Normal Brain

What is the foramen magnum?

the opening in the base of the cranium that allows passage of spinal canal

What divides the two hemispheres of the cerebrum?

interhemispheric fissure

What does the cerebrum contain?

sulci and gyri

What are the 3 layers of meninges?

• pia mater (inner)

• arachnoid (middle)

• dura mater (outer)

What is the falx cerebri?

a double fold of dura mater which folds into the interhemispheric fissure and separates the 2 cerebral hemispheres

What is the cavum septum pellucidum (CSP)?

• box-shaped, midline brain structure seen between frontal horns of lateral ventricles

• does not communicate with ventricular system

• closes after 37 weeks

• landmark for corpus callosum

What is the corpus callosum?

• bridge between 2 hemispheres and provides communication between 2 sides

• normalized by seeing a normal CSP

What is the thalmus?

2 lobes of thalamus located on either side of falx

What is the massa intermedia?

connects 2 lobes of thalami together and 3rd ventricle travels within

What is the function of the ventricular system?

produces and transports CSF to cushion the brain

Where is CSF produced?

by the choroid plexus within the lateral ventricles

How does the CSF flow to the third ventricle from the choroid plexus?

via the foramen of Monro

What connects the 3rd ventricle to the 4th ventricle?

aqueduct of Sylvius (cerebral aqueduct)

With what condition is the aqueduct of Sylvius abnormal?

hydrocephalus

How does the CSF flow from the 4th ventricle to the cisterna magna and subarachnoid space?

foramina of Luschka and foramen of Magendie

Where do we image the lateral ventricles?

superior to the level of thalamus

What is the normal lateral ventricle measurement?

<10mm

What makes up the posterior fossa?

cerebellum, cisterna magna, and nuchal fold

What structures should NOT be seen while performing posterior fossa measurements?

orbits and mandible

What joins the 2 cerebellum lobes?

cerebellar vermis

What is the normal transcerebellar size?

match the weeks in gestational age in mm

What is the normal cisterna magna measurement?

2-10 mm

What is the normal nuchal fold measurement?

<6 mm

Where do the calipers go for nuchal fold measurement?

outer to outer

Where do the calipers go during nuchal translucency in the first trimester?

inner to inner

What is the normal measurement for nuchal translucency in the first trimester?

<3mm

What is the most accurate measurement for gestational age in 2nd trimester?

HC

What is the cephalic index?

ratio of BPD/OFD

What cephalic index indicates dolichocephaly (flattened)?

<0.75

What cephalic index indicates mesocephaly (normal)?

0.75-0.85

What cephalic index indicates brachycephaly (circular)?

>0.85