INTRODUCTION:

• Chiari malformation -
  
  
  Chiari I - Downward displacement of the cerebellar tonsil without displacement of the 4th ventricle/medulla.
  
  Chiari II - Commonest anomaly and is almost always associated with spina bifida and meningomyelocele. Here, there is downward displacement of the cerebellar tonsils along with pons and medulla through an enlarged foramen magnum into the upper spinal canal. 4th ventricle is also elongated into the upper spinal canal and posterior fossa in small.
  
  Chiari III - High cervical or occipital encephalocele.
  
  Chiari IV - Severe cerebellar hypoplasia



• Dandy-Walker malformation-
  
  Presents with large posterior fossa cyst, which communicates with the 4th ventricle, hypoplastic cerebellar hemispheres and absent/rudimentary inferior vermis. This must be differentiated from other posterior fossa cystic abnormalities like cisterna magna, trapped 4th ventricle and arachnoid cyst.



• Agenesis of the corpus callosum-
  
  It may be partial / complete and usually associated with other anomalies.



• Holoprosencephaly -
  
  May be alobar, semilobar, lobar and usually associated with facial & calvarial anomalies.



• Hydranencephaly -
  
  Could be confused with alobar holoprosencephaly but the presence of 'falx' helps to differentiate this lesion. It is difficult to differentiate it from severe hydrocephalus but a thin rim of cortex should be seen in hydrocephalus.

Hydrocephalus -
For diagnosis, grading severity and post-shunt follow up.

Hemorrhage-
Germinal matrix hemorrhage may occur in subependymal, intraventricular or intraparenchymal region and is more commonly seen in premature and low birth weight infants.

Subdural, epidural and subarachnoid haemorrhages are other less common sites of intracranial haemorrhage.

Hypoxic ischemic encephalopathy (HIE)-
Periventricular leukomalacia and periventricular haemorrhagic infarction are the primary manifestations of HIE in the premature infant. Perinatal asphyxia in the term infant can cause diffuse cerebral edema which may progress to brain atrophy / multi cystic encephalomalacia. Doppler studies would reveal lack of Doppler signal / flow

Infections-
Inflammation, edema and vasculitis are common to all cerebral infections. Ultrasound plays an important role in identifying and following both antenatal and neonatal complications (echogenic sulci, intra-axial fluid collection, hydrocephalus, ventriculitis, abnormal parenchymal echogenicity, abscess, encephalomalacia and calcifications) from congenital (TORCH) infections.

Intracranial masses-
Most tumours presenting before 2yrs of age are congenital (PNET, low grade astrocytoma, craniopharyngioma, teratoma). Ultrasound has a role in screening infants and helps to differentiate solid, cystic or vascular components of the masses.
Cystic lesions in the brain include arachnoid cysts, Dandy Walker cysts, porencephalic cysts, choroid plexus cysts, subependymal and colloid cysts.

Vascular malformations-
Duplex / colour Doppler ultrasound helps to differentiate arteriovenous malformation such as Vein of Galen aneurysm from other cystic lesions.