Anatomical description of the vertebrobasilar and carotid systems forming the cerebral arterial circle in the equine brain.

Overview

• This study provides a detailed anatomical description of the arterial blood supply to the horse brain, focusing on the vertebrobasilar and carotid systems and their contributions to the cerebral arterial circle.
• The research clarifies how these systems interconnect to maintain continuous brain perfusion in horses, highlighting differences from ruminant species.

Introduction to Cerebral Blood Supply in Horses

• The brain receives blood through major arterial systems that ensure oxygen and nutrient delivery.
• In horses, two primary systems maintain cerebral blood flow:
  • The carotid system
  • The vertebrobasilar system
• These systems converge to form the cerebral arterial circle (also known as the circle of Willis), which provides collateral circulation vital for uninterrupted brain perfusion.

Objectives of the Study

• To comprehensively describe the origins, paths (courses), and connections (anastomoses) of the vertebrobasilar and carotid arterial systems in the equine brain.
• To identify any anatomical variations, especially concerning the cerebellar arteries and communicating arteries within the circle.
• To compare the equine cerebrovascular anatomy with that of ruminants, which have unique features such as the carotid rete mirabile.

Methodology

• Sample: Ten adult horses euthanized for reasons unrelated to neurological disease.
• Preparation:
  • Specimens were perfused with 10% formaldehyde to preserve tissue.
  • Colored latex was injected into arterial systems to visualize vessels clearly.
• Dissection focused on intracranial vessels, examining:
  • Major arterial branches
  • Patterns of vessel origin and course
  • Connections forming the cerebral arterial circle

Anatomical Findings: Vertebrobasilar System

• The vertebral arteries and ventral spinal arteries merge to form the basilar artery.
• The basilar artery courses rostrally (toward the front) along the ventral aspect of the brainstem.
• Branches arising from the basilar artery include:
  • Medullary arteries supplying the medulla oblongata.
  • Pontine arteries supplying the pons.
  • Cerebellar arteries supplying the cerebellum.
• The basilar artery then connects with the caudal communicating arteries, linking the vertebrobasilar system to the carotid system.

Anatomical Findings: Carotid System

• Internal carotid arteries enter the cranial cavity and are major contributors to cerebral blood flow.
• These arteries give off primary branches:
  • Rostral cerebral arteries (supplying the anterior brain regions).
  • Middle cerebral arteries (supplying the lateral hemispheres of the brain).
  • Caudal communicating arteries that link with the vertebrobasilar system.
• The carotid and vertebrobasilar systems together form a complete and functional cerebral arterial circle.

Anatomical Variations Observed

• Minor differences noted in:
  • The origin points of cerebellar arteries.
  • The size (caliber) of some cerebellar arteries.
  • The presence or absence of the rostral communicating artery.
• Despite these variations, the cerebral arterial circle remained intact and functional in all specimens, indicating robust collateral circulation.

Comparative Anatomy and Significance

• Unlike ruminants, horses:
  • Do not have a carotid rete mirabile—a specialized vascular network that replaces the internal carotid artery in ruminants.
  • Have patent (open and functional) internal carotid arteries.
  • Possess a functional basilar artery contributing to cerebral blood flow.
• This dual inflow system (carotid and vertebrobasilar) provides:
  • Redundant blood supply routes, enhancing vascular stability.
  • Neurovascular adaptations that may be important in equine physiology, possibly providing resilience against ischemia.
• The findings contribute valuable information to veterinary neuroanatomy and may inform clinical approaches to equine neurological conditions.