Distinguishing atypical focal areas of signal intensity from probable low-grade gliomas in the posterior fossa of children with neurofibromatosis type 1 - 10/08/25

Doi : 10.1016/j.arcped.2025.05.010

Agnès Viguier ^a, Bastien Estublier ^a, Anne-Isabelle Bertozzi ^b, Marion Gambart ^b, Annick Sevely ^c, Nicolas Leboucq ^d, Pierre Antherieu ^e, François Rivier ^f, Pierre Meyer ^f, Didier Bessis ^g, Yves Chaix ^a,^h, Eloïse Baudou ^a,^h,^⁎
^a Département de neuropédiatrique et centre de réference maladie rare Neurofibromatose de type 1 de l’enfant, hôpital des enfants, CHRU Toulouse, France
^b Neuro-oncologie pédiatrique, hôpital des enfants, CHRU Toulouse, France
^c Neuro-radiologie pédiatrique, hôpital Pierre Paul Riquet, CHRU Toulouse, France
^d Neuroradiologie, hôpital Gui de Chauliac, CHRU Montpellier, France
^e Neurochirugie pédiatrique, hôpital Pierre Paul Riquet, CHRU Toulouse, France
^f Neuropédiatrie, CHRU Montpellier, PhyMedExp, CNRS, INSERM, Université de Montpellier, France
^g Département de dermatologie et centre de référence des maladies dermatologiques génétiques rares (MAGEC), hôpital Saint-Eloi, CHRU Montpellier, 80, avenur Augustin Fliche, 34295 Montpellier cedex 5, France
^h ToNIC, Toulouse NeuroImaging Center, Université de Toulouse, Inserm, UPS, France

^⁎Corresponding author at: Département de neuropédiatrique et centre de réference maladie rare Neurofibromatose de type 1 de l’enfant, hôpital des enfants, CHRU Toulouse, 330 avenue de Grande-Bretagne, 31300 Toulouse, France.Département de neuropédiatrique et centre de réference maladie rare Neurofibromatose de type 1 de l’enfanthôpital des enfantsCHRU Toulouse330 avenue de Grande-BretagneToulouse31300France

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Highlights

•	50 % of atypical posterior fossa FASI regressed over time.
•	Cystic/exophytic lesions, enhancement and sharp margins were specific for glioma.
•	Atypical radiological features are not uncommon in posterior fossa FASI.

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Abstract

Introduction

Focal areas of signal intensity (FASI) in the posterior fossa are common in children with neurofibromatosis type 1 (NF1). These can be difficult to distinguish from tumour processes when they are atypical. This study aimed to describe the initial radiological features of atypical posterior fossa FASI, depending on the clinical and radiological evolution of the lesion.

Methods

We conducted a multicentre retrospective study of NF1 children with atypical FASI in the posterior fossa. The lesions were classified according to their evolution over time: ‘non-neoplastic FASI’ if they regressed, or ‘possible neoplastic FASI’ if they remained stable or progressed.

Results

Forty-two lesions from 31 patients were analyzed. The mean follow-up period between the first and last MRI scans was 7.1 years. Twenty-one atypical FASI were classified as ‘non-neoplastic FASI’ and 21 as ‘possible neoplastic FASI’. Younger age at diagnosis, pontine location, and blurred contours were more indicative of ‘non-neoplastic FASI’ on the initial MRI, whereas symptomatic, cystic or exophytic lesions, the presence of enhancement after gadolinium injection, sharp contours, and clear mass effect were more indicative of a ‘possible neoplastic FASI’. Unexpectedly, abnormal initial spectroscopy and small mass effect could be found in ‘non-neoplastic FASI’, as could the presence of hypointensity on T1-weighted images.

Conclusion

This study is important in specifying which posterior fossa hyperintensities on T2-weighted MRIs require specific clinical and radiological follow-up.

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Keywords : Neurofibromatosis type 1, Children, Unidentified bright object, Focal areas of signal intensity, MRI, Brain tumor