Updated diagnostic criteria and nomenclature for neurofibromatosis type 2 and schwannomatosis: An international consensus recommendation.

PURPOSE: Neurofibromatosis type 2 (NF2) and schwannomatosis (SWN) are genetically distinct tumor predisposition syndromes with overlapping phenotypes. We sought to update the diagnostic criteria for NF2 and SWN by incorporating recent advances in genetics, ophthalmology, neuropathology, and neuroimaging. METHODS: We used a multistep process, beginning with a Delphi method involving global disease experts and subsequently involving non-neurofibromatosis clinical experts, patients, and foundations/patient advocacy groups. RESULTS: We reached consensus on the minimal clinical and genetic criteria for diagnosing NF2 and SWN. These criteria incorporate mosaic forms of these conditions. In addition, we recommend updated nomenclature for these disorders to emphasize their phenotypic overlap and to minimize misdiagnosis with neurofibromatosis type 1. CONCLUSION: The updated criteria for NF2 and SWN incorporate clinical features and genetic testing, with a focus on using molecular data to differentiate the 2 conditions. It is likely that continued refinement of these new criteria will be necessary as investigators study the diagnostic properties of the revised criteria and identify new genes associated with SWN. In the revised nomenclature, the term "neurofibromatosis 2" has been retired to improve diagnostic specificity.

Revised diagnostic criteria for neurofibromatosis type 1 and Legius syndrome: an international consensus recommendation.

PURPOSE: By incorporating major developments in genetics, ophthalmology, dermatology, and neuroimaging, to revise the diagnostic criteria for neurofibromatosis type 1 (NF1) and to establish diagnostic criteria for Legius syndrome (LGSS). METHODS: We used a multistep process, beginning with a Delphi method involving global experts and subsequently involving non-NF experts, patients, and foundations/patient advocacy groups. RESULTS: We reached consensus on the minimal clinical and genetic criteria for diagnosing and differentiating NF1 and LGSS, which have phenotypic overlap in young patients with pigmentary findings. Criteria for the mosaic forms of these conditions are also recommended. CONCLUSION: The revised criteria for NF1 incorporate new clinical features and genetic testing, whereas the criteria for LGSS were created to differentiate the two conditions. It is likely that continued refinement of these new criteria will be necessary as investigators (1) study the diagnostic properties of the revised criteria, (2) reconsider criteria not included in this process, and (3) identify new clinical and other features of these conditions. For this reason, we propose an initiative to update periodically the diagnostic criteria for NF1 and LGSS.

First International Conference on RASopathies and Neurofibromatoses in Asia: Identification and advances of new therapeutics.

The neurofibromatoses, which include neurofibromatosis type I (NF1), neurofibromatosis type II (NF2), and schwannomatosis, are a group of syndromes characterized by tumor growth in the nervous system. The RASopathies are a group of syndromes caused by germline mutations in genes that encode components of the RAS/mitogen-activated protein kinase (MAPK) pathway. The RASopathies include NF1, Noonan syndrome, Noonan syndrome with multiple lentigines, Costello syndrome, cardio-facio-cutaneous syndrome, Legius syndrome, capillary malformation arterio-venous malformation syndrome, and SYNGAP1 autism. Due to their common underlying pathogenetic etiology, all these syndromes have significant phenotypic overlap of which one common feature include a predisposition to tumors, which may be benign or malignant. Together as a group, they represent one of the most common multiple congenital anomaly syndromes estimating to affect approximately one in 1000 individuals worldwide. The subcontinent of India represents one of the largest populations in the world, yet remains underserved from an aspect of clinical genetics services. In an effort to bridge this gap, the First International Conference on RASopathies and Neurofibromatoses in Asia: Identification and Advances of New Therapeutics was held in Kochi, Kerala, India. These proceedings chronicle this timely and topical international symposium directed at discussing the best practices and therapies for individuals with neurofibromatoses and RASopathies.

Recent developments in neurofibromatoses and RASopathies: management, diagnosis and current and future therapeutic avenues.

Neurofibromatosis type 1 (NF1) was the first RASopathy and is now one of many RASopathies that are caused by germline mutations in genes that encode components of the Ras/mitogen-activated protein kinase (MAPK) pathway. Their common underlying pathogenetic etiology causes significant overlap in phenotypic features which includes craniofacial dysmorphology, cardiac, cutaneous, musculoskeletal, GI and ocular abnormalities, and a predisposition to cancer. The proceedings from the symposium "Recent Developments in Neurofibromatoses (NF) and RASopathies: Management, Diagnosis and Current and Future Therapeutic Avenues" chronicle this timely and topical clinical translational research symposium. The overarching goal was to bring together clinicians, basic scientists, physician-scientists, advocate leaders, trainees, students and individuals with Ras pathway syndromes to discuss the most state-of-the-art basic science and clinical issues in an effort to spark collaborations directed towards the best practices and therapies for individuals with RASopathies.

Cognition in children with neurofibromatosis type 1: data from a population-based study.

AIM: This study aimed to investigate the core cognitive deficits in children with neurofibromatosis type 1 (NF1). METHOD: The study recruited 49 children with NF1 (25 males, 24 females; mean age 11y 9mo [SD 3y 2mo]), 19 healthy siblings of children with NF1 (sibling comparisons; mean age 12y 7mo [SD 2y 7mo], 9 males, 10 females) and 29 healthy children from the community (community comparisons; mean age 11y [SD 2y 7mo], 12 males, 17 females). Participants completed a battery of cognitive tests including tests of intelligence, academic achievement, attention, visuoperceptual functioning, visual learning, executive functioning, and non-verbal working memory tests. RESULTS: Our study, using a population-based sample, confirmed previous findings from studies using variable sampling methods. Children with NF1 had significantly lower Full-scale IQs (p=0.04) and lower academic achievement (p=0.026-0.005) than their siblings. Compared with their siblings, they also had significantly poorer visuospatial processing (p=0.007), visual associate learning (p=0.014), non-verbal working memory (p=0.023), and executive function (p<0.001). Data from the community comparisons were not included because they were subject to significant selection bias. INTERPRETATION: Population-based frequencies for cognitive deficits in children with NF1 are similar to the frequencies in non-population based samples. This study highlights the heterogeneous nature of cognitive problems in children with NF1 and the need for monitoring and support at school.

Clinical delineation and natural history of the PIK3CA-related overgrowth spectrum.

Somatic mutations in the phosphatidylinositol/AKT/mTOR pathway cause segmental overgrowth disorders. Diagnostic descriptors associated with PIK3CA mutations include fibroadipose overgrowth (FAO), Hemihyperplasia multiple Lipomatosis (HHML), Congenital Lipomatous Overgrowth, Vascular malformations, Epidermal nevi, Scoliosis/skeletal and spinal (CLOVES) syndrome, macrodactyly, and the megalencephaly syndrome, Megalencephaly-Capillary malformation (MCAP) syndrome. We set out to refine the understanding of the clinical spectrum and natural history of these phenotypes, and now describe 35 patients with segmental overgrowth and somatic PIK3CA mutations. The phenotypic data show that these previously described disease entities have considerable overlap, and represent a spectrum. While this spectrum overlaps with Proteus syndrome (sporadic, mosaic, and progressive) it can be distinguished by the absence of cerebriform connective tissue nevi and a distinct natural history. Vascular malformations were found in 15/35 (43%) and epidermal nevi in 4/35 (11%) patients, lower than in Proteus syndrome. Unlike Proteus syndrome, 31/35 (89%) patients with PIK3CA mutations had congenital overgrowth, and in 35/35 patients this was asymmetric and disproportionate. Overgrowth was mild with little postnatal progression in most, while in others it was severe and progressive requiring multiple surgeries. Novel findings include: adipose dysregulation present in all patients, unilateral overgrowth that is predominantly left-sided, overgrowth that affects the lower extremities more than the upper extremities and progresses in a distal to proximal pattern, and in the most severely affected patients is associated with marked paucity of adipose tissue in unaffected areas. While the current data are consistent with some genotype-phenotype correlation, this cannot yet be confirmed.

Can the diagnosis of NF1 be excluded clinically? A lack of pigmentary findings in families with spinal neurofibromatosis demonstrates a limitation of clinical diagnosis.

BACKGROUND: Consensus clinical diagnostic criteria for neurofibromatosis type I (NF1) include café-au-lait macules and skinfold freckling. The former are frequently the earliest manifestation of NF1, and as such are of particular significance when assessing young children at risk of the condition. A phenotype of predominantly spinal neurofibromatosis has been identified in a small minority of families with NF1, often in association with a relative or absolute lack of cutaneous manifestations. An association with splicing and missense mutations has previously been reported for spinal neurofibromatosis, but on the basis of molecular results in only a few families. METHOD: Patients with spinal NF1 were identified through the Manchester nationally commissioned service for complex NF1. RESULTS: Five families with spinal NF1 were identified, with a broad spectrum of NF1 mutations, providing further evidence that this phenotype may arise in association with any genre of mutation in this gene. Pigmentary manifestations were absent or very mild in affected individuals. Several further affected individuals, some with extensive spinal root tumours, were ascertained when additional family members were assessed. CONCLUSIONS: Clinical NF1 consensus criteria cannot be used to exclude the diagnosis of spinal NF1, especially in childhood. This emphasises the importance of molecular confirmation in individuals and families with atypical presentations of NF1.

Spinal bone defects in neurofibromatosis type I with dural ectasia: stress fractures or dysplastic? A case series.

OBJECTIVES: Neurofibromatosis type I (NF1) is a multisystem neurocutaneous disorder with varied musculoskeletal manifestations. Dural ectasia is a known association, whilst pedicular anomalies have been described, although not as frequently as other skeletal manifestations. However, reports of pedicular and other spinal clefts or fractures in combination with dural ectasia in NF1 are scarce. We aimed to identify osseous defects in the posterior elements of NF1 patients with dural ectasia. METHODS: Images of patients with NF1 and back pain were reviewed for osseous defects in the posterior elements. RESULTS: Four patients were identified with NF1, back pain, dural ectasia and bone defects. The imaging appearances of the defects are illustrated. CONCLUSIONS: Defects in the spinal posterior elements of patients with NF1, back pain and dural ectasia may be dysplastic, stress fractures or, most probably, multifactorial in origin. Computed tomography demonstrates these defects most clearly.

Behaviour in children with neurofibromatosis type 1: cognition, executive function, attention, emotion, and social competence.

AIM: This systematic review aimed to pull together the findings from research into behavioural systems and attention in children with neurofibromatosis type 1 (NF1) and to identify areas that need further study. METHOD: Relevant papers were identified through searches of electronic databases (MEDLINE, PsycINFO, EMBASE) and manual searches through reference lists. In total, 5746 articles were identified and 57 met the inclusion criteria. The data were synthesized using the narrative approach, as the studies varied considerably in terms of participants and measures. RESULTS: The results of the review showed that intelligence, academic skills, visuospatial skills, social competence, and attention are impaired in children with NF1. Evidence of deficits in memory, motor functioning, language, and executive functions was less clear. INTERPRETATION: Research has made marked progress in outlining the behavioural phenotype of NF1. However, although the general areas of impairment are becoming better known, the exact nature of the impairment is still not understood in many areas of behaviour. Care needs to be taken with the way in which behavioural constructs are defined and measured, and the variability of problems in NF1 is a particular challenge. Nevertheless, research is steadily moving towards comprehensive understanding of behaviour in children with NF1.

Autism and other psychiatric comorbidity in neurofibromatosis type 1: evidence from a population-based study.

AIM: To investigate psychopathology in children with neurofibromatosis type 1 (NF1), particularly the prevalence of autism spectrum disorder (ASD) and attention-deficit-hyperactivity disorder (ADHD) symptomatology, using a population-based sampling approach. METHOD: Standard questionnaire screen reports were analysed for ASD (Social Responsiveness Scale, SRS), ADHD (Conners' Parent Rating Scale- Revised, CPRS-R), and other psychiatric morbidity (Strengths and Difficulties Questionnaire, SDQ) from parents and teachers of children aged from 4 to 16 years (112 females, 95 males) on the UK North West Regional Genetic Service register for NF1. RESULTS: Parental response rate was 52.7% (109/207 children; 59 females, 50 males, mean age 9 y 11 mo, SD 3 y 3 mo). The SRS showed that in 29.4% (32/109) of children, autism was in the severe, clinical range (T-score>75) and in 26.6% (29/109) in the mild to moderate range (T-score 60-75). CPRS-R scores showed that in 53.8% (57/106) of children autism was in the clinical ADHD range (ADHD index T-score>65). Based on their scores on the SDQ total difficulties scale, 41.5% (44/106) of children were in the abnormal range and 14.2% (15/106) were in the borderline range. Twenty-five per cent (26/104) of children met criteria for both clinical autism and ADHD. INTERPRETATION: This representative population-based sample of children with NF1 indicates a high prevalence of ASD symptoms associated with NF1 as well as substantial co-occurrence with ADHD symptoms. The findings clarify the psychopathology of NF1 and show the disorder as a potentially important single-gene cause for autism symptoms.

Life expectancy in hereditary cancer predisposing diseases: an observational study.

BACKGROUND: Neurofibromatosis 1 (NF1), neurofibromatosis 2 (NF2), familial adenomatous polyposis (FAP), von Hippel-Lindau syndrome (VHL), and Gorlin syndrome (GS) are single gene diseases that predispose to early onset tumours. Few studies have assessed the effect of these diseases on life expectancy. This study's aim was to assess this effect, and to test the hypothesis that genetic registers increase survival. METHOD: NF1, NF2, VHL, FAP, and GS patients were identified through the North West Regional Genetic Register Service and the North West Cancer Intelligence Service. Information on benign and malignant tumours, and deaths were obtained. Kaplan-Meier curves were used to show actuarial survival rates for each disease, compared to the local population, and in patients diagnosed pre/post the regional genetic register. Log rank (Mantel-Cox) tests were used to compare survival between groups. RESULTS: Life expectancies were significantly reduced for all diseases investigated compared with the local population (80.0 years) (p=0.05). GS had the longest life expectancy at 73.4 years, followed by NF1 at 71.5 years, NF2 at 69.0 years, FAP at 63.6 years, and VHL at 52.5 years. Patients diagnosed after establishment of the genetic register had an increase in survival compared to those diagnosed pre-1990: NF2 (14.7 years), FAP (13.9 years), VHL (16.3 years), and GS (11.2 years). CONCLUSION: Life expectancy for all five diseases was less than normal, although in recent years this reached the level of the local population in GS. Although there have been improvements in all conditions which may in part be attributable to better targeted care through the genetic register service, more needs to be done to address the very poor life expectancy in VHL.

Consensus recommendations for current treatments and accelerating clinical trials for patients with neurofibromatosis type 2.

Neurofibromatosis type 2 (NF2) is a tumor suppressor syndrome characterized by bilateral vestibular schwannomas (VS) which often result in deafness despite aggressive management. Meningiomas, ependymomas, and other cranial nerve and peripheral schwannomas are also commonly found in NF2 and collectively lead to major neurologic morbidity and mortality. Traditionally, the overall survival rate in patients with NF2 is estimated to be 38% at 20 years from diagnosis. Hence, there is a desperate need for new, effective therapies. Recent progress in understanding the molecular basis of NF2 related tumors has aided in the identification of potential therapeutic targets and emerging clinical therapies. In June 2010, representatives of the international NF2 research and clinical community convened under the leadership of Drs. D. Gareth Evans (University of Manchester) and Marco Giovannini (House Research Institute) to review the state of NF2 treatment and clinical trials. This manuscript summarizes the expert opinions about current treatments for NF2 associated tumors and recommendations for advancing therapies emerging from that meeting. The development of effective therapies for NF2 associated tumors has the potential for significant clinical advancement not only for patients with NF2 but for thousands of neuro-oncology patients afflicted with these tumors.

Cranial meningiomas in 411 neurofibromatosis type 2 (NF2) patients with proven gene mutations: clear positional effect of mutations, but absence of female severity effect on age at onset.

BACKGROUND: Meningiomas have been reported to occur in approximately 50% of neurofibromatosis type 2 (NF2) patients. The NF2 gene is commonly biallelically inactivated in both schwannomas and meningiomas. The spectrum of NF2 mutations consists mainly of truncating (nonsense and frameshift) mutations. A smaller number of patients have missense mutations, which are associated with a milder disease phenotype. METHODS: This study analysed the cumulative incidence and gender effects as well as the genotype-phenotype correlation between the position of the NF2 mutation and the occurrence of cranial meningiomas in a cohort of 411 NF2 patients with proven NF2 mutations. RESULTS AND CONCLUSION: Patients with mutations in exon 14 or 15 were least likely to develop meningiomas. Cumulative risk of cranial meningioma to age 50 years was 70% for exons 1-3, 81% for exons 4-6, 49% for exons 7-9, 56% for exons 10-13, and 28% for exons 14-15. In the cohort of 411 patients, no overall gender bias was found for occurrence of meningioma in NF2 disease. Cumulative incidence of meningioma was close to 80% by 70 years of age for both males and females, but incidence by age 20 years was slightly increased in males (male 25%, female 18%; p=0.023). Conversely, an increased risk of meningiomas in women with mosaic NF2 disease was also found.

Back to the future: proceedings from the 2010 NF Conference.

The neurofibromatoses (NF) encompass the rare diseases NF1, NF2, and schwannomatosis. The NFs affect 100,000 Americans; over 2 million persons worldwide; and are caused by mutation of tumor suppressor genes. Individuals with NF1 in particular may develop tumors anywhere in the nervous system; additional manifestations can include learning disabilities, bone dysplasia, cardiovascular defects, unmanageable pain, and physical disfigurement. Ultimately, the NFs can cause blindness, deafness, severe morbidity, and increased mortality and NF1 includes a risk of malignant cancer. Today there is no treatment for the NFs (other than symptomatic); however, research efforts to understand these genetic conditions have made tremendous strides in the past few years. Progress is being made on all fronts, from discovery studies-understanding the molecular signaling deficits that cause the manifestations of NF-to the growth of preclinical drug screening initiatives and the emergence of a number of clinical trials. An important element in fuelling this progress is the sharing of knowledge, and to this end, for over 20 years the Children's Tumor Foundation has convened an annual NF Conference, bringing together NF professionals to share ideas and build collaborations. The 2010 NF Conference held in Baltimore, MD June 5-8, 2010 hosted over 300 NF researchers and clinicians. This paper provides a synthesis of the highlights presented at the Conference and as such, is a "state-of-the-field" for NF research in 2010.

What's new in neurofibromatosis? Proceedings from the 2009 NF Conference: new frontiers.

The NF Conference is the largest annual gathering of researchers and clinicians focused on neurofibromatosis and has been convened by the Children's Tumor Foundation for over 20 years. The 2009 NF Conference was held in Portland, Oregon from June 13 to June 16, 2009 and co-chaired by Kathryn North from the University of Sydney and The Children's Hospital at Westmead, Sydney, Australia; and Joseph Kissil from the Wistar Institute, Philadelphia. The Conference included 80 platform presentations in 9 sessions over 4 days; over 100 abstracts presented as posters; and three Keynote presentations. To date, there have been tremendous advances in basic research in the pathogenesis of neurofibromatosis, and more recently in progress toward identifying effective drug therapies and the commencement of neurofibromatosis clinical trials. The NF Conference attendees have significantly increased (doubling from 140 in 2005 to 280 attending in 2009) with a significant increase in attendance of physicians and clinical researchers. Correspondingly the NF Conference scope has expanded to include translational research, clinical trials and clinical management issues while retaining a core of basic research. These themes are reflected in the highlights from the 2009 NF Conference presented here.

What are the implications in individuals with unilateral vestibular schwannoma and other neurogenic tumors?

OBJECTIVES: Individuals who develop a unilateral vestibular schwannoma (VS) and other neurogenic tumors are at high risk of having the inherited condition neurofibromatosis Type 2 (NF2). The risk of bilateral disease and transmission risk to offspring are important in surgical planning and counseling. The authors have attempted to resolve these risks. METHODS: A large NF2 dataset was interrogated for individuals who had initially presented with a unilateral VS and other tumors before developing bilateral disease, to assess the contralateral and offspring risks. RESULTS: Ninety-six patients with a unilateral VS and additional neurogenic tumors had a bilaterality rate of 48% at 20 years in those initially diagnosed when > 18 years of age and 82% if presenting earlier. Constitutional NF2 mutations were found in blood in 25 (27%) of 92, but 13 (76%) of 17 patients presenting with unilateral VS at < or = 18 years of age. Tumor analysis suggests that the vast majority of the remainder are mosaic for an NF2 mutation. CONCLUSIONS: Patients with unilateral VS and other NF2-related tumors who fulfill Manchester criteria have a high risk of developing a contralateral tumor, especially if presenting in childhood. Transmission risks are reduced for offspring, particularly in the older patients who are likely to be mosaic.

Guidelines for the diagnosis and management of individuals with neurofibromatosis 1.

Neurofibromatosis 1 (NF1) is a common neurocutaneous condition with an autosomal dominant pattern of inheritance. The complications are diverse and disease expression varies, even within families. Progress in molecular biology and neuroimaging and the development of mouse models have helped to elucidate the aetiology of NF1 and its clinical manifestations. Furthermore, these advances have raised the prospect of therapeutic intervention for this complex and distressing disease. Members of the United Kingdom Neurofibromatosis Association Clinical Advisory Board collaborated to produce a consensus statement on the current guidelines for diagnosis and management of NF1. The proposals are based on published clinical studies and on the pooled knowledge of experts in neurofibromatosis with experience of providing multidisciplinary clinical and molecular services for NF1 patients. The consensus statement discusses the diagnostic criteria, major differential diagnoses, clinical manifestations and the present strategies for monitoring and management of NF1 complications.

Mosaic RAS/MAPK variants cause sporadic vascular malformations which respond to targeted therapy.

BACKGROUND: Sporadic vascular malformations (VMs) are complex congenital anomalies of blood vessels that lead to stroke, life-threatening bleeds, disfigurement, overgrowth, and/or pain. Therapeutic options are severely limited, and multidisciplinary management remains challenging, particularly for high-flow arteriovenous malformations (AVM). METHODS: To investigate the pathogenesis of sporadic intracranial and extracranial VMs in 160 children in which known genetic causes had been excluded, we sequenced DNA from affected tissue and optimized analysis for detection of low mutant allele frequency. RESULTS: We discovered multiple mosaic-activating variants in 4 genes of the RAS/MAPK pathway, KRAS, NRAS, BRAF, and MAP2K1, a pathway commonly activated in cancer and responsible for the germline RAS-opathies. These variants were more frequent in high-flow than low-flow VMs. In vitro characterization and 2 transgenic zebrafish AVM models that recapitulated the human phenotype validated the pathogenesis of the mutant alleles. Importantly, treatment of AVM-BRAF mutant zebrafish with the BRAF inhibitor vemurafinib restored blood flow in AVM. CONCLUSION: Our findings uncover a major cause of sporadic VMs of different clinical types and thereby offer the potential of personalized medical treatment by repurposing existing licensed cancer therapies. FUNDING: This work was funded or supported by grants from the AVM Butterfly Charity, the Wellcome Trust (UK), the Medical Research Council (UK), the UK National Institute for Health Research, the L'Oreal-Melanoma Research Alliance, the European Research Council, and the National Human Genome Research Institute (US).

The heterogeneous nature of germline mutations in NF1 patients with malignant peripheral serve sheath tumours (MPNSTs).

Malignant peripheral nerve sheath tumours (MPNSTs) are a major cause of mortality in patients with neurofibromatosis 1 (NF1). We have analysed lymphocyte DNA samples from 30 NF1 patients with MPNSTs to determine their underlying constitutional NF1 gene mutations. Mutations were detected in 27/30 (90%) of these patients. NF1 mutations identified included nonsense, missense, frameshift, splice site mutation and single or multi-exonic deletions and with no obvious clustering of the mutations across the gene. Fourteen of the mutations represent novel gene changes. There did not appear to be any relationship between the mutation type and the level of clinical severity observed. Of the 20 patients with high grade MPNSTs, seven patients had small (<20 bp) and multi-exonic deletions and three had small insertions (<20 bp). Several studies have suggested that NF1 patients with a constitutional 1.5 Mb deletion of the NF1 gene have an increased risk of developing malignant peripheral nerve sheath tumours (MPNSTs). None of our patients had a 1.5 Mb deletion. Larger prospective studies are needed to ascertain whether there is a different spectrum of NF1 mutations in NF1 patients with high grade compared to low grade MPNSTs and of patients with the 1.5Mb deletion, in order to determine the true frequency of MPNST in this sub-group of NF1 patients.

The natural history of cerebellar hemangioblastomas in von Hippel-Lindau disease.

BACKGROUND AND PURPOSE: Cerebellar hemangioblastomas (HBs) are traditionally classified into different morphologic types: cystic and solid. We have observed the progression from solid to cystic and have reviewed the cases seen at the regional von Hippel-Lindau (VHL) clinic to document the frequency of this progression. METHODS: A retrospective review of the notes and images of all patients with VHL disease seen at a regional referral clinic since its inception in 1991. Sporadic HBs were not included in this study. RESULTS: In eight patients, a total of 28 tumors were detected. Fourteen of these had or developed cysts. Of the 14 cystic tumors, eight increased in size over the follow-up period. Of the 14 solid tumors, only one increased in size without cystic change. In four patients, the tumor progressed from a cerebellar nodule to an enlarging cyst with a nodule, with the subsequent development of symptoms requiring surgical excision. CONCLUSION: We have demonstrated that, in VHL, cerebellar HBs begin as nodules, and some subsequently develop enlarging cysts that cause pressure symptoms. In our patient population, tumors that remained solid were asymptomatic and well tolerated in the cerebellum.