Topic 11 - cranial pathology Flashcards
What are the three types of chiari malformation?
- Type I – displacement of the elongated cerebellar tonsils below the foramen magnum; no medulla or fourth ventricle displacement.
- Type II (most common) – displacement of cerebellum, tonsils, medulla and fourth ventricle into upper spinal canal, almost invariably associated with myelomeningocele and hydrocephalus; there may be multiple other associated intracranial anomalies.
- Type III – displacement of a dysplastic cerebellum, the medulla, and fourth ventricle into a high encephalocele (cervical or occipital).
What are the signs of the dandy walker malformation?
- Enlarged fourth ventricle connects to Dandy-Walker cyst posteriorly
- Large posterior fossa
- Hypoplastic cerebellar vermis
- Hypoplastic cerebellar hemispheres displaced laterally by fourth ventricle
- Small brainstem
- Hydrocephalus (80%)
- Obstruction above and below fourth ventricle
- Absent or dysgenetic corpus callosum (up to 70%)
Describe the dandy walker variant
• Dandy Walker variant is characterised by less severe changes, with milder posterior fossa enlargement and fourth ventricle dilation. The cerebellum is minimally affected, the hemispheres essentially normal, and the vermis hypoplastic.
What are two differential diagnoses of posterior fossa cystic lesions that mimic Dandy-Walker syndrome?
A mega–cisterna magna is described as the mildest form of this spectrum and includes no mass effect, no hydrocephalus, and a normal cerebellar vermis, fourth ventricle, and cerebellar hemisphere
• A posterior fossa subarachnoid cyst can be differentiated from Dandy-Walker malformation or spectrum by the lack of communication of the cyst with the fourth ventricle. The normal fourth ventricle, vermis, and cerebellum are displaced by the arachnoid cyst
What are the ultrasound signs of agenesis of the corpus callosum?
- the corpus callosum may be fully or partially absent.
- The lateral ventricles will appear parallel and widely spaced, with slightly larger occipital horns.
- The frontal horns demonstrate wide spacing and sharp angulation.
- In the occipital and parietal region, the sulci and gyri are radially arranged, appearing perpendicular in relation to the roof of the third ventricle. (sunburst sign)
- Absent cingulate gyrus and sulcus
- Extremely narrow frontal horns (slitlike)
- Colpocephaly (dilated atria and occipital horns)
- Elevated third ventricle extending between lateral ventricles, continuous with
- Absent septum pellucidum
Although there are different forms of holoprosencephaly what is common to all?
• The septum pellucidum is absent in all forms of holoprosencephaly
What are the three classifications of holoprosencephaly?
• (alobar, semilobar and lobar), each representing a different degree of fusion of the paired cerebral hemispheres, lateral ventricles, olfactory and optical tracts.
What is schizencephaly?
- migrational anomaly
- clefts form extending from the lateral ventricle to the cortical surface of the brain.
- may be unilateral or bilateral, asymmetric or symmetric.
What is lissencephaly?
Complete lack of sulcal formation
recognized on ultrasound when the sulcal pattern does not match that expected for gestational age.
Hourglass or “figure 8” has been described as typical of the cortical surface.
The sylvian fissures are often open owing to failure of the opercularization process
Describe the sonographic appearances of the Chiari II malformation.
- lateral ventricular enlargement with the occipital horns larger than the anterior horns (colpocephaly);
- the frontal ventricular horns demonstrating a batwing configuration, with an anterior and inferior pointed configuration;
- an enlarged massa intermedia filling almost the entirety of the third ventricle, which is also enlarged;
- the fourth ventricle small or not visualised due to compression and displacement;
- the pons, medulla and vermis elongated and, along with the fourth ventricle, inferiorly displaced.
- involvement of the cerebellum in this downward displacement - inferiorly displaced into the cervical spinal canal;
- widening of the interhemispheric fissure, and a serated, jagged appearance to the gyri; and
- there may also be associated partial or complete absence of the corpus callosum.
In which congenital abnormality does one see the ‘sunburst sign’ and what is this describing?
The sunburst sign is seen in agenesis of the corpus callosum.
describes the appearance that the occipital and parietal gyri and sulci demonstrate with an absent or partially absent corpus callosum.
The gyri and sulci are seen to be radially arranged, and are perpendicular to the roof of the third ventricle, which is elevated.
It is this radial arrangement and the appearance that results on ultrasound that lends this sonographic finding to the name “sunburst sign”.
Describe haemorrhage in pre term infants
- originates in the germinal matrix
- which lines the entire ventricular system.
- This highly vascular structure decreases in size from approximately 23-24 weeks gestation onwards
- it completely disappears by approximately 36 weeks.
- This developmental occurrence limits this condition to the premature infant.
Where is haemorrhage most commonly identified in the pre term infant?
the caudothalamic groove, which lies between the thalamus and the caudate nucleus head.
What are the different grades of pre term haemorrhage?
- Grade I – subependymal (germinal matrix) haemorrhage only;
- Grade II –germinal matrix and intraventricular hemorrhage without hydrocephalus;
- Grade III – germinal matrix and intraventricular hemorrhage with ventricular enlargement
- Grade IV – germinal matrix hemorrhage, intraventricular hemorrhage with or without ventricular enlargement, and intraparenchymal blood.
What is different about a grade 4 haemorrhage?
is the result of hemorrhagic cerebral infarction rather than direct extension of blood from the germinal matrix
hemorrhage obstructs the drainage of these small terminal veins causing venous hypertension and ultimately hemorrhagic infarction.
What are the ultrasound appearances of grade 1 GMH?
- increased echogenicity immediately anterior to or within the caudothalamic groove.
- may elevate the floor of the lateral ventricle, compressing or obliterating the frontal horn or body.
- Doppler sonography can help in differentiating hemorrhage from the echogenic choroid plexus.
- As the clot retracts, it undergoes central liquefaction, either completely resolving or forming a subependymal cyst.
- Posthemorrhagic subependymal cysts usually measure between 3 and 5 mm in diameter
- Subependymal cysts are not specific for hemorrhage.
What are the ultrasound appearances of grade 2 GMH?
- results when the germinal matrix ruptures through the ependymal wall, entering the lateral ventricles
- appears as echogenic material that fills part or all of a nondilated ventricular system
- difficult to diagnose by sonography.
- CSF– blood fluid level in the dependent part of the ventricle (i.e., the occipital horn or ventricular trigone)
- Posterior fontanelle scanning facilitates the detection
- the echogenic clot may adhere to the choroid plexus and be indistinguishable from it.
- Asymmetric enlargement and irregularity of the choroid plexus and extension of the trigonal choroid plexus into the occipital horns are findings that favor intraventricular blood and clot adherent to the choroid plexus.
- Color Doppler flow imaging also can be used to differentiate between clot and the choroid plexus.
What are the ultrasound appearances of grade 3 GMH?
- expands one or both lateral ventricular cavities
- blood may completely fill the ventricular cavity
- A blood– cerebrospinal fluid level may be seen in the occipital horn.
- Blood also may fill the third and fourth ventricles and the cavum septi pellucidi.
- As the clot retracts, it can produce a “ventricle within a ventricle” appearance
- Over time, the echogenic clot becomes hypoechoic and may resolve completely or persist as linear septations or bands.
What are the ultrasound appearances of a grade 4 GMH?
- hemorrhagic infarction of the periventricular parenchyma
- intraparenchymal hemorrhage (IPH) appears as an intensely echogenic focus with irregular margins in the parenchyma adjacent to one or both lateral ventricles
- most common in the frontal and parietal lobes
- usually unilateral and tends to be located on the same side as the germinal matrix intraventricular hemorrhage.
- Similar to the other types of hemorrhages, the parenchymal clot liquefies and retracts over 2 to 4 weeks.
- By 2 to 4 weeks following the injury, the clot retracts from the surrounding brain parenchyma, and by 2 to 3 months, a cystic area (encephalomalacia) develops
- The encephalomalacic area can communicate with the ipsilateral ventricle, which often is dilated.
What are the multiple sites haemorrhage may arise from in the term infant?
Subarachnoid
Subdural
Choroid plexus
Parenchymal
How does sub arachnoid haemorrhage appear on ultrasound?
- ultrasound is insensitive for small bleeds because the echogenicity of the blood and brain surface is similar
- large bleeds will be seen as hypoechoic fluid collections over the brain surface.
- There may be debris seen within the fluid, depending on the age of the bleed.
- unilateral or bilateral fluid collections in the interhemispheric fissure, sylvian fissure, or subarachnoid cisterns or over the cerebral convexities.
What are the two types of sub dural haemorrhage?
Supra tentorial
Infra tentorial
How does a supratentorial subdural bleed appear on ultrasound?
• supratentorial - extra axial fluid collections - a widened interhemispheric fissure - flattening of the cortex surface - possible mass effect flattening the ventricles o mass effect with flattening of gyri o and shift of midline structures
How does a infratentorial subdural bleed appear on ultrasound?
o fluid collection between the tentorium and the cerebellar hemisphere
o The fluid may cause mass effect, resulting in compression of the cerebellum, brainstem, and fourth ventricle, and it may silhouette the contours of these structures
o hydrocephalus results if the hematoma compresses the fourth ventricle or aqueduct.
