Meninges Arteries

Question 1

What Are the 4 cranial meninges?

Answer 1

• There are four layers of cranial meninges: Dura mater (two layers), arachnoid and pia mater.
• The periosteal dura mater adheres to the inner surface of the skull. Arteries supplying the meninges thus dwell against and indent the skull.
• Dural folds (formed by the inner or meningeal layer of the dura) dwell between the major subdivisions of the brain, forming large septa (falx cerebri, tentorium cerebelli).
• Dural venous sinuses (large valveless vessels) lie between the two layers of dura mater.
• The thin avascular arachnoid lies under the dura mater.
• The pia mater is highly vascular and covers the outer surface of the brai

Question 2

What are the causes of epidural hemorrhages?

Answer 2

• Epidural hemorrhages commonly reflect the
traumatically induced rupture of meningeal
arteries (e.g., middle meningeal artery), with
a fractured bone cutting the vessel. Leaking
blood separates the stiff periosteal dura from
the skull, yielding a characteristic biconvex
(lentiform; lens-shaped) mass adjacent to the
fracture. The hematoma is contained by the
penetrations of the periosteal dura into the
sutures of the skull. Pressure arising from the
accumulating blood compresses/distorts the
brain. Dangers typically peak within hours of
arterial involvement but may go fatally
unrecognized

Question 3

Whhat are the causes of subdural hemorrhages?

Answer 3

Subdural hemorrhages commonly reflect trauma-induced ruptures of the delicate veins that traverse the meningeal layer of the dura from the subarachnoid space (bridging veins). Bleeds arising from tearing of the meningeal dura are also subdural. Because the pressure in the venous system is much lower than in the arterial system, crescent-shaped subdural masses of blood often develop slowly before manifestations arise (e.g., hours-to-weeks)

Question 4

What is characteristic of subarachnoid hemorrhage?

Answer 4

Many arteries reside between the arachnoid and pia mater (surrounded by CSF within the subarachnoid space). These vessels may rupture with trauma or spontaneously (e.g., in cases of aneurysm). The leaking blood assumes a tree-like appearance, while following sulci. Intense pain due to meningeal irritation is characteristic of subarachnoid hemorrhage

Question 5

What caused intercerebral heemorrhages?

Answer 5

Intracerebral hemorrhages reflect rupture of intraparenchymal branches of subarachnoid arteries, such as the lenticulostriate arteries (indicated by black box), which branch from the middle cerebral artery, supplying the internal capsule and basal ganglia

Question 6

What isbthe predisposing factor that leads ti intraceregral hemorrhage?

Answer 6

Small penetrating branches of major arteries are vulnerable to rupture (ventricular system may fill with
blood)

Question 7

Where do internal carotid and vertebral arteries travel?

Answer 7

The arteries travel independently until entering the cranium, wherein they interface directly or indirectly via the anastomotic arterial circle of Willis.

• The right common carotid artery generally arises from the brachiocephalic trunk, and the left commonly arises from the aortic arch. At the level of the thyroid cartilage, the common carotids bifurcate, yielding the external and internal carotid arteries. The internal carotid arteries ascend through the deep neck, the carotid canals of the petrous bones and the cavernous sinus. They emit the ophthalmic and posterior communicating arteries. They divide, terminating as the anterior and middle cerebral arteries

Question 8

What are the vertebral arteries?

Answer 8

The vertebral arteries are the first branches of the subclavian arteries. They ascend through the transverse foramina of the upper 6 cervical vertebrae and enter the skull through the foramen magnum. They commonly emit the posterior inferior cerebellar arteries (PICA), which usually spawn the posterior spinal arteries. The vertebral arteries then emit the anterior spinal arteries before unifying to form the basilar artery.

Question 9

What does the basillar artery give rise to?

Answer 9

• The basilar artery gives rise to the anterior inferior cerebellar arteries (AICA). The superior cerebellar arteries arise from the basilar artery, just prior to its bifurcation into the two posterior cerebral arteries at the midbrain.

Question 10

What is the arterial circle of Willis formed by?

Answer 10

The arterial circle of Willis is formed by a group of arteries that surround the optic chiasm, optic tract, mammillary bodies and the remaining ventral hypothalamus. Their perforating branches supply deep structures.

Question 11

How did the vertebral and internal carotid arteries anastamose?

Answer 11

• Vertebral and internal carotid arteries anastomose at the basal diencephalon (by forming the circle of Willis)

• Thevertebral arteries supply the basilar,
cerebellar and cerebral arterie

Question 12

What are the anterior and middle cerebral arteries?

Answer 12

Anterior and middle cerebral arteries are the terminal divisions of the internal carotid artery, which reaches the ventral surface of the brain lateral to the optic chiasm. Arising from the junction of the internal carotid and middle cerebral arteries is the posterior communicating artery, which will join the vertebral arterial circulation.

Question 13

Where does the anterior cerebellar artery run?

Answer 13

• The anterior cerebral artery runs medially and anterior to the optic chiasm. Bridging the two anterior cerebral arteries is the anterior communicating artery.

• Major branches of the anterior cerebral
arteries pass to the medial aspect of the
frontal and parietal lobes, anterior perforated
substance, septum pellucidum, and corpus
callosum (often feeding all but the most
posterior zones of this commissure)

Question 14

What do the striate arteries supply?

Answer 14

• Striate arteries (early branches of the anterior cerebral artery) supply the basal ganglia and anterior limb of the internal capsule.

• The middle cerebral artery extends laterally in
lateral fissure over the insula, sending
branches to the lateral aspect of frontal,
temporal, and parietal lobes. During its early
course, the middle cerebral artery emits the
lenticulostriate arteries, which target the basal
ganglia and the entire internal capsule. These
arteries are particularly vulnerable to rupture
and are a major source of intracerebral
(periventricular) hemorrhag

Question 15

What is the importance of the anterior and middle cerebral arteries?

Answer 15

• Internal carotid arteries feed the middle and anterior cerebral arteries
• Middle cerebral arteries emit the lenticulostriate arteries
• The anterior communicating artery connects the anterior cerebral arteries

Question 16

What is the connection of posterior cerebral arteries to the basilar artery?

Answer 16

The posterior cerebral arteries are the terminal branches of the basilar artery. They receive the posterior communicating arteries from the internal carotid. They travel laterally and dorsally around the midbrain to reach the thalamus and third ventricle. Cerebral branches supply medial temporal, occipital, and parietal structures

Question 17

What does the posterior cerebellar arteries anastamose with?

Answer 17

Posterior cerebral
arteries arise from the basilar artery, anastomosing with the internal carotid system via the posterior communicating arteries

Question 18

How can vascular pathologies be predicted?

Answer 18

Based on the regional distribution of blood to the cerebrum, deficits related to specific vascular pathology can be predicted. For example, occlusion of the left middle cerebral artery often yields language deficits, as this artery normally supplies cortical regions subserving verbal and literal elements of speech

Question 19

Summarize medial distribution of cerebral arteries

Answer 19

• The anterior cerebral artery feeds the anteromedial cerebral surface
• The posterior cerebral artery feeds the posteromedial cerebral surface

Question 20

What are the basics of cerebral arteries?

Answer 20

When considering the territory of the cerebral arteries, it is important to understand the somatotopic organization of the primary motor and somatosensory cortices and the concept of a homunculus.
A homunculus is a map of the human body or some part thereof that is superimposed on an area (nuclei or tracts) of the brain or spinal cord, indicating specific areas of the body that are functionally tied to specific central nervous tissue. A given homunculus may indicate motor or somatosensory function.

A motor homunculus (written or graphic) overlaps with Brodmann’s area 4 (i.e. primary motor cortex).

A somatosensory homunculus overlaps with Brodmann areas 3,1,2 (i.e. primary somatosensory cortex).

In class we will illustrate the importance of integrating knowledge of the somatosensory and motor homunculi with an understanding of the territorial distribution of the cerebral arteries.

Question 21

What are the cerebral vascular syndromes?

Answer 21

You are not expected to fully understand all aspects of the syndromes listed below. However, it would be useful to consider how you can apply your current knowledge of form and function to make general predictions about lesions affecting the cerebral arteries.

Anterior cerebral artery syndrome: Since the ACA supplies the medial part of the frontal and parietal lobes, it supplies the anterior paracentral gyrus (the origin of motor control for the leg) and posterior paracentral gyrus (concerned with processing sensory information from the leg). In ACA syndrome, contralateral weakness and reduced sensation, mainly in the leg, can result.

Middle cerebral artery syndrome: The MCA supplies pre- and postcentral gyri on the lateral surface. MCA syndrome can therefore result in contralateral weakness and sensory loss predominantly affecting the upper extremity and face. Why is the lower extremity unaffected? If the lesion affects the left hemisphere, language deficits (aphasia) may also occur. An occlusion closer to the point of origin of the MCA (proximal stem occlusion) may affect deeper structures such as internal capsule. In this instance, weakness and sensory loss affecting the leg may also be expected. Why

Question 22

What is posterior cerebral artery syndrome?

Answer 22

Posterior cerebral artery syndrome: interruption of the calcarine branch of the PCA results in partial loss of vision (details discussed in visual system lectures) due to involvement of primary visual cortex in the occipital lobe. Somatosensory pathways (for touch, vibration, proprioception, pain and temperature) involve specific thalamic nuclei. Occlusion of PCA branches supplying these nuclei may result in somatosensory deficits.

Question 23

What artery dominates the laateral cerebral surface?

Answer 23

The middle cerebral artery

Question 24

What arteries feed the posteromedial and anteromedial cerebral surface?

Answer 24

• The anterior cerebral artery feeds the anteromedial cerebral surface
• The posterior cerebral artery feeds the posteromedial cerebral surface