Chapter 3: Secondary Effects and Sequelae of CNS Trauma

Question 1

These occur when one or more structures is displaced from its normal or “native” compartment into an adjacent space.

They are the most common secondary manifestation of any expanding intracranial mass, regardless of etiology.

Answer 1

Herniation Syndromes

Question 2

Bony ridges and dural folds divide the intracranial cavity into three compartments. Which are?

Answer 2

Two supratentorial hemicrania (right and left halves) and the posterior fossa

Question 3

What are the two layers of the mater?

Answer 3

Outer layer - periosteal

Inner layer - meningeal layer

Question 4

Layer of the dura that thightly applied to the inner surface of the calvaria, especially at suture lines.

Answer 4

Periosteal layer

Question 5

The meningeal layer folds inward to form two important fibrocollageneous sheets. What are these sheets?

Answer 5

Falx cerebri and tentorium cerebelli

Question 6

This anatomic landmark separates the right and left hemisphere from each other.

Answer 6

Falx cerebri

Question 7

This anatomic landmark separates the supratentorial from infratentorial compartment.

Answer 7

Tentorium cerebelli

Question 8

The superior portion of the falx cerebri contains what important venous vessel?

Answer 8

Superior sagittal sinus

Question 9

The concave inferior “free” margin of the falx contains what vessel?

Answer 9

Inferior sagittal sinus

Question 10

As the falx cerebri courses posteriorly, the inferior margin of the falx forms a large open space above what structures?

This open space allows potential displacement of brain and blood vessels from one side toward the other.

The opening is largest in the front and becomes progressively smaller, ending where the falx joins the tentorium cerebeill at its apex.

Answer 10

Corpus callosum and cingulate gyrus

Question 11

This is a tent-shaped dural sheet that extends inferolaterally from its confluence with the falx, where their two merging dural folds contain the straight sinus.

Answer 11

Tentorium cerebelli

Question 12

The tentorium cerebelli is attached laterally to the petrous ridges, anteroinferiorly to the dorsum sellae, and posteriorly to the occipital bone.

It has two concave medial edges that contain a large U-shaped opening called what?

Answer 12

Tentorial incisura.

Displacement of brain structures and accompanying blood vessels from the supratentorial compartment or posterior fossa can occur in either direction - up or down - through the tentorial incisura.

Question 13

This hypothesis states that

“The sum of volumes of brain, CSF, and intracranial blood is constant in an intact skull. An increase in one should cause a decrease in one or both of the remaining two.”

Answer 13

Monro-Kellie hypothesis

Question 14

This is the most common cerebral herniation.

Answer 14

Subfalcine herniation

Question 15

This herniation occurs as the affect hemisphere pushes across the midline under the inferior “free” margin of the falx, extending into the contralateral hemicranium.

Answer 15

Subfalcine herniation

Question 16

In subfalcine herniation.

What structures herniate aunder the falx?

Answer 16

Cingulate gyrus and accompanying anterior cerebral arteries

Question 17

What is the early complication of subfalcine herniation?

Answer 17

Hydrocephalus

Enlargement of the contralateral ventricle

Question 18

What is an expected complication in severe cases of subfalcine herniation?

Answer 18

Secondary ACA infarction

The herniating anterior cerebral artery can become pinned against the inferior “free” margin of the falx cerebri and then occluded.

Question 19

Imaging findings of subfalcine herniation.

Answer 19

Cingulate gyrus, ACA, internal cerebral veins displaced across midline

Foramen of Monro kinked, obstructed

Ipsilateral ventrcle small, contralateral enlarged

Question 20

These are brain displacements that occur through the tentorial incisura.

Answer 20

Transtentorial herniations

Question 21

What is more common, descending herniation or ascending herniation?

Answer 21

Descending herniations

Question 22

This is the second most common type of intracranial herniation syndrome.

Answer 22

Descending transtentorial herniations

Question 23

Pathophysiology of descending transtentorial herniation.

Answer 23

It is caused by a hemispheric mass that initially produces side-to-side brain displacement.

As the mass effect increases, the uncus of the temporal lobe is pushed medially and begins to encroach on the suprasellar cistern.

The hippocampus soon follows and starts to efface the ipsilateral quadrigeminal cistern.

With progressively increasing mass effect, both the uncus and hippocampus herniate inferiorly through the tentorial incisura.

Question 24

This occurs when a hemispheric mass effect pushes the uncus and hippocampus of the ipsilateral temporal lobe over the edge of the tentorial incisura.

Answer 24

Unilateral descending transtentorial herniation

Question 25

This occurs when both temporal lobes herniate medially into the tentorial hiatus.

Answer 25

Bilateral descending transtentorial herniation

Question 26

This occurs when both hemispheres are so swollen that the whole central brain is flattened against the skull base.

All the basal cisterns are obliterated as the hypothalamus and optic chiasm are crushed againts the sulla turcica, and the suprasellar and quadrigeminal cisterns are completely effaced.

Answer 26

Central descending herniation

The medial temporal and posterior frontal lobes become acutely ischemic.

Question 27

DTH can compress what cranial nerve?

Answer 27

Third cranial nerve (oculomotor) nerve as it exits from the interpenducular fossa nad courses anterolaterally toward the cavernous sinus.

This may produce a pupil-involving third nerve palsy

Question 28

What artery is affected in DTH?

Answer 28

As the temporal lobe is displaced inferomedially, it pushes the posterior cerebral artery (PCA) below the tentorial incisura.

The PCA can be come kinked and evatually even occluded as it passes back up over the medial edge of the tentorium, causing a secondary PCA (occipital) infarct.

Question 29

As the herniating temporal lobe pushes the midbrain toward the opposite side of the incisura, the contralateral cerebral peduncle is forced againts the hard, knife-like edge of the tentorium, forming a ____________.

Answer 29

Kernohan notch

Pressure ischemia leads to an ipsilateral (not contralateral) hemiplegia, the “false localizing” sign.

Question 30

Perforating arteries that arise from the top of the basilar artery are compressed and buckled inferiorly, eventually occluding and causing secondary hemorrhagic midbrain infarct.

This is known as what?

Answer 30

Duret hemorrhage

Question 31

With complete bilateral DTH , perforating arteries that arise from the circle of Willis are compressed against the central skull base and also occlude, causing infarcts where?

Answer 31

Hypothalamic and basal ganglia infarcts

Question 32

What are the two types of herniations that occur with posterior fossa masses?

Answer 32

Tonsillar herniation

and

ascending transtentorial herniation

Question 33

The cerebellar tonsils are displaced inferiorly and become impacted into the foramen magnum.

Answer 33

Tonsillar herniation

Question 34

True or false:

Tonsiliar herniation can be either congenital OR acquired.

Answer 34

True

Question 35

In what case where tonsils are pulled downward by abnormally low intraspine CSF pressure?

Answer 35

Intracranial hypotension

Question 36

Tonsils more than __ mm below the foramen magnum are generally abnormal, especially if they are peg-like or pointed (rather than round).

Answer 36

5 mm

Question 37

What are the complications of tonsillar herniation?

Answer 37

Obstructive hydrocephalus

and

tonsillar necrosis

Question 38

Type of herniation in which the cerebellar vermis and hemispheres are pushed upwards through the tentorial incisura into the supratentorial compartment.

Answer 38

Ascending transtentorial herniation

Question 39

What is a more common cause of ascending transtentorial herniation, neoplasm or trauma?

Answer 39

Neoplasm

Question 40

This herniation occurs when the brain herniates across the greater sphenoid wing (GSW) or “ala”.

Answer 40

Transalar herniation

Cane be either ascending (the most common) or descending

Question 41

This herniation is caused by a large middle cranial fossa mass.

An intratemporal or large extraaxial mass displaces part of the temporal lobe together with the sylvian fissure and middle cerebral artery up over the greater wing of sphenoid.

Answer 41

Ascending transalar herniation

Question 42

Ascending transalar herniation is best depicted on:

a. off-midline sagittal MR
b. axial MR
c. off-midline sagittal CT
d. axial CT

Answer 42

A. Off-midline sagittal MR

The GSW is seen as the body junction between the anterior and middle cranial fossae.

The MCA branches and sylvian fissure are elevated, and the superior temporal gyrus is pushed above the GSW

Question 43

What is the caused of descending transalar herniation.

Answer 43

Caused by a large anterior cranial fossa mass.

Here the gyrus rectus is forced posteroinferiorly over the GSW, displacing the sylvian fissure and shifting the MCA backward.

Question 44

Sometimes called a “brain fungus” by neurosurgeon.

Answer 44

Transdural/trancranial herniation

For this herniation to occur, the dura must be lacerated, a skull defect (fracture or craniotomy) must be present, and ICP must be elevated.

Question 45

Transcranial/transdural herniation is best appreciated on what modality?

Answer 45

Axial T2WI