Congenital Anomalies of the Central Nervous System

Question 1

What maternal hormone level between 16 and 18 weeks’ gestation identifies infants at high risk for neural tube defects?

Answer 1

An elevated materna serum α-fetoprotein level.

Question 2

What drug taken during pregnancy greatly increases the risk of neural tube defects in the infant?

Answer 2

Valproic acid

Question 3

What maternal supplement is used to reduce the risk of neural tube defects in the infant?

Answer 3

Folic acid. 50% or more of neural tube defects are prevented with periconceptional folic acid supplementation.

Question 4

What is spina bifida?

Answer 4

It is a congenital defect in which a portion of the neural tube does not form properly. Symptoms vary depending on the type and the location of the lesion, but can include motor and/or sensory defects in the lower body, loss of bladder and bowel control, scoliosis, hydrocephalus, learning disabilities, and deformities of the hip, leg, and/or foot.

Question 5

What are the three types of spina bifida?

Answer 5

Spina bifida occulta (mild effects, if any; very common), meningocele (moderate severity; rare), and myelomeningocele (very severe; most common).

Question 6

Which type of spina bifida is most common?

Answer 6

Myelomeningocele

Question 7

What is a meningocele?

Answer 7

It is the rarest form of spina bifida involving herniation of the meninges - but not the spinal cord - through a defect in the posterior vertebral arches.

Question 8

What might one see on physical exam in a patient with a meningocele?

Answer 8

On transillumination along the vertebral column you might find a fluctuant midline mass, typically in the lower back. Most are covered with skin and pose no urgent problem.

Question 9

Which meningoceles require immediate surgical intervention?

Answer 9

Children with CSF leaking from the meningocele or with incomplete skin covering need immediate surgical repair to prevent meningitis.

Question 10

What family history finding increases the risk for development of myelomeningocele?

Answer 10

Risk increases with an increased number of affected siblings.

Question 11

Which structures are involved in myelomeningoceles?

Answer 11

Nerve roots, spinal cord, meninges, vertebral bodies, and skin.

Question 12

Where are myelomeningoceles most likely to occur?

Answer 12

They can be located anywhere along the neuraxis but are most commonly located in the lumbosacral region.

Question 13

What is the general rule for estimating extent and degree of neurologic deficit based on the location of the myelomeningocele?

Answer 13

As a general rule, the lower the lesion is along the spine, the less severe the neurologic defects. The exception is the cervical and upper thoracic regions which, if affected, actually cause minimal neurologic manifestations.

Question 14

What other neurological abnormality commonly accompanies myelomeningoceles?

Answer 14

Myelomeningoceles cause a downward displacement of the brain stem and cerebellar tonsils down into the spinal column, known as Chiari II malformation. This, in turn, causes an obstruction to normal CSF flow, with a resulting hydrocephalus occuring 85% of the time.

Question 15

How is myelomeningocele usually treated?

Answer 15

Treatment involves a multidisciplinary team, with surgical repair usually occurring within the first few days of life. After repair, many infants require a VP shunt for ongoing management of hydrocephalus.

Question 16

What GU abnormality should providers be on the lookout for in patients with myelomeningocele?

Answer 16

Pay special attention to the GU system and bladder catheterization because neurogenic bladder is common and easy to miss.

Question 17

Describe spina bifida occulta.

Answer 17

Spina bifida occulta consists of a midline defect of the spinous processes without protrusion of the spinal cord or meninges. The defect is usually covered with skin and not obvious on external physical exam. The defect is relatively common and rarely causes any problems.

Question 18

What can a patch of hair located at the lower back indicate?

Answer 18

Cutaneous markers such as a patch of hair, lipoma, skin-color changes, or a dermal sinus in the midline of the lower back may be the only indication of underlying spina bifida occulta and occur due to the abnormal neuroectodermal differentiation in that area.

Question 19

What is the usual therapy for spina bifida occulta?

Answer 19

For symptomatic patients, surgical treatment is often warranted. Asymptomatic patients need close monitoring to evaluate for development of neurological or urological problems.

Question 20

What is a dermoid sinus and what might its presence indicate?

Answer 20

A dermoid sinus presents as a small skin opening leading into a narrow duct below the skin. It sometimes has protruding hairs, a hairy patch, or a vascular nevus on the surface. It often occurs in association with spina bifida occulta. In the lumbar region, it can indicate the presence of a meningocele. In the occipital region, it can indicate the presence of an encephalocele.

Question 21

What anatomic abnormality might one suspect in a patient with recurrent bacterial meningitis?

Answer 21

Occasionally, a dermoid sinus will pass through the dura and result in recurrent infections such as recurrent bacterial meningitis.

Question 22

What is an encephalocele?

Answer 22

An encephalocele is a herniation of the brain, its coverings, or both through a skull defect.

Question 23

Where do encephaloceles most commonly occur?

Answer 23

75% of the time, encephaloceles occur in the occipital region.

Question 24

What finding correlates with neurological outcome in patients with encephalocele?

Answer 24

Significant brain tissue involvement correlates with poor neurological outcome, while the presence of only meninges is correlated with few, if any, neurological defects.

Question 25

What is the treatment for encephalocele?

Answer 25

Prompt surgical removal of the sac and closure of the defect.

Question 26

What is anencephaly?

Answer 26

In anencephaly, both cerebral hemispheres and large parts of the cranium are absent, with associated malformations of the face and eyes commonly occuring as well. It is a uniformly lethal condition.

Question 27

What is the embryologic abnormality which leads to the development of anencephaly?

Answer 27

Anencephaly occurs due to failure of closure of the anterior neural tube (neuropore), which normally closes by 24 days postconception.

Question 28

What dose of folic acid is recommended for women of childbearing age to prevent neural tube defects in their offspring?

Answer 28

The recommended dose is 0.4 to 0.8 mg of folic acid daily.

Question 29

What folic acid dose should be used in women who are on anticonvulsant therapy or who have had a previous child affected with spina bifida?

Answer 29

These women should take 4mg/day of folic acid starting 1 month before attempting conception and continuing through the 1st trimester.

Question 30

What is hydromyelia?

Answer 30

Hydromyelia is a symmetric dilation of the central canal of the spinal cord by CSF and typically communicates with the 4th ventricle.

Question 31

With what (3) conditions does hydromyelia commonly co-occur?

Answer 31

Communicating hydrocephalus, Chiari malformation, and aqueductal stenosis.

Question 32

What are the typical symptoms and management of hydromyelia?

Answer 32

The hydromyelia itself doesn’t usually cause problems, and does not require treatment. However, the conditions it occurs alongside may cause symptoms or require treatment.

Question 33

What is syringomyelia?

Answer 33

It is a paracentral cavity (syrinx) in the spinal cord. It can be localized or involve multiple segments, especially in the cervical spine.

Question 34

With what two other CNS abnormalities is syringomyelia commonly associated?

Answer 34

Chiari I malformation and lumbar myelomeningocele.

Question 35

What symptoms would one expect to be caused by syringomyelia?

Answer 35

Symptoms depend on the location of the syrinx. Wasting of the small muscles of the hand, sensory deficits of the arms, or absence of deep tendon reflexes in the upper extremities are commonly seen with cervical syrinx.

Question 36

What is a Chiari malformation?

Answer 36

It is a hindbrain abnormality in which there is downward displacement of the brainstem and cerebellum.

Question 37

How is syringomyelia typically treated?

Answer 37

Isolated clinically significant syringomyelia is treated with shunting.

Question 38

Describe the anatomic abnormalities which make up the Chiari I malformation.

Answer 38

The cerebellar tonsils or vermis are pushed down below the level of the foramen magnum. Generally, > 0.5 cm displacement is considered significant. ***Include Image 12-2

Question 39

What other CNS abnormality is commonly found in patients with Chiari I malformation?

Answer 39

Chiari I has a strong association with syringomyelia.

Question 40

What are the common symptoms of Chiari I malformation?

Answer 40

Most lesions are asymptomatic and discovered incidentally. Those that cause symptoms are associated with: dysphagia, vertigo, sleep apnea, ataxia, headache, and neck pain, which occur due to dysfunction of the lower cranial nerves, brainstem, and/or spinal cord.

Question 41

Which type of Chiari malformation is most commonly diagnosed at birth?

Answer 41

Chiari II

Question 42

Describe the anatomic abnormalities which make up the Chiari II malformation.

Answer 42

Chiari II occurs when the 4th ventricle and lower medulla are pushed down below the level of the foramen magnum (more than with Chiari I). It blocks the outflow of CSF and 85% of patients have hydrocephalus.

Question 43

What other CNS abnormality is almost always found when myelomeningocele is present?

Answer 43

Chiari II malformation

Question 44

What is the anatomical abnormality that characterizes a Chiari III malformation?

Answer 44

Herniation of the cerebellum occurs through a cervical spina bifida defect. This is an extremely rare phenomenon.

Question 45

What is the treatment for asymptomatic Chiari I malformation?

Answer 45

No treatment is necessary.

Question 46

What is the treatment for symptomatic Chiari I, and all cases of Chiari II or Chiari III malformation?

Answer 46

Surgery, including suboccipital decompression with or without cervical laminectomies.

Question 47

What is Klippel-Feil syndrome triad?

Answer 47

It is characterized by the congenital fusion of various vertebral segments. Clinically, it is characterized by a triad of short neck, low posterior hairline, and limited range of neck motion.

Question 48

Define lissencephaly.

Answer 48

Lissencephaly is caused by defective neuronal migration during embryonic development, causing a smooth cerebral surface with thickened cortical mantle and a lack of cerebral folds (gyri) and grooves (sulci). ***Image 12-3

Question 49

What symptoms are commonly seen in patients with lissencephaly?

Answer 49

FTT, developmental delay, and severe epilepsy. Some are also blind.

Question 50

How is lissencephaly usually managed?

Answer 50

Treatment consists of anticonvulsants to manage the seizures and supportive care for feeding difficulties and impaired motor functioning.

Question 51

What syndrome is associated with lissencephaly?

Answer 51

~15% of cases of lissencephaly occur in association with Miller-Dieker syndrome.

Question 52

What is Miller-Dieker syndrome?

Answer 52

It is caused by a partial deletion of chromosome 17. Patients have prominent forehead, bitemporal “hollowing”, anteverted nostrils, prominent upper lip, micrognathia, and lissencephaly. These patients die early, rarely reaching 10 years of age.

Question 53

Define schizencephaly.

Answer 53

“Split brain” - it is characterized by the occurrence of unilateral or bilateral clefts within the cerebral hemispheres.

Question 54

What clinical manifestations are associated with the presence of schizencephaly?

Answer 54

Patients with bilateral clefts typically have severe epilepsy, microcephaly, severe intellectual disability, and spastic quadriparesis. Those with unilateral clefts often have focal epilepsy and hemiplegic cerebral palsy.

Question 55

How is schizencephaly treated?

Answer 55

Anticonvulsants and physical therapy.

Question 56

Define porencephaly.

Answer 56

Porencephaly refers to the presence of cysts or cavities within the brain.

Question 57

Differentiate between lissencephaly, schizencephaly, and porencephaly.

Answer 57

Lissencephaly = absence of gyri and sulci (smooth brain). Schizencephaly = clefts within the cerebral hemispheres, unilateral or bilateral (split brain). Porencephaly = cysts or cavities within the brain, can be congenital or acquired (holey brain).

Question 58

What is holoprosencephaly?

Answer 58

It is a disorder in the development of the brain due to defective cleavage of the prosencephalon. There are 3 main types (alobar, semilobar, and lobar), but all have lack of forebrain and ventricular division into two distinct hemispheres. Associated facial anomalies are common.

Question 59

Which chromosomal abnormality is most commonly associated with holoprosencephaly?

Answer 59

Holoprosencephaly is most often seen with Trisomy 13, but can also be caused by many other genetic mutations and teratogens.

Question 60

How can agenesis of the corpus callosum be inherited?

Answer 60

It can be inherited as an X-linked dominant, X-linked recessive, or autosomal dominant trait.

Question 61

What is Aicardi syndrome?

Answer 61

It is an X-linked dominant disorder characterized by the triad of agenesis of the corpus callosum, infantile spasms, and retinal abnormalities.

Question 62

Use of what illicit drug by pregnant women has been noted to increase the risk of agenesis of the corpus callosum?

Answer 62

Cocaine use

Question 63

Define hydrocephalus.

Answer 63

An excessive volume of intracranial CSF with ventricular dilatation caused by either impairment of CSF circulation and absorption or increased CSF production.

Question 64

Starting with the paired lateral ventricles, trace the normal flow of CSF through the CNS: Paired lateral ventricles > ** > ** > ** > ** > ** > ** > ** > **.

Answer 64

Paired lateral ventricles > paired foramina of Monro > single midline 3rd ventricle > aqueduct of Sylvius > midline 4th ventricle > 3 exit openings: paired lateral foramina of Luschka and a midline foramen of Magendie > spinal subarachnoid space > intracranial subarachnoid space over the cerebral convexities > absorbed into the venous sinuses via the arachnoid granulations.

Question 65

What is the difference between a noncommunicating and a communicating hydrocephalus?

Answer 65

A noncommunicating (AKA obstructive) hydrocephalus is due to a blockage of CSF flow somewhere in the ventricular system, typically in the foramina of Monro, the aqueduct of Sylvius, or the 4th ventricle and its outlets. A communicating hydrocephalus is due to impaired CSF absorption, most commonly caused by impaired absorption at the arachnoid granulations, often as sequelae of arachnoiditis caused by blood or pus.

Question 66

How might one differentiate between communicating and noncommunicating hydrocephalus based on the imaging?

Answer 66

Noncommunicating hydrocephalus will reveal enlargement of the ventricular system proximal to the blockage, whereas communicating hydrocephalus will reveal universal dilation of the ventricular system.

Question 67

What are the two most common causes of communicating hydrocephalus?

Answer 67

Meningitis and subarachnoid hemorrhage.

Question 68

What is the Dandy-Walker malformation?

Answer 68

It consists of a posterior fossa cyst which is continuous with the 4th ventricle, partial or complete absence of the cerebellar vermis, and hydrocephalus.

Question 69

In older children, what is the most common, nonspecific symptom of hydrocephalus?

Answer 69

Headaches. Hydrocephalus often presents with early-morning headaches along with nausea and vomiting.

Question 70

What is the characteristic physical exam finding in infants with hydrocephalus?

Answer 70

Excessive head growth.

Question 71

If increased intracranial pressure occurs due to hydrocephalus, which cranial nerves are likely affected?

Answer 71

Increased ICP can result in papilledema and extraocular muscle palsies, especially involving cranial nerves 3 and 6.

Question 72

What is the Cushing triad?

Answer 72

It is a sign of increased intracranial pressure and is characterized by bradycardia, systemic hypertension, and altered respiratory rates.

Question 73

What is the setting-sun sign?

Answer 73

It occurs when upward gaze is impaired because of pressure on the midbrain from increased ICP, and the sclera above the iris becomes visible.

Question 74

What are the appropriate studies to diagnose hydrocephalus in newborns, older infants, and children?

Answer 74

In newborns, US is used to confirm diagnosis. In older infants and children, CT or MRI is used to make the diagnosis.

Question 75

What is the typical treatment for hydrocephalus?

Answer 75

It depends on the etiology, but usually involves surgical management, which is often ventriculoperitoneal shunt placement.

Question 76

What is the most common organism responsible for VP shunt malfunction due to an infectious cause?

Answer 76

Staph epidermidis accounts for > 50% of occurences and usually responds only to vancomycin.

Question 77

List five common organisms responsible for infectious VP shunt malfunction.

Answer 77

Staph epidermidis > S. aureus > E. coli and other gram negatives > diphtheroids (propionibacterium acnes and corynebacterium jeikeium) > strep species