Anatomic Variations in the Giraffe Conferring Protection from Intracranial Hemorrhage and Orthostatic Hypotension

Abstract

Research Question: Can our understanding of human cerebral hypertensive and hypotensive disorders be improved by utilizing the giraffe as a model to study vascular adaptations? Background/Significance/Rationale: Humans can suffer hemorrhagic strokes at blood pressures over 220/110, causing widespread death and disability throughout the world. In other populations, when blood pressures drop to 90/60 through dysregulation of the autonomic nervous system, patients may experience palpitations, dizziness, and syncope. These extreme changes in blood pressure can result in extreme morbidity and limitations in quality of life. The giraffe, on the other hand, can sustain these extreme variations in blood pressure throughout the day via changes in body position, yet dysautonomia or strokes are not commonly seen in these animals. This investigation aims to publish the first brain MRI of the giraffe on an infant and adult giraffe and will study the gross anatomic structures. The eventual goal of this project is to translate many of the cerebral and cardiac adaptions of the giraffe into discovery of therapeutics and protective measures for strokes and dysautonomia states in humans. Methods: To investigate the unique cerebrovascular giraffe adaptations, we propose a comparative analysis of 1) the gross anatomic structures of the giraffe neck vasculature and 2) a brain MRI of both infant and adult giraffe. Via partnerships with zoos across the county, giraffe specimen was selected after death from natural causes. A post-mortem dissection was performed 30 minutes after time of death to identify anatomy. Two other giraffes, one infant and one adult, were imaged one week from time of death to obtain brain MRIs.

Results: The post-mortem dissection revealed a non-collapsible common carotid artery that progressed into the external carotid artery, followed by bifurcation into the maxillary and lingual artery. An internal jugular vein was also present, which was collapsible in nature. The vertebral venous plexus was unable to be identified, though further efforts will be committed to identify the structures from fixed vertebral sections. A brain MRI without contrast from the infant and adult giraffe was significant for a unique carotid rete originating from the external carotid artery.

Conclusion: The study confirms a non-collapsible common carotid artery and a collapsible internal jugular vein, like humans. The external carotid artery perfuses the brain via the maxillary artery. The brain MRI identified a net-like structure originating from the maxillary artery, called the carotid rete, that is unlike human anatomy. This structure likely reduces resistance to blood flow in the brain and normalizes the blood pressure compared to what has been documented near the aorta.