Diagnostic Medical Sonography Program Vascular Technology Lecture: 17 Cerebrovascular Gross Anatomy Holdorf

Cerebrovascular Gross Anatomy Anterior Circulation: Common Carotid Artery (CCA) Right CCA is a branch of the right innominate, while the left CCA is a branch off the aortic arch. The majority of blood flows into the internal carotid Internal carotid artery (ICA) Originates from common carotid artery (CCA) Travels into base of skull without branching Intracranial branches include: Ophthalmic artery: originates near carotid siphon, a significant curve of ICA Posterior Communicating artery

ICA continued;… Terminates in the middle cerebral artery (MCA) and anterior cerebra artery (ACA) Distributes blood to low-resistance vascular beds

External Carotid Artery (ECA) Originates from the CCA Has eight major branches, the first branch is usually the superior thyroid artery Distributes blood to high-resistance vascular beds

Posterior Circulation Vertebral arteries First branch off the subclavian artery Right usually smaller than the left Unite after entering skull to form basilar artery Basilar artery Formed by confluence of vertebral arteries Divides into posterior cerebral arteries

Circle of Willis A hexagonal arrangement of : Distal internal carotid (ICA), anterior cerebral arteries (ACA), joined together by the anterior communicating artery (AComm), posterior cerebral arteries (PCA) joined together by the posterior communicating arteries (Pcomm)

Collateral Pathways Largest intra-arterial connection: circle of Willis Important anastomoses include: ECA-ICA connections via orbital and ophthalmic arteries Occipital branch of ECA with atlantic branch of vertebral Deep cervical and ascending cervical branches of subclavian to branches of lower vertebral artery

Physiology and Hemodynamics Pressure/Flow Relationships The Bernoulli principle: total fluid energy along a streamline of fluid flow is constant Velocity E and Pressure E are inversely proportional: velocity = Pressure Velocity = Pressure

Poiseuille’s Law combined with Resistance equation: Pressure gradients or areas of flow separation are set up: can occur in a vessel because of a geometry change, with or without intra-luminal disease Poiseuille’s Law combined with Resistance equation: Quantity of flow(Q) is related to the pressure gradient across an arterial segment (P), radius of the vessel (r), viscosity of the fluid (n), and length of the vessel (L):

Poiseuille’s Law combined with Resistance equation

Vertebrobasilar Insufficiency with Vertigo Accompanying Symptoms Common Visual Diplopia : double vision Illusions Hallucinations Visual field deficits Drop attacks: sudden spontaneous falls while standing or walking, with complete recovery in seconds or minutes. Incoordination Weakness

Less frequent symptoms Confusion Headache Hearing loss Numbness Loss of consciousness Dysarthria : difficult or unclear speech Tinnitus

Amaurosis Fugax (Latin fugax meaning fleeting, Greek amaurosis meaning darkening, dark, or obscure) is a painless transient monocular or binocular visual loss (i.e., loss of vision in one or both eyes that is not permanent).

Effects of Stenosis on Flow Characteristics Velocity acceleration results because velocity and area are inversely proportional; acceleration causes increased energy loss Blood flow must change direction as the flow stream narrows entering the stenosis and enlarges as it exits; eddy current, turbulence, and vortices cause energy loss through inertia

Pre stenosis At the stenosis Post stenosis

Additional Notes; Lecture 17 Cerebrovascular Gross Anatomy   Know your anatomy Anterior Circulation Posterior Circulation The right vertebral artery is just a bit smaller (diameter wise) than the left. Viscosity of the fluid (blood) is effected by hematocrit (the volume percentage of red blood cells in blood-normally about 45% in men and 40% in women.

Homework Text book: Chapter 18 SDMS Assignments Gross Anatomy, Physiology, and Fluid Dynamics Pages 199 – 206 SDMS Assignments