Cranial and Spinal Dysraphisms
The term cranium bifidum is used to designate a defective closure of the skull by analogy with that of its spinal counterpart (spina bifida). Both malformations are regarded as neural tube defects (NTD); however, only anencephaly is a true NTD. The term e
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7.1 Cranial and Spinal Dysraphisms
7.1.1
Encephaloceles and Related Malformations
Juan F. Martínez-Lage and Miguel Angel Pérez-Espejo 7.1.1.1
Introduction: Concepts and Definitions
The term cranium bifidum is used to designate a defective closure of the skull by analogy with that of its spinal counterpart (spina bifida). Both malformations are regarded as neural tube defects (NTD); however, only anencephaly is a true NTD. The term encephalocele or meningoencephalocele designates a protrusion of any of the intracranial contents through a congenital defect in the skull, whether at the cranial vault or at the base [1, 3, 4, 7]. An encephalocele includes brain parenchyma (Figs. 7.1.1–7.1.3), while a cranial meningocele (Fig. 7.1.4) contains only cerebrospinal fluid (CSF) and is lined by arachnoid [1, 3, 4, 7]. In certain cases, encephaloceles may comprise parts of a ventricle or choroid plexus [1, 3, 4, 7]. Atretic cephalocele (Fig. 7.1.5) refers to a small-sized midline subscalp lesion
that contains no cerebral tissue but neural remnants [5, 7, 10]. There is no clear-cut limit to separate the diverse clinical forms that constitute the spectrum of cranium bifidum. At present, the terms cephalocele and encephalocele are used interchangeably to encompass all these lesions [7]. Table 7.1.1 summarizes the definitions of the spectrum of cranial congenital defects, and Table 7.1.2 classifies cephaloceles into four main types according to their composition.
Table 7.1.2 Classification of the four main forms of cranium bifidum according to their contents Brain CSF NeuroectoSkull dermal origin defect tissues Encephalocele
+
+
−
+
Cranial meningocele
−
+
+/−
+
Atretic cephalocele
−
−
+
+
Subscalp nodules of heterotopic tissue
−
−
+
−
Table 7.1.1 Some terms and definitions of the spectrum of cranium bifidum malformations Term
Definition
Cranium bifidum
Any congenital defect of the skull and/or meningeal or cerebral tissue
Cranium bifidum occultum
Cranial defect covered by normal skin
Acalvaria
Congenital absence of the cranial vault
Anencephaly (acrania)
Absence of the skull vault and of cerebral tissue
Exencephaly
Severely malformed and exposed brain with absence of the skin and cranial vault; a forerunner of anencephaly
Cephalocele
Skull defect associated with herniation of some intracranial content
Encephalocele
Herniation of brain through a cranial defect
Ventriculoencephalocele
Same as above plus extracranial protrusion of ventricle
Cranial meningocele
Sac with herniated meninges and CSF through a skull defect
Atretic cephalocele
Small subscalp lesion with cerebral, vascular and meningeal rests
Subscalp heterotopic nodules
Small subscalp lesion containing vestigial tissues and no cranial defect
Scalp aplasia cutis congenita
Focal absence of the scalp with or without meningeal or cranial defect
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7.1 Cranial and Spinal Dysraphisms
7.1.1.2
Anencephaly
Anencephaly is a lethal birth defect characterized by the absence of all or part of the scalp and skull (acran
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