Clinical Correlations

A. Variations of spina bifida and encephalocele (Figure 12-5). Spina bifida occurs when the bony vertebral arches fail to form properly, creating a vertebral defect, usually in the sacrolumbar region. Encephalocele occurs when the bony skull fails to form properly, creating a skull defect, usually in the occipital region.

Dura and arachnoid

Skin

Dura and arachnoid

Skin

Hairs

Dura and arachnoid

Hairs

Dura and arachnoid

Dura And Arachnoid
Dura and arachnoid
Spina Bifida Occulta Tuft Hair

Dura and arachnoid

Skin

Dura and arachnoid

Skin

Spina bifida with rachischisis

Spina bifida occulta

Spina bifida with meningocele

Spina bifida with meningomyelocele

Spina bifida with rachischisis

Dura and arachnoid Skin

Occipital Meningomyelocele Mri

Meningocele

Dura and arachnoid Skin

Dura and arachnoid Skin

Cerebella Meningoencephalocele

Meningoencephalocele

Meningocele

Meningoencephalocele

Meningohydroencephalocele

Dura and arachnoid Skin

Cranial Bifida Meningohydroencephalocele

Meningohydroencephalocele

Dura and arachnoid Skin

Figure 12-5. Variations of spina bifida and encephalocele. SP = spinal cord; CSF = cerebrospinal fluid; V = ventricle. (Modified from Haines DE [edj: Fundamental Neuroscience. New York, Churchill Livingstone, 1997, p 69.)

1. Spina bifida occulta (Figure 12-6 A) is evidenced by a tuft of hair in the sacroiumbar region. It is the least severe variation and occurs in 10% of the pop-illation.

2. Spina bifida with meningocele occurs when the meninges project through a vertebral defect and form a sac filled with CSF. The spinal cord remains in its normal position.

3. Spina bifida with meningomyelocele (Figure 12-6 B). This form occurs when the meninges and spinal cord project through a vertebral defect to form a sac.

4. Spina bifida with rachischisis (Figure 12-6 C) occurs when the posterior neuro-pore fails to close, thus creating an open neural tube that lies on the surface of the back. It is the most severe type of spina bifida, causing paralysis from the level of the defect caudally.

5. Meningocele (Figure 12-6 D) occurs when the meninges project through the skull defect. It is a rare condition.

6. Meningoencephalocele occurs when the meninges and brain protrude through rhe skull defect. This defect usually comes to medical attention within the infant's first few days or weeks of life. The outcome is poor (i.e., approximately 75% of the infants die or are severely retarded).

7. Meningohydroencephalocele (Figure 12-6 E) occurs when the meninges, brain, and a portion of the ventricle protrude through the skull defect.

B. Anencephaly (meroanencephaly) (see Figure 12-6 F, Q) occurs when the anterior neuropore fails to close. It results in failure of the brain to develop (however, a rudimentary brain stem is present), failure of the lamina terminalis to form, and failure of the bony cranial vault to form.

1. Anencephaly is incompatible with extrauterine life. If not stillborn, infants with anencephaly survive for only a few hours or few weeks. Anencephaly is the most common serious birth defect seen in stillborn infants.

2. Anencephaly is easily diagnosed by ultrasound, and a therapeutic abortion is usually performed at the mother's request.

C. Arnold-Chiari malformation (Figure 12-7 A) occurs when vermis and tonsils of the cerebellum and medulla oblongata herniate through the foramen magnum.

1. Clinical signs are caused by compression of the medulla oblongata and stretching of CN IX, CN X, and CN XII. They include spastic dysphonia, difficulty in swallowing, laryngeal stridor (vibrating sound heard during respiration as a result of obstructed airways), diminished gag reflex, apnea, and vocal cord paralysis.

2. This malformation is commonly associated with a lumbar meningomyelocele, platybasia (bone malformation of base of skull) along with malformation of the oc-cipitovertebral joint, and hydrocephalus (caused by several factors; however, approximately 50% of cases demonstrate aqueductal stenosis).

D. Hydrocephalus is a dilatation of the ventricles caused by an excess of CSF, which may result from either a blockage of CSF circulation or rarely an overproduction of CSF (e.g., due to a choroid plexus papilloma).

1. Communicating (nonobstructive) hydrocephalus. In this type of hydrocephalus there is free communication between the ventricles and the subarachnoid space. The blockage of CSF in this type of hydrocephalus is usually in the subarachnoid space or arachnoid granulations and results in the enlargement of all the ventricular cavities as well as the subarachnoid space.

Information Spina Bifida

Figure 12-6. (A) Spina bifida occulta. Note the presence of the bony vertebral bodies (VB) along the entire length of the vertebral column. However, the bony spinous processes terminate much higher (*) because the vertebral arches fail to form properly. This creates a vertebral defect. The spinal cord is intact. ¡B) Spina bifida with meningomyelocele as seen on an ultrasonogram of a 14-week-old fetus. Note the cyst-like protrusion (m = meningomyelocele) and the normal vertebrae (v) superior to the meningomyelocele. (C) Spina bifida with rachischisis in a newborn infant. Note the open neural tube. (D) Photograph of an occipital meningocele (*) in a fetus. (E) Meningohydroencephalocele as seen on magnetic resonance image (MRI). (F) Anencephaly in newborn infant. (G) Anencephaly as seen on an ultrasonogram of a 14-week-old fetus. Note the orbit (o) and the remnant of brain (b). (A and E, from Haines DE [edj: Fundamental Neuroscience. New York, Churchill Livingstone, 1997, pp 68, 69. B and G, Courtesy of Dr. Lyndon M. Hill, Magee-Women's Hospital, Pittsburgh, PA. From Moore KL and Persaud TVN: The Developing Human, 6th ed. Philadelphia, WB Saunders, 1998, p 464, 480. C, From Papp Z [ed): Atlas of Fetal Diagnosis. Amsterdam, Elsevier, 1992, p 128. D, From Carlson BM: Human Embryology and Developmental Biology, 2nd ed. St. Louis, CV Mosby, 1999, p 244.)

Figure 12-6. (A) Spina bifida occulta. Note the presence of the bony vertebral bodies (VB) along the entire length of the vertebral column. However, the bony spinous processes terminate much higher (*) because the vertebral arches fail to form properly. This creates a vertebral defect. The spinal cord is intact. ¡B) Spina bifida with meningomyelocele as seen on an ultrasonogram of a 14-week-old fetus. Note the cyst-like protrusion (m = meningomyelocele) and the normal vertebrae (v) superior to the meningomyelocele. (C) Spina bifida with rachischisis in a newborn infant. Note the open neural tube. (D) Photograph of an occipital meningocele (*) in a fetus. (E) Meningohydroencephalocele as seen on magnetic resonance image (MRI). (F) Anencephaly in newborn infant. (G) Anencephaly as seen on an ultrasonogram of a 14-week-old fetus. Note the orbit (o) and the remnant of brain (b). (A and E, from Haines DE [edj: Fundamental Neuroscience. New York, Churchill Livingstone, 1997, pp 68, 69. B and G, Courtesy of Dr. Lyndon M. Hill, Magee-Women's Hospital, Pittsburgh, PA. From Moore KL and Persaud TVN: The Developing Human, 6th ed. Philadelphia, WB Saunders, 1998, p 464, 480. C, From Papp Z [ed): Atlas of Fetal Diagnosis. Amsterdam, Elsevier, 1992, p 128. D, From Carlson BM: Human Embryology and Developmental Biology, 2nd ed. St. Louis, CV Mosby, 1999, p 244.)

Arnold Chiari Malformation

Figure 12-7. (A) Arnold-Chiari malformation as seen on a magnetic resonance image (MRI). Note the herniation of the brain stem and cerebellum (arrow) through the foramen magnum, (ß) Congenital aqueductal stenosis as seen on an MRI. Note the selective enlargement of the lateral ventricle (LV) and third ventricle (3V). The fourth ventricle (4V) is normal in size. (C) Dandy-Walker syndrome as seen on MRI. LV = lateral ventricle; 3V = rhird ventricle; (J = cerebellar vermis; CT = cyst; 4 V = fourth ventricle. (D) Holoprosen-cephaly. Note the fuse thalami at the base of the one large ventricle. (E) A tethered spinal cord as seen on MRI. Note the tethered spinal cord (arrow) and a dilated thecal sac (*) along with a posterior bone defect. (A and E, from Heimer L: The Human Brain and Spinal Cord: Functional Neuroanatomy and Dissection Guide, 2nd ed. New York, Springer-Verlag, 1995, p 39. B and C, from Afifi AK, Bergman RA: Functional Neuroanatomy: Text and Atlas. New York, McGraw-Hill, 1998, pp 580 and 585. D, From Papp Z [ed]: Atlas of Fetal Diagnosis. Amsterdam, Elsevier, 1992, p 101.)

Figure 12-7. (A) Arnold-Chiari malformation as seen on a magnetic resonance image (MRI). Note the herniation of the brain stem and cerebellum (arrow) through the foramen magnum, (ß) Congenital aqueductal stenosis as seen on an MRI. Note the selective enlargement of the lateral ventricle (LV) and third ventricle (3V). The fourth ventricle (4V) is normal in size. (C) Dandy-Walker syndrome as seen on MRI. LV = lateral ventricle; 3V = rhird ventricle; (J = cerebellar vermis; CT = cyst; 4 V = fourth ventricle. (D) Holoprosen-cephaly. Note the fuse thalami at the base of the one large ventricle. (E) A tethered spinal cord as seen on MRI. Note the tethered spinal cord (arrow) and a dilated thecal sac (*) along with a posterior bone defect. (A and E, from Heimer L: The Human Brain and Spinal Cord: Functional Neuroanatomy and Dissection Guide, 2nd ed. New York, Springer-Verlag, 1995, p 39. B and C, from Afifi AK, Bergman RA: Functional Neuroanatomy: Text and Atlas. New York, McGraw-Hill, 1998, pp 580 and 585. D, From Papp Z [ed]: Atlas of Fetal Diagnosis. Amsterdam, Elsevier, 1992, p 101.)

2. Noncommunicating (obstructive) hydrocephalus. In this type of hydrocephalus there is a lack of communication between the ventricles and the subarachnoid space. The blockage of CSF in this type of hydrocephalus is in the foramen of Monro, cerebral aqueduct, or foramina of Magendie and Luschka and results in the enlargement of only those ventricular cavities proximal to the blockage. There are two types of congenital hydrocephalus, both of which produce a noncommunicating (obstructive) hydrocephalus:

a. Congenital aqueductal stenosis (Figure 12-7 B) is the most common cause of congenital hydrocephalus. This type may be transmitted by an X-linked trait, or it may be caused by cytomegalovirus or toxoplasmosis.

b. Dandy-Walker syndrome (see Figure 12-7 C) appears to be associated with atresia of the outlet foramina of Luschka and Magendie, although this remains controversial. This syndrome is usually associated with dilatation of the fourth ventricle, agenesis of the cerebellar vermis, occipital meningocele, and frequently agenesis of the splenium of the corpus callosum.

E. Holoprosencephaly (arhinencephaly) (Figure 12-7 D) occurs when the prosencephalon fails to cleave down the midline such that the telencephalon contains a sin-gle ventricular cavity.

1. Holoprosencephaly is characterized by the absence of olfactory bulbs and tracts (arhinencephaly).

2. Holoprosencephaly is often seen in trisomy 13 (Patau's syndrome).

3. This is the most severe manifestation of fetal alcohol syndrome, resulting from alcohol abuse during pregnancy (especially in the first 4 weeks of pregnancy).

F. Tethered spinal cord (Figure 12-7 E) occurs when a thick and short filum terminate forms. The result is weakness and sensory deficits in the lower extremity and also a neurogenic bladder. Tethered spinal cord is frequently associated with lipomatous tumors or lipomyelomeningoceles. Deficits usually improve after transection.

G. Chordoma is a tumor that arises from remnants of the notochord.

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