CNS

INDEX

________________________________________________________________

Dandy-Walker malformation

Congenital anomaly
Mainly infratentorial abnormality

the 4th ventricle is in connection with the CSF space posteriorly
Absence of vermis


It is easier to remember the CT/MRI findings after understanding the pathophysiology:


complete/partial outflow obstruction of CSF via the foramina of Magendie & Luschka
=> dilatation of 4th ventricle, extending posteriorly
=> cerebellar hemisphere unable to fuse, vermis unable to form

*foramen of Magendie and Luschka are the passage of CSF via the 4th ventricle:
Median for Magendie: it opens in midline
Lateral for Luschka: both open laterally

============================================


CT findings:
- Cystic dilatation to the posterior fossa from the 4th ventricle
- Vermis of the cerebellum: Absence or Partially absent
- Torcular-lambdoid inversion: torcula-herophili raised above the lambdoid suture
- Hydrocephalus

MRI:
- Findings as in CT
- CSF signal intensity in the cyst
- High-riding of the torcula-herophili is more readily appreciable

other associated findings:
- agenesis of corpus callosum
- polymicrogyria (excessive thin cortical convolutions)

- cerebral heterotopia

- holoprosencephaly (incomplete separation of the cerebral hemispheres)
- schizencephaly (abnormal migration of neuron from ependyma to the surface)
- meningoencephaloceles
- infundibular hamartoma
- olives malformation
- hydromyelia

=============================================

Often a/w other syndrome:

- PHACES syndrome
- Walker-Walburg syndrome

- Trisomy 9, 13 (Patau), 18 (Edwards)

- X-linked cerebellar hypoplasia
- Klippel Feil syndrome



- TORCH infection

- Warfarin embryopathy

- Fetal alcohol syndrome

*PHACES: Posterior fossa malformation, Haemangioma, Arterial anomalies, Cardiac defects, Eye anomalies, Sternal defects

*TORCH + S (or TORCHES): TOxoplasmosis, Rubella, CMV, HSV + Syphillis

==============================================

Differential diagnosis for Dandy-Walker malformation:
  • Arachnoid cyst
  • Dandy-Walker variant
  • Giant cisterna magna

*Dandy-Walker complex: umbrella term for Dandy-Walker malformation and its variants
________________________________________________________________

ACUTE STROKE - DENSE MCA SIGN

Patient presented with acute onset dense right hemiplegia, eye deviated to the left.

Hyperdense left MCA vessel.

Findings: Dense MCA vessel on the left.

This signifies a hyperacute MCA territorial infarction / ischaemia, usually due to embolic occlusion.
The dense MCA / dense vessel sign is usually found in the M1 segment.

However, it is of low sensitivity but high specificity.

The corresponding MR image on GRE sequence will show blooming effect.
To differentiate from a normal non-occluded vessel on GRE sequence...
...A normal cerebral vessel should show intraluminal hypointensity (flow void), but with hyperintensity peripheral to the vessel as blood carries its signal to the surrounding tissue via perfusion.

To confirm diagnosis: look for other signs of acute infarction on CT, or look for ischaemic/infarct signal changes on MRI.

MR changes in ischaemic infartion
DWI: High SI (Restricted)
ADC:
- First 4 days: Low SI
- 4-10days: Pseudonormalisation
- >10days: SI tend to rise

Rx:
Within the golden hours – 3hr on IV, 6hr on intra-arterial thrombolysis


________________________________________________________________

SDH - ACUTE on CHRONIC

Case of chronic headache in an elderly patient with vague history of "minor falls".
CT brain was performed:


Findings:

Crescentic shape, layers of hypo and hyperdensities in the left frontal and less so in the left parietal region.

Presence of mass effect, compressing the left frontal lobe and frontal horn of the left lateral ventricle, and causing 5mm midline shift to the right.

Others: Hypodensities in the right corona radiata, both lentiform nuclei and both anterior limbs of the internal capsule.


Conclusion?

(1) Crescent shape haematoma = Subdural haematoma (SDH)

(2) Different layers of densities = blood products of different ages, ie There are chronic components and acute or subacute components. This means there has been recurrent intermittent bleed.

(3) Subdural haematoma takes up space within the skull which has a fixed volume, thus some other structures have to be compromised => brain, ventricles. ie Mass effect.

(4) Background of chronic infarcts => which are not really significant in the acute presentation.


Bits of basics:

How does SDH occurs? Tearing of the cortical bridging veins.

SDH => crescent shape, as opposed to Extradural haemorrhage (EDH) which is biconvex.
SDH is not limited by the sutures, as opposed to the EDH
but SDH is limited by the interhemispheric fissue and tentorium

Density of blood products changes over time.
in acute bleed (<1week) = hyperdense
in subacute bleed (1-2 weeks) = isodense
in chronic bleed (3 weeks and after) = hypodense

Population, note, that is in these acute on chronic SDH cases:
- Elderly
- Chronic alcoholic (small brain)
- Anticoagulants (think alcohol => liver disease => coagulopathy)
- Trauma
- Previous shunting of ventricles
- Less often: in patients with AVM eg Dural AV fistula.

*remember: small brains = longer bridging veins to attach = veins easily stretched and leak when the brain "rotates" within the fixed skull
________________________________________________________________


TUBEROUS SCLEROSIS

aka Bourneville's disease
Sporadic (60%) or Autosomal dominant. Multisystem neurocutaneous disorder.

Classic triad of presentation: (but in only 1/3 of patients)
1. Mental underdevelopment
2. Seizure
3. Adenoma sebaceum (facial angiofibroma)

CNS:
Pathology happens between the germinal matrix and the cortex, therefore abnormalities can be seen from the subependymal area to the cortex.
- Subependymal hamartoma: nodules along the wall of foramen of Monro & lateral ventricles - calcifies with age
- Cortical & Subcortical tubers: may calcify. Mostly in frontal lobes. Cortical tubers: High risk of malignant transformation
- Grey matter heterotopia: lies perpendicular to the ventricular walls


CT:
- Calcified subependymal hamartoma
- Cortical/Subcortical tubers: Broad gyri with underlying hypodense lesions
- Grey matter heterotopia

MR:
- Grey matter heterotopia
  -- Paed: High T1, Low T2 (due to unmyelinated white matter)
  -- Adult: Low T1, Hight T2
- Subependymal hamartoma
- Cortical/Subcortical tubers:
  -- Sensitive on FLAIR
  -- High T2 tubers, High T1 calcified tubers
  -- Thickened, increased T2 SI gyri
- Subependymal hamartoma & the tubers may show enhancement

Associated with other conditions:
CNS:
Giant cell astrocytoma - subependymal, near foramen of Monro => obstructive hydrocephalus. Enhances.
Pilocytic astrocytoma of optic disc
Eye:
Retinal hamartomas
Cutaneous / MSK:
Shagreen patches
Cardio-thoracic:
Cardiac rhabdomyomas
Lymphangiomyomatosis of the lung (LAM)
Abdomen:
AML of kidney

MSK:
- Sclerotic calvarial patches / bone islands
- Thickening of diploe
- Expansion and sclerosis of ribs
- Periosteal thickening of long bones


________________________________________________________________



________________________________________________________________

No comments:

Post a Comment

Subscribe to: Posts (Atom)