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D. Andrew Mong, MD, and

Avrum N. Pollock, MD

Pediatric Neuroradiology

1. How does myelinated brain differ from nonmyelinated brain on an infant magnetic

resonance imaging (MRI) examination? Where do you expect to see myelinization

occur first?

Myelinated brain white matter, as in adults, appears hyperintense relative to gray matter on T1-weighted MR images and

hypointense on T2-weighted images. In nonmyelinated brain, this pattern is reversed. Myelinization of the infant brain

occurs in a predictable pattern, beginning in the brainstem and cerebellum and progressing to the posterior limb of the

internal capsule, optic pathways, and parietal lobes. This pattern of change occurs from caudal to cephalad, dorsal to

ventral, and central to peripheral. Myelinization should appear complete on MRI by 24 months, but may be incomplete

in the terminal zones up to approximately 4 to 5 years of age and in rare cases not until the first decade.

2. What are migrational anomalies of the central nervous system (CNS)?

Normal neuronal migration occurs during fetal brain development as neurons migrate from the germinal matrix to the

cortex along radial glial fibers. Partial or total arrest of this process leads to a migrational anomaly. These anomalies

include the following:

•

Subependymal heterotopias (abnormal gray matter lining the ventricles)

•

Band heterotopias (an extra band of gray matter exists partially or completely underneath a normal-appearing cortex

and a strip of white matter)

•

Schizencephaly (a cleft lined by gray matter extending from the outer cortex to the ventricles)

•

Polymicrogyria (too many gyri)

•

Pachygyria (abnormally thickened gyri)

•

Lissencephaly (complete absence of gyri).

Children typically present with developmental delay

or seizures (

Fig. 62-1

).

3. Name the three kinds of

holoprosencephaly.

Holoprosencephaly refers to incomplete differentiation

of the fetal prosencephalon (forebrain) into separate

ventricles. Holoprosencephaly may manifest as

alobar, resulting in one ventricle and fusion of the

thalami; semilobar, two hemispheres posteriorly but

not anteriorly; or lobar, the mildest form, which may

manifest with only mild midline abnormalities, such

as absence of the septum pellucidum and subtle

incomplete visualization of the interhemispheric

fissure associated with an azygous anterior cerebral

artery. The mildest form along the continuum is

thought to include septo-optic dysplasia.

4. What is the differential diagnosis for

what appears to be massively dilated

ventricles on a prenatal ultrasound

(US) examination?

The appearance of massively dilated ventricles may be

secondary to holoprosencephaly, hydranencephaly, or

hydrocephalus. Hydranencephaly results from massive

necrosis of the cerebral hemispheres and may be

Figure 62-1.

Axial T2-weighted MR image through the level of the

basal ganglia shows abnormally thickened and enlarged large gyri

(arrows) of the frontal cortex, which is consistent with pachygyria.

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pediatric radiology

secondary to vascular disease with bilateral internal carotid occlusion, infection, or trauma with severe hydrocephalus. There

is usually a thin residual remnant of cerebral cortex applied to the inner table of the calvaria. The most common causes of

prenatal hydrocephalus include Arnold-Chiari malformation II, intracranial hemorrhage, aqueductal stenosis, and Dandy-

Walker malformation.

5. Describe the classification of germinal matrix hemorrhage.

The germinal matrix lies in the caudothalamic groove. This is a highly vascular region of the prenatal and premature brain

and is prone to hemorrhage, with rupture of the thin venules subsequent to decreased perfusion or oxygenation. Morbidity

and mortality can be predicted based on the grade of the hemorrhage:

•

Grade I hemorrhage is confined to the germinal matrix.

•

Grade II hemorrhage extends into the lateral ventricle.

•

Grade III hemorrhage expands into and dilates the lateral ventricle.

•

Grade IV hemorrhage extends into the adjacent parenchyma.

US of the premature infant’s head through the anterior fontanelle is the modality of choice for diagnosis and follow-up

of germinal matrix hemorrhage.

6. How does the premature brain respond to ischemic injury?

Periventricular leukomalacia is characterized by ischemia in an endarterial distribution—in the watershed regions of

white matter that surround the ventricles. US examination may show increase in periventricular echogenicity soon after

the initial insult. Cystic change in these regions can be seen later in the subacute stage, as the white matter begins to

be resorbed. MRI shows abnormal periventricular signal intensity and volume loss. Before 28 weeks of gestation, the

developing brain does not display a leukomalacic response, and only volume loss results. This volume loss may take the

form of dilated ventricles and expanded extra-axial spaces or even porencephalic cysts (expanded cystlike dilations from

the ventricles, which may reach the cortex). A porencephalic cyst can be differentiated from schizencephaly by noting that,

in the former entity, there is no gray matter lining the cyst.

7. Describe the three main types of Chiari malformation.

•

Chiari I malformation involves herniation of the cerebellar tonsils into the foramen magnum (>5 mm in patients

<15 years old) (

Fig. 62-2

).

•

Chiari II malformation is more severe, involving herniation of the medulla and vermis and elongation and downward

displacement of the brainstem. Chiari II is virtually always associated with a meningomyelocele. Prenatal US may show

crowding of the posterior fossa (“banana” sign appearance of the cerebellar hemispheres as they wrap around the

brainstem). Lacunar skull (lückenschädel) may also be shown in Chiari II, but is thought to be due to a bony dysplasia, rather

than the copper-beaten appearance associated with increase in intracranial pressure. Lacunar skull appears on plain film

as multiple focal areas of thinning in the skull, which

resolves with age.

•

Chiari III malformation involves herniation of

contents of the posterior fossa through the occiput

or upper cervical canal via a bony defect (i.e., akin

to an encephalocele).

8. How does the corpus callosum

develop, and why is this important?

The corpus callosum develops front to back except

for the rostrum (anterior genu, body, splenium, and

rostrum last). This is important because an in utero

insult may result in destruction of part of the corpus

callosum. If posterior portions of the corpus callosum

are present and anterior portions are not, this

means that they were present at one point and were

destroyed. If posterior portions are absent instead,

this may mean that they did not develop.

Figure 62-2.

Sagittal T1-weighted MR image through the

craniocervical junction shows inferior displacement of the cerebellar

tonsils (arrow) below the level of the foramen magnum.

Key Points: Grading of Germinal Matrix

Hemorrhage in Neonates

1. Grade I: Confined to the caudothalamic groove

2. Grade II: Extension into the lateral ventricle

3. Grade III: Extension into and dilation of the lateral ventricle

4. Grade IV: Extension into the adjacent parenchyma

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pediatric Neuroradiology

9. What entity does not follow the normal rule of corpus callosum development?

Holoprosencephaly, previously described, may follow an atypical pattern of corpus callosum development, in which the

posterior portions develop and the anterior portions do not. This is termed atypical callosal dysgenesis.

10. What are TORCH infections?

The TORCH acronym stands for infections caused by toxoplasmosis, other (varicella), rubella, cytomegalovirus (CMV),

and herpes/human immunodeficiency virus (HIV).

11. How do TORCH infections appear radiographically?

It is often impossible to distinguish TORCH infections radiographically. Intracranial calcification patterns may aid in

differentiating them. CMV calcifications are classically present only in the periventricular (circumventricular) regions,

whereas toxoplasmosis and rubella also have basal ganglia and cortical calcifications. CMV may also be associated

with migrational abnormalities previously discussed. HIV infection may manifest as atrophy with bilateral basal ganglia

calcifications. Cerebral atrophy may be present in any infection.

12. Discuss the CNS manifestations of neurofibromatosis type 1 (NF1).

Patients with NF1 may have plexiform neurofibromas, which are present along a nerve distribution and insinuate

within the fascial planes of the head and neck. Sphenoid wing dysplasia, with its resultant harlequin eye appearance,

is also a common finding. Nonspecific areas of high T2 signal may be present (NF spots) in the basal ganglia,

brainstem, and cerebellum, and are referred to as spongiform dysplasia. Gliomas may develop anywhere along the

optic pathway.

In the spine, patients with NF1 may develop lateral meningoceles, which herniate from the thecal sac into the thorax.

Plain films of the spine may also show posterior vertebral body scalloping (from dural ectasia) or enlargement of the

neural foramina (from neurofibromas) and inferior rib notching/remodeling secondary to the growth of the neurofibromas

along the course of the intercostal nerves.

13. How is neurofibromatosis type 2 (NF2) different from NF1?

The gene for NF2 is on chromosome 22, as opposed to chromosome 17 for NF1. NF2 tumors can be remembered with

the mnemonic MISME, which stands for multiple inherited schwannomas, meningiomas, and ependymomas. Classically,

these appear as bilateral cerebellopontine angle tumors, representing bilateral acoustic schwannomas (but may involve

any of the cranial nerves), which is diagnostic of NF2.

14. What is tuberous sclerosis?

Tuberous sclerosis is an autosomal dominant disorder with variable expressivity, which manifests as hamartomatous

lesions in multiple organ systems. Tuberous sclerosis consists of the clinical triad of seizures, adenoma sebaceum,

and mental retardation. In the CNS, subependymal nodules and subcortical tubers occur. The tubers have a typical

appearance of wispy high signal on T2-weighted images in the subcortical white matter. Giant cell astrocytomas may

occur at the foramen of Monro and cause an obstructive hydrocephalus. Involvement outside of the CNS includes

angiomyolipomas (fat-containing masses) in the kidneys, rhabdomyomas of the heart, cystic lung disease, and bony

involvement (

Fig. 62-3

).

15. Describe the manifestations of Sturge-Weber syndrome.

Sturge-Weber syndrome, also known as encephalotrigeminal angiomatosis, includes venous angiomatous

malformations within the leptomeninges and choroid plexus with an associated port-wine stain in the distribution of a

branch of the trigeminal nerve on the side of the hemispheric involvement. On cross-sectional imaging, there is a focal

region of leptomeningeal enhancement, often overlying a region of cortical atrophy. There is usually also abnormal

enhancement in the enlarged ipsilateral choroid plexus. Computed tomography (CT) examination also detects “tram-

track” subcortical calcifications and ipsilateral hemispheric volume loss, which is not seen in early infancy because they

take some time to occur.

Key Points: Central Nervous System

Manifestations of Neurofibromatosis Type 1

1. Plexiform neurofibromas

2. Optic pathway gliomas

3. NF spots in the basal ganglia

4. Sphenoid wing dysplasia

5. Lateral meningoceles

6. Dural ectasia and posterior vertebral scalloping

7. Enlargement of the neural foramina from neurofibromas

pediatric Neuroradiology

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pediatric radiology

16. What are the most common brain

tumors in infants?

Although pediatric tumors generally are more likely

to occur in the posterior fossa, in infants 2 years old

or younger, the most common individual tumors are

supratentorial. These include teratoma, astrocytomas

(e.g., glioblastoma multiforme), choroid plexus

papilloma and carcinomas (in the lateral ventricles),

and primitive neuroectodermal tumors.

17. Name the major posterior fossa

tumors in children.

Most pediatric brain tumors are infratentorial. These

include pilocytic astrocytoma, fibrillary astrocytoma,

medulloblastoma, and ependymomas.

18. Describe the typical tumors that occur

in the suprasellar region of a child.

Craniopharyngiomas are cystic lesions that often

contain calcium (

Fig. 62-4

). These may be confused

with Rathke cleft cysts, which are remnants of Rathke

pouch, the structure that forms the anterior portion

of the pituitary gland. Other tumors include tumors of

hypothalamic origin (gliomas or hamartomas), optic

nerve tumors (e.g., tumors seen

in NF1), germinomas arising from the pituitary stalk,

and pituitary adenomas. Langerhans cell histiocytosis

(eosinophilic granuloma) can manifest as thickening

of the infundibulum and loss of visualization of

the normal posterior pituitary bright spot and is

associated with a clinical history of growth delay.

19. Why is thickening of the pituitary

stalk an important finding?

The pituitary stalk is considered thickened if it is

greater than 2 mm at the insertion of the gland.

Close interval follow-up is warranted because this

thickening may be a manifestation of a germinoma

or Langerhans cell histiocytosis. Alternatively, the

thickening may be idiopathic.

20. What is the differential diagnosis for

a pediatric cystic neck mass?

This is a broad differential that may be narrowed

by location. Type II branchial cleft cysts (the most

common) are suprahyoid lesions that classically

push the sternocleidomastoid muscle posteriorly and

have a tongue of tissue arising between the external

and internal carotid arteries. Thyroglossal duct cysts

are remnants of the thyroglossal duct and are found

in the midline, usually at or below the hyoid bone

beneath the strap muscles. Teratomas or dermoids

may occur anywhere, but can be identified by the

presence of fat or calcium or both. Lymphangiomas

have a typical appearance of a cystic mass, often

with septations, that insinuates through fascial

planes (sometimes inferiorly into the mediastinum).

21. What is the differential diagnosis for

leukocoria?

Leukocoria is defined as an abnormal white

papillary reflex. Retinoblastoma is the most

concerning cause. Other causes include congenital

Figure 62-4.

Coronal T1-weighted MR image after the administration

of intravenous contrast agent shows ring-enhancing craniopharyngioma

in the suprasellar region.

Figure 62-3.

Axial T2-weighted MR image through the brain shows

dark subependymal nodules (arrows) lining the lateral ventricles

and wispy high signal in scattered subcortical areas, representing

hamartomas.

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pediatric Neuroradiology

cataract, infection (e.g., toxocariasis), persistent hyperplastic primary vitreous, retinopathy of prematurity, and Coats

disease (fusiform dilation of retinal vessels, often with associated retinal detachment and subretinal exudate). Historical

clues are helpful in differentiating these entities. The average age of patients with retinoblastoma is 13 months, whereas

Coats disease generally occurs in boys older than 4 years old, and toxocariasis occurs generally after 6 years of age.

The presence of calcification may aid in the diagnosis on CT because 95% of retinoblastomas contain calcium.

22. What is meant by trilateral retinoblastoma?

Bilateral retinoblastomas often occur in the familial form of the disease, which is characterized genetically as a mutation

in the Rb1 tumor suppressor gene. These patients are also at risk for developing a third primitive intracranial neoplasm,

usually in the pineal gland, the so-called third-eye. Trilateral retinoblastoma involves tumor in both eyes and in the

pineal gland. As in the retina, even a fleck of calcium in the pineal gland of a child younger than 6 years old should be

considered suggestive of neoplasm.

23. What is fibromatosis colli? Describe its imaging characteristics.

Fibromatosis colli is benign focal or fusiform enlargement of the sternocleidomastoid muscle in infants that usually

regresses by 6 to 8 months of age and is thought to be due to trauma to the sternocleidomastoid muscle or to an in

utero positioning abnormality. US of the muscle shows either diffuse enlargement or a focal hyperechoic mass. If there is

question about the diagnosis, MRI may be useful. MRI should show low signal on T2-weighted images, which represents

fibrosis in the sternocleidomastoid muscle.

24. Where do cholesteatomas typically arise, and what is the role of the radiologist in

their evaluation?

A cholesteatoma is squamous epithelium that is trapped in the skull base, often creating expansion and erosion of

adjacent bony structures. Cholesteatomas may be congenital, in which case they are well defined and rounded, and

typically occur in the anterior mesotympanum or in the region of the eustachian tube, near the cochlear promontory.

Cholesteatomas may also occur as a result of tympanic membrane perforation (i.e., acquired), in which case they

typically occur in the epitympanum, adjacent to the scutum and involving Prussak space, or into the posterior middle

ear. CT examination of the temporal bones often cannot be used to distinguish between cholesteatoma and fluid or

inflammatory tissue, but it is often helpful in defining whether there are effects on adjacent bony structures. Radiologists

may comment on the integrity of the ossicles, erosion of the scutum, the presence or absence of labyrinthine fistulas,

or defects in the roof of the middle ear (tegmen tympani). MRI is not as helpful for evaluating bony structures, but may

be an important problem-solving tool if there are questions concerning intracranial extension.

25. What is the role of the radiologist in the evaluation of sacrococcygeal teratoma?

The presence of a sacrococcygeal teratoma may be detected in utero with US or fetal MRI. Because the mass may be

cystic, the differential diagnosis may include a meningocele (outpouching of meninges through a defect in the posterior

elements in the lumbosacral spine). High-output cardiac failure caused by a teratoma may result from flow to the mass,

leading to hydrops fetalis; placentomegaly; and polyhydramnios, which may necessitate cesarean section or fetal

surgery. MRI may be useful in the evaluation of these masses because the prognosis and surgical approach may depend

on which components of the mass are within the abdomen and pelvis. Lesions confined to the true pelvis tend to be

benign histologically, whereas lesions that extend beyond the confines of the sacrum tend to be malignant.

B

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