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

Expanding on MRI characteristics of neuromuscular choristoma: a single center retrospective review

OBJECTIVE

Neuromuscular choristoma (NMC) is a rare condition affecting peripheral nerves, most commonly the proximal sciatic nerve. It is characterized by the presence of muscle tissue within the nerve. Patients typically present with neuropathic symptoms. NMC is associated with the development of NMC-associated desmoid-type fibromatosis (NMC-DTF). In this study, we report findings of qualitative and quantitative MRI signal intensities to further expand on known MRI imaging features of NMC.

METHODS AND MATERIALS

Retrospective analysis of NMC cases of the sciatic nerve from our institution was conducted. The sciatic nerve was selected as a model example due to its common involvement. Inclusion criteria were a confirmed NMC diagnosis and available MR exams. MRI signal intensities from the affected nerves and normal contralateral nerves were compared, normalized to muscle signal intensity for consistency across different MRI sequences.

RESULTS

Fourteen patients (8 men, 6 women) met the inclusion criteria. No significant differences in T1 or T2 signal intensities were found between NMC and unaffected nerves. However, NMC demonstrated significantly higher post-contrast signal intensities (p = 0.003) compared to unaffected nerves. These findings were consistent across the proximal and distal segments of the affected nerve.

CONCLUSION

Our study expands the understanding of MRI features in NMC. The increased post-contrast enhancement in NMC may serve as a useful diagnostic tool and could potentially play a role in detecting areas at risk for future DTF development. This highlights the importance of comprehensive imaging, including post-contrast sequences and ideally imaging of the entire course of the affected nerve.

Surgical management of adult hand macrodactyly in a 49-year-old patient: A case report

BACKGROUND

Macrodactyly is a rare congenital malformation characterized by an increase in the size of all structures of a digit, accounting for less than 1% of all congenital upper extremity conditions.

CASE SUMMARY

We report a case involving a 49-year-old woman who presented for the first time with untreated, radial-sided hand macrodactyly. We performed soft tissue debulking, amputation, median nerve neurotomy and coaptation, and carpal tunnel release. At the 6-year follow-up, no significant growth was observed in the bone or soft tissue of the affected area.

CONCLUSION

Tissue overgrowth in patients with progressive macrodactyly can continue and progress excessively with age. Median nerve neurotomy and coaptation play a crucial role in preventing recurrence of the deformity.

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".

PIK3CA mutation testing as a valuable molecular surrogate for lipomatosis of the median nerve: clinicopathological and molecular analysis of six cases

Lipomatosis of peripheral nerves (LPN, also known as fibrolipomatous or lipofibromatous hamartoma of peripheral nerves) is a very rare, benign, intraneural, tumorous lesion that predominantly involves the median nerve but may rarely affect any peripheral nerve. Recently, PIK3CA mutations have been reported in macrodactyly, a rare condition related to LPN, and in other localized lipomatous overgrowth syndromes. In this retrospective study, we report 6 cases of FPN involving the median nerve (4 of them identified among 570 patients with carpal tunnel syndrome who underwent surgical decompression at our center from 2012 to 2022 and two seen in consultation by one of the authors). All cases were diagnosed via biopsy or resection supplemented by MRI. Patients were 4 males and 2 females aged 23 to 60 years (mean 38 years). One patient with bilateral lesions had in addition extensive angiomatosis of the paravertebral region. Histological examination showed an abnormal amount of mature fatty tissue containing disordered fibrous bands, entrapping normal-looking nerve fibers with prominent perineurial and endoneurial fibrosis. Genetic analysis using snapshot assay constructed to detect hotspots mutations in PIK3CA revealed similar PIK3CA mutations (p.H1047R; c.3140A>G) in 5/6 cases (83.3%). Our study represents a further contribution to the literature on LPN and highlights the diagnostic value of PIK3CA mutation testing as surrogate tool in equivocal cases and in those lesions without associated macrodactyly, especially as the biopsy findings of this lesion are essentially nonspecific.

Fibrolipomatous hamartoma of the median nerve: An unusual cause of carpal tunnel syndrome

Fibrolipomatous hamartoma is a rare benign tumor-like condition that affects most commonly the median nerve. The diagnosis is usually confirmed through its typical appearance on magnetic resonance imaging (MRI) without the need for a nerve biopsy. There are divergent views regarding treatment of this entity, but open carpal tunnel release for nerve decompression currently constitutes the standard care for alleviation of compressive neuropathy of the median nerve. In this report, we describe a case of fibrolipomatous hamartoma that was diagnosed via MRI and underwent open carpal tunnel release, with alleviation of the patient's symptoms.

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.

Fibrolipomatous hamartoma of the median nerve: a case report and literature review

Fibrolipomatous hamartoma (FLH) of the nerve, also known as lipomatosis of the nerve, neurofibrillary lipomatous lesion, or intraneural li-poma, is a rare benign soft tissue tumor which mainly occurs in the nerves of the upper limb, especially in the median nerve.In April 2021, a 30-year-old male patient was secondly admitted to our hospital and underwent his third surgery, due to the recurrence of a mass and pain in the right palm, noticeable swelling and numbness of the right index and ring fingers, and limited flexion and extension activities of the right ring finger. He first visited our hospital in December 2017 due to a mass and pain in the right palm and swelling and numbness of the right index and ring fingers. When the clinician asked for the patient medical history, his parents stated that his right middle finger was swol-len after birth. When the patient was ten years old; he was diagnosed with “mac-rodactyly” at the local county hospital, not in our hospital, and subsequently, the middle finger was amputated at the metacarpophalangeal joint level at the local county hospital. The postoperative pathological examination was not per-formed at that time, which was the first surgery the patient received.FLH is clinically rare, and its exact epidemiology and etiology are poorly understood. FLH is highly suspected in cases where a painless mass is present in the wrist, combined with macrodactyly. Magnetic resonance imaging and pathological examination are helpful in clarifying the diagnosis. Although FLH is a benign tumor, an individual treatment plan is the best choice according to the severity of the patient’s symptoms. Therefore, further exploration and understanding of this disease by clinicians radiologists, and pathologists is necessary.

PIK3CA Mutational Analysis in Patients With Macrodactyly

BACKGROUND

Somatic mosaicism for PIK3CA mutations causes various types of growth disorders, which have been summarized under the term PROS (PIK3CA related overgrowth spectrum). Targeted therapy with PI3K inhibitors seems to be a promising alternative for severe PROS cases. Therefore, PIK3CA testing may become more relevant in the future.

METHODS

We report on 14 PROS patients, who had surgery for macrodactyly in the majority of cases. Clinical data were retrieved from the patient's records. Macroscopic and microscopic findings were retrospectively reviewed. Mutational analysis was performed on formalin-fixed paraffin-embedded (FFPE) material.

RESULTS

Patient age ranged from 7 months to 35 years. Five patients showed additional anomalies. One patient had CLOVES syndrome. The majority of the specimens were ray resections characterized by hypertrophic fat tissue. Overall, microscopy was subtle. The abnormal adipose tissue showed lobules exhibiting at least focally fibrous septa. In each case, we could detect a PIK3CA mutation.

CONCLUSION

Histology of affected fat tissue in PROS patients is overall nonspecific. Therefore, mutational analysis represents the key to the diagnosis, especially in unclear clinical cases. We demonstrated that FFPE material is suitable for PIK3CA testing, which can be considered as basis for targeted therapy with PI3K inhibitors.

Multiple congenital malformations arise from somatic mosaicism for constitutively active Pik3ca signaling

Recurrent missense mutations of the PIK3CA oncogene are among the most frequent drivers of human cancers. These often lead to constitutive activation of its product p110α, a phosphatidylinositol 3-kinase (PI3K) catalytic subunit. In addition to causing a broad range of cancers, the H1047R mutation is also found in affected tissues of a distinct set of congenital tumors and malformations. Collectively termed PIK3CA-related disorders (PRDs), these lead to overgrowth of brain, adipose, connective and musculoskeletal tissues and/or blood and lymphatic vessel components. Vascular malformations are frequently observed in PRD, due to cell-autonomous activation of PI3K signaling within endothelial cells. These, like most muscle, connective tissue and bone, are derived from the embryonic mesoderm. However, important organ systems affected in PRDs are neuroectodermal derivatives. To further examine their development, we drove the most common post-zygotic activating mutation of Pik3ca in neural crest and related embryonic lineages. Outcomes included macrocephaly, cleft secondary palate and more subtle skull anomalies. Surprisingly, Pik3ca-mutant subpopulations of neural crest origin were also associated with widespread cephalic vascular anomalies. Mesectodermal neural crest is a major source of non-endothelial connective tissue in the head, but not the body. To examine the response of vascular connective tissues of the body to constitutive Pik3ca activity during development, we expressed the mutation by way of an Egr2 (Krox20) Cre driver. Lineage tracing led us to observe new lineages that had normally once expressed Krox20 and that may be co-opted in pathogenesis, including vascular pericytes and perimysial fibroblasts. Finally, Schwann cell precursors having transcribed either Krox20 or Sox10 and induced to express constitutively active PI3K were associated with vascular and other tumors. These murine phenotypes may aid discovery of new candidate human PRDs affecting craniofacial and vascular smooth muscle development as well as the reciprocal paracrine signaling mechanisms leading to tissue overgrowth.

The Pathological Links between Adiposity and the Carpal Tunnel Syndrome

An association between obesity and carpal tunnel syndrome is found in many epidemiological studies. Therefore, there is a need to evaluate the physiopathological links that could explain the association between these two entities. Ectopic adipose tissue is responsible for metabolic syndrome and inflammation, and is a major risk factor for diabetes and cardiovascular diseases. Taking these elements into consideration, we conducted an extensive literature revision of the subject, considering as ectopic fat-related mechanisms the following: (a) the direct compression and the association with the metabolic syndrome of the fat deposition around the wrist, (b) the insulin resistance, dyslipidemia, inflammatory, and oxidative mechanisms related to the central deposition of the fat, (c) the impaired muscle contraction and metabolism related to myosteatosis. Each section presents the cellular pathways which are modified by the ectopic deposition of the adipose tissue and the impact in the pathogeny of the carpal tunnel syndrome. In conclusion, the experimental and clinical data support the epidemiological findings. Efforts to reduce the obesity epidemics will improve not only cardio-metabolic health but will reduce the burden of the disability-free life expectancy due to the carpal tunnel syndrome.

Lipofibromatous Hamartoma of Digital Nerve: A Case Report

A 9-year-old girl was investigated for a long-standing soft tissue swelling in her ring digit that recently developed tenderness and rapid growth within the last 3 months before presentation. Exploration of the swelling was done meticulously with total excision of the swelling from within its attachment to the digital nerve. The swelling was then sent for histopathological examination. The pathology report stated the presence of mature adipose tissue intersected by fiprocellular collagenic stroma infiltrating perineurium, epineurium, and nerve fascicles, which established the diagnosis of lipofipromatous hamartoma (LFH) of the nerve. LFH is a rare benign neoplasm that mainly affects the median nerve, but other nerves all over the body were also reported. Women are more affected than men.

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.