[18F]FDG PET/CT in the diagnosis of malignant peripheral nerve sheath tumours in neurofibromatosis type-1

FDG-PET/CT Avid Uptake of a Biopsy-Proven Aggressive Melanotic Schwannoma of the S2 Spinal Nerve Root

Malignant melanotic nerve sheath tumors (MMNSTs), also known as a melanocytic schwannoma (MS), are a rare type of peripheral nerve sheath tumors including Schwann cells with melanocytic differentiation. Only a few cases of spinal MMNST have been reported in literature. Fluorine-18 fluorodeoxyglucose positron emission tomography/computed tomography ( 18 F-FDG-PET/CT) could be used to detect these lesions. A 70-year-old man with a 6-month history of backache was admitted to our hospital. PET/CT showed a paravertebral soft tissue mass along the spinal nerve at the S2 level with strong FDG uptake, and a nodule with increased FDG uptake in the right lobe of the left liver. A CT-guided biopsy of the S2 lesion was performed. The final diagnosis was spinal MS with hepatic metastasis. The patient received stereotactic body radiation therapy. Herein, we report the PET/CT findings of a case of MS with hepatic metastasis. FDG-PET/CT is helpful in the differential diagnosis of benign and malignant lesions although nonspecific.

Discrimination of benign, atypical, and malignant peripheral nerve sheath tumours in neurofibromatosis type 1 - intraindividual comparison of positron emission computed tomography and diffusion-weighted magnetic resonance imaging

BACKGROUND

To intraindividually compare the diagnostic performance of positron emission computed tomography (F-18-FDG-PET/CT) and diffusion-weighted magnetic resonance imaging (DW-MRI) in a non-inferiority design for the discrimination of peripheral nerve sheath tumours as benign (BPNST), atypical (ANF), or malignant (MPNST) in patients with neurofibromatosis type 1 (NF1).

RESULTS

In this prospective single-centre study, thirty-four NF1 patients (18 male; 30 ± 11 years) underwent F-18-FDG-PET/CT and multi-b-value DW-MRI (11 b-values 0 - 800 s/mm²) at 3T. Sixty-six lesions corresponding to 39 BPNST, 11 ANF, and 16 MPNST were evaluated. Two radiologists independently assessed the maximum standardized uptake value (SUVmax) and mean and minimum apparent diffusion coefficient (ADCmean/min) as well as the ADC in areas of lowest signal intensity in each lesion (ADCdark). The AUCs of DW-MRI and F-18-FDG-PET/CT were compared to determine whether the ADC is non-inferior to SUVmax (non-inferiority margin equal to -10%). Follow-up of ≥ 24 months (BPNST) or histopathological evaluation (MPNST + ANF) served as diagnostic reference standard. Both SUVmax and ADC parameters demonstrated good diagnostic accuracy (AUCSUVmax 94.0%; AUCADCmean/min/dark 91.6% / 90.1% / 92.5%). However, non-inferiority could not be demonstrated for any of the three ADC parameters (lower limits of the confidence intervals of the difference between the AUC of ADCmean/min/dark and SUVmax -12.9% / -14.5% / -11.6%). Inter-rater reliability was excellent for both imaging techniques (Krippendorff's alpha all > 0.94).

CONCLUSIONS

Both PET/CT-derived SUVmax and MRI-derived ADC allow sensitive and non-invasive differentiation of benign and (pre)-malignant peripheral nerve sheath tumours. Nevertheless, DW-MRI cannot be considered as non-inferior to F-18-FDG-PET/CT in this prospective single-centre study.

Perioperative Observations and Outcome in Surgical Treatment of Malignant Peripheral Nerve Sheath Tumors

BACKGROUND/OBJECTIVES

This retrospective observational study aimed to investigate the perioperative outcome in Malignant Peripheral Nerve Sheath Tumors (MPNSTs) with and without relation to Neurofibromatosis Type 1 (NF1) and to detect possible influencing factors.

METHODS

Clinical reports, histopathological evaluations, imaging, and treatment characteristics were reviewed in 35 operated MPNSTs in 33 patients. Possible predictive valuables included disease type, preoperative tumor volume, SUV and MIB-1 proliferation index, resection margins, the presence of metastasis, and whether radio-/chemotherapy was received.

RESULTS

Patients with NF1 were younger (mean age: 29 ± 13, 8-54 years) than sporadic cases (mean age: 45 ± 13, 24-67 years) and exhibited significantly larger preoperative tumor volumes (mean 299 vs. 18 cm3, p = 0.048). Most tumors were located in the facial/cervical/neck area (34%, n = 12), followed by the trunk (31%, n = 11), lower extremity (17%, n = 6), upper extremity (14%, n = 5), and intraspinal area (3%, n = 1). NF1-associated MPNSTs appeared predominantly on the trunk (39%) and sporadically in the facial/cervical/neck area (50%). Complete resection was possible in 66% and an improvement in or stability of function was achieved in most cases (motor 69%, sensory 74%), as well as a decrease in pain intensity (63%). NF1-associated MPNSTs exhibited more severe pain scores (median VRS scale 2, p = 0.002) compared to sporadic tumors (median VRS scale 0.5). Sporadic MPNSTs located at the head/facial/brachial plexus and upper extremities exhibited better preoperative functions compared to those on the lower extremities. In 12 cases with available [18F]FDG PET, the mean preoperative SUV (9.8 ± 7.2) positively correlated with the mean maximum MIB-1 index (34 ± 26%, p = 0.005) and the mean preoperative tumor volume (474.7 ± 68.6 cm3, p = 0.047). The overall survival (OS) was significantly longer in tumors with higher resection extents (R0, p = 0.01) and without accompanying metastasis (p = 0.046), and tended to be longer, but not significantly so, in sporadic MPNSTs. In six and seven tumors, with R1/R2 resection margins and present metastasis, respectively, solid or combined neo-/adjuvant radio-/chemotherapy led to a significantly shorter OS (p = 0.014).

CONCLUSIONS

NF1-associated MPNSTs have larger tumor volumes, higher SUVs and MIB-1 proliferation indices, and a shorter overall survival period. Nevertheless, surgery can improve symptoms, particularly medication-resistant pain, and should also be considered in advanced disease for symptom control/improvement.

Whole-Body Positron Emission Tomography with 18F-Fluorodeoxyglucose/Magnetic Resonance Imaging as a Screening Tool for the Detection of Malignant Transformation in Individuals with Neurofibromatosis Type 1

Malignant peripheral nerve sheath tumors (MPNSTs) are the leading cause of death in patients with neurofibromatosis type 1. They can result from premalignant neurofibromas, including neurofibromas with atypia and atypical neurofibromatous neoplasms of uncertain biologic potential. Some phenotypic characteristics have been described as associated with their development. The aim of this study was to outline our use of whole-body positron emission tomography with 18F-fluorodeoxyglucose/magnetic resonance imaging in adults with neurofibromatosis type 1, especially in the screening of asymptomatic individuals with a higher risk of developing an MPNST, and to study its impact on neurofibroma classification (malignant vs premalignant) and MPNST staging over time. Individuals with neurofibromatosis type 1 who underwent a positron emission tomography with 18F-fluorodeoxyglucose/magnetic resonance imaging between 2017 and 2021 were included, analyzing separately the screened population. Maximum standard uptake value and diffusion-weighted imaging were assessed. Biopsy/surgery confirmed the diagnosis. In all, 345 positron emission tomography with 18F-fluorodeoxyglucose/magnetic resonance imaging were performed in 241 patients, including 149 asymptomatic (62%) but at-risk patients. Eight MPNSTs in 8 screened individuals (5%), 6 neurofibromas with atypia in 4 individuals (3%), and 29 atypical neurofibromatous neoplasms of uncertain biologic potential in 23 individuals (15%) were diagnosed. Over time, the proportion of grade 3 MPNST and the malignant/premalignant ratio in screened individuals significantly decreased (P = .03 and P < .001, respectively). This study emphasizes the diagnostic and screening performances of whole-body positron emission tomography with 18F-fluorodeoxyglucose/magnetic resonance imaging in adults with neurofibromatosis type 1.

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.

Direct comparison of the diagnostic accuracy of 2-[18F]-fluoro-2-deoxy-d-glucose PET/CT and MRI for the differentiation of malignant peripheral nerve sheath tumour in neurofibromatosis type I: a meta-analysis

AIM

To compare the diagnostic test of integrated 2-[18F]-fluoro-2-deoxy-d-glucose positron-emission tomography/computed tomography (FDG PET/CT) with that of magnetic resonance imaging (MRI) for the differentiation of malignant peripheral nerve sheath tumours (MPNSTs) in neurofibromatosis type 1 (NF1) patients.

MATERIALS AND METHODS

A systematic search was performed in PubMed and EMBASE (last updated in 30 November 2022). Studies investigating the performance of FDG PET/CT and MRI for differentiation of MPNSTs were eligible for inclusion. Only studies reporting a direct comparison between these imaging methods were considered to establish precise summary estimates in the same setting of patients.

RESULTS

The pooled estimate of sensitivity of FDG PET/CT was 0.99 and a pooled specificity of 0.53. The pooled estimate of sensitivity of MRI was 0.85 and a pooled specificity of 0.85.

CONCLUSION

Analysis of the available studies indicated that FDG PET/CT and MRI had similar diagnostic performances for differentiation of MPNSTs in patients with NF1; however, either technique can be a complement to the other rather than being used singly.

Tips and Tricks in Thoracic Radiology for Beginners: A Findings-Based Approach

This review has the purpose of illustrating schematically and comprehensively the key concepts for the beginner who approaches chest radiology for the first time. The approach to thoracic imaging may be challenging for the beginner due to the wide spectrum of diseases, their overlap, and the complexity of radiological findings. The first step consists of the proper assessment of the basic imaging findings. This review is divided into three main districts (mediastinum, pleura, focal and diffuse diseases of the lung parenchyma): the main findings will be discussed in a clinical scenario. Radiological tips and tricks, and relative clinical background, will be provided to orient the beginner toward the differential diagnoses of the main thoracic diseases.

Whole body imaging in musculoskeletal oncology: when, why, and how

The use of whole-body imaging has become increasingly popular in oncology due to the possibility of evaluating total tumor burden with a single imaging study. This is particularly helpful in cases of widespread disease where dedicated regional imaging would make the evaluation more expensive, time consuming, and prone to more risks. Different techniques can be used, including whole-body MRI, whole-body CT, and PET-CT. Common indications include surveillance of cancer predisposing syndromes, evaluation of osseous metastases and clonal plasma cell disorders such as multiple myeloma, and evaluation of soft tissue lesions, including peripheral nerve sheath tumors. This review focuses on advanced whole-body imaging techniques and their main uses in musculoskeletal oncology.

A worldwide bibliometric analysis of malignant peripheral nerve sheath tumors from 2000 to 2022

Background

Currently, malignant peripheral nerve sheath tumors (MPNST) are the subject of intense research interest. However, bibliometric studies have not been conducted in this field. The purpose of the study was to identify historical trends and presents a bibliometric analysis of the MPNST literature from 2000 to 2022.

Methods

For the bibliometric analysis, publications were retrieved from the Web of Science database based on the following search terms: [TI = (MPNST) OR TI= (malignant peripheral nerve sheath tumors) AND PY = (2000-2022)]. The following information was collected for each document: the publication trends and geographical distribution, important authors and collaboration, keyword distribution and evaluation, most popular journals, and most influential articles.

Results

We included 1400 documents for bibliometric analysis, covering five categories: 824 articles, 17 proceedings papers, 68 letters, 402 meeting abstracts, and 89 reviews. Corrections, editorials, book chapters, data papers, publications with expressed concerns, and retractions were excluded from our research.

Conclusion

Since 2000, the number of publications on MPNST has continuously increased. Among all countries that contributed to the MPNST research, the USA, Japan, and China were the three most productive countries. The journal Modern Pathology has the most publications on MPNST, while those in the Cancer Research journal were the most frequently cited. The University of Texas MD Anderson Cancer Center may be a good partner to collaborate with. Recent research trends in MPNST have focused on tumorigenesis, clinical management, and predictive biomarkers.

Diagnostic value of 18F-FDG PET-CT in detecting malignant peripheral nerve sheath tumors among adult and pediatric neurofibromatosis type 1 patients

Purpose

Detecting malignant peripheral nerve sheath tumors (MPNSTs) remains difficult. ¹⁸F-FDG PET-CT has been shown helpful, but ideal threshold values of semi-quantitative markers remain unclear, partially because of variation among scanners. Using EU-certified scanners diagnostic accuracy of ideal and commonly used ¹⁸F-FDG PET-CT thresholds were investigated and differences between adult and pediatric lesions were evaluated.

Methods

A retrospective cohort study was performed including patients from two hospitals with a clinical or radiological suspicion of MPNST between 2013 and 2019. Several markers were studied for ideal threshold values and differences among adults and children. A diagnostic algorithm was subsequently developed.

Results

Sixty patients were included (10 MPNSTs). Ideal threshold values were 5.8 for SUVmax (sensitivity 0.70, specificity 0.92), 5.0 for SUVpeak (sensitivity 0.70, specificity 0.97), 1.7 for TLmax (sensitivity 0.90, specificity 0.86), and 2.3 for TLmean (sensitivity 0.90, specificity 0.79). The standard TLmean threshold value of 2.0 yielded a sensitivity of 0.90 and specificity of 0.74, while the standard SUVmax threshold value of 3.5 yielded a sensitivity of 0.80 and specificity of 0.63. SUVmax and adjusted SUV for lean body mass (SUL) were lower in children, but tumor-to-liver ratios were similar in adult and pediatric lesions. Using TLmean > 2.0 or TLmean < 2.0 and SUVmax > 3.5, a sensitivity and specificity of 1.00 and 0.63 can be achieved.

Conclusion

¹⁸F-FDG PET-CT offers adequate accuracy to detect MPNSTs. SUV values in pediatric MPNSTs may be lower, but tumor-to-liver ratios are not. By combining TLmean and SUVmax values, a 100% sensitivity can be achieved with acceptable specificity.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11060-021-03936-y.

A Bayesian approach for diagnostic accuracy of malignant peripheral nerve sheath tumors: a systematic review and meta-analysis

Background

Malignant peripheral nerve sheath tumors (MPNST) carry a dismal prognosis and require early detection and complete resection. However, MPNSTs are prone to sampling errors and biopsies or resections are cumbersome and possibly damaging in benign peripheral nerve sheath tumor (BPNST). This study aimed to systematically review and quantify the diagnostic accuracy of noninvasive tests for distinguishing MPNST from BPNST.

Methods

Studies on accuracy of MRI, FDG-PET (fluorodeoxyglucose positron emission tomography), and liquid biopsies were identified in PubMed and Embase from 2000 to 2019. Pooled accuracies were calculated using Bayesian bivariate meta-analyses. Individual level-patient data were analyzed for ideal maximum standardized uptake value (SUV_max) threshold on FDG-PET.

Results

Forty-three studies were selected for qualitative synthesis including data on 1875 patients and 2939 lesions. Thirty-five studies were included for meta-analyses. For MRI, the absence of target sign showed highest sensitivity (0.99, 95% CI: 0.94-1.00); ill-defined margins (0.94, 95% CI: 0.88-0.98); and perilesional edema (0.95, 95% CI: 0.83-1.00) showed highest specificity. For FDG-PET, SUV_max and tumor-to-liver ratio show similar accuracy; sensitivity 0.94, 95% CI: 0.91-0.97 and 0.93, 95% CI: 0.87-0.97, respectively, specificity 0.81, 95% CI: 0.76-0.87 and 0.79, 95% CI: 0.70-0.86, respectively. SUV_max ≥3.5 yielded the best accuracy with a sensitivity of 0.99 (95% CI: 0.93-1.00) and specificity of 0.75 (95% CI: 0.56-0.90).

Conclusions

Biopsies may be omitted in the presence of a target sign and the absence of ill-defined margins or perilesional edema. Because of diverse radiological characteristics of MPNST, biopsies may still commonly be required. In neurofibromatosis type 1, FDG-PET scans may further reduce biopsies. Ideal SUV_max threshold is ≥3.5.

FDG PET/CT and MRI Features of Pathologically Proven Schwannomas

PURPOSE

The aim of this study was to examine the MRI and FDG PET/CT imaging features of pathologically proven schwannomas.

PATIENTS AND METHODS

This institutional review board-approved retrospective study examined biopsy-proven schwannomas that underwent FDG PET/CT and/or MRI at our institution between January 1, 2002, and April 1, 2018. PET/CT features analyzed included SUVmax, metabolic ratios, volumetric metabolic measures, presence of calcification, and pattern of FDG activity. MRI features included T1/T2 signal, enhancement pattern, margins, perilesional edema, presence of muscular denervation, and size.

RESULTS

Ninety-five biopsy-proven schwannomas were identified (40 with both PET and MRI, 35 with PET only, and 20 with MRI only), 46 females and 49 males, average age of 57.7 ± 15.3 years. The average largest dimension was 4.6 ± 2.7 cm, the average SUVmax was 5.4 ± 2.7, and lesion SUVmax/liver SUVmean was 2.2 ± 1.2. Eleven (15%) of 75 lesions had SUVmax greater than 8.1, 26/75 (35%) had SUVmax greater than 6.1, and 14/75 (19%) had lesion SUVmax/liver SUVmean greater than 3.0. On MRI, 29/53 (55%) demonstrated internal nonenhancing areas. Twenty-eight (70%) of 40 lesions with both MRI and PET demonstrated at least 1 imaging feature concerning for malignant peripheral nerve sheath tumor (irregular margins, internal nonenhancement, perilesional edema, heterogeneous FDG uptake, or SUVmax >8.1). Lesions with heterogeneous FDG activity had higher SUVmax (6.5 ± 0.5 vs 4.7 ± 0.4, P = 0.0031) and more frequent internal nonenhancement on MRI (P = 0.0218).

CONCLUSIONS

Schwannomas may be large, be intensely FDG avid, and demonstrate significant heterogeneity, features typically associated with malignant peripheral nerve sheath tumors. A significant proportion exhibit FDG activity above cutoff levels previously thought useful in differentiating malignant from benign peripheral nerve sheath tumors.

FDG PET/CT of an Advanced Case of Malignant Nerve Sheath Tumor of Pleura

ABSTRACT

We present a rare case of malignant nerve sheath tumor of pleura referred for the evaluation of metastases and local invasion. FDG PET/CT demonstrated a hypermetabolic tumoral lesion extensively involving the right pleura with no involvement of mediastinal structures or pulmonary parenchyma and no clear evidence of distant metastasis. Malignant nerve sheath tumor of pleura is an extremely rare entity, and FDG PET/CT is valuable in demonstrating the extent of disease and can have potential role for postsurgical as well as postchemotherapy assessment of possible residual disease.

Imaging of the Posterior/Paravertebral Mediastinum

A wide variety of abnormalities may be encountered in the paravertebral mediastinum, ranging from congenital lesions to malignant neoplasms. A combination of localizing mediastinal masses to the paravertebral compartment, characterizing them with cross-sectional imaging techniques, and correlating the imaging findings with demographics and other clinical history typically enables the development of a focused differential diagnosis. Radiologists must be familiar with these concepts in order to help guide subsequent imaging and/or intervention and, when appropriate, treatment planning for neoplasms and other abnormalities.

Genetic basis of neurofibromatosis type 1 and related conditions, including mosaicism

INTRODUCTION

Neurofibromatosis type 1 (NF1) is a frequent autosomal dominant disorder characterised by café-au-lait maculae (CALM), skinfold freckling, iris Lisch nodules and benign peripheral nerve sheath tumours (neurofibromas).

MECHANISM

The NF1 gene is a tumour suppressor gene and NF1 individuals have an increased risk for a long list of tumours, all resulting from a second hit in the normal copy of the NF1 gene. Remarkably, some non-tumour phenotypes such as CALM and pseudarthrosis are also caused by a "second hit". Germline mutations inactivating the NF1 gene show a large variability in genetic mechanisms ranging from single-nucleotide substitutions and somatic mosaicism to large deletions affecting neighbouring genes. Molecular confirmation of the clinical diagnosis is becoming increasingly more important to differentiate NF1 from other syndromes such as Legius syndrome, to investigate genotype-phenotype correlations relevant in 10% of cases and to detect somatic mosaicism.

SURVEILLANCE AND THERAPY

Some degree of learning difficulties, attention deficit and social problems are observed in most children and affect quality of life. There is a large individual variability in complications and the evolution of the disease is difficult to predict. Specialised outpatient clinics for children have been widely established and are important for surveillance and guidance. Regular surveillance is also important for adolescents and adults because many tumour complications can be detected by whole-body MRI and treated even before symptoms develop and irreversible damage occurs. Recent data on nodular plexiform neurofibromas with continued growth in adolescents and young adults show that many of these tumours are premalignant lesions called atypical neurofibromatous neoplasm of uncertain biological potential (ANNUBP). Specific surveillance and timely local resection of these benign peripheral nerve sheath tumours might be important to prevent malignant degeneration. In the last years, targeted therapy with MEK inhibitors has shown promise to treat unresectable and symptomatic plexiform neurofibromas. Many more challenges remain to find the best way to monitor children and adults for potential complications and to find a satisfying cure for many complications in this disorder.

Role of 18F-FDG PET/computed tomography in prognostication and management of malignant peripheral nerve sheath tumors

AIM

Malignant peripheral nerve sheath tumors (MPNSTs) are rare tumors arising from a peripheral nerve or in extraneural soft tissue which shows high metastatic potential and poor prognosis. They can arise de-novo or through malignant transformation in neurofibromatosis (NF-1). The purpose of our study is to evaluate potential role of fluorodeoxyglucose (FDG) PET/computed tomography (CT) in prognostication and management of MPNSTs.

MATERIALS AND METHODS

We have performed a retrospective analysis in patients of MPNSTs who underwent F-FDG PET/CT imaging for staging and restaging. Standardized uptake values (SUVmax and SUVmean) and texture parameters (calculated using radiomics package version 0.1.3) were measured for primary/recurrent lesions and were compared between two groups based on presence of event (recurrence/progression). Student t-test was applied for comparative analyses using the SPSS software package (version 23.0; IBM), with a significance level of 0.05.

RESULTS

Thirty patients (17 male, 13 female; mean age 42.7 ± 15.66 years) were included, who underwent F-FDG PET/CT for staging (n = 10) and restaging (n = 20). Change in management was observed in four patients at baseline and in three patients in follow-up imaging for response assessment, who had progressive disease which prompted treatment intensification. SUVmax of primary/recurrent lesion showed correlation with histopathologic grade (r = 0.712, P = 0.034). Textural analysis showed more heterogeneity in lesions in the high-risk group with recurrence and progression.

CONCLUSION

F-FDG PET/CT can be used for staging and restaging in MPNSTs leading to change in management. Texture analysis and quantitative F-FDG PET/CT parameters can help in prognostication at both baseline and relapse.

Neurofibromatosis 1 French national guidelines based on an extensive literature review since 1966

Neurofibromatosis type 1 is a relatively common genetic disease, with a prevalence ranging between 1/3000 and 1/6000 people worldwide. The disease affects multiple systems with cutaneous, neurologic, and orthopedic as major manifestations which lead to significant morbidity or mortality. Indeed, NF1 patients are at an increased risk of malignancy and have a life expectancy about 10-15 years shorter than the general population. The mainstay of management of NF1 is a patient-centered longitudinal care with age-specific monitoring of clinical manifestations, aiming at the early recognition and symptomatic treatment of complications as they occur. Protocole national de diagnostic et de soins (PNDS) are mandatory French clinical practice guidelines for rare diseases required by the French national plan for rare diseases. Their purpose is to provide health care professionals with guidance regarding the optimal diagnostic and therapeutic management of patients affected with a rare disease; and thus, harmonizing their management nationwide. PNDS are usually developed through a critical literature review and a multidisciplinary expert consensus. The purpose of this article is to present the French guidelines on NF1, making them even more available to the international medical community. We further dwelled on the emerging new evidence that might have therapeutic potential or a strong impact on NF1 management in the coming feature. Given the complexity of the disease, the management of children and adults with NF1 entails the full complement healthcare providers and communication among the various specialties.

Current status and recommendations for imaging in neurofibromatosis type 1, neurofibromatosis type 2, and schwannomatosis

Neurofibromatosis type 1 (NF1), neurofibromatosis type 2 (NF2), and schwannomatosis (SWN) are three clinically distinct tumor predisposition syndromes with a shared tendency to develop peripheral and central nervous system neoplasms. Disease expression and complications of NF1, NF2, and SWN are highly variable, necessitating a multidisciplinary approach to care in order to optimize outcomes. This review will discuss the imaging appearance of NF1, NF2, and SWN and highlight the important role that imaging plays in informing management decisions in people with tumors associated with these syndromes. Recent technological advances, including the role of both whole-body and localized imaging strategies, routine anatomic and advanced magnetic resonance (MR) imaging sequences such as diffusion-weighted imaging (DWI) with quantitative apparent diffusion coefficient (ADC) mapping, and metabolic imaging techniques (MR spectroscopy and positron emission testing) are discussed in the context of the diagnosis and management of people with NF1, NF2, and SWN based on the most up-to-date clinical imaging studies.

Treatment of malignant peripheral nerve sheath tumors in pediatric NF1 disease

BACKGROUND

Malignant peripheral nerve sheath tumors (MPNSTs) are rare yet highly aggressive soft tissue sarcomas. Children with neurofibromatosis type 1 (NF1) have a 10% lifetime risk for development of MPNST. Prognosis remains poor and survival seems worse for NF1 patients.

METHODS

This narrative review highlights current practices and pitfalls in the management of MPNST in pediatric NF1 patients.

RESULTS

Preoperative diagnostics can be challenging, but PET scans have shown to be useful tools. More recently, functional MRI holds promise as well. Surgery remains the mainstay treatment for these patients, but careful planning is needed to minimize postoperative morbidity. Functional reconstructions can play a role in improving functional status. Radiotherapy can be administered to enhance local control in selected cases, but care should be taken to minimize radiation effects as well as reduce the risk of secondary malignancies. The exact role of chemotherapy has yet to be determined. Reports on the efficacy of chemotherapy vary as some report lower effects in NF1 populations. Promisingly, survival seems to ameliorate in the last few decades and response rates of chemotherapy may increase in NF1 populations when administering it as part of standard of care. However, in metastasized disease, response rates remain poor. New systemic therapies are therefore desperately warranted and multiple trials are currently investigating the role of drugs. Targeted drugs are nevertheless not yet included in first line treatment.

CONCLUSION

Both research and clinical efforts benefit from multidisciplinary approaches with international collaborations in this rare malignancy.

Imaging biomarkers for malignant peripheral nerve sheath tumors in neurofibromatosis type 1

OBJECTIVE

To determine the utility of quantitative metrics obtained from fMRI using diffusion-weighted imaging (DWI)/apparent diffusion coefficient (ADC) mapping compared with metabolic (¹⁸F-fluorodeoxyglucose [FDG]-PET/CT) imaging in patients with neurofibromatosis type 1 (NF1) for the characterization of peripheral nerve sheath tumors (PNSTs) as benign or malignant.

METHODS

This Institutional Review Board-approved, Health Insurance Portability and Accountability Act-compliant study retrospectively reviewed imaging of 55 PNSTs in 21 patients with NF1. Imaging included anatomic (unenhanced T1, fluid-sensitive, contrast-enhanced T1-weighted), functional DWI (b = 50, 400, 800 s/mm²) and ADC mapping, magnetic resonance sequences, and FDG-PET/CT imaging. Anatomic (size), functional (minimum ADC values), and metabolic (maximum standardized uptake values [SUVmax]) imaging characteristics were recorded. ADC values were correlated with SUVmax. With histologic correlation for all malignant PNSTs (MPNSTs) or clinical or imaging stability (>12 months) for benign lesions used as reference standards, diagnostic accuracy was calculated.

RESULTS

Of 55 PNSTs, there were 19 (35%) malignant and 36 (65%) benign PNSTs. Benign PNSTs were overall smaller than MPNSTs (largest diameter 4.3 ± 1.3 vs 8.2 ± 3.3 cm, respectively, p = 0.014). Benign PNSTs had higher ADCmin (×10^-3 mm²/s) than MPNSTs (1.6 ± 0.4 vs 0.6 ± 0.2, respectively, p < 0.0001) and lower SUVmax than MPNSTs (3.2 ± 1.8 vs 8 ± 3.9, p < 0.0001, respectively). ADCmin correlated inversely with SUVmax (correlation coefficient r = -0.0.58, p < 0.0001). Maintaining a sensitivity of 100% with threshold values of ADCmin ≤1 or SUVmax >3.2, DWI yielded a specificity of 94% while FDG-PET/CT offered a specificity of 83%.

CONCLUSIONS

Both quantitative metabolic imaging and functional imaging offer high sensitivity for the characterization of PNSTs in NF1; however, DWI/ADC mapping offers increased specificity and may be a more useful modality.

CLASSIFICATION OF EVIDENCE

This study provides Class II evidence that for patients with NF1, MRI using DWI/ADC mapping accurately distinguishes malignant and benign PNSTs.

Diagnostic Imaging and Management of Common Intra-articular and Peri-articular Soft Tissue Tumors and Tumorlike Conditions of the Knee

Intra-articular (IA) and peri-articular (PA) tumors of the knee are frequently encountered by orthopaedic surgeons. Nonetheless, due to the possibility of great morbidity and potential mortality, it is important to recognize and differentiate between benign and malignant lesions in a timely manner. Therefore, the purpose of this article is to provide a concise, practical, and updated review of commonly encountered IA and PA tumors including intratendinous gout, synovial chondromatosis, schwannoma, pigmented villonodular synovitis, and synovial sarcoma, and a detailed description of differentiating features to include various imaging modalities.

Can we differentiate malignant peripheral nerve sheath tumor from benign neurofibroma without invasive sampling

One of the most important benign tumors in neurofibromatosis type 1 (NF1) is plexiform neurofibroma, and there is a risk of developing malignant peripheral nerve sheath tumor (MPNST) throughout life approximately 10%. However lesion characterization by anatomical imaging methods are not possible. Because of that most of cases goes to biopsy. Using of fluorodeoxyglucose-positron emission tomography/computed tomography (FDG-PET/CT) for lesion characterization can be helpful in NF1 patients. We aimed to present an example of the efficacy of FDG-PET/CT in distinguishing benign neurofibroma from MPNST. A 6-year-old male patient who had NF1 admitted to emergency service due to high fever. Acute upper respiratory tract infection was diagnosed; antipyretic and abundant fluid intake was suggested. When high fever continued, the patient referred to our hospital on detection of axillary lymphadenopathy. Leukocytosis was detected in patient's blood count. Sedimentation was 54 mm/h, C-reactive protein 166 g/L, and lactate dehydrogenase 276U/L. Blood and throat cultures did not show pathogenic bacteria. In serological tests, VZV-IgG, EBV-VCA-IgG, and CMV-IgG were avidite positive; Hepatitis B Ag, Anti-HIV, Anti-HAV IgG and IgM, Anti-HCV, EBV-VCA IgM, and VZV-IgM were negative. Based on these results, cervical and thoracic contrast-enhanced computed tomography was performed on preliminary diagnosis of MPNST. Solid lesions with rounded margins, large one being 49 mm in size, that extend from superior mediastinum to posterior mediastinum, left axillary region, and left part of neck were detected, and they were surrounding the vascular structures. Since neurofibroma, MPNST, and lymphoma could not be distinguished, patient referred to FDG-PET/CT scanning. In FDG-PET/CT, highest lesion maximum standardized uptake value (SUV_max) was 1.5; SUV_max lesion/SUV_max liver 1.0, and SUV_max/ SUV mean liver 1.5. Biopsy from mediastinal and axillary region did not have LN structure and was positive for S-100 immunostaining, and patient was diagnosed as benign neurofibroma. We believe that there is no need for biopsy in lesions considered benign based on FDG-PET/CT parameters.

PET in the Diagnostic Management of Soft Tissue Sarcomas of Musculoskeletal Origin

Soft tissue sarcomas (STSs) account for less than 1% of adult solid tumors and about 7% of pediatric malignancies, causing 2% of cancer-related deaths. With the advent of PET-computed tomography (CT), the value of (18) fluorine-2-fluoro-2-deoxy-d-glucose (FDG) PET imaging to improve the management of STSs has been explored. FDG PET imaging has been found useful in restaging and treatment response assessment. This article reviews current knowledge and application of FDG PET-CT in initial diagnosis, staging, restaging, treatment response monitoring, and prognosis, with a brief overview of the most common histologic subtypes of STS.

Head and Neck Sarcomas: A Review of Clinical and Imaging Findings Based on the 2013 World Health Organization Classification

OBJECTIVE

Head and neck sarcomas are a complex, heterogeneous group of tumors that present a diagnostic challenge to radiologists because they have many overlapping imaging features. The purpose of this article is to review the imaging and clinical features and highlight distinguishing features of head and neck sarcomas.

CONCLUSION

An understanding of characteristic imaging and clinical features of head and neck sarcomas is important for the radiologist to narrow the differential diagnosis and help guide management.

Evaluation of the most commonly used (semi-)quantitative parameters of 18F-FDG PET/CT to detect malignant transformation of neurofibromas in neurofibromatosis type 1

In patients with neurofibromatosis type 1, transformation of neurofibromas into a malignant peripheral nerve sheath tumor (MPNST) is a severe complication of the disease. Fluorine-18-fluorodeoxyglucose PET/computed tomography (PET/CT) is a viable option for detecting malignant tumors in neurofibromatosis type 1 patients. The aim of this review was to assess the diagnostic performance of the most frequently used parameters of PET/CT in detecting MPNST. An extensive computer search was performed using the Cochrane Library, Pubmed, and Medline/Embase databases. Two reviewers independently extracted data of relevant studies and assessed the methodological quality (QUADAS-2). The diagnostic performance of PET/CT parameters in individual studies was determined by calculating a diagnostic odds ratio (DOR) using the absolute numbers of true-positive, true-negative, false-positive, and false-negative test results. A total of eight studies were included, of which three evaluated the standardized uptake value as a diagnostic parameter, two assessed the tumor-to-liver (T/L) ratio, and three articles described both parameters. The cut-off values for maximum standardized uptake value (SUVmax) ranged from 3.2 to 4.5; for the T/L ratio, the cut-off values were between 1.0 and 4.3. The sensitivity and specificity ranged from 90 to 100% and from 80 to 100%, respectively (SUVmax). T/L ratios were associated with 92-100% sensitivity and 72-94% specificity. The corresponding DORs ranged from 57 to 145 (SUVmax) and 35 to 655 (T/L ratio). Both the SUV and the T/L ratio are associated with high sensitivity combined with acceptable specificity in detecting MPNST. There is a tendency toward higher DORs using the T/L ratio, but the number of studies is limited.

Malignant Peripheral Nerve Sheath Tumors in Neurofibromatosis: Impact of Family History

OBJECTIVE

The main objective of this study was to determine if family history of malignant peripheral nerve sheath tumor (MPNST) increases risk of developing an MPNST in patients with neurofibromatosis-1 (NF-1).

MATERIALS AND METHODS

Individuals with NF-1 registered with the Children's Tumor Foundation's Neurofibromatosis Registry were emailed an anonymous 15-minute survey with regard to personal and family history of NF-1, MPNST, ages of onset, and symptomatology. Participation was voluntary and information was self-reported.

RESULTS

The survey was sent to 4801 registrants, 878 responded. Presence of a family history of MPNST was found to be a risk factor for the development of MPNST; 19.4% of respondents confirming a family history of MPNST developed MPNST compared with 7.5% of respondents with no family history (odds ratio, 2.975; 95% confidence interval, 1.232-7.187; P=0.021). NF-1 patients with a positive family history developed MPNST at a younger age than those with no family history (8.3% vs. 0.5% P=0.003 and 13.9% vs. 2.4% P=0.003, for onset before 10 and 20, respectively). In the MPNST population with a known family history, onset prior to age 10 was significantly more prevalent (42.9% vs. 7% P=0.029).

CONCLUSIONS

These results suggest a positive family history of MPNST represents a risk factor for the development and early onset of MPNST in individuals with NF-1.

Radiomic biomarkers informative of cancerous transformation in neurofibromatosis-1 plexiform tumors

BACKGROUND

This study explores whether objective, quantitative radiomic biomarkers derived from magnetic resonance (MR), positron emission tomography (PET), and computed tomography (CT) may be useful in reliably distinguishing malignant peripheral nerve sheath tumors (MPNST) from benign plexiform neurofibromas (PN).

METHODS

A registration and segmentation pipeline was established using a cohort of NF1 patients with histopathological diagnosis of PN or MPNST, and medical imaging of the PN including MR and PET-CT. The corrected MR datasets were registered to the corresponding PET-CT via landmark-based registration. PET standard-uptake value (SUV) thresholds were used to guide segmentation of volumes of interest: MPNST-associated PET-hot regions (SUV≥3.5) and PN-associated PET-elevated regions (2.0<SUV<3.5). Quantitative imaging features were extracted from the MR, PET, and CT data and compared for statistical differences. Intensity histogram features included (mean, media, maximum, variance, full width at half maximum, entropy, kurtosis, and skewness), while image texture was quantified using Law's texture energy measures, grey-level co-occurrence matrices, and neighborhood grey-tone difference matrices.

RESULTS

For each of the 20 NF1 subjects, a total of 320 features were extracted from the image data. Feature reduction and statistical testing identified 9 independent radiomic biomarkers from the MR data (4 intensity and 5 texture) and 4 PET (2 intensity and 2 texture) were different between the PET-hot versus PET-elevated volumes of interest.

CONCLUSIONS

Our data suggests imaging features can be used to distinguish malignancy in NF1-realted tumors, which could improve MPNST risk assessment and positively impact clinical management of NF1 patients.

Analysis of intratumor heterogeneity in Neurofibromatosis type 1 plexiform neurofibromas and neurofibromas with atypical features: Correlating histological and genomic findings

Plexiform neurofibromas (PNFs) are benign peripheral nerve sheath tumors involving large nerves present in 30%-50% Neurofibromatosis type 1 (NF1) patients. Atypical neurofibromas (ANF) are distinct nodular lesions with atypical features on histology that arise from PNFs. The risk and timeline of malignant transformation in ANF is difficult to assess. A recent NIH workshop has stratified ANFs and separated a subgroup with multiple atypical features and higher risk of malignant transformation termed atypical neurofibromatous neoplasms with uncertain biological potential (ANNUBP). We performed an analysis of intratumor heterogeneity on eight PNFs to link histological and genomic findings. Tumors were homogeneous although histological and molecular heterogeneity was identified. All tumors were 2n, almost mutation-free and had a clonal NF1(-/-) origin. Two ANFs from the same patient showed atypical features on histology and deletions of CDKN2A/B. One of the ANFs exhibited different areas in which the degree of histological atypia correlated with the heterozygous or homozygous loss of the CDKN2A/B loci. CDKN2A/B deletions in different areas originated independently. Results may indicate that loss of a single CDKN2A/B copy in NF1(-/-) cells is sufficient to start ANF development and that total inactivation of both copies of CDKN2A/B is necessary to form an ANNUBP.

Cancer and Central Nervous System Tumor Surveillance in Pediatric Neurofibromatosis 1

Although the neurofibromatoses consist of at least three autosomal dominantly inherited disorders, neurofibromatosis 1 (NF1), neurofibromatosis 2 (NF2), and schwannomatosis, NF1 represents a multisystem pleiotropic condition very different from the other two. NF1 is a genetic syndrome first manifesting in childhood; affecting multiple organs, childhood development, and neurocognitive status; and presenting the clinician with often complex management decisions that require a multidisciplinary approach. Molecular genetic testing (see article for detailed discussion) is recommended to confirm NF1, particularly in children fulfilling only pigmentary features of the diagnostic criteria. Although cancer risk is not the major issue facing an individual with NF1 during childhood, the condition causes significantly increased malignancy risks compared with the general population. Specifically, NF1 is associated with highly elevated risks of juvenile myelomonocytic leukemia, rhabdomyosarcoma, and malignant peripheral nerve sheath tumor as well as substantial risks of noninvasive pilocytic astrocytoma, particularly optic pathway glioma (OPG), which represent a major management issue. Until 8 years of age, clinical assessment for OPG is advised every 6 to 12 months, but routine MRI assessment is not currently advised in asymptomatic individuals with NF1 and no signs of clinical visual pathway disturbance. Routine surveillance for other malignancies is not recommended, but clinicians and parents should be aware of the small risks (<1%) of certain specific individual malignancies (e.g., rhabdomyosarcoma). Tumors do contribute to both morbidity and mortality, especially later in life. A single whole-body MRI should be considered at transition to adulthood to assist in determining approaches to long-term follow-up. Clin Cancer Res; 23(12); e46-e53. ©2017 AACRSee all articles in the online-only CCR Pediatric Oncology Series.

Comparison of hybrid 18F-fluorodeoxyglucose positron emission tomography/magnetic resonance imaging and positron emission tomography/computed tomography for evaluation of peripheral nerve sheath tumors in patients with neurofibromatosis type 1

Rapidly enlarging, painful plexiform neurofibromas (PN) in neurofibromatosis type 1 (NF1) patients are at higher risk for harboring a malignant peripheral nerve sheath tumor (MPNST). Fludeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) has been used to support more invasive diagnostic and therapeutic interventions. However, PET/CT imparts an untoward radiation hazard to this population with tumor suppressor gene impairment. The use of FDG PET coupled with magnetic resonance imaging (MRI) rather than CT is a safer alternative but its relative diagnostic sensitivity requires verification. Ten patients (6 females, 4 males, mean age 27 years, range 8–54) with NF1 and progressive PN were accrued from our institutional NF Clinic. Indications for PET scanning included increasing pain and/or progressive disability associated with an enlarging PN on serial MRIs. Following a clinically indicated whole-body FDG PET/CT, a contemporaneous PET/MRI was obtained using residual FDG activity with an average time interval of 3–4 h FDG-avid lesions were assessed for both maximum standardized uptake value (SUVmax) from PET/CT and SUVmax from PET/MR and correlation was made between the two parameters. 26 FDG avid lesions were detected on both PET/CT and PET/MR with an accuracy of 100%. SUVmax values ranged from 1.4–10.8 for PET/CT and from 0.2-5.9 for PET/MRI. SUVmax values from both modalities demonstrated positive correlation (r = 0.45, P < 0.001). PET/MRI radiation dose was significantly lower (53.35% ± 14.37% [P = 0.006]). In conclusion, PET/MRI is a feasible alternative to PET/CT in patients with NF1 when screening for the potential occurrence of MPNST. Reduction in radiation exposure approaches 50% compared to PET/CT.

Monitoring of plexiform neurofibroma in children and adolescents with neurofibromatosis type 1 by [18 F]FDG-PET imaging. Is it of value in asymptomatic patients?

PURPOSE

About 10% of patients with neurofibromatosis type 1 (NF-1) develop malignant peripheral nerve sheath tumours (MPNST) mostly arising in plexiform neurofibroma (PN); 15% of MPNST arise in children and adolescents. 2-[¹⁸ F]fluoro-2-deoxy-d-glucose ([¹⁸ F]FDG)-PET (where PET is positron emission tomography) is a sensitive method in differentiating PN and MPNST in symptomatic patients with NF-1. This study assesses the value of [¹⁸ F]FDG-PET imaging in detecting malignant transformation in symptomatic and asymptomatic children with PN.

METHODS

Forty-one patients with NF-1 and extensive PN underwent prospective [¹⁸ F]FDG imaging from 2003 to 2014. Thirty-two of the patients were asymptomatic. PET data, together with histological results and clinical course were re-evaluated retrospectively. Maximum standardised uptake values (SUVmax) and lesion-to-liver ratio were assessed.

RESULTS

A total of 104 examinations were performed. Mean age at first PET was 13.5 years (2.6-22.6). Eight patients had at least one malignant lesion; four of these patients were asymptomatic. Two of four symptomatic patients died, while all patients with asymptomatic malignant lesions are alive. All malignant tumours could be identified by PET imaging in both symptomatic and asymptomatic patients. All lesions judged as benign by [¹⁸ F]FDG imaging and clinical judgment were either histologically benign if removed or remained clinically silent during follow-up. SUVmax of malignant and benign lesions overlapped, but no malignant lesion showed FDG uptake ≤3.15. Asymptomatic malignant lesions were detected with a sensitivity of 100%, a negative predictive value of 100% and a specificity of 45.1%.

CONCLUSION

Malignant transformation of PN also occurs in asymptomatic children and adolescents. Detection of MPNST at early stages could increase the possibility of oncologically curative resections.

Does elevated glucose metabolism correlate with higher cell density in Neurofibromatosis type 1 associated peripheral nerve sheath tumors?

PURPOSE

To investigate whether elevated glucose metabolism in neurofibroma, determined by [F18]-FDG-PET, is correlated with cell density in MRI, as expressed through the apparent diffusion coefficient.

MATERIALS AND METHODS

Patients diagnosed with neurofibromatosis type 1 and peripheral nerve sheath tumors (PNST) were enrolled in this prospective, IRB-approved study. After a single [F18]-FDG injection, patients consecutively underwent [F18]-FDG-PET/CT and [F18]-FDG-PET/MRI on the same day. Maximum and mean standardized uptake values (SUVmax, SUVmean) on [F18]-FDG-PET/CT and [F18]-FDG-PET/MRI were compared, and correlated with minimum and mean apparent diffusion coefficients (ADCmean, ADCmin).

RESULTS

A total of 12 (6 male/6 female, mean age was 16.2 ± 5.2 years) patients were prospectively included and analyzed on a per-lesion (n = 39) basis. The SUVmean of examined PNST showed a moderate negative correlation with the ADCmean (r = -.441) and ADCmin (r = -.477), which proved to be statistically significant (p = .005 and p = .002). The SUVmax of the respective lesions, however, showed a weaker negative correlation for ADCmean (r: -.311) and ADCmin (r: -.300) and did not reach statistical significance (p = .054 and p = .057). Lesion-based correlation between [F18]-FDG-PET/MRI and [F18]-FDG-PET/CT showed a moderate correlation for SUVmax (r = .353; p = .027) and a strong one for SUVmean (r = .879; p = .001)). Patient-based liver uptake (SUVmax and mean) of [F18]-FDG-PET/MRI and [F18]-FDG-PET/CT were strongly positively correlated (r = .827; p < .001 and r = .721; p < .001) but differed significantly (p < .001).

CONCLUSIONS

We found a statistically significant, negative correlation between glucose metabolism and cell density in PNST. Thus, ADCmean and ADCmin could possibly add complimentary information to the SUVmax and SUVmean and may serve as a potential determinant of malignant transformation of PNST.

The effect of post-injection 18F-FDG PET scanning time on texture analysis of peripheral nerve sheath tumours in neurofibromatosis-1

BACKGROUND

Texture features are being increasingly evaluated in 18F-fluorodeoxyglucose positron emission tomography (18F-FDG PET) as adjunctive imaging biomarkers in a number of different cancers. Whilst studies have reported repeatability between scans, there have been no studies that have specifically investigated the effect that the time of acquisition post-injection of 18F-FDG has on texture features. The aim of this study was to investigate if texture features change between scans performed at different time points post-injection.

RESULTS

Fifty-four patients (30 male, 24 female, mean age 35.1 years) with neurofibromatosis-1 and suspected malignant transformation of a neurofibroma underwent 18F-FDG PET/computed tomography (CT) scans at 101.5 ± 15.0 and 251.7 ± 18.4 min post-injection of 350 MBq 18F-FDG to a standard clinical protocol. Following tumour segmentation on both early and late scans, first- (n = 37), second- (n = 25) and high-order (n = 31) statistical features, as well as fractal texture features (n = 6), were calculated and a comparison was made between the early and late scans for each feature. Of the 54 tumours, 30 were benign and 24 malignant on histological analysis or on clinical follow-up for at least 5 years. Overall, 25/37 first-order, 9/25 second-order, 13/31 high-order and 3/6 fractal features changed significantly (p < 0.05) between early and late scans. The corresponding proportions for the 30 benign tumours alone were 22/37, 7/25, 8/31 and 2/6 and for the 24 malignant tumours, 11/37, 6/25, 8/31 and 0/6, respectively.

CONCLUSIONS

Several texture features change with time post-injection of 18F-FDG. Thus, when comparing texture features in intra- and inter-patient studies, it is essential that scans are obtained at a consistent time post-injection of 18F-FDG.

Malignant peripheral nerve sheath tumours of the pericardium in a patient with Neurofibromatosis type 1: The diagnostic value of 18F-FDG PET-CT and I-123 MIBG SPECT-CT

A 25 year old female with known neurofibromatosis type 1 with a large anterior mediastinal mass was investigated. F18-FDG PET-CT revealed a radiotracer avid anterior mediastinal mass with SUVmax of 4.3 and demonstrating a hypoactive center. The Iodine-123 MIBG SPECT-CT study performed subsequently did not demonstrate any uptake, thereby excluding for the most part the diagnoses of paraganglioma or neuroblastoma. At final pathology, a malignant peripheral nerve sheath tumour (MPNST) of the pericardium with areas of chondrosarcomatous and angiosarcomatous differentiation was diagnosed.

[Simultaneous whole-body PET-MRI in pediatric oncology : More than just reducing radiation?]

Diagnostic imaging plays an essential role in pediatric oncology with regard to diagnosis, therapy-planning, and the follow-up of solid tumors. The current imaging standard in pediatric oncology includes a variety of radiological and nuclear medicine imaging modalities depending on the specific tumor entity. The introduction of combined simultaneous positron emission tomography (PET) and magnetic resonance imaging (MRI) has opened up new diagnostic options in pediatric oncology. This novel modality combines the excellent anatomical accuracy of MRI with the metabolic information of PET. In initial clinical studies, the technical feasibility and possible diagnostic advantages of combined PET-MRI have been in comparison with alternative imaging techniques. It was shown that a reduction in radiation exposure of up to 70 % is achievable compared with PET-CT. Furthermore, it has been shown that the number of imaging studies necessary can be markedly reduced using combined PET-MRI. Owing to its limited availability, combined PET-MRI is currently not used as a routine procedure. However, this new modality has the potential to become the imaging reference standard in pediatric oncology in the future. This review article summarizes the central aspects of pediatric oncological PET-MRI based on existing literature. Typical pediatric oncological PET-MRI cases are also presented.

Characterisation of malignant peripheral nerve sheath tumours in neurofibromatosis-1 using heterogeneity analysis of 18F-FDG PET

PURPOSE

Measurement of heterogeneity in 18F-fluorodeoxyglucose (18F-FDG) positron emission tomography (PET) images is reported to improve tumour phenotyping and response assessment in a number of cancers. We aimed to determine whether measurements of 18F-FDG heterogeneity could improve differentiation of benign symptomatic neurofibromas from malignant peripheral nerve sheath tumours (MPNSTs).

METHODS

18F-FDG PET data from a cohort of 54 patients (24 female, 30 male, mean age 35.1 years) with neurofibromatosis-1 (NF1), and clinically suspected malignant transformation of neurofibromas into MPNSTs, were included. Scans were performed to a standard clinical protocol at 1.5 and 4 h post-injection. Six first-order [including three standardised uptake value (SUV) parameters], four second-order (derived from grey-level co-occurrence matrices) and four high-order (derived from neighbourhood grey-tone difference matrices) statistical features were calculated from tumour volumes of interest. Each patient had histological verification or at least 5 years clinical follow-up as the reference standard with regards to the characterisation of tumours as benign (n = 30) or malignant (n = 24).

RESULTS

There was a significant difference between benign and malignant tumours for all six first-order parameters (at 1.5 and 4 h; p < 0.0001), for second-order entropy (only at 4 h) and for all high-order features (at 1.5 h and 4 h, except contrast at 4 h; p < 0.0001-0.047). Similarly, the area under the receiver operating characteristic curves was high (0.669-0.997, p < 0.05) for the same features as well as 1.5-h second-order entropy. No first-, second- or high-order feature performed better than maximum SUV (SUVmax) at differentiating benign from malignant tumours.

CONCLUSIONS

18F-FDG uptake in MPNSTs is higher than benign symptomatic neurofibromas, as defined by SUV parameters, and more heterogeneous, as defined by first- and high-order heterogeneity parameters. However, heterogeneity analysis does not improve on SUVmax discriminative performance.

Management of peripheral nerve sheath tumors: 17 years of experience at Toronto Western Hospital

OBJECTIVE A surgical series of 201 benign and malignant peripheral nerve sheath tumors (PNSTs) was assessed to characterize the anatomical and clinical presentation of tumors and identify predictors of neurological outcome, recurrence, and extent of resection. METHODS All surgically treated PNSTs from the Division of Neurosurgery at Toronto Western Hospital from 1993 to 2010 were reviewed retrospectively. Data were collected on patient demographics, clinical presentation, surgical technique, extent of resection, postoperative neurological outcomes, and recurrence. RESULTS One hundred seventy-five patients with 201 tumors had adequate follow-up for analysis. There were 182 benign and 19 malignant PNSTs. Of the benign lesions, 133 were schwannomas, 21 of which were associated with a diagnosis of schwannomatosis. There were 49 neurofibromas, and 26 were associated with neurofibromatosis Type 1 (NF1). Patients presenting with schwannomas were significantly older than those with neurofibromas. Schwannomas were more readily resected than neurofibromas, with the extent of resection of the former influenced by tumor location. Patients with benign PNSTs typically presented with a painful mass and less frequently with motor deficits. The likelihood of worsened postoperative motor function was decreased in patients with fully resected tumors or preoperative deficits. Recurrence of schwannomas and neurofibromas were seen more frequently in patients diagnosed with NF3 and NF1, respectively. Subtotal resection was associated with the increased recurrence of all benign lesions. CONCLUSIONS Outcomes following resection of benign PNSTs depend on tumor histopathology, tumor location, and genetic predisposition syndrome. Gross-total resection should be attempted for benign lesions where possible. The management of malignant PNSTs remains challenging, requiring a multimodal approach.

Neurofibromatosis type 1

Neurofibromatosis type 1 is a complex autosomal dominant disorder caused by germline mutations in the NF1 tumour suppressor gene. Nearly all individuals with neurofibromatosis type 1 develop pigmentary lesions (café-au-lait macules, skinfold freckling and Lisch nodules) and dermal neurofibromas. Some individuals develop skeletal abnormalities (scoliosis, tibial pseudarthrosis and orbital dysplasia), brain tumours (optic pathway gliomas and glioblastoma), peripheral nerve tumours (spinal neurofibromas, plexiform neurofibromas and malignant peripheral nerve sheath tumours), learning disabilities, attention deficits, and social and behavioural problems, which can negatively affect quality of life. With the identification of NF1 and the generation of accurate preclinical mouse strains that model some of these clinical features, therapies that target the underlying molecular and cellular pathophysiology for neurofibromatosis type 1 are becoming available. Although no single treatment exists, current clinical management strategies include early detection of disease phenotypes (risk assessment) and biologically targeted therapies. Similarly, new medical and behavioural interventions are emerging to improve the quality of life of patients. Although considerable progress has been made in understanding this condition, numerous challenges remain; a collaborative and interdisciplinary approach is required to manage individuals with neurofibromatosis type1 and to develop effective treatments.

ITMIG Classification of Mediastinal Compartments and Multidisciplinary Approach to Mediastinal Masses

Division of the mediastinum into specific compartments is beneficial for a number of reasons, including generation of a focused differential diagnosis for mediastinal masses identified on imaging examinations, assistance in planning for biopsies and surgical procedures, and facilitation of communication between clinicians in a multidisciplinary setting. Several classification schemes for the mediastinum have been created and used to varying degrees in clinical practice. Most radiology classifications have been based on arbitrary landmarks outlined on the lateral chest radiograph. A new scheme based on cross-sectional imaging, principally multidetector computed tomography (CT), has been developed by the International Thymic Malignancy Interest Group (ITMIG) and accepted as a new standard. This clinical division scheme defines unique prevascular, visceral, and paravertebral compartments based on boundaries delineated by specific anatomic structures at multidetector CT. This new definition plays an important role in identification and characterization of mediastinal abnormalities, which, although uncommon and encompassing a wide variety of entities, can often be diagnosed with confidence based on location and imaging features alone. In other scenarios, a diagnosis may be suggested when radiologic features are combined with specific clinical information. In this article, the authors present the new multidetector CT-based classification of mediastinal compartments introduced by ITMIG and a structured approach to imaging evaluation of mediastinal abnormalities. ^©RSNA, 2017.