Xcongenital Malformations Of The

A. Anencephaly (meroanencephaly) results from failure of the anterior neuropore to close. As a result, the brain does not develop. The frequency of this condition is 1:1000.

Third ventricle

Optic chiasm

Adenohypophysis (anterior lobe)

Pars tuberalis of adenohypophysis

Craniopharyngeal Canal

Sphenoid bone

Infundibulum of hypothalamus

Diaphragma sellae

Neurohypophysis (posterior lobe)

Dura

Pars intermedia of anterior lobe

Craniopharyngeal canal

Remnant of Rathke's pouch

Figure 4-5. Midsagittal section through the hypophysis and sella turcica. The adenohypophysis, including the pars tuberalis and pars intermedia, is derived from Rathke's pouch (oroectoderm). The neurohypophysis arises from the infundibulum of the hypothalamus (neuroectoderm).

Third ventricle

Sphenoid bone

Craniopharyngeal canal

Remnant of Rathke's pouch

Optic chiasm

Infundibulum of hypothalamus

Diaphragma sellae

Adenohypophysis (anterior lobe)

Neurohypophysis (posterior lobe)

Dura

Pars tuberalis of adenohypophysis

Pars intermedia of anterior lobe

Figure 4-5. Midsagittal section through the hypophysis and sella turcica. The adenohypophysis, including the pars tuberalis and pars intermedia, is derived from Rathke's pouch (oroectoderm). The neurohypophysis arises from the infundibulum of the hypothalamus (neuroectoderm).

Craniopharyngioma Infundibulum

Figure 4-6. Midsagittal section through the brain stem and diencephalon. A craniopharyngioma (arrows) lies suprasellar in the midline. It compresses the optic chiasm and hypothalamus. This tumor is the most common supratentorial tumor that occurs in childhood and the most common cause ot hypopituitarism in children. I his is a T1-weighted magnetic resonance imaging scan.

Figure 4-6. Midsagittal section through the brain stem and diencephalon. A craniopharyngioma (arrows) lies suprasellar in the midline. It compresses the optic chiasm and hypothalamus. This tumor is the most common supratentorial tumor that occurs in childhood and the most common cause ot hypopituitarism in children. I his is a T1-weighted magnetic resonance imaging scan.

Children With Chiari Malformation

Figure 4-7. Amold-Chiari malformation. Midsagittal section. (A) Normal cerebellum, fourth ventricle, and brain stem. (B) Abnormal cerebellum, fourth ventricle, and brain stem showing the common congenital anomalies: (1) beaking ol the rectal plate, (2) aqucductal stenosis, (3) kinking and rranstoraminal herniation of the medulla into the vertebral canal, and herniation and unrolling of the cerebellar vermis into the vertebral canal. An accompanying meningomyelocele is common. (Reprinted with permission from Fix JD: BRS Neuroanatomy. Baltimore, Williams «Si Wilkins, 1996, p. 72.)

Fix Neuroanatomy Chiari

Figure 4-7. Amold-Chiari malformation. Midsagittal section. (A) Normal cerebellum, fourth ventricle, and brain stem. (B) Abnormal cerebellum, fourth ventricle, and brain stem showing the common congenital anomalies: (1) beaking ol the rectal plate, (2) aqucductal stenosis, (3) kinking and rranstoraminal herniation of the medulla into the vertebral canal, and herniation and unrolling of the cerebellar vermis into the vertebral canal. An accompanying meningomyelocele is common. (Reprinted with permission from Fix JD: BRS Neuroanatomy. Baltimore, Williams «Si Wilkins, 1996, p. 72.)

Corpus callosum Polymicrogyria

Corpus callosum Polymicrogyria

Polymicrogyria

Figure 4-8. Dandy-Walker malformation. Midsagittal section. An enormous dilation of the fourth ventricle results from failure of the foramina of Luschka and Magendie to open. This condition is associated with occipital meningocele, elevation of the confluence of the sinuses (torcular Herophili), agenesis of the cerebellar vermis, and splenium of the corpus callosum. (Reprinted with permission from Dudek RW, Fix JO: BRS Embryology. Baltimore, Williams & Wilkins, 1997, p. 97.)

Figure 4-8. Dandy-Walker malformation. Midsagittal section. An enormous dilation of the fourth ventricle results from failure of the foramina of Luschka and Magendie to open. This condition is associated with occipital meningocele, elevation of the confluence of the sinuses (torcular Herophili), agenesis of the cerebellar vermis, and splenium of the corpus callosum. (Reprinted with permission from Dudek RW, Fix JO: BRS Embryology. Baltimore, Williams & Wilkins, 1997, p. 97.)

B. Spina bifida results from failure of the posterior neuropore to form. The defect usually occurs in the sacrolumbar region. The frequency of spina bifida occulta is 10%.

C. Cranium bifidum results from a defect in the occipital bone through which meninges, cerebellar tissure, and the fourth ventricle may herniate.

D. Arnold-Chiari malformation (type 2) has a frequency of 1:1000 (Figure 4-7).

E. Dandy^Walker malformation has a frequency of 1:25000. It may result from riboflavin inhibitors, posterior fossa trauma, or viral infection (Figure 4-8).

F. Hydrocephalus is most commonly caused by stenosis of the cerebral aqueduct during development. Excessive cerebrospinal fluid accumulates in the ventricles and subarachnoid space. This condition may result from maternal infection (cytomegalovirus and toxoplasmosis). The frequency is 1:1000.

G. Fetal alcohol syndrome is the most common cause of mental retardation. It includes microcephaly and congenital heart disease; holoprosencephaly is the most severe manifestation.

H. Holoprosencephaly results from failure of midline cleavage of the embyonic forebrain. The telencephalon contains a singular ventricular cavity; is seen is trisomy 13 (Patau syndrome); the corpus callosum may be absent; holoprosencephaly is the most severe manifestation of the fetal alcohol syndrome.

I. Hydranencephaly results from bilateral hemispheric infarction secondary to occlusion of the carotid arteries. The hemispheres are replaced by hugely dilated ventricles.

Essentials of Human Physiology

Essentials of Human Physiology

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