Agenesis of the corpus callosum

 This is an MRI of a child with absent corpus callosum












The parts of a normal corpus callosum are the rostrum ( beak), genu ( bend), body, isthmus, splenium (padding/bandage)

In partial agenesis of the corpus callosum the posterior portion including splenium may be missing. In holoprosencephaly the agenesis may be atypical with rostrum and splenium missing.

In 75% no etiology is traceable.

Antenatal diagnosis by USG is possible by 20 weeks.

MRi saggital view is most useful.

CT head may show parallel ventricles, colpocephaly,  a high up third ventricle between the lateral ventricles.

Clinical spectrum includes
1. Severe neuro deficits especially when other brain malformations associated
2. Neurodevelopmental defects such as autism
3. Near normal IQ with some subtle defects of higher order cognition and social skills

Holoprosencephaly

It is a spectrum of fore brain disorders characterized by different degrees of frontal lobe fusion.

Alobar holoprosencephaly is when their is no interhemispheric fissure, single ventricle and basal ganglia and thalami are fused.

Semilobar holoprosencephaly is when the interhemispheric fissure is present posteriorly, basal ganglia, hypothalamus, caudate and thalami may be partially fused and there are partial formation of occipital and temporal horns.

"The face predicts the brain"

That means one can suspect it from various midline facial defects athat are often present including-

midline cleft, central incisor, absent superior frenulum, single nostril.

Seizures, dystonia and endocrine dysfunction is common. Posterior pituitary dysfunctions are more common than anterior pituitary deficiencies.

Workup includes high resolution chromosomal studies and HPE genetic mutations, electrolytes, cortisol, TSH, ACTH.

Recurrence risk is 6%. First trimester USG and fetal MRI can pick up holoprosencephaly.

SEGA-Subependymal giant cell astrocytoma

SEGA or sub ependymal giant cell astrocytomas are WHO grade I tumours often belived to have arisen from sub ependymal nodules. They grow into the ventricles and are often near the Foramen of Munro. They may remain asymptomatic or as they slowly enlarge produce obstructive hydrocephalus.

CT findings- are iso or heteroeintense with grey matter and enhance with contrast. Often larger than 1 cm

MR findings- 

• T1 : heterogenous and hypo to iso intense to grey matter 
• T2 : heterogenous and hyper intense to grey matter ; calcific components can be hypo intense
• T1 C+ (Gd) : can show marked enhancement

 Treatment options: Surgical resection . May sometimes recur if not fully resected.

Everolimus is a drug which has shown to reduce the size of SEGA's.

It acts by inhibiting the m TOR complex 1which are normally inhibited by the TSC1 and TSC 2 gene missing in tuberous sclerosis.

EEG in subacute sclerosing pan encephalitis (SSPE)

SSPE is a chronic progressive neurodegenerative disorder due to persistent infection by the measles virus.It occurs in children and young adults. It manifests with progressive cognitive decline, myoclonic jerks and ends in a persistent vegetative state.
The EEG is very characteristic with the well known Rademecker complex. This consists of high voltage 300 to 1500uv repetitive polyphasic sharp and slow waves lasting 0.5 to 2 secs and occuring regularly at every 4-15 secs. As the disease progresses the interburst periods may decrease.

Sub arachnoid haemorrhage

Sub arachnoid haemorrhage (SAH) presents as an acute neurological dysfunction.
Non contrast CT is the imaging modality of choice.
CT is positive in 95% in the first 24 hours and pick up rate drops to 50% after a week.
The first 2 pictures are of an acute SAH in the first 24 hours and third picture is after 2 weeks.
SAH appears as high attenuating substance in the normally dark coloured CSF filled sub arachnoid space.
Blood in the anterior interhemispheric fissure suggests ACA aneurysm, in the sylvian fissure suggests MCA aneurysm and post interhemispheric fissure suggest posterior circulation aneurysm.
In children AV malformations are a more common cuse of SAH than aneurysms unlike adults.

Polymicrogyria

Polymicrogyria comes from the greek words poly ( many), micro ( small) and gyri (folds) on the surface of the brain.

It means there are many small gyri packed together. Sometimes they are so tightly packed together they are mistaken for pachygyri or thick and fewer gyri.

When they are bilateral and especially involve the fronto parietal region they may have a genetic basis ( gene identified - GPR56) and have an  autosomal recessive inheritance. Perisylvian polymicrogyria may have AD, AR or XLR inheritence.

Degree of involvement of the brain decides the severity of MR, seizures, developmental delay.

On histopath the cortex may have 1 or 4 layers unlike the ususal 6 layers.

Causes include environmental insults during intrauterine life ( eg CMV or other TORCH infections), genetic disorders ( GRP56 deletion), metabolic disorders ( non ketotic hyperglycenemia, PDH def, glutaric aciduria II def, neonatal adrenoleukodystrophy)

( Ref: Polymicrogyria Overview -

Bernard Chang   http://www.ncbi.nlm.nih.gov/books/NBK1329/)

sturge weber syndrome

Sturge Weber Syndorme is a neurocutaneous syndrome with a facial nevus and angiomas involving the leptomeninges. Glaucoma may or may not be present.
It occurs because of a failure of regression of embryonal blood vessels around the cephalic portion of the neural tube
Neurological dysfunction occurs because of hypoxia, infarction, ischemia, venous occlusion and vasomotor phenomenon in the leptomeningeal angiomas.
Port wine stain in the V1 area of the trigeminal nerve is most likely to have SWS.
Seizures ocur in 75-90%. Glaucoma occurs only if the eyelid is involved.
The port wine stain can be treated with laser therapy.