Stroke Subtypes

The accessory meningeal artery may also arise from the maxillary artery or from the middle meningeal artery. It ascends through the foramen ovale to supply the trigeminal ganglion and the adjacent dura within the middle cranial fossa.

The bone and dura of the posterior fossa are supplied by (1) the meningeal branches of the ascending pharyngeal artery, which pass through the jugular foramen, foramen lacerum, and the hypoglossal canal; (2) the meningeal branches of the occipital artery, which pass through the jugular foramen and the condylar canal; and (3) the small mastoid branch of the occipital artery, which passes through the mastoid foramen.

Branches of the Internal Carotid System. The meningohypophyseal trunk has three major branches. The tentorial branch enters the tentorium cerebelli at the apex of the petrous bone, supplying the anterolateral free margin of the tentorial incisura and the base of the tentorium near the attachment to the petrous bone. A dorsal branch supplies the dura mater of the dorsum sella and clivus, sending small twigs to supply the dura around the internal auditory canal. The artery to the inferior portion of the cavernous sinus originates from the lateral aspect of the cavernous segment of the internal carotid artery.

An anterior meningeal artery arises from the anterior aspect of the cavernous carotid artery and passes over the top of the lesser wing of the sphenoid to supply the dura of the floor of the anterior fossa.

As the ophthalmic artery passes medially and then above the optic nerve, it gives off a lacrimal branch. The recurrent meningeal artery arises from this branch and passes through the superior orbital fissure to supply the dura of the anterior wall of the middle cranial fossa.

The ophthalmic artery also provides several ethmoidal branches. The posterior ethmoidal artery leaves the orbit to supply the posterior ethmoid air cells and the dura of the planum sphenoidale and the posterior half of the cribriform plate. The anterior ethmoidal artery passes through the anterior ethmoidal canal to supply the mucosa of the anterior and middle ethmoidal air cells and the frontal sinus. It then enters the cranial cavity, where it gives off an anterior meningeal branch (anterior falx artery) to the dura mater and the anterior portion of the falx cerebri.

Branches of the Vertebral Artery. The meningeal branches enter the skull through the foramen magnum. The anterior meningeal branch originates from the distal part of the second segment of the vertebral artery just before its lateral bend at the level of the atlas. It ascends and passes anteromedially to supply the dura of the anterior margin of the foramen magnum. The posterior meningeal branch arises from the third segment of the vertebral artery between the atlas and the foramen magnum. It passes between the dura and the calvaria, supplying the posterior rim of the foramen magnum, the falx cerebelli, and the posteromedial portion of the dura of the posterior fossa.

TYPES OF STROKE

Strokes are divided into two broad categories: hemorrhage and ischemia. Hemorrhage refers to bleeding inside the skull into the brain or cerebrospinal fluid or membranes surrounding the brain. Brain ischemia refers to insufficient blood flow. Hemorrhage and ischemia are polar opposites. Hemorrhage is characterized by too much blood inside the skull, and in ischemia, there is not enough blood supply to allow continued normal functioning of the effected brain tissue. Brain ischemia is much more common than hemorrhage. About four fifths of strokes are ischemic.

Hemorrhage

The four designations of hemorrhage are named for their locations. Hemorrhages within brain substance (inside the pia mater) are called intracerebral hemorrhages; those between the pia mater and arachnoid are labeled subarachnoid hemorrhages. Hemorrhages outside the arachnoid but inside the dura mater are called subdural hemorrhages, and hemorrhages outside the dura mater but inside the skull are called epidural hemorrhages. The different sites of bleeding have different causes.

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