Cerebrovascular Embryology October 6, 2000 Brain School Resident: Dr. Charles Matouk Supervisor: Dr. Chris Wallace Primitive Aortic Arches Key Points 1) Cephalic location of primitive heart 2) 6 pairs of primitive aortic arches 3) Thoracic migration of heart and step-wise arch regression Primitive Aortic Arches Major Events 1) Regression of dorsal aorta between 3rd and 4th arches 2) Derivation of subclavian arteries from 6th intersegmental arteries 3) Attenuation of R 4th aortic arch 4-mm Fetal Stage 1st arch – involution and mandibular artery remnant 2nd arch – involution and hyoid artery remnant 3rd arch – precursor of ICA and ECA 4-mm Fetal Stage Cranial division of primitive ICA – primitive ACA Caudal division – precursor of PComA ACA is the direct embryonic continuation of ICA, not MCA!!! 4-mm Fetal Stage In hindbrain, arterial vasculature defined by paired, separate longitundinal nerual plexi Supplied by anastomotic branches of primitive ICA and C1 segmental artery, and others Embryonic Carotid-Basilar Anastomoses 1) Persistent trigeminal artery 2) Otic artery 3) Hypoglossal artery 4) Proatlantal intersegmental artery 5-6-mm Fetal Stage Ventral pharnygeal artery (precursor of proximal ECA vasculature) now prominent Caudal division of ICA forms anastomoses with cranial-end of bilateral longitudinal neural arteries 7-12-mm Fetal Stage Ventral pharyngeal system more extensive with identifiable branches (precursor of proximal ECA) Hyoid artery (precursor of upper portion of ECA) 7-12-mm Fetal Stage Vertebral arteries formed by coalescence of longitudinal anastomoses between cervical segmental arteries Drapkin AJ. The double lumen sign: a pathognomonic sign of arterial dissection? Diagnostic Neuroradiology 42:203-205;2000. 12-14-mm Fetal Stage Plexiform anastomosis between ACAs evolve into AComA 16-18-mm Fetal Stage Stapedial artery (branch of hyoid artery) at zenith of development) Its development defines distal ECA circulation and middle meningeal artery. 16-18-mm Fetal Stage Fate of stapedial artery … proximal trunk regression with annexation of territories by ventral pharnygeal trunk and ophthalmic arteries Evolution of Primitive Ophthalmic Arteries 1) Ventral (from ACA) ophthalmic artery 2) Dorsal ophthalmic artery When dorsal persists or is dominant, ophthalmic artery originates from cavernous segment of ICA Evolution of Posterior Circulation PCA arising from ICA, predominantly or exclusively, is described as being of ‘fetal origin’ Review Review Review Review References 1. Morris, P. Practical Angiography. 1997. Williams & Wilkins, Baltimore, Maryland. Chapter 5, pp 89- 98. 2. Osborn, A. Diagnostic Neuroradiology. 1994. Mosby, St. Louis, Missouri. Chapter 6, pp 117-153. 3. Moore KL and Persaud TVN. 1998. W.B. Saunders Company, Philadelphia, Pennsylvania. Chapter 349-403.
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