Image-Based Differentiation of Benign and Malignant Peripheral Nerve Sheath Tumors in Neurofibromatosis Type 1

From benign neurofibromas to malignant peripheral nerve sheath tumors (MPNST): a gaming among multiple factors

Almost all patients of Neurofibromatosis Type I (NF1) develop benign peripheral nerve tumors called neurofibromas, which are derived from neural crest Schwann cell lineage progenitors with biallelic NF1 gene mutations. More than 90% of NF1 patients develop dermal neurofibromas (DN), and 25-50% develop plexiform neurofibromas (PN). In 8-13% of individuals with NF1, PN can transform into malignant peripheral nerve sheath tumors (MPNSTs), a type of nerve soft tissue sarcoma that is the main cause of mortality of NF1 patients. In addition to arising from benign neurofibromas (50%), MPNSTs can also occur spontaneously (~40%) or following radiation therapy (~10%). Treatment for MPNST is limited to complete resection with negative margins. Still, the high recurrence of MPNST is a major concern. However, full resection of the pre-malignant lesions can largely reduce the recurrence and mortality of patients. So, early diagnosis and distinguishing malignancy from benign and premalignant lesions are particularly important. During the progression from benign neurofibromas to malignancy, a variety of changes including tumor morphology, genetic mutations, expression of multiple signaling pathways-related proteins and genome instability gradually occur. In this review, we detail these changes with the goals of identifying the histological and/or molecular signs of malignancy initiation, and an optimal therapeutic intervention window, to inhibit tumor progression and reduce the rate of mortality.

Malignant peripheral nerve sheath tumor presenting in the cauda equina: diagnostic and biological pearls. Illustrative case

BACKGROUND

Malignant peripheral nerve sheath tumors (MPNSTs) are rare and highly malignant tumors of neural crest origin. No matter their anatomical location, they are difficult to treat and carry a poor prognosis.

OBSERVATIONS

This report highlights the complexities of the diagnosis and management of a patient with MPNST of the cauda equina. The tumor retained the expression of H3K27me3, which is expected in spinal MPNSTs but uncommon in most sporadic and neurofibromatosis type 1-driven MPNSTs.

LESSONS

The described diagnostic nuance should be taken into consideration in patients with suspected MPNST of the cauda equina, as these tumors require swift neurosurgical intervention in order to maintain neurological function. Additional treatment modalities include neoadjuvant and adjuvant chemotherapy and radiotherapy. Although improvements in local control and progression-free survival have been reported, the role of radiation therapy and chemotherapy has been underinvestigated due to the rarity of MPNSTs presenting in this region. https://thejns.org/doi/10.3171/CASE24723.

Imaging of Peripheral Intraneural Tumors: A Comprehensive Review for Radiologists

BACKGROUND/OBJECTIVES

Intraneural tumors (INTs) pose a diagnostic challenge, owing to their varied origins within nerve fascicles and their wide spectrum, which includes both benign and malignant forms. Accurate diagnosis and management of these tumors depends upon the skills of the radiologist in identifying key imaging features and correlating them with the patient's clinical symptoms and examination findings.

METHODS

This comprehensive review systematically analyzes the various imaging features in the diagnosis of intraneural tumors, ranging from basic MR to advanced MR imaging techniques such as MR neurography (MRN), diffusion tensor imaging (DTI), and dynamic contrast-enhanced (DCE) MRI.

RESULTS

The article emphasizes the differentiation of benign from malignant lesions using characteristic MRI features, such as the "target sign" and "split-fat sign" for tumor characterization. The role of advanced multiparametric MRI in improving biopsy planning, guiding surgical mapping, and enhancing post-treatment monitoring is also highlighted. The review also underlines the importance of common diagnostic pitfalls and highlights the need for a multi-disciplinary approach to achieve an accurate diagnosis, appropriate treatment strategy, and post-therapy surveillance planning.

CONCLUSIONS

In this review, we illustrate the main imaging findings of intraneural tumors, focusing on specific MR imaging features that are crucial for an accurate diagnosis and the differentiation between benign and malignant lesions.

[Clarification the terms and definitions related to neurofibromatosis type 1]

Objective

To summarize the terms and definitions related to neurofibromatosis type 1 (NF1) with a view to standardizing and unifying the existing terminology system.

Methods

To review the research literature related to NF1 at home and abroad, and to summarize the expressions of the disease and related terms.

Results

There are still some limitations in the current knowledge of NF1, especially in the expression of the terminology, and there are discrepancies in the description and naming of NF1-related features in different medical literatures and clinical guides. There are differences in the description and naming of NF1-related features in different medical literature and clinical guidelines. Through a systematic review of the literature, this paper provides a detailed compendium and summary of the terms and definitions of NF1-related clinical manifestations, pathological features, and genetic types, and further standardizes and unifies existing diagnostic criteria and terminology systems.

Conclusion

The terms and definitions of NF1-related clinical manifestations are summarized to enhance the knowledge of clinicians and researchers related to NF1.

Treatment of giant neurofibromas in extremities and trunk wall of neurofibromatosis type 1 patients: a Chinese 12-year single-institution experience

BACKGROUNDS

Giant neurofibromas occurring in individuals diagnosed with neurofibromatosis type 1 (NF1) often result in considerable disfigurement, functional impairment, and diminished quality of life. Although debulking surgery poses inherent risks of complications, it remains the most efficacious approach to address these issues. The primary objective of this study was to share our surgical experience with giant neurofibromas in the extremities and trunk wall of NF1 patients which may help surgeons to minimize intraoperative bleeding and facilitate tumor excision.

METHODS

A retrospective review was conducted at a single center, encompassing 36 NF1 patients with giant neurofibromas in the extremities and trunk wall who underwent debulking surgery from July 2010 to July 2022.

RESULTS

Twenty-one male and fifteen female NF1 patients who received one to four surgical interventions were evaluated. The average age at the time of surgery was 17.8 years. The median follow-up time was 52 months. Our findings revealed relatively low rates of complications and recurrence. Notably, patients expressed satisfaction with both the aesthetic and functional results.

CONCLUSIONS

Debulking surgery of giant neurofibromas in the extremities and trunk wall of NF1 patients can effectively reduce the tumor burden, leading to improvements in both the appearance and function.

PET Imaging of Neurofibromatosis Type 1 with a Fluorine-18 Labeled Tryptophan Radiotracer

Neurofibromatosis type 1 (NF1) is a neurocutaneous disorder. Plexiform neurofibromas (PNFs) are benign tumors commonly formed in patients with NF1. PNFs have a high incidence of developing into malignant peripheral nerve sheath tumors (MPNSTs) with a 5-year survival rate of only 30%. Therefore, the accurate diagnosis and differentiation of MPNSTs from benign PNFs are critical to patient management. We studied a fluorine-18 labeled tryptophan positron emission tomography (PET) radiotracer, 1-(2-[18F]fluoroethyl)-L-tryptophan (L-[18F]FETrp), to detect NF1-associated tumors in an animal model. An ex vivo biodistribution study of L-[18F]FETrp showed a similar tracer distribution and kinetics between the wild-type and triple mutant mice with the highest uptake in the pancreas. Bone uptake was stable. Brain uptake was low during the 90-min uptake period. Static PET imaging at 60 min post-injection showed L-[18F]FETrp had a comparable tumor uptake with [1⁸F]fluorodeoxyglucose (FDG). However, L-[18F]FETrp showed a significantly higher tumor-to-brain ratio than FDG (n = 4, p < 0.05). Sixty-minute-long dynamic PET scans using the two radiotracers showed similar kidney, liver, and lung kinetics. A dysregulated tryptophan metabolism in NF1 mice was further confirmed using immunohistostaining. L-[18F]FETrp is warranted to further investigate differentiating malignant NF1 tumors from benign PNFs. The study may reveal the tryptophan-kynurenine pathway as a therapeutic target for treating NF1.

Impact of CT and MRI in the diagnostic workup of malignant triton tumour-a monocentric analysis and review of the literature

OBJECTIVES

Malignant triton tumours (MTTs) are rare but aggressive subtypes of malignant peripheral nerve sheath tumours (MPNSTs) with a high recurrence rate and 5-year survival of 14%. Systematic imaging data on MTTs are scarce and mainly based on single case reports. Therefore, we aimed to identify typical CT and MRI features to improve early diagnosis rates of this uncommon entity.

METHODS

A systematic review on literature published until December 2022 on imaging characteristics of MTTs was performed. Based on that, we conducted a retrospective, monocentric analysis of patients with histopathologically proven MTTs from our department. Explorative data analysis was performed.

RESULTS

Initially, 29 studies on 34 patients (31.42 ± 22.6 years, 12 female) were evaluated: Literature described primary MTTs as huge, lobulated tumours (108 ± 99.3 mm) with central necrosis (56% [19/34]), low T1w (81% [17/21]), high T2w signal (90% [19/21]) and inhomogeneous enhancement on MRI (54% [7/13]). Analysis of 16 patients (48.9 ± 13.8 years; 9 female) from our institution revealed comparable results: primary MTTs showed large, lobulated masses (118 mm ± 64.9) with necrotic areas (92% [11/12]). MRI revealed low T1w (100% [7/7]), high T2w signal (100% [7/7]) and inhomogeneous enhancement (86% [6/7]). Local recurrences and soft-tissue metastases mimicked these features, while nonsoft-tissue metastases appeared unspecific.

CONCLUSIONS

MTTs show characteristic features on CT and MRI. However, these do not allow a reliable differentiation between MTTs and other MPNSTs based on imaging alone. Therefore, additional histopathological analysis is required.

ADVANCES IN KNOWLEDGE

This largest published systematic analysis on MTT imaging revealed typical but unspecific imaging features that do not allow a reliable, imaging-based differentiation between MTTs and other MPNSTs. Hence, additional histopathological analysis remains essential.