Central neuronal tumors in childhood: relationship to dysplasia

Lessons we can learn from neurons to make cancer cells quiescent

Cancer is a major concern for contemporary societies. However, the incidence of cancer is unevenly distributed among tissues and cell types. In particular, the evidence indicates that neurons are absolutely resistant to cancer and this is commonly explained on the basis of the known postmitotic state of neurons. The dominant paradigm on cancer understands this problem as a disease caused by mutations in cellular genes that result in unrestrained cell proliferation and eventually in tissue invasion and metastasis. However, the evidence also shows that mutations and gross chromosomal anomalies are common in functional neurons that nevertheless do not become neoplastic. This fact suggests that in the real nonexperimental setting mutations per se are not enough for inducing carcinogenesis but also that the postmitotic state of neurons is not genetically controlled or determined, otherwise there should be reports of spontaneously transformed neurons. Here we discuss the evidence that the postmitotic state of neurons has a structural basis on the high stability of their nuclear higher order structure that performs like an absolute tumor suppressor. We also discuss evidence that it is possible to induce a similar structural postmitotic state in nonneural cell types as a practical strategy for stopping or reducing the progression of cancer.

mTOR signaling in epilepsy: insights from malformations of cortical development

Over the past decade enhanced activation of the mammalian target of rapamycin (mTOR)-signaling cascade has been identified in focal malformations of cortical development (MCD) subtypes, which have been collectively referred to as "mTORopathies." Mutations in mTOR regulatory genes (e.g., TSC1, TSC2, AKT3, DEPDC5) have been associated with several focal MCD highly associated with epilepsy such as tuberous sclerosis complex (TSC), hemimegalencephaly (HME; brain malformation associated with dramatic enlargement of one brain hemisphere), and cortical dysplasia. mTOR plays important roles in the regulation of cell division, growth, and survival, and, thus, aberrant activation of the cascade during cortical development can cause dramatic alterations in cell size, cortical lamination, and axon and dendrite outgrowth often observed in focal MCD. Although it is widely believed that structural alterations induced by hyperactivated mTOR signaling are critical for epileptogenesis, newer evidence suggests that mTOR activation on its own may enhance neuronal excitability. Clinical trials with mTOR inhibitors have shown efficacy in the treatment of seizures associated with focal MCD.

Fetal brain tumors: Prenatal diagnosis by ultrasound and magnetic resonance imaging

Congenital central nervous system tumors diagnosed during pregnancy are rare, and often have a poor prognosis. The most frequent type is the teratoma. Use of ultrasound and magnetic resonance image allows the suspicion of brain tumors during pregnancy. However, the definitive diagnosis is only confirmed after birth by histology. The purpose of this mini-review article is to describe the general clinical aspects of intracranial tumors and describe the main fetal brain tumors.

Focal malformations of cortical development: new vistas for molecular pathogenesis

Focal malformations of cortical development (FMCD) are highly associated with several neurological disorders including intractable epilepsy and neurocognitive disabilities. Over the past decade, several FMCD subtypes have been linked to hyperactivation of the mammalian target of rapamycin (mTOR) signaling cascade. In view of the roles that mTOR plays in cell proliferation, size, motility, and stem cell phenotype, many of the features of FMCD such as cytomegaly, disorganized lamination, and expression of stem cell markers can be explained by enhanced mTOR signaling. FMCD result from several distinct and fascinating molecular mechanisms including biallelic gene inactivation, somatic mutation, and potentially, viral infection. These mechanisms have been directly linked to mTOR activation. Perhaps most compelling, pharmacological inhibition of mTOR has been implemented successfully in clinical trials for select FMCD and provides a new vista for treatment.

Cortical dysplasia: a possible substrate for brain tumors

The similarities between brain tumor stem cells and neural stem cells suggest a possible stem cell origin of tumorigenesis. Recently, cells with features of stem cells have been observed in lesions of adult and pediatric cortical dysplasia (CD). Given the evidence for a close relationship between CD and certain brain tumors, together with the finding that CD neural stem cells/progenitors are abnormally developed, we propose that CD is a possible substrate for brain tumors. The neural stem cells/progenitors in CD have accumulating abnormalities, and these abnormal stem/progenitor cells may be the initiating, transformed cells of brain tumors, when subsequently exposed to a carcinogen.

Ganglioglioma arising from dysplastic cortex

We report the case of a child who presented at 3 months of age with complex partial seizures, a linear facial nevus, and magnetic resonance imaging (MRI) showing delayed myelination and thickened cortex in the left temporal, parietal, and occipital regions. A repeat 3Tesla MRI scan with and without contrast at 6 months again showed cortical dysplasia of the left hemisphere. No other abnormalities were seen. A third scan at 3 years 6 months showed a 2.5 cm, round, hyperintense lesion on both T(2) and T(1) sequences. The lesion and surrounding dysplastic cortex were resected. Palmini grade IIA dysplasia and a ganglioglioma were diagnosed. These findings suggest that cellular components of cortical dysplasias have oncogenic potential.

Differential cellular gene expression in ganglioglioma

PURPOSE

Gangliogliomas (GGs) are neuronal-glial tumors highly associated with epilepsy. We hypothesized that the expression of select gene families including neurotransmitter receptor subunits and growth factors would be distinct in neurons and astrocytes within GG compared with adjacent cortex and that these changes would yield insights into seizure onset and lesion formation.

METHODS

Candidate gene expression was defined in single immunohistochemically labeled neurons and astrocytes microdissected from GG specimens compared with neurons and astrocytes microdissected from morphologically intact cortex adjacent to the GG or normal control cortex.

RESULTS

Differential expression of 16 genes including glutamate transporter (EAAC1) and receptor (NMDA2C, mGluR5), growth factor (hepatocyte growth factor), and receptor (platelet derived growth factor receptor beta, fibroblast growth factor receptor 3) mRNAs was detected in GG neurons compared with control neurons. In astrocytes, altered expression of p75NGF, mGluR3, TGFbeta3 and Glt-1 mRNAs was detected. Nestin mRNA, a gene that exhibits enhanced expression in balloon cell cortical dysplasia, was increased in GG neurons. Because of the morphological similarities between GG and cortical dysplasia, we show that there is activation of the mTOR cascade in GG as evidenced by enhanced expression of phospho-p70S6kinase and phosphoribosomal S6 proteins.

CONCLUSION

We find differential candidate gene expression in neurons and astrocytes in GG compared with adjacent cortex and show that there is activation of the mTOR pathway. These changes highlight pathways that may be pivotal for epileptogenesis and lesion growth.

Outcome of epilepsy surgery in focal cortical dysplasia

OBJECTIVE

To describe the outcome of surgery in patients with drug resistant epilepsy and a histopathological diagnosis of focal cortical dysplasia.

METHODS AND SUBJECTS

Analysis of histories and presurgical and follow up data was carried out in 53 patients with a histological diagnosis of focal cortical dysplasia. Their mean age was 24.0 years (range 5 to 46), and they included 14 children and adolescents. Mean age at seizure onset was 12.4 years (0.4 to 36) and mean seizure duration was 11.6 years (1 to 45).

RESULTS

The presurgical detection rate of focal cortical dysplasia with magnetic resonance imaging (MRI) was 96%. There were 24 temporal and 29 extratemporal resections; additional multiple subpial transections were done in 12 cases to prevent spread of seizure discharges. There was a 6% rate of complications with permanent neurological deficit, but no deaths. All resected specimens were classified by neuropathological criteria as focal cortical dysplasia. Balloon cells were seen in most cases of extratemporal focal cortical dysplasia. After a mean follow up of 50 months, 38 patients (72%) were seizure-free, two (4%) had less than two seizures a year, nine (17%) had a reduction of seizure frequency of more than 75%, and four (8%) had no improvement. Seizure outcome was similar after temporal and extratemporal surgery. The patients in need of multilobar surgery had the poorest outcome.

CONCLUSIONS

Circumscribed lesionectomy of focal dysplastic lesions provides seizure relief in patients with chronic drug resistant temporal and extratemporal epilepsy. There was a trend for the best seizure outcome to be in patients with early presurgical evaluation and early surgery, and in whom lesions were identified on the preoperative MRI studies.

II. Perinatal brain tumors: a review of 250 cases

Central nervous system tumors occur considerably less often in the fetus and neonate than in the older child. They are not entirely the same as those present later in life. Their location, biologic behavior, response to therapy, and histologic types are different. Fetal and neonatal brain tumors (n = 250) were collected from the literature and studied for this review. The overall survival rate was 28%. The entire cranial cavity may be filled with tumor, and stillbirth is not uncommon. Macrocephaly was the most frequent presentation regardless of histology. Outcome is related to the size and location of the tumor, the histologic type, surgical resectability, and the condition of the infant at the time of diagnosis. Neonates with choroid plexus papillomas, gangliogliomas, and low-grade astrocytomas have the best prognosis, whereas those with teratomas and primitive neuroectodermal tumors have the worst prognosis.

Treatment of central neurocytomas

Central neurocytomas are uncommon tumors of the CNS, representing approximately 0.1-0.5% of all primary CNS tumors. Patients most often present with symptoms of increased intracranial pressure (headache, nausea/vomiting, diplopia) due to obstructive hydrocephalus. Rarely, central neurocytomas may present with a hemorrhage. Central neurocytomas are intraventricular tumors with a predilection for arising in either the lateral or third ventricles. CT or MR cranial imaging demonstrates a circumscribed mass in the ventricles, frequent calcification and moderate contrast enhancement. Surgery provides definitive treatment, as little evidence exists as to response of these tumors to either radiotherapy or chemotherapy. Histopathology reveals a homogenous neoplastic cell population with neuronal differentiation, frequent calcification, occasional perivascular pseudorosettes and infrequent mitoses. Uncommonly, anaplastic variants of central neurocytomas (malignant central neurocytomas) are encountered and are distinguished by frequent mitoses, necrosis and endothelial cell proliferation. Following complete resection, central neurocytomas have a favorable prognosis usually obviating the need for either radiotherapy or chemotherapy.

Disorders of cortical formation: radiologic-pathologic correlation

The advent of newer imaging techniques, such as high-resolution MR imaging and surface reconstructions of three-dimensional data sets, has led to a greater in vivo understanding of cortical malformations of the brain. Disorders of cortical formation are illustrated with routine imaging, surface reconstruction, and pathogenic specimens.

Desmoplastic Neuroepithelial Tumor of Infancy in the Nevus Sebaceus Syndrome

The nevus sebaceus syndrome (NSS) is a neurocutaneous disorder characterized by unilateral hyperplasia of skin appendages and skeletal hemihypertrophy, hemimegalencephaly, or hemiatrophy along with disabling seizures. Despite the proneness of the dermal stigmata to eventually undergo neoplastic transformation, the malformative lesions of the central nervous system rarely evolve into frank tumors. We present the case of a 10-year-old girl with left-sided sebaceus nevi, ipsilateral enlargement of the skull, and a desmoplastic neuroepithelial tumor (DNET) in the right fronto-parietal area of the brain. The tumor was removed by surgery. Histologically, it corresponded to a mitotically active small-cell anaplastic astrocytoma with genuine desmoplasia. Investigative methods included immunohistochemical positivity for glial fibrillary acidic protein, lack of expression of neuronal markers, and ultrastructural documentation of sheaths of basal lamina and collagen around tumor cells. A survey of the literature of brain tumors associated with NSS revealed two cases of histologically verified pilocytic astrocytomas, and one each of a choroid plexus papilloma, a mixed glioma, and a meningioma, as well as a subependymal giant cell astrocytoma--the latter possibly in an overlap syndrome of NSS and tuberous sclerosis. We hypothesize that the tumor described herein, one involving both atypical differentiation and enhanced growth potential, is paradigmatic of neuropathological events to be expected in the NSS.

Malignant transformation of a dysembryoplastic neuroepithelial tumor. Case report

A 29-year-old man presented in 1984 with a recent onset of partial seizures marked by speech arrest. Electroencephalography identified a left frontotemporal dysrhythmia. Computerized tomography (CT) scanning revealed a superficial hypodense nonenhancing lesion in the midleft frontal convexity, with some remodeling of the overlying skull. The patient was transferred to the London Health Sciences Centre for subtotal resection of what was diagnosed as a "fibrillary astrocytoma (microcystic)." He received no chemotherapy or radiation therapy and remained well for 11 years. The patient presented again in late 1995 with progressive seizure activity. Both CT and magnetic resonance imaging demonstrated a recurrent enhancing partly cystic lesion. A Grade IV astrocytoma was resected, and within the malignant tumor was a superficial area reminiscent of a dysembryoplastic neuroepithelial tumor (DNT). Data on the lesion that had been resected in 1984 were reviewed, and in retrospect the lesion was identified as a DNT of the complex form. It was bordered by cortical dysplasia and contained glial nodules, in addition to the specific glioneuronal element. The glial nodules were significant for moderate pleomorphism and rare mitotic figures. The Ki67 labeling index averaged 0.3% in the glial nodules and up to 4% focally. Cells were rarely Ki67 positive within the glioneuronal component. This case is the first documented example of malignant transformation of a DNT. It serves as a warning of the potential for malignant transformation in this entity, which has been traditionally accepted as benign. This warning may be especially warranted when confronted with complex forms of DNT. The completeness of resection in the benign state is of paramount importance.

Brain tumors in surgical neuropathology of intractable epilepsies, with special reference to cerebral dysplasias

Surgical specimens from 30 patients (13 males and 17 females) with intractable epilepsy with brain tumors and allied lesions were histopathologically examined: 4 of nonneurogenic origin (1 angiolipoma with cortical dysplasia and 3 cavernous hemangiomas), 2 low-grade fibrillary astrocytomas, 1 pleomorphic xanthoastrocytoma, 3 pilocytic astrocytomas with nuclear polymorphism, 1 oligoastrocytoma, 9 gangliogliomas, 3 gangliogliomatous lesions combined with tuberous sclerosis-like dysplastic changes, and 7 undetermined lesions suspected of being mixed glioma, dysembryoplastic neuroectodermal tumor (DNT), or dysplasia. They were all located supratentorially: in the temporal lobe in 21, frontal lobe in 6, and parietooccipital lobe in 3. The age of onset was under 20 years in most patients. Some kinds of dysplasias, such as focal cortical dysplasia, glioneuronal heterotopia, and clustered neurons in the hippocampus and amygdaloid nucleus, were combined in 11 cases, especially those with age of onset under 10 years. Pilocytic astrocytoma-like features were seen in 5 of the gangliogliomas and 3 of the undetermined lesions, and DNT-like features in 2 of the former and 3 of the latter. Gangliogliomas, pilocytic astrocytomas, mixed gliomas, DNTs, and dysplasias may be closely inter-related in the development of intractable epilepsies of young patients.

[Temporal lobe epilepsy and ganglioglioma in children. Clinical aspects, imagery and neuropathology; nosological discussion of six cases]

BACKGROUND

Gangliogliomas belong to debated nosological entity. They are classified as neuronal or neuroglial tumors.

PATIENTS AND METHODS

Six children aged from 4 months to 15 years (mean age: 4 years and 6 months) were initially seen for partial seizures resistant to treatment. Tumoral resection was performed in all six. Diagnosis was made from immunohistological study of the tumor.

DISCUSSION

Gangliogliomas are non-malignant, with a good prognosis, even if inaugural clinical manifestations are severe. Neuroradiological diagnosis with astrocytomas and cortical dysplasia is not easy, and pathological distinction from cortical dysplasia is difficult.

CONCLUSION

The immunohistochemical confirmation of diagnosis permits a logical therapeutic attitude: complete resection of tumor is followed by an excellent outcome.

The current state of epilepsy surgery

Epilepsy surgery is an effective therapy for many patients with refractory partial seizures. The results of epilepsy surgery have improved with advances in the evaluation of patients for surgery and the care of patients during and after surgery. This review looks at recent innovations in imaging modalities to identify the candidates for surgery who will benefit most, to identify subtle pathology, to resect the epileptogenic focus more precisely, and to preserve functionally important cortex in order to achieve the best possible outcome. Patient selection and the identification and removal of the epileptogenic focus, in a safe manner, are crucial for good outcome.