Optic pathway gliomas in neurofibromatosis-1: controversies and recommendations

Optic pathway glioma: long-term visual outcome in children without neurofibromatosis type-1

BACKGROUND

Little is known about the visual outcome of children affected by an optic pathway glioma (OPG).

PROCEDURES

We evaluated the long-term visual outcome of 32 consecutive children affected by OPG without neurofibromatosis type-1 referred to the Pediatric Department of Padua University and managed according to standardized strategies.

RESULTS

Eight children received chemotherapy, 10 radiotherapy, 7 both chemotherapy and radiotherapy, whereas 7 were untreated. At presentation, visual acuity (VA) was normal in 22 children (13 unilaterally and 9 bilaterally), and reduced in 10. At follow-up, VA had improved in 6 patients; it was stable in 8 and worse in 18. Visual field, assessed in 29 children, was normal in 9 and reduced in 20. The number of children with some grade of visual impairment increased from 7 to 10 during follow-up. Of the 17 children in whom the tumor became significantly smaller, VA improved in 6, was stable in 3, and worse in 8. Of the 6 children with improved VA, 5 received radiotherapy, and their papilla was normal or mildly pale. After a median follow-up of 6 years, 26 patients are alive with stable disease.

CONCLUSIONS

The visual prognosis of children with OPG is unsatisfactory. Older children treated with radiotherapy seem to have a better visual outcome than younger children. Severe optic pallor at diagnosis or during follow-up may be indicative of a negative prognosis.

Optical coherence tomography in the evaluation of neurofibromatosis type-1 subjects with optic pathway gliomas

PURPOSE

Neurofibromatosis type 1 (NF1) is the most common neurocutaneous disorder, with an approximate incidence of 1 in 3,500. Optic pathway gliomas (OPGs) develop in 15% of individuals with NF1, commonly in childhood. OPGs are difficult to detect via a clinical inspection in children, often requiring magnetic resonance imaging (MRI). Given the significant visual risks associated with OPGs in NF1, there is a need for improved noninvasive techniques to diagnose OPGs in children; therefore, we studied optical coherence tomography (OCT) as a potential tool to assess optic nerve and retinal nerve fiber layer (RNFL) abnormalities. This prospective study was designed to evaluate OCT detection of RNFL loss from optic atrophy attributable to OPGs in a cohort of pediatric patients with NF1.

METHODS

With the use of Stratus OCT, directed testing with the Fast Macular Thickness and Fast RNFL Thickness protocol scans were performed on 9 subjects with NF1 and known OPGs, 6 subjects with NF1 without OPGs, and 15 controls.

RESULTS

NF1 subjects with OPGs had thinner RNFLs and macula when compared with age-matched controls and to NF1 subjects without OPGs. After applying the equivalence equation, the average RNFL thickness and macular volume in NF1 subjects without OPGs was equivalent to controls.

CONCLUSIONS

Our study suggests that OCT can be used to detect RNFL thinning secondary to OPGs in NF1 subjects. This objective tool shows promise as a useful adjunct to routine clinical ophthalmologic evaluation in children with NF1.

CXCL12 alone is insufficient for gliomagenesis in Nf1 mutant mice

Tumorigenesis requires interactions between tumor progenitors and their microenvironment. We found that low cAMP levels were sufficient for tumorigenesis in a mouse model of Neurofibromatosis-1 (NF1)-associated optic pathway glioma (OPG). We hypothesized that the distinct pattern of glioma in NF1 reflected spatiotemporal differences in CXCL12 effects on cAMP levels. Thus, we sought to alter the pattern of gliomagenesis through manipulation of CXCL12-CXCR4 pathway activation in Nf1 OPG mice. Forced CXCL12 expression induced glioma at a low frequency. Further, treatment of Nf1 OPG mice with AMD3100, a CXCR4 antagonist, did not attenuate glioma growth. Thus, it appears, CXCL12 alone cannot promote gliomagenesis in NF1 mice.

The diagnostic and clinical significance of café-au-lait macules

Café-au-lait, also referred to as café-au-lait spots or café-au-lait macules, present as well-circumscribed, evenly pigmented macules and patches that range in size from 1 to 2 mm to greater than 20 cm in greatest diameter. Café-au-lait are common in children. Although most café-au-lait present as 1 or 2 spots in an otherwise healthy child, the presence of multiple café-au-lait, large segmental café-au-lait, associated facial dysmorphism, other cutaneous anomalies, or unusual findings on physical examination should suggest the possibility of an associated syndrome. While neurofibromatosis type 1 is the most common syndrome seen in children with multiple café-au-lait, other syndromes associated with one or more café-au-lait include McCune-Albright syndrome, Legius syndrome, Noonan syndrome and other neuro-cardio-facialcutaneous syndromes, ring chromosome syndromes, and constitutional mismatch repair deficiency syndrome.

Neurofibromatosis-1 regulates neuroglial progenitor proliferation and glial differentiation in a brain region-specific manner

Recent studies have shown that neuroglial progenitor/stem cells (NSCs) from different brain regions exhibit varying capacities for self-renewal and differentiation. In this study, we used neurofibromatosis-1 (NF1) as a model system to elucidate a novel molecular mechanism underlying brain region-specific NSC functional heterogeneity. We demonstrate that Nf1 loss leads to increased NSC proliferation and gliogenesis in the brainstem, but not in the cortex. Using Nf1 genetically engineered mice and derivative NSC neurosphere cultures, we show that this brain region-specific increase in NSC proliferation and gliogenesis results from selective Akt hyperactivation. The molecular basis for the increased brainstem-specific Akt activation in brainstem NSCs is the consequence of differential rictor expression, leading to region-specific mammalian target of rapamycin (mTOR)/rictor-mediated Akt phosphorylation and Akt-regulated p27 phosphorylation. Collectively, these findings establish mTOR/rictor-mediated Akt activation as a key driver of NSC proliferation and gliogenesis, and identify a unique mechanism for conferring brain region-specific responses to cancer-causing genetic changes.

Oligodendrocyte progenitor cell numbers and migration are regulated by the zebrafish orthologs of the NF1 tumor suppressor gene

Neurofibromatosis type 1 is the most commonly inherited human cancer predisposition syndrome. Neurofibromin (NF1) gene mutations lead to increased risk of neurofibromas, schwannomas, low grade, pilocytic optic pathway gliomas, as well as malignant peripheral nerve sheath tumors and glioblastomas. Despite the evidence for NF1 tumor suppressor function in glial cell tumors, the mechanisms underlying transformation remain poorly understood. In this report, we used morpholinos to knockdown the two nf1 orthologs in zebrafish and show that oligodendrocyte progenitor cell (OPC) numbers are increased in the developing spinal cord, whereas neurons are unaffected. The increased OPC numbers in nf1 morphants resulted from increased proliferation, as detected by increased BrdU labeling, whereas TUNEL staining for apoptotic cells was unaffected. This phenotype could be rescued by the forced expression of the GTPase-activating protein (GAP)-related domain of human NF1. In addition, the in vivo analysis of OPC migration following nf1 loss using time-lapse microscopy demonstrated that olig2-EGFP(+) OPCs exhibit enhanced cell migration within the developing spinal cord. OPCs pause intermittently as they migrate, and in nf1 knockdown animals, they covered greater distances due to a decrease in average pause duration, rather than an increase in velocity while in motion. Interestingly, nf1 knockdown also leads to an increase in ERK signaling, principally in the neurons of the spinal cord. Together, these results show that negative regulation of the Ras pathway through the GAP activity of NF1 limits OPC proliferation and motility during development, providing insight into the oncogenic mechanisms through which NF1 loss contributes to human glial tumors.

Optic nerve biopsy via a medial transconjunctival orbitotomy approach in the diagnosis of optic nerve and sheath tumors

PURPOSE

To evaluate the role of optic nerve biopsy in the diagnosis and management of optic nerve and sheath tumors.

METHODS

Seven patients with progressive optic nerve and sheath tumors for whom treatment was deemed necessary were included in this study. Optic nerve biopsy via a medial transconjunctival orbitotomy approach was performed in all patients

RESULTS

There were no complications related to the surgical procedure. Histopathological examination revealed that five patients had juvenile pilocytic astrocytoma (JPA) and two patients had optic nerve sheath meningioma (ONSM). All patients received external beam radiotherapy (EBRT).

CONCLUSIONS

Many other benign and malignant optic nerve and sheath tumors have imaging features similar to those seen in JPA and ONSM. Therefore, it is important to establish histopathologic diagnosis before embarking on treatment. Furthermore, tissue diagnosis is required prior to EBRT in many institutions because of concerns about medicolegal liability. Optic nerve biopsy via a transconjunctival orbitotomy procedure in seven patients yielded histopathologic confirmation of the existing pathology and was not associated with any complications in this series.

Clinicopathologic study of glioblastoma in children with neurofibromatosis type 1

BACKGROUND

Neurofibromatosis type 1 (NF1) is characterized by low-grade tumors of the central and peripheral nervous system. There is also an increased risk of developing malignant tumors. Glioblastoma is an uncommon, malignant tumor of children that is even less frequently observed in children with NF1.

PROCEDURE

We performed a retrospective review of patients with NF1 and glioblastoma to determine specific clinical and pathologic indicators of overall prognosis.

RESULTS

Five patients were identified from the CHB/DFCI database for whom pathologic and imaging studies were available. All pathologic specimens demonstrated vascular proliferation and necrosis. All samples stained positively for p53. Chromogenic in situ hybridization (CISH) for epidermal growth factor receptor (EGFR) copy numbers was increased, PTEN copy numbers were normal and the promoter of the O(6)-methylguanine-DNA methyltransferase (MGMT) gene was unmethylated in the one patient evaluated. In the same time period, there were 56 patients without NF1 diagnosed with glioblastoma who were treated at our institution. Although the small sample size precludes formal statistical analysis, the 2-year survival of patients with NF1 is 60% with median overall survival of 9.25 years compared to non-NF1 patients with a 2-year survival of 25% and median overall survival 1.08 years.

CONCLUSIONS

This study provides preliminary evidence that children with NF1 may be at risk for glioblastoma, but that these patients have an increased survival compared to children without NF1. Additional molecular studies will be required to determine if the pathogenesis of these tumors differs from glioblastoma in children without NF1.

Function-related structural plasticity of the GnRH system: a role for neuronal-glial-endothelial interactions

As the final common pathway for the central control of gonadotropin secretion, GnRH neurons are subjected to numerous regulatory homeostatic and external factors to achieve levels of fertility appropriate to the organism. The GnRH system thus provides an excellent model in which to investigate the complex relationships between neurosecretion, morphological plasticity and the expression of a physiological function. Throughout the reproductive cycle beginning from postnatal sexual development and the onset of puberty to reproductive senescence, and even within the ovarian cycle itself, all levels of the GnRH system undergo morphological plasticity. This structural plasticity within the GnRH system appears crucial to the timely control of reproductive competence within the individual, and as such must have coordinated actions of multiple signals secreted from glial cells, endothelial cells, and GnRH neurons. Thus, the GnRH system must be viewed as a complete neuro-glial-vascular unit that works in concert to maintain the reproductive axis.

Endocrine tumours in neurofibromatosis type 1, tuberous sclerosis and related syndromes

Neurofibromatosis type 1 (NF-1) and tuberous sclerosis complex (TSC) are two familial syndromes known as phakomatoses that may be associated with endocrine tumours. These hereditary cutaneous conditions affect the central nervous system and are characterised by the development of hamartomas. Over the past 20 years, there have been major advances in our understanding of the molecular basis of these diseases. Both NF-1 and TSC are disorders of unregulated progression through the cell cycle, in which causative genes behave as tumour suppressor genes. The pathogenesis of these familial syndromes is linked by the shared regulation of a common pathway, the protein kinase mammalian target of rapamycin (mTOR). Additional related disorders that also converge on the mTOR pathway include Peutz-Jeghers syndrome and Cowden syndrome. All of these inherited cancer syndromes are associated with characteristic skin findings that offer a clue to their recognition and treatment. The discovery of mTOR inhibitors has led to a possible new therapeutic modality for patients with endocrine tumours as part of these familial syndromes.

Optic nerve tumor in tuberous sclerosis complex is not responsive to sirolimus

A 12-year-old girl with clinically established tuberous sclerosis complex, and without signs of neurofibromatosis type 1, developed a right retro-ocular optic nerve tumor. After rapid growth for 1 year after its discovery, the optic nerve tumor demonstrated modest progression. The patient received the mammalian target of rapamycin inhibitor, sirolimus, for recurrent subependymal giant cell brain tumors. Although her left ventricular subependymal giant cell tumor demonstrated a 49% reduction in volume, the optic nerve tumor did not respond, and even underwent slight (6%) growth during the 16-month treatment. The quality of this child's vision has remained normal in both eyes, and she is otherwise asymptomatic with regard to the optic nerve tumor.

Inherited cancer syndromes in children and young adults

Geneticists estimate that 5% to 10% of all cancers diagnosed in the pediatric age range occur in children born with a genetic mutation that directly increases their lifetime risk for neoplasia. However, despite the fact that only a fraction of cancers in children occur as a result of an identified inherited predisposition, characterizing genetic mutations responsible for increased cancer risk in such syndromes has resulted in a profound understanding of relevant molecular pathways involved in carcinogenesis and/or resistance to neoplasia. Importantly, because most cancer predisposition syndromes result in an increased risk of a small number of defined malignancies, personalized prophylactic surveillance and preventive measures can be implemented in affected patients. Lastly, many of the same genetic targets identified from cancer-prone families are mechanistically involved in the majority of sporadic cancers in adults and children, thereby underscoring the clinical relevance of knowledge gained from these defined syndromes and introducing novel therapeutic opportunities to the broader oncologic community. This review highlights the clinical and genetic features of many of the known constitutional genetic syndromes that predispose to malignancy in children and young adults.

Optic pathway gliomas in patients with neurofibromatosis type 1: follow-up of 44 patients

BACKGROUND

Children born with neurofibromatosis type 1 (NF1) have an increased risk of developing optic pathway gliomas (OPGs) during childhood. The aim of this study is to evaluate the clinical course of NF1 patients with OPGs at our institution with respect to visual and endocrinologic morbidity.

METHODS

Retrospective case series of patients with OPGs and NF1 seen at the Montreal Children's Hospital, where screening imaging is performed on all NF1 patients. Details on patient demographics, tumor location, and progression of disease were recorded.

RESULTS

Of 331 NF1 patient charts reviewed, 44 had confirmed OPG (13%). Average follow-up was 7 years. Mean age at presentation was 6 years, with 16 patients (36%) presenting past age 6. A total of 8 patients were symptomatic secondary to the OPG (defined as decreased vision or precocious puberty), with 5 of the 8 patients receiving treatment. These 8 patients all demonstrated chiasmal and/or retrochiasmal tumor in addition to nerve involvement. Final visual acuity was 20/40 or better in both eyes in 34 patients (77%); central, steady, and maintained in 3 preverbal children; and decreased vision secondary to OPG in 4 children (9%).

CONCLUSIONS

OPGs can present and progress beyond the preschool years, and children should be screened with clinical ophthalmological examinations accordingly. The location of OPG as demonstrated on magnetic resonance imaging (MRI) cannot be used as a prognostic indicator because visual outcomes were similar between optic nerve/chiasmal and retrochiasmal tumors.

[Optic nerve glioma in children]

Optic pathway gliomas are rare tumors accounting for 3-5% of brain tumors in children; 90% are observed in children. They account for 4% of orbital tumors in children. Association with NF 1 is classical and the incidence of NF 1 in patients with optic pathway gliomas is estimated at 30-58%. Usually these tumors are pilocytic astrocytomas and their regression, particularly in patients with NF 1, has been described. Exophthalmos and loss of visual acuity or blindness are the usualpresentation in progressive disease. CT and above all MRI study of the orbit and the brain are necessary to make a complete evaluation of the disease. Gross total removal of the tumor provides 100% cure, but surgery can be proposed only for growing tumor with severe exophthalmos and no useful field of view or blindness. Chemotherapy must be proposed as first-line treatment for growing tumor with moderate exophthalmos and useful vision when the tumor is strictly confined in the orbit. The place of radiotherapy for pure intraorbital gliomas has not been defined and proton beam therapy has to be evaluated.

Approach to optic neuropathies: clinical update

Visual loss is a common symptom brought to the attention of the practicing neurologist. In this circumstance, the proper identification of an optic neuropathy is critical. Recognition of key clinical clues will permit the clinician to construct a likely differential diagnosis and pursue appropriate testing. This review first addresses the elements of the history and examination which are most useful in evaluating a patient with visual loss, and then briefly discusses the main entities responsible for causing unilateral and bilateral optic neuropathies.

Utility of positron emission tomography for tumour surveillance in children with neurofibromatosis type 1

PURPOSE

There is little consensus regarding optimal surveillance of optic pathway glioma (OPG) and plexiform neurofibroma (PNF) in childhood neurofibromatosis type 1 (NF1). (18)F-2-Fluoro-2-deoxy-D: -glucose (FDG) positron emission tomography and computed tomography (PET/CT) is employed in the surveillance of adult PNFs; but its utility has neither been specifically studied in children with PNFs nor in children with OPG.

METHODS

Review of PET/CT studies was performed in NF1 children with OPG or PNF. FDG-avidity of tumours was semi-quantitatively analysed and graded by calculating the maximum standardised uptake value (SUV(max)) [grade 1: <3 (low), grade 2: >3-<4 (intermediate), grade 3: >4 (intense)].

RESULTS

Eighteen children (ten girls; median age: 8.5-years) had PET/CT. Nineteen OPGs were imaged. The SUV(max) could be measured in 16. Ten were grade 1 and three each were grade 2 and grade 3. FDG-avidity reduced from grade 3 to grade 1 in two symptomatic OPGs following chemotherapy and this was associated with clinical improvement. PET/CT diagnosed symptomatic OPGs with a sensitivity of 0.625 [95% confidence interval (CI): 0.259-0.897] and specificity of 0.875 (95% CI: 0.466-0.993). Sixteen PNFs were imaged. Twelve were grade 1 and two each were grade 2 and grade 3. The two grade 3 PNFs were confirmed malignant peripheral nerve sheath tumours. PET/CT diagnosed malignant transformation with a sensitivity of 1.0 (95% CI: 0.197-1.0) and specificity of 0.857 (95% CI: 0.561-0.974).

CONCLUSION

PET/CT may contribute useful information to the surveillance of OPG in childhood NF1-particularly to identify progressive, symptomatic tumours. As in adults, PET/CT is useful for the detection of malignant transformation in PNFs in children with NF1.

MAPK pathway activation and the origins of pediatric low-grade astrocytomas

Low-grade astrocytomas (LGAs) are the most common type of brain tumor in children. Until recently, very little was known about the underlying biology and molecular genetics of these tumors. However, within the past year a number of studies have shown that the MAPK pathway is constitutively activated in a high proportion of LGAs. Several genetic aberrations which generate this deregulation of the MAPK pathway have been identified, most notably gene fusions between KIAA1549 and BRAF. In this review we summarize these findings, discuss how these gene fusions may arise and consider possible implications for diagnosis and treatment.

Neurooncology of familial cancer syndromes

The majority of tumors of the nervous system are sporadic. However, a subset of patients with tumors and their families are predisposed to developing cancers of the central nervous system and other organs because of a germline mutation. In the last decade, many of the genes responsible for these typically autosomal dominant familial tumor syndromes have been identified. Additionally, our understanding of the mechanisms of carcinogenesis in these syndromes has increased, allowing for more targeted therapies for these patients as well as those with sporadic cancers. Because these patients present a unique set of issues regarding diagnosis and neurooncological management, the most common familial cancer syndromes involving the nervous system are reviewed: neurofibromatosis type 1 and 2; tuberous sclerosis complex; von Hippel Lindau, Li-Fraumeni, Gorlin, and Turcot syndrome.

Pediatric low-grade gliomas

Pediatric low-grade gliomas encompass a heterogeneous set of tumors of different histologies. Cerebellar pilocytic astrocytomas occur most frequently followed by supratentorial diffuse fibrillary astrocytomas. Recent research has implicated activation of the RAS/RAF/MEK pathway in tumorigenesis of these tumors. Surgery is the mainstay of therapy. Overall survival rates for patients whose tumors are completely resected are 90% or greater, 10 years from diagnosis. Conversely, most optic pathway/hypothalamic, deep midline, and brain stem gliomas have minimal potential for resection; these tumors can be difficult to treat and deserve special attention. Combination chemotherapy is currently recommended as front-line adjuvant treatment for progressive or recurrent tumors. Second-line radiotherapy can also improve overall survival but is associated with more frequent and significant neurocognitive, endocrine, and other long-term toxicities.

[Usefulness of systematic brain magnetic resonance imaging in children with neurofibromatosis type 1]

BACKGROUND AND AIM

The aim of this study was to evaluate the usefulness of systematic screening of asymptomatic neurofibromatosis type 1 (NF1) children with magnetic resonance imaging (MRI).

PATIENTS AND METHODS

We retrospectively reviewed the MRIs of children diagnosed with NF1 disease according to the National Institutes of Health criteria, who had been followed for at least 1 year by the department of pediatric neurology (Lyon, France). Brain MRI was systematically performed in asymptomatic patients under 6 years of age.

RESULTS

One hundred patients with a median follow-up of 3.7 years (range, 1-8.6 years) were reviewed. Brain MRI was performed in a total of 94 children. Nine optic pathway gliomas were detected in symptomatic patients. Six children had symptoms caused by the tumor. Gliomas remained stable in 10 patients; 1 symptomatic glioma in an 8-year-old girl required treatment. Spontaneous regression was seen in 1 patient.

CONCLUSION

Our results suggest that MRI screening of asymptomatic children to detect optic pathway gliomas does not improve the therapeutic decision and should not be performed systematically. We suggest further investigation in collaboration with the French NF Network.

Neurofibromatosis type 1

Neurofibromatosis type 1 (NF1) is an autosomal dominant, multisystem disorder affecting approximately 1 in 3500 people. Significant advances in the understanding of the pathophysiology of NF1 have been made in the last decade. While no medical therapies for NF1 are currently available, trials are ongoing to discover and test medical treatments for the various manifestations of NF1, primarily plexiform neurofibromas, learning disabilities, and optic pathway gliomas. In addition, mutational analysis has become available on a clinical basis and is useful for diagnostic confirmation in individuals who do not fulfill diagnostic criteria or when a prenatal diagnosis is desired. There are several disorders that may share overlapping features with NF1; in 2007, a disorder with cutaneous findings similar to NF1 was described. This paper addresses the dermatologist's role in diagnosis and management of NF1 and describes the variety of cutaneous and extracutaneous findings in NF1 to which the dermatologist may be exposed.

LEARNING OBJECTIVES

After completing this learning activity, participants should be able to discuss the indications and limitations of genetic testing in neurofibromatosis type 1, distinguish common and uncommon cutaneous findings, and recognize the dermatologist's role in diagnosis and management.

Optic nerve dysfunction in a mouse model of neurofibromatosis-1 optic glioma

Individuals with neurofibromatosis type 1 (NF1) are prone to develop optic pathway gliomas that can result in significant visual impairment. To explore the cellular basis for the reduced visual function resulting from optic glioma formation, we used a genetically engineered mouse model of Nf1 optic glioma (Nf1+/-(GFAP)CKO mice). We performed multimodal functional and structural analyses both before and after the appearance of macroscopic tumors. At 6 weeks of age, before obvious glioma formation, Nf1+/-(GFAP)CKO mice had decreased visual-evoked potential amplitudes and increased optic nerve axon calibers. By 3 months of age, Nf1+/-(GFAP)CKO mice exhibited pronounced optic nerve axonopathy and apoptosis of neurons in the retinal ganglion cell layer. Magnetic resonance diffusion tensor imaging showed a progressive increase in radial diffusivity between 6 weeks and 6 months of age in the optic nerve proximal to the tumor indicating ongoing deterioration of axons. These data suggest that optic glioma formation results in early axonal disorganization and damage, which culminates in retinal ganglion cell death. Collectively, this study shows that Nf1+/-(GFAP)CKO mice can provide a useful model for defining mechanisms of visual abnormalities in children with NF1 and lay the foundations for future interventional studies aimed at reducing visual loss.

Primary optic nerve tumours

PURPOSE OF REVIEW

Advances have been made in the treatment of primary optic nerve tumours. With a focus on the last few years' publications, recommendations for clinical management are being developed.

RECENT FINDINGS

In low-grade optic nerve glioma, two divergent developments are observed: an increasing reluctance in treating such tumours because of reports about treatment toxicity (secondary tumours, moyamoya syndrome) and a steady and marked improvement both in radiotherapy and chemotherapy. Many reports on beneficial effects of radiotherapy on optic nerve meningioma have been published. Radiotherapy does not only preserve but in many cases even improves or restores visual function and has, therefore, become the therapy of choice in this tumour.

SUMMARY

Establishing a treatment plan in cases of optic nerve glioma is difficult and must be made on an individual basis. Although both chemotherapy and radiotherapy can stabilize and sometimes improve vision in progressive tumours, chemotherapy is the preferred modality in children younger than 9 years and in patients with neurofibromatosis 1. In functionally progressive optic nerve meningioma with useful visual function, multifractioned stereotactic conformal radiotherapy is the treatment of choice.

Radiation-sensitive genetically susceptible pediatric sub-populations

Major advances in pediatric cancer treatment have resulted in substantial improvements in survival. However, concern has emerged about the late effects of cancer therapy, especially radiation-related second cancers. Studies of childhood cancer patients with inherited cancer syndromes can provide insights into the interaction between radiation and genetic susceptibility to multiple cancers. Children with retinoblastoma (Rb), neurofibromatosis type 1 (NF1), Li-Fraumeni syndrome (LFS), and nevoid basal cell carcinoma syndrome (NBCCS) are at substantial risk of developing radiation-related second and third cancers. A radiation dose-response for bone and soft-tissue sarcomas has been observed in hereditary Rb patients, with many of these cancers occurring in the radiation field. Studies of NF1 patients irradiated for optic pathway gliomas have reported increased risks of developing another cancer associated with radiotherapy. High relative risks for second and third cancers were observed for a cohort of 200 LFS family members, especially children, possibly related to radiotherapy. Children with NBCCS are very sensitive to radiation and develop multiple basal cell cancers in irradiated areas. Clinicians following these patients should be aware of their increased genetic susceptibility to multiple primary malignancies enhanced by sensitivity to ionizing radiation.

Optic nerve sheath fenestration for an isolated optic nerve glioma

The treatment modalities for neurofibromatosis type 1-associated optic gliomas include chemotherapy, radiation therapy, and surgical excision. The current recommendation is to consider treatment for an optic nerve glioma only if there is clear evidence of either ophthalmologic or radiographic progression with significant visual dysfunction. We report a case of a child with neurofibromatosis type 1 and an isolated optic nerve glioma with documented progression and visual loss in which clinical signs improved and visual deterioration stabilized after optic nerve sheath fenestration.

Pediatric low-grade gliomas and the need for new options for therapy: Why and how?

Pediatric low-grade gliomas are the most common tumors of the central nervous system in children, accounting for almost 50% of all childhood brain tumors. They are a heterogeneous group of tumors with different histologic subtypes. Most treatment studies address low-grade gliomas as a single entity, depriving us of histology-specific treatment outcomes. This is mostly due to a lack of understanding of tumor biology at the molecular level. Pediatric low-grade gliomas are not benign, and most incompletely resected tumors will progress and negatively affect quality of life. The advancements made in understanding sporadic pilocytic astrocytoma and neurofibromatosis 1-associated pilocytic astrocytoma in particular have paved the way for potential targeted therapy and biological stratification. Such progress in pilocytic astrocytoma needs to be consolidated and expanded to other histologic varieties of pediatric low-grade gliomas.

A patient with loss of vision in the right eye and neurofibromatosis type 1

Neurofibromatosis type 1 is a common autosomal dominant condition that affects about 1 in 5000 people. We describe a 75-year-old man who, in addition to many classic developmental changes of the disease in his skin, eyes and nervous system, had blindness in his right eye as a complication.

Pediatric gliomas

Pediatric gliomas comprise a clinically, histologically, and molecularly very heterogeneous group of CNS tumors. In addition, these tumors are largely different from their counterparts occurring in adults, although they are histologically indistinguishable and uniformly classified by the current WHO classification for CNS tumors. Pilocytic astrocytoma (WHO grade I), mainly arising in the posterior fossa, is the most common representative in children, whereas glioblastoma multiforme (WHO grade IV) predominates in adults. When radical surgical resection is possible in low-grade gliomas, it will likely cure the patient. If complete surgical resection is not possible, however, for example in brainstem gliomas, which are defined by their anatomic localization rather than by their histological or molecular features, therapeutic options are limited and prognosis is usually poor. Recent genome-wide analyses applying different microarray-based methods to investigate DNA copy-number aberrations, mRNA expression signatures, and methylation patterns have shed some light on the pathways involved in the pathogenesis of pediatric glio-mas. Mitogen-activated protein kinase (MAPK) and PI3K/AKT signaling were identified as prominent oncogenic pathways in astrocytic tumors in several studies, whereas NOTCH signaling was implicated in the pathogenesis of a subset of intracranial ependymomas. Future therapeutic strategies targeting these (and other) pathways or conferring epigenetic modifications in the tumor might contribute to a better treatment outcome of patients with unresectable or disseminated tumors at diagnosis. Consideration of reliable molecular markers for outcome prediction will most likely result in a better stratification of patients into different risk groups with adjusted treatment intensity in the future.

Neurofibromatosis type 1 revisited

Neurofibromatosis type 1 (NF1) is an autosomal dominant condition with a worldwide incidence of approximately 1 per 2500 to 3000 individuals. Caused by a germ-line-inactivating mutation in the NF1 gene on chromosome 17, the disease is associated with increased morbidity and mortality. In the past several years, significant progress has been made in standardizing management of the major clinical features of neurofibromatosis type 1. Moreover, improved understanding of how the neurofibromatosis type 1 protein, neurofibromin, regulates cell growth recently provided insight into the pathogenesis of the disease and has led to the development of new therapies. In this review, we describe the clinical manifestations, recent molecular and genetic findings, and current and developing therapies for managing clinical problems associated with neurofibromatosis type 1.

Diffusion-weighted and dynamic contrast-enhanced imaging as markers of clinical behavior in children with optic pathway glioma

BACKGROUND

Optic pathway gliomas (OPGs) are common pediatric brain tumors that pose significant clinical challenges with regard to predicting which tumors are likely to become symptomatic and require treatment. These tumors can arise sporadically or in the context of the inherited cancer predisposition syndrome neurofibromatosis type 1 (NF1). Few studies have suggested biological or imaging markers that predict the clinical course of this disease.

OBJECTIVE

In this cross-sectional study, we hypothesized that the clinical behavior of OPGs in children can be differentiated by diffusion-weighted (DW) and dynamic contrast-enhanced (DCE) MRI.

MATERIALS AND METHODS

A total of 27 children with OPG were studied using DW and DCE MRI protocols. Diffusivity and permeability were calculated and correlated with the clinical behavior the OPG.

RESULTS

Mean diffusivity values of 1.39 microm2/ms and mean permeability values of 2.10 ml/min per 100 cm3 of tissue were measured. Clinically aggressive OPGs had significantly higher mean permeability values (P = 0.05) than clinically stable tumors. In addition, there was a strong correlation between clinical aggressiveness and the absence of NF1 (P < 0.01).

CONCLUSION

These results suggest that DCE MRI might be a useful biomarker for clinically aggressive OPG, which should be confirmed in larger prospective longitudinal studies.

BRAF gene duplication constitutes a mechanism of MAPK pathway activation in low-grade astrocytomas

The molecular pathogenesis of pediatric astrocytomas is still poorly understood. To further understand the genetic abnormalities associated with these tumors, we performed a genome-wide analysis of DNA copy number aberrations in pediatric low-grade astrocytomas by using array-based comparative genomic hybridization. Duplication of the BRAF protooncogene was the most frequent genomic aberration, and tumors with BRAF duplication showed significantly increased mRNA levels of BRAF and a downstream target, CCND1, as compared with tumors without duplication. Furthermore, denaturing HPLC showed that activating BRAF mutations were detected in some of the tumors without BRAF duplication. Similarly, a marked proportion of low-grade astrocytomas from adult patients also had BRAF duplication. Both the stable silencing of BRAF through shRNA lentiviral transduction and pharmacological inhibition of MEK1/2, the immediate downstream phosphorylation target of BRAF, blocked the proliferation and arrested the growth of cultured tumor cells derived from low-grade gliomas. Our findings implicate aberrant activation of the MAPK pathway due to gene duplication or mutation of BRAF as a molecular mechanism of pathogenesis in low-grade astrocytomas and suggest inhibition of the MAPK pathway as a potential treatment.

Extraventricular neurocytoma in neurofibromatosis Type 1: case report

Neurocytomas are rare tumors of the central nervous system that are typically located in the ventricular system. The authors report a case of a child with neurofibromatosis Type 1 (NF1) who had a tumor of the optic nerves and chiasm with signal abnormality extending through the diencephalon, as well as an occipital lobe mass, which was presumed to be part of the visual pathway neoplasm. Because the occipital lobe lesion slowly increased in size over time, while the other areas remained stable, a biopsy was performed. Pathological evaluation revealed an extraventricular neurocytoma of extraventricular neurocytoma. To the authors' knowledge, neurocytomas have not been previously reported in patients with NF1. Because visual pathway gliomas are extremely common in children with NF1, they are often treated empirically as low-grade gliomas without histological confirmation. The importance of obtaining a biopsy in lesions that have atypical imaging features is highlighted.

Assessment of chemotherapeutic response in children with proptosis due to optic nerve glioma

INTRODUCTION

Some children with optic pathway gliomas present with proptosis related to intraorbital tumor extension. The radiological assessment of chemotherapeutic response in these patients can be complicated by irregular tumor shape and lack of relation between tumor volume and cosmetic effect.

METHOD

We propose that proptosis measurements and derivation of a proptosis index can be a useful adjunct to the measurement of tumor volume in the radiological assessment of chemotherapeutic response. The proptosis index was derived as the ratio of the difference in proptosis between eyes postchemotherapy to that prechemotherapy. A series of six patients with proptosis and the diagnosis of an optic nerve tumor from an optic pathway glioma registry demonstrate by case example the correlation between the proptosis index and the clinical and radiographic response to chemotherapy.

CONCLUSIONS

We have found that a proptosis index <1 correlates with a chemotherapeutic maintained response and an index >1 correlates with progressive disease.