Chapter 18

Question 1

Most defects of the spinal cord result from abnormal closure of the neural folds in the third and fourth weeks of development. The resulting abnormalities, ____, may involve the meninges, vertebrae, muscles, and skin.

Answer 1

neural tube defects [NTDs]

Question 2

_____ is a general term for NTDs affecting the spinal region. It consists ofa splitting of the vertebral arches and may or may not involve underlying neural tissue

Answer 2

Spina bifida

Question 2

___ is a defect in the vertebral arches that is covered by skin and normally does not involve underlying neural tissue

Answer 2

Spina bifida occulta

Question 2

Occasionally, the neural folds do not elevate but remain as a flattened mass of neural tissue [spina bifida with myeloschisis or ____]

Answer 2

rachischisis

Question 2

In some cases, only fluid filled meninges protrude through the defect [____]; in others, neural tissue is included in the sac [___]

Answer 2

meningocele - myelomeningocele

Question 3

___ requiring intervention develops in 80% to 90% of children born with severe NTDs and is often related to the presence of an ____ [herniation of part of the cerebellum into the foramen magnum], which obstructs the flow of cerebrospinal fluid and causes the hydrocephalus.

Answer 3

Hydrocephaly - Arnold-Chiari malformation

Question 4

The origin of most NTDs is multifactorial, and the likelihood of having a child with such a defect increases significantly once one affected offspring is ___

Answer 4

born

Question 5

Prevention of many NTDs is possible if women take ___ starting at least 1 month prior to conception and then throughout their pregnancy. Such a protocol reduces the occurrence of NTDs by as much as 50% to 70%.

Answer 5

folic acid [400 ug/day]

Question 6

Occasionally, a small portion of Rathke pouch persists in the roof of the pharynx as a ___.

Answer 6

pharyngeal hypophysis

Question 6

Folic acid may also reduce the incidence of ___. Because approximately 50% of all pregnancies are unplanned, it is recommended that all women of childbearing age take a multivitamin containing 400 ug of folic acid daily

Answer 6

autism spectrum disorder [ASD]

Question 7

___ arise from remnants of Rathke pouch. They may form within the sella turcica or along the stalk of the pituitary but usually lie above the sella. They may cause hydrocephalus and pituitary dysfunction [e.g., diabetes insipidus, growth failure]

Answer 7

Craniopharyngiomas

Question 8

_____ refers to a spectrum of abnormalities in which a loss of midline structures results in malformations of the brain and face

Answer 8

Holoprosencephaly [HPE]

Question 9

In severe cases, the lateral ventricles merge into a single ___the eyes are fused, and there is a single nasal chamber along with other midline facial defects

Answer 9

telencephalic vesicle [alobar HPE],

Question 10

Mutations in ___, the gene that regulates establishment of the ventral midline in the CNS, result in some forms of HPE

Answer 10

SHH

Question 11

Another cause is defective ____ leading to
_____

Answer 11

cholesterol biosynthesis - Smith-Lemli-Opitz syndrome

Question 12

These children have craniofacial and limb defects, and 5% have HPE. Smith—Lemli - Opitz syndrome is an autosomal recessive condition due to abnormalities in ____, which metabolizes 7-dehydrocholesterol to cholesterol

Answer 12

7-dehydrocholesterol reductase

Question 13

Other genetic causes include mutations in the transcription factors ____, ___, and the ___

Answer 13

SINE OCULIS HOMEOBOX 3 [SIX3] - TG-INTERACTING FACTOR [TGIF] - ZINC FINGER PROTEIN [ZIC2]

Question 14

____ is a rare disorder in which large clefts occur in the cerebral hemispheres, sometimes causing a loss of brain tissue. Mutations in the homeobox gene ___ appear to account for some of these cases.

Answer 14

Schizencephaly - EMX2

Question 15

Ossification defects in bones of the skull can result in ____, ____, and ___

Answer 15

meningoceles - meningoencephallocates - meningohydroencephalceles

Question 16

If the opening of the occipital bone is small, only meninges bulge through it [___], but if the defect is large, part of the brain and even part of the ventricle may penetrate through the opening into the meningeal sac

Answer 16

meningocele

Question 17

The latter two malformations are known as ___ and ___, respectively. These defects occur in 1/12,000 births

Answer 17

meningoencephalocele - meningohydroencephocele

Question 18

___ is characterized by failure of the cephalic part of the neural tube to close. As a result, the vault of the skull does not form, leaving the malformed brain exposed.

Answer 18

Exencephaly

Question 19

Later, this tissue degenerates, leaving a mass of necrotic tissue. This defect is called ___, although the brainstem remains intact

Answer 19

anencephaly

Question 20

In some cases, the closure defect of the neural tube extends caudally into the spinal cord, and the abnormality is called
____

Answer 20

craniorachischisis

Question 21

Because anencephalic fetuses lack a swallowing reflex, the last 2 months of pregnancy are characterized by ___

Answer 21

polyhydramnios

Question 22

____ is characterized by an abnormal accumulation of ___ within the ventricular system. In most cases, hydrocephalus in the newborn is due to an obstruction of the ____

Answer 22

Hydrocephalus - CSF - aqueduct of Sylvius [aqueductal stenosis]

Question 23

____ describes a cranial vault that is smallerthan normal. Because the size of the cranium depends on growth of the brain, the underlying defect is in brain development. Causation of the abnormality is varied; it may be genetic [autosomal recessive] or caused by prenatal insults, such as infection or exposure to drugs or other teratogens. lntellectual disability occurs in more than half the cases

Answer 23

Microcephaly

Question 24

For example, the ___ may be partially or completely absent without much functional disturbance. Likewise, partial or complete absence of the cerebellum may result in only a slight disturbance of coordination

Answer 24

corpus callosum

Question 25

On the other hand, cases of severe ____ may not be associated with morphologically detectable brain abnormalities

Answer 25

intellectual disability

Question 26

The leading cause of intellectual disability is, however, ____

Answer 26

maternal alcohol abuse

Question 27

____ are rare tumors involving chromaffin cells that result in excessive production and release of epinephrine and norepinephrine causing paroxysmal episodes of hypertension, increased heart rate, headaches, and other associated symptoms. 25% are familial and have been associated with mutations in the ___ that plays a role in neural crest cell migration

Answer 27

Pheochromocytomas - RET gene

Question 28

____ results from a failure of parasympathetic ganglia to form in the wall of a part or all of the colon and rectum because the neural crest cells fail to migrate

Answer 28

Congenital megacolon [Hirschsprung disease]

Question 29

Most familial cases of Hirschsprung disease are caused by mutations in the ___, which codes for a cell membrane ___

Answer 29

RETgene - tyrosine kinase receptor

Question 30

The ligand for the receptor is ____ secreted by mesenchyme cells through which crest cells migrate

Answer 30

GLIAL CELL DERIVED NEUROTROPHIC GROWTH FACTOR