Chapter 3: Secondary Effects and Sequelae of CNS Trauma Flashcards
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.
Herniation Syndromes
Bony ridges and dural folds divide the intracranial cavity into three compartments. Which are?
Two supratentorial hemicrania (right and left halves) and the posterior fossa
What are the two layers of the mater?
Outer layer - periosteal
Inner layer - meningeal layer
Layer of the dura that thightly applied to the inner surface of the calvaria, especially at suture lines.
Periosteal layer
The meningeal layer folds inward to form two important fibrocollageneous sheets. What are these sheets?
Falx cerebri and tentorium cerebelli
This anatomic landmark separates the right and left hemisphere from each other.
Falx cerebri
This anatomic landmark separates the supratentorial from infratentorial compartment.
Tentorium cerebelli
The superior portion of the falx cerebri contains what important venous vessel?
Superior sagittal sinus
The concave inferior “free” margin of the falx contains what vessel?
Inferior sagittal sinus
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.
Corpus callosum and cingulate gyrus
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.
Tentorium cerebelli
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?
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.
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.”
Monro-Kellie hypothesis
This is the most common cerebral herniation.
Subfalcine herniation
This herniation occurs as the affect hemisphere pushes across the midline under the inferior “free” margin of the falx, extending into the contralateral hemicranium.
Subfalcine herniation
In subfalcine herniation.
What structures herniate aunder the falx?
Cingulate gyrus and accompanying anterior cerebral arteries
What is the early complication of subfalcine herniation?
Hydrocephalus
Enlargement of the contralateral ventricle
What is an expected complication in severe cases of subfalcine herniation?
Secondary ACA infarction
The herniating anterior cerebral artery can become pinned against the inferior “free” margin of the falx cerebri and then occluded.
Imaging findings of subfalcine herniation.
Cingulate gyrus, ACA, internal cerebral veins displaced across midline
Foramen of Monro kinked, obstructed
Ipsilateral ventrcle small, contralateral enlarged
These are brain displacements that occur through the tentorial incisura.
Transtentorial herniations
What is more common, descending herniation or ascending herniation?
Descending herniations
This is the second most common type of intracranial herniation syndrome.
Descending transtentorial herniations
Pathophysiology of descending transtentorial herniation.
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.
This occurs when a hemispheric mass effect pushes the uncus and hippocampus of the ipsilateral temporal lobe over the edge of the tentorial incisura.
Unilateral descending transtentorial herniation
This occurs when both temporal lobes herniate medially into the tentorial hiatus.
Bilateral descending transtentorial herniation
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.
Central descending herniation
The medial temporal and posterior frontal lobes become acutely ischemic.
DTH can compress what cranial nerve?
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
What artery is affected in DTH?
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.
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 ____________.
Kernohan notch
Pressure ischemia leads to an ipsilateral (not contralateral) hemiplegia, the “false localizing” sign.
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?
Duret hemorrhage
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?
Hypothalamic and basal ganglia infarcts
What are the two types of herniations that occur with posterior fossa masses?
Tonsillar herniation
and
ascending transtentorial herniation
The cerebellar tonsils are displaced inferiorly and become impacted into the foramen magnum.
Tonsillar herniation
True or false:
Tonsiliar herniation can be either congenital OR acquired.
True
In what case where tonsils are pulled downward by abnormally low intraspine CSF pressure?
Intracranial hypotension
Tonsils more than __ mm below the foramen magnum are generally abnormal, especially if they are peg-like or pointed (rather than round).
5 mm
What are the complications of tonsillar herniation?
Obstructive hydrocephalus
and
tonsillar necrosis
Type of herniation in which the cerebellar vermis and hemispheres are pushed upwards through the tentorial incisura into the supratentorial compartment.
Ascending transtentorial herniation
What is a more common cause of ascending transtentorial herniation, neoplasm or trauma?
Neoplasm
This herniation occurs when the brain herniates across the greater sphenoid wing (GSW) or “ala”.
Transalar herniation
Cane be either ascending (the most common) or descending
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.
Ascending transalar herniation
Ascending transalar herniation is best depicted on:
a. off-midline sagittal MR
b. axial MR
c. off-midline sagittal CT
d. axial CT
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
What is the caused of descending transalar herniation.
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.
Sometimes called a “brain fungus” by neurosurgeon.
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.
Transcranial/transdural herniation is best appreciated on what modality?
Axial T2WI
