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Objective: Pheochromocytoma (PHEO) may occur in 0.1-5.7% of patients presenting with a neurofibromatosis type 1 (NF1). Current recommendations are to explore only symptomatic patients. The objective of the study is to evaluate the prevalence and the interest of a systematic PHEO screening in this population., Design: A prospective study in a French tertiary center including consecutive NF1 patients older than 18 years., Methods: A systematic screening combining abdominal imaging and urinary fractionated metanephrines was proposed. In case of positivity of one or both exams, (123)I-metaiodobenzylguanidine scintigraphy or [(18)F]-fluoro-dihydroxyphenylalanine PET imaging was performed. The diagnosis of secreting PHEO was retained in case of elevated urinary metanephrines associated with positive scintigraphy and non-secreting PHEO when urinary metanephrines were normal with a positive scintigraphy., Results: Between January 2014 and August 2015, 234 patients were included and 156 patients (66.7%) completed both exams. In these 156 patients, 12 PHEOs were diagnosed, representing a prevalence of 7.7%. Of these, six PHEOs were secreting, with only two symptomatic patients. The tumor size of these PHEOs were bigger than that of non-secreting PHEO (25.2 ± 6.6 vs 14 ± 6.9 mm, P = 0.0165). One lesion was bilateral. Mean metanephrine and normetanephrine levels were 3.2 ± 2.6N and 2.8 ± 1N respectively. Three patients underwent surgery. The six patients with non-secreting PHEO were asymptomatic. One of them had bilateral lesion and one underwent surgery., Conclusions: PHEO in NF1, whether or not secreting, are mostly asymptomatic. The current strategy to explore only symptomatic patients leads to an underestimation of prevalence with the risks inherent to the existence of an unrecognized PHEO., (© 2016 European Society of Endocrinology.)

Background: Malignant peripheral nerve sheath tumors (MPNST) are one of the most frequent causes of death in patients with neurofibromatosis type 1 (NF1). Early detection is crucial because complete surgical resection is the only curative treatment. It has been previously reported that an 18F-fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) image with a T/L (Tumor/Liver) SUV max ratio > 1.5 provides a high negative predictive value; however, it is not specific enough to make a NF1-related MPNST diagnosis. A formal proof of malignant transformation from a histological analysis is necessary before surgical excision because the procedure can cause mutilation. The objective of the present work was to investigate the effectiveness of and complications associated with PET/CT-guided percutaneous biopsies for an NF1-related MPNST diagnosis., Methods: PET/CT-guided percutaneous biopsy procedures performed on 26 NF1 patients with a clinical suspicion of MPNST and a suspect lesion from a PET/CT scan (T/L SUV max ratio > 1.5) were retrospectively evaluated. The localization of the suspected malignant site was determined using PET/CT. A stereotactic (ultrasonic and CT control) core biopsy technique was used with a local anesthesia., Results: The first PET/CT-guided percutaneous biopsies enabled a pathological diagnosis for all of the patients (no "inconclusive " results were obtained), and no secondary procedures were needed. Among the 26 patients, the histopathological results from the biopsy were malignant in 17 cases and benign (BPNST with atypical cells) in nine cases. No complications from the diagnostic procedure were observed. A surgical resection was performed in 18 patients (seven benign and 11 malignant biopsies), removing the fine needle biopsy scar. In addition, six locally advanced/metastatic MPNST were treated with chemo/radiotherapy, and two BPNST had no progression after a follow-up of 14 and 39 months, respectively. The PET/CT-guided percutaneous biopsy gave 25 accurate diagnoses and one false negative (BPNST with atypical cells on the biopsy and MPNST on the operated tumor), resulting in a diagnostic accuracy rate of 96%. This false negative case may be explained by the high heterogeneity of the tumor: benign areas were contiguous with the malignant ones and associated with inflammation., Conclusions: PET/CT-guided percutaneous biopsies are an effective and relatively non-traumatic procedure for diagnosis of NF1-related MPNST. It is the most reliable approach for early detection of MPNST.

Background: Malignant peripheral nerve sheath tumors (MPNSTs) are a serious complications of neurofibromatosis type 1 associated with poor prognosis and deeper lesions can be difficult to diagnose. 18-FDG PET improves the detection of malignancies. However, the criteria for malignancy, notably the SUVmax threshold, are not standardized. Therefore, the aim of the study was to evaluate a semi-quantitative index for the reproducible detection of MPNST with FDG PET., Methods: It is a multicenter retrospective study conducted between 2000 to 2012. All patients with NF1 referred for suspected MPNST underwent PET. Since SUVmax was not available until 2004 in our centers, we had to settle for the semi-quantitative method used at that time, the uptake ratio between the tumor and the normal liver (T/L ratio) with 1.5 as the cut-off for malignancy. When dedicated PET with SUVmax became available, the semi-quantitative analysis of PET images remained, along with SUVmax., Results: 113 patients with 145 tumors were included. PET assessment revealed 65 suspected lesions with T/L >1.5 and among these, 40 were MPNSTs. 80 tumors were classified as non-suspicious, and 79 were benign. The 1.5 T/L cut-off had a negative predictive value (NPV) of 98,8% and a positive predictive value of 61,5%. The positive likelihood ratio (LR) was 4,059, the negative LR was 0,032 with 97% sensitivity and 76% specificity., Conclusions: This study, which is among the largest published, confirms the utility of PET for detecting NF1-associated MPNSTs. A semi-quantitative index, the T/L ratio with a cut-off of 1.5, allowed sensitive and specific differentiation of malignant from benign tumors better than SUVmax. When T/L was <1.5, MPNSTs were ruled out with 98,8% NPV. When T/L was >1.5, there was a strong suspicion of malignancy. This semi-quantitative analytical method is as simple as SUVmax, but is more sensitive, more reproducible and non-user-dependent.