Neurofibromatosis type 1 in children: MR imaging and follow-up studies of central nervous system findings
Introduction
Neurofibromatosis type 1 (NF1) is the most prevalent neurocutaneous syndrome. The disease results from a mutation that involves the long arm of chromosome 17 [1]. It is transmitted as an autosomal dominant fashion, but around half of the cases represent new mutations. The diagnosis of NF1 is based on NIH Consensus criteria [2].
Prior to MR imaging, an optic pathway glioma was the most common neuroradiological finding [3]. MR imaging better defines the posterior extension of optic gliomas [4], and helps to differentiate optic sheath thickening from optic nerve glioma [5]. With increasing use of MR imaging in the evaluation of patients with NF1, high-signal-intensity foci seen on long repetition time (TR) spin-echo images are now considered the most frequent and characteristic intracranial lesions, occurring in about two-thirds of patients 5, 6, 7, 8, 9, 10, 11. These focal areas of increased signal intensity on long TR images predominate in the basal ganglia, cerebellum and brain stem 8, 10. Usually, these lesions do not have associated mass effect and do not enhance. Unlike the white matter foci, basal ganglia lesions may have accompanying slight mass effect and show hyperintensity on short TR images 5, 10, 12, 13.
The nature of these signal intensity alterations remains mainly unknown. In the few studies correlating MR imaging findings with pathological data, the changes were described as malformations rather than neoplastic [14]. Knowledge of their behavior in follow-up studies is important in an attempt to further characterize these lesions. There are few recorded observations concerning the evolution of these apparently age specific lesions 8, 13, 15, 16, 17.
In order to analyze the MR findings and evolutional characteristics of brain lesions, we reviewed the cranial MR findings in 89 children with an established or suspected clinical diagnosis of NF1. The follow-up studies in 45 children were also reviewed. A final diagnosis of NF1 was made in 72 patients. Since the foci of increased signal intensity on long TR images are now used as additional imaging criteria for diagnosing NF1, we will evaluate their diagnostic impact and their evolution with time in a large series of children with NF1.
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Subjects and methods
We have reviewed the cranial MR examinations of 89 consecutive paediatric patients, aged between 10 months and 14 years (mean, 7 years) with an established or suspected diagnosis of NF1. Fifty-three had an established diagnosis by the NIH Consensus criteria [2]. The other 36 patients, with suspected disease, presented with multiple large (6 or more lesions larger than 5 mm) café-au-lait spots as the only diagnostic feature. In this latter group MR imaging findings confirmed the diagnosis of NF1
Results
MR imaging abnormalities were found in 56 of 72 (78%) children with a final diagnosis of NF1 (Table 1). In the group of clinically suspected disease MR imaging findings contributed to the final diagnosis in 19 of 36 cases, making a positive diagnostic contribution in 53% of these previously unclassified children.
The most frequent cranial MR imaging findings were high-signal lesions on long TR images, predominating in the globus pallidus (72%), cerebellar white matter (57%), and brain stem
Discussion
NF1 is a multisystem disorder exhibiting a wide variety of central nervous system (CNS) manifestations. The disease is transmitted by autosomal dominant inheritance, but around 50% of cases represent new mutations [1]. Neuroradiological findings constitute an important basis in the diagnosis, influencing the clinical accuracy and the genetic councel in these patients.
MR imaging has been extensively used in the evaluation of patients with NF1. Foci of hyperintensity on long TR images, mainly
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