BACKGROUND

Macrodystrophia lipomatosa (MDL) is characterized by progressive overgrowth affecting soft tissues and bony structures and is part of lipomatous overgrowth syndromes. MDL has been associated with lipomatosis of the nerve (LN), an adipose lesion of nerve that has a pathognomonic magnetic resonance imaging (MRI) appearance as well as a mutation in the PIK3CA gene. The authors present a case of occult LN in the setting of MDL.

OBSERVATIONS

A 2-year-old boy with progressive soft tissue overgrowth of his proximal right lower extremity was initially diagnosed with neurofibromatosis type 1 (NF1). At our institution, NF1 as well as other overgrowth syndromes including PTEN hamartoma tumor syndrome were excluded. He was diagnosed as having so-called MDL. Upon reinterpretation of the patient's MRI studies, short-segment LN involving the proximal sciatic nerve and part of lumbosacral plexus was identified. He underwent 2 debulking/liposuction procedures for soft tissue overgrowth. Genetic testing of tissue revealed a mutation in PIK3CA.

LESSONS

Thorough clinical examination (for signs of overgrowth) as well as an MRI study of the entire neural pathway is a critical part of the diagnostic workup to evaluate for LN. The authors believe that an increasing association of LN, even when occult, will emerge that will explain many cases with marked nerve-territory overgrowth.

The Growth Factors of Subcutaneous Benign Lipoma: Consideration from Anatomical Position of Occurrence

Subcutaneous lipomas are the most common benign soft-tissue tumors. Theoretically, adipocyte sites could be the primary foci; however, lipomas are likely located in the occipital, neck, shoulder, torso, and thigh areas. To date, no study has reported the anatomical relationship between these subcutaneous structures and lipomas. Therefore, we aimed to investigate the anatomical locations of lipomas and considered their growth factors. In addition, we discussed the mechanism of fat amplification to improve the success of fat grafting.

METHODS

In the present study, lipomas measuring more than 5 cm in diameter from patients hospitalized between 2017 and 2021 were retrospectively examined using preoperative computed tomography and magnetic resonance imaging as well as clinical records with intraoperative pictures.

RESULTS

In total, 22 lipomas of 22 patients were examined. All lesions (100%) were accompanied by neurovascular perforators. Nineteen lesions (86%) were located deep in the superficial fascia, where it was clearly defined. Moreover, all lesions were located at the mobile adipofascial layer adjacent to an anchored fixed or less mobile structure.

CONCLUSIONS

Lipoma growth might require neurovascular perforators that supply both blood flow and continuous stretching stimuli. The mobile adipofascial layer with bones adjacent to a fixed or less mobile area might also be necessary to grow lipomas. If these findings can be used as clues to elucidate the mechanism of fat amplification in the future, it may lead to an improvement in the survival rate of fat grafts.

Rare case of Intraneural Lipoma of Digital Nerve

Lipomas, although ubiquitous, are extremely uncommon in digital nerves. We present a 68-year-old male patient with right ring finger radial digital nerve intraneural lipoma. The tumor was enucleated preserving all the nerve fascicles. We present this case to highlight the rare occurrence of lipomas within a digital nerve.

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.

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.

Neuromuscular choristoma-associated desmoid-type fibromatosis: Establishing a nerve territory concept

INTRODUCTION

Desmoid-type fibromatosis (DTF) frequently arises in patients with neuromuscular choristoma (NMC). We hypothesize that NMC-associated DTF occurs in soft tissues innervated by the NMC-affected nerve, and arises from CTNNB1-mutated (myo) fibroblasts within or directly adjacent to the NMC.

MATERIALS AND METHODS

A retrospective review of patients treated at our institution was performed for patients with biopsy-confirmed diagnosis of NMC-DTF. Clinical presentation, physical examination, electrodiagnostic findings and radiological features (MR and FDG PET/CT images for each NMC-DTF) and pathologic re-review of available materials were analyzed. A literature review was also performed.

RESULTS

Eight patients from our institution met the inclusion criteria. All patients presented with neuropathic symptoms and soft tissue or bone changes in the nerve territory innervated by the NMC. All MR images (N=8 cases) showed the characteristic features of NMC, and also showed direct contact between unifocal (N=5) or multifocal (N=3) DTF(s) and the NMC-affected nerve NMC. FDG PET/CT (N=2 cases) showed diffuse, increased FDG uptake along the entire affected nerve segment, contiguous with the FDG-avid DTF. In all cases, the DTFs arose in the soft tissues of the NMC-affected nerve's territory. No patient developed DTF at any other anatomic site.

CONCLUSIONS

These data demonstrate that NMC-DTF arises solely within the NMC-affected nerve territory, and has direct contact with the NMC itself. Based on all these findings and the multifocality of NMC in several cases, we recommend imaging and surveillance of the entire NMC-affected nerve (from spine to distal extremity) to identify clinically-occult DTF in patients with NMC.

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.

PIK3CA mutations in lipomatosis of nerve with or without nerve territory overgrowth

Lipomatosis of nerve is a rare malformation characterized by a fibrolipomatous proliferation within peripheral nerve. Lipomatosis of nerve most frequently involves the median nerve, and manifests clinically as a compressive neuropathy. However, 30-60% of cases are associated with tissue overgrowth within the affected nerve's territory (e.g., macrodactyly for lipomatosis of nerve in the distal median nerve). Somatic activating PIK3CA mutations have been identified in peripheral nerve from patients with lipomatosis of nerve with type I macrodactyly, which is now classified as a PIK3CA-related overgrowth spectrum disorder. However, the PIK3CA mutation status of histologically confirmed lipomatosis of nerve, including cases involving proximal nerves, and cases without territory overgrowth, has not been determined. Fourteen histologically confirmed cases of lipomatosis of nerve involving the median (N = 6), brachial plexus (N = 1), ulnar (N = 3), plantar (N = 2), sciatic and superficial peroneal nerves (N = 1 each) were included. Ten cases had nerve territory overgrowth, ranging from macrodactyly to hemihypertrophy; and four cases had no territory overgrowth. Exome sequencing revealed "hotspot" activating PIK3CA missense mutations in 6/7 cases. Droplet digital polymerase chain reaction for the five most common PIK3CA mutations (p.H1047R, p.H1047L, p.E545K, p.E542K, and p.C420R) confirmed the exome results and identified an additional six cases with mutations (12/14 total). PIK3CA mutations were found in 8/10 cases with territory overgrowth (N = 7 p.H1047R and N = 1 p.E545K), including two proximal nerve cases with extremity overgrowth, and 4/4 cases without territory overgrowth (p.H1047R and p.H1047L, N = 2 each). The variant allele frequency of PIK3CA mutations (6-32%) did not correlate with the overgrowth phenotype. Three intraneural lipomas had no detected PIK3CA mutations. As PIK3CA mutations are frequent events in lipomatosis of nerve, irrespective of anatomic site or territory overgrowth, we propose that all phenotypic variants of this entity be classified within the PIK3CA-related overgrowth spectrum and termed "PIK3CA-related lipomatosis of nerve".

A Clear Mystery: Recognizing Lipomatosis of the Nerve

Lipomatosis of the nerve (LN) commonly presents with neurologic dysfunction due to massive fibro-fatty enlargement of the peripheral nerves. It is uniquely associated with adipose proliferation in the subcutaneous tissue and muscle in the innervated territory, along with osseous abnormalities. Herein, we present the case of a 56-year-old woman who presented with severe right ulnar distribution pain involving the medial forearm and hand (9/10 on a numerical rating scale), declining right-hand strength, movement-dependent hypoesthesias, paresthesias, and a pronounced claw deformity of the right hand with intrinsic atrophy. Electrodiagnostic studies demonstrated pronounced fibrillations, decreased voluntary activation, and minimal collateral reinnervation in the abductor digiti minimi and abductor pollicis brevis, consistent with dysfunction of the lower trunk of the right brachial plexus. Magnetic resonance imaging (MRI) and computed tomography (CT) of the brachial plexus were interpreted as a tumor on the right supra- and infraclavicular brachial plexus. At surgery, the brachial plexus was embedded in relatively tight connective tissue with a typical lipoma posteriorly. The lipoma was resected, and the plexus was explored extensively. This case is the 10th report of LN involving the brachial plexus and demonstrated the cardinal features of LN. It provides insight into the pattern of lesions associated with innervation by LN.

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.