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KEY POINTS

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KEY POINTS

  1. Fetal brain tumors are rare and usually diagnosed only in the 3rd trimester of pregnancy or even only after delivery.

  2. Most types have a poor prognosis lipomas and choroid plexus papillomas are the exception having a better prognosis.

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CONGENITAL CENTRAL NERVOUS SYSTEM TUMORS

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Definition

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Congenital central nervous system (CNS) tumors represent a distinct group of tumors that differs from familial and genetic CNS tumors. It is accepted that these tumors include those present at birth or diagnosed during the first year of life.

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Incidence/Prevalence

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Congenital CNS tumors have been reported to represent between 0.5% and 1.5% of all pediatric brain tumors.1 The fact that many of the congenital CNS tumors often result in intrauterine fetal demise makes the accurate assessment of the true incidence difficult.

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The incidence in the United States as reported in the Third National Cancer Survey in 1971 was 14 CNS tumors per 1 million live births per year.2 A similar study from Germany showed an incidence much higher (3.6 per 100,000 births).3

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Pathogenesis

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We still have no knowledge or means to identify the cause or causes of malignancies that occur in early life. Fetal and/or maternal exposure to exogenous factors, including ionizing irradiation, drugs, and viruses, may start the biological mechanisms responsible for tumor formation.4 Developmental errors during embryonic and fetal maturation may result in congenital tumors.5 More than 100 years ago, Durante6 and Cohnheim7 proposed the "cell rest" theory that may be adapted to embryonic tumors. These authors believed that more cells are produced than required for the formation of an organ or tissue and that the origins of embryonic tumors rest in developmental errors in these surplus embryonic rudiments. Embryonic tumors developing after infancy are explained by the persistence of cell rests or developmental vestiges.8 Developmentally anomalous tissues (ie, hamartomas and dysgenic gonads) are a source of neoplasms in older children and adults. When any of these developmentally abnormal tissues are present at birth, it is inferred that the cells failed to mature, migrate, or differentiate properly during intrauterine life.

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A genetic model of carcinogenesis has been introduced in an attempt to clarify the pathogenesis and behavioral peculiarities of certain embryonic tumors.9 According to this hypothesis, embryonic neoplasms arise as a result of two mutational events in the genome. The first mutation is prezygotic in familial cases and postzygotic in nonfamilial; the second mutation is always postzygotic.

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The concept that teratogenesis and oncogenesis have shared mechanisms has been well documented by numerous examples. There is probably simultaneous or sequential cellular and tissue reaction to specific injurious agents. The degree of cytodifferentiation, the metabolic or immunological state of the embryo or fetus, and the length of time of exposure to the ...

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