Topic 11 - cranial ultrasound

Question 1

Why is abnormal development of the brain common?

Answer 1

• Because of the complexity of its embryologic history, abnormal development of the brain is common (approximately 3 of 1000 births).
• Most major birth defects result from defective closure of the rostral neuropore

Question 2

What is an encephalocele?

Answer 2

• herniation of intracranial contents resulting from a defect in the cranium
• most common in the occipital region
• The hernia may contain meninges (meningocele)
• meninges and part of the brain (meningoencephalocele)
• or meninges, part of the brain, and part of the ventricular system (meningohydroencephalocele) .

Question 3

What is meroencephaly?

Answer 3

• severe defect of the calvaria and brain that results from failure of the rostral neuropore to close during the fourth week.
• The forebrain, midbrain, and most of the hindbrain and calvaria are absent
• Most of the embryo’s brain is exposed or extruding from the cranium (exencephaly) .
• The remains of the brain appear as a spongy, vascular mass consisting mostly of hindbrain structures.
• a common lethal defect , occurring in at least 1 of 1000 births.
• it is always associated with acrania (complete or partial absence of neurocranium).
• It may be associated with rachischisis ( failure of fusion of neural arches) when defective neural tube closure is extensive

Question 4

What is microcephaly?

Answer 4

• neurodevelopmental disorder .
• The calvaria and brain are small, but the face is normal sized
• These infants are grossly mentally deficient because the brain is underdeveloped.

Question 5

What causes microcephaly?

Answer 5

• Microcephaly is the result of a reduction in brain growth .
• Inadequate pressure from the growing brain leads to the small size of the neurocranium (bones of cranium)

Question 6

What is agenesis of the corpus callosum?

Answer 6

• there is a complete or partial absence of the corpus callosum
• which is the main neocortical commissure of the cerebral hemispheres
• The condition may be asymptomatic, but seizures and mental deficiency are common.
• Agenesis of the corpus callosum is associated with more than 50 human congenital syndromes.

Question 7

What can cause hydrocephalus?

Answer 7

• impaired circulation and absorption of CSF and, in rare cases, from increased production of CSF by a choroid plexus adenoma (benign tumor).
• A premature infant may develop intraventricular hemorrhage leading to hydrocephalus through the obstruction
• Rarely, impaired CSF circulation results from congenital aqueductal stenosis

Question 8

What happens to the cranium when hydrocephalus occurs in neonates?

Answer 8

• Blockage of CSF circulation results in dilation of the ventricles proximal to the obstruction, internal accumulation of CSF , and pressure on the cerebral hemispheres
• This squeezes the brain between the ventricular fluid and the neurocranium.
• In infants, the internal pressure results in an accelerated rate of expansion of the brain and neurocranium because most of the fibrous sutures are not fused

Question 9

What is non obstructive hydrocephalus?

Answer 9

• Hydrocephalus resulting from obliteration of the subarachnoid cisterns or malfunction of the arachnoid villi is called nonobstructive or communicating hydrocephalus .

Question 10

How does the appearance of the premature brain differ from the term brain?

Answer 10

• lateral ventricles are slightly larger
• cavum septi pellucidi extends back to become the cavum vergae between the lateral ventricle bodies and occipital horns.
• There are only a few sulci, and the sylvian fissures are wider and typically appear boxlike rather than as thin fissures.
• The basal ganglia in premature infants are normally diffusely homogeneously echogenic, an appearance that is more prominent than in the thalami and typically more echogenic than the cerebral cortex.
• Basal ganglia and thalami do not show increased echogenicity at term-equivalent age.

Question 11

What are some normal anatomical variants?

Answer 11

• cavum septum pellucidum and vergae
• choroid plexus cysts
• extra axial fluid
• sulcal variations according to gestational age.

Question 12

Describe the persistent fetal fluid filled spaces

Answer 12

• The CSP is a midline fluid-filled space located anteriorly and between the frontal horns of the lateral ventricles
• formed from failed septal laminae fusion
• If the space extends posterior to the fornices, it is termed cavum vergae.
• A cavum veli interpositi is located even further posteriorly as a separate fluid-filled space found in the pineal region.
• Due to the location of the cavum veli interpositi. It must be distinguished from other commonly occurring manifestations in this region, specifically, congenital pineal cysts and vein of Galen malformations

Question 13

How does brain sulcation change over time?

Answer 13

• The infant brain becomes increasingly sulcated during development.
• Cerebral cortices in neonates born prior to the 24th week gestational age contain only Sylvian fissures in an otherwise smooth cerebral cortex making lissencephaly in this age group an avoidable diagnosis
• At 24 weeks gestational age, the parietooccipital fissure is seen.
• This is followed by the appearance of the cingulate sulci at 28 weeks gestational age with additional branching occurring into full term

Question 14

How does choroid plexus appear on ultrasound?

Answer 14

• The choroid plexus is located at the roof of the third ventricle and travels through the foramen of Monro into the lateral ventricles
• It does not extend into the frontal or occipital horns
• so hyperechoic material in these areas should suggest pathology.
• Choroid appearing substance anterior to the caudothalamic groove is likely a germinal matrix hemorrhage
• while interventricular hemorrhage may be indicated by hyperechoic material in the dependent portions of the occipital horns

Question 15

How do you differentiate normal choroid from haemorrhage?

Answer 15

• Color Doppler ultrasound will differentiate the normal highly vascular choroid from similarly echogenic, but avascular, clot

Question 16

What is the significance of choroid cysts?

Answer 16

• choroid cysts are commonly identified
• When seen in isolation and measuring less than 1cm, they are considered a benign finding
• When choroid cysts are found to be multiple, bilateral, or greater than 1 cm in size, this may suggest a chromosomal abnormality

Question 17

Describe the significance of the periventricular halo affect

Answer 17

• hyperechoic white matter pseudolesions found adjacent to ventricles
• are discovered more often in preterm than term infants and are caused by anisotropic effect.
• These artifacts tend to disappear on tangential imaging and should have less echogenicity than neighboring choroid plexus
• Pathological findings such as periventricular hemorrhage, leukmalacia, or other abnormalities, are seen in two planes
Normal echogenicity in the periventricular white matter is symmetric and homogenous.
Periventricular leukomalacia is asymmetric, heterogeneous, and more echogenic than the adjacent choroid plexus.

Question 18

Describe the peritrigonal blush appearance

Answer 18

• Sagittal sonography almost always reveals a normal hyperechoic peritrigonal blush in the parietal lobe just posterior and superior to the ventricular trigones on parasagittal views
• It is caused by the interface of numerous parallel fibers that are perpendicular to the longitudinal angle of the ultrasound beam passing through the anterior fontanelle.
• This is an anisotropic effect artifact that occurs when the beam is perpendicular to the fibers through the anterior fontanelle

Question 19

What is Lenticulostriate vasculopathy and how does it appear on ultrasound?

Answer 19

• appears as linear, branching or punctate increased echogenicity within the thalami
• can be unilateral or bilateral
• associated with congenital infections (TORCH infections), metabolic syndromes (peroxisomal biogenesis disorders), severe congenital heart disease, and chromosomal anomalies (Patau’s syndrome) which are all believed to cause lenticulostriate artery wall thickening
• Sometimes, however, no specific cause can be ascertained making lenticulostriate vasculopathy a non-specific finding

Question 20

Why is it important to establish if the infant is term or preterm?

Answer 20

• This is important as the pathology that can occur in the neonate varies with the age of the patient.
• A premature infant will suffer different problems from a term infant.
• The sonographic appearances of the normal neonatal brain anatomy will also vary with gestational age.

Question 21

What is an example protocol of a coronal image sweep?

Answer 21

Image 1. orbital plate:

Image 2. Circle of Willis: sphenoid bone landmark - forms floor of middle cranial fossa. Anterior germinal matrix between head of caudate nucleus
floor of anterior horns of lateral ventricle.
Mid-line corpus callosum
septum pellucidum between medial walls of anterior horn.

Image 3. 3rd ventricle: mid line, slit like with echogenic choroid in its roof, inferior to septum pellucidum.
The Foramen of Munro should be included in this plane.

Image 4. Bodies of lateral ventricles

Image 5. Bodies of lateral ventricles: distinctive intra ventricular echogenic choroid plexus.
tentorial edge

Image 6. Bodies of lateral ventricles to show distinctive echogenic choroid plexus .
Comparison of choroid echogenicity to surrounding white matter.

Image 7. Occipital region.

Question 22

Example protocol of sagittal sweep

Answer 22

Image 8. Right sylvian fissure and periventricular white-matter in parasagittal plane

Image 9. Right caudate-thalamic groove in parasagittal plane

Image 10: Mid line sagittal image defining corpus callosum, the 3rd ventricle and quadrageminal cistern. Cerebellar vermis in mid line sagittal plane of posterior fossa - echogenic with 4th ventricle immediately anterior.
then move left

Question 23

What is the caudothalamic groove and why is it important to recognise?

Answer 23

• The caudate nucleus and the thalamus surround the third ventricle and are within the arms of the ventricle
• The caudothalamic groove at the junction of these two structures is an important area to recognize, because this is the most common site of germinal matrix hemorrhage (GMH) in the subependymal region of the ventricle.

Question 24

Why is the posterior fontanelle imaging useful?

Answer 24

• useful to evaluate the occipital horns for the diagnosis of intraventricular hemorrhage (IVH).
extremely useful for detecting dependently layering clot and clot attached to the choroid plexus.