ANATOMIC REPORT MICROSURGICAL ANATOMY OF THE DURAL ARTERIES Carolina Martins, M.D. OBJECTIVE: The objective was to examine the microsurgical anatomy basic to the Department of Neurological microsurgical and endovascular management of lesions involving the dural arteries. Surgery, University of Florida, Gainesville, Florida METHODS: Adult cadaveric heads and skulls were examined using the magnification provided by the surgical microscope to define the origin, course, and distribution of Alexandre Yasuda, M.D. the individual dural arteries. Department of Neurological RESULTS: The pattern of arterial supply of the dura covering the cranial base is more Surgery, University of Florida, complex than over the cerebral convexity. The internal carotid system supplies the Gainesville, Florida midline dura of the anterior and middle fossae and the anterior limit of the posterior Alvaro Campero, M.D. fossa; the external carotid system supplies the lateral segment of the three cranial Department of Neurological fossae; and the vertebrobasilar system supplies the midline structures of the posterior Surgery, University of Florida, fossa and the area of the foramen magnum. Dural territories often have overlapping Gainesville, Florida supply from several sources. Areas supplied from several overlapping sources are the parasellar dura, tentorium, and falx. The tentorium and falx also receive a contribution Arthur J. Ulm, M.D. from the cerebral arteries, making these structures an anastomotic pathway between Department of Neurological Surgery, University of Florida, the dural and parenchymal arteries. A reciprocal relationship, in which the territories Gainesville, Florida of one artery expand if the adjacent arteries are small, is common. CONCLUSION: The carotid and vertebrobasilar arterial systems give rise to multiple Necmettin Tanriover, M.D. branches that supply the dura in a complex and overlapping pattern. A knowledge of Department of Neurological the microsurgical anatomy of these dural arteries and their assessment on pretreatment Surgery, University of Florida, Gainesville, Florida evaluations plays a major role in safe and accurate treatment of multiple lesions. KEY WORDS: Cranial base, Cranial nerves, Dura mater, External carotid artery, Internal carotid artery, Albert Rhoton, Jr., M.D. Intracranial arteries, Microsurgical anatomy, Skull base, Vertebral artery Department of Neurological Surgery, University of Florida, Neurosurgery 56[ONS Suppl 2]:ONS-211–ONS-251, 2005 DOI: 10.1227/01.NEU.0000144823.94402.3D Gainesville, Florida Reprint requests: Albert Rhoton, Jr., M.D., he dural arteries arise from the internal MATERIALS AND METHODS Department of Neurological and external carotid arteries and the ver- Surgery, University of Florida tebrobasilar system. These arteries may Five dry skulls and 20 adult cadaveric College of Medicine, T ϫ ϫ be the site of formation of saccular aneurysms, heads were examined using 3to 40 mag- P.O. Box 100265, nification of the surgical microscope (Carl Gainesville, FL 32610-0265. pseudoaneurysms, and arteriovenous fistulae Email: and the source of traumatic and spontaneous Zeiss Inc., Göttingen, Germany). The arteries [email protected] hemorrhage into the epidural, subdural, and and veins were perfused with colored silicon intraparenchymal areas, in addition to their (Dow Corning, Midland, MI; Crayola, Easton, Received, March 26, 2004. well-known role in the vascularization of me- PA). The dissections were performed to dem- Accepted, August 13, 2004. ningiomas, other tumors, and parenchymal onstrate and photograph the individual dural arteriovenous malformations (AVMs). Ad- artery branches and their common areas of vances in the microsurgical and endovascular supply. management of lesions involving these arter- ies have created the need for a deeper under- GENERAL STRUCTURE: standing of the dural arterial network. This ENDOSTEAL AND study examined the microsurgical anatomy of MENINGEAL LAYERS this network important in planning the thera- peutic approach not only to lesions invading The cranial dura mater is a thick, collage- the cranial base, convexity dura, tentorium, nous sheath that lines the cranial cavity and is and falx but also to numerous intraparenchy- continuous with the spinal dura at the fora- mal lesions. men magnum. The dura is adherent to the NEUROSURGERY VOLUME 56 | OPERATIVE NEUROSURGERY 2 | APRIL 2005 | ONS-211 MARTINS ET AL. surrounding bones, especially at the sutures, at the cranial and their anastomotic pattern forms a regular polygonal net- base, and around the foramen magnum. With increasing age, work (29). Penetrating vessels arise from primary and second- the dura becomes less pliable and more firmly adherent to the ary anastomotic arteries, leave the dural surface, and extend to inner surface of the cranium, particularly the calvaria. within 5 to 15 ␮m of the inner and juxta-arachnoid surface of The dura is composed of an endosteal layer that faces the the dura, to end in the capillary network. Capillaries, 8 to 12 bone and a meningeal layer that faces the brain (16). These ␮m in diameter, are present throughout dura, including the layers are distinguished as separate sheaths at the venous falx and tentorium, and are especially rich parasagittally, sinuses, foramen magnum, and optic canal. The meningeal where they may form several layers. The capillary bed is layer is continuous with the dural covering of the spinal cord located on the inner or cerebral surface of dura, being sepa- and optic nerves, providing tubular sheaths for the cranial rated from arachnoid by only a few micrometers (29). nerves as they pass through the cranial foramina. These The arteries to the cranium originated from the primary sheaths fuse with the epineurium as the cranial nerves emerge anastomotic vessels. They are clearly seen when the dura is from the cranium, except at the optic nerve, where the dural stripped from the cranium and many small arteries are torn sheath blends into the sclera. At the vascular foramina, the out of the diploe, revealing their tiny foramina on the inner meningeal layer fuses with the adventitia of the vessel. The table of the cranium. They measure 40 to 80 ␮m and supply meningeal layer folds inward to form the falx cerebri, the the metabolic needs of the cranium and diploic contents. tentorium cerebelli, the falx cerebelli, and the diaphragm sel- These vessels, which are often enlarged in dural AVMs, can be lae, which partially divide the cranial cavity into freely com- a source of copious bleeding during elevation of the bone flap municating spaces. The endosteal layer of dura is continuous during craniotomy. through the cranial sutures and foramina with the pericra- nium and through the superior orbital fissure and optic canal OVERVIEW OF DURAL SUPPLY with the periorbita (16). This section provides an overview of the supply of the VASCULAR ORGANIZATION OF intracranial dura before discussing the origin, course, and THE DURA territory of each of the individual dural arteries. The dura covering the anterior fossa floor draws its supply from the The origin of the membranes of the cranium starts when the anterior and posterior ethmoidal arteries, the superficial re- embryo has a crown-to-hump length of 12 to 20 mm, at which current ophthalmic artery, and the middle meningeal artery time the differentiation of the cranium, dura, arachnoid, and (Fig. 1)(Tables 1–3). The middle meningeal artery will not pia begins. The gradual cleavage of the vascular system into contribute to the supply of the dura lining the floor of the external, dural, and cerebral layers also takes place at this anterior fossa if the artery or its anterior branch arises from the stage, which has been referred to as the third stage of the ophthalmic arterial system. The territory of the anterior con- cerebrovascular development (79). As the membranes cover- vexity and parasagittal area is supplied by both the anterior ing the brain differentiate, the anastomosing channels that branch of the middle meningeal artery and the anterior men- connect the deep capillary plexus with the superficial vessels ingeal branch from the ophthalmic artery (Fig. 2). close, thus separating the vessels surrounding the brain from The supply to the middle fossa and paracavernous dura those belonging to the cranium and its coverings (79, 80). The derives laterally from the middle meningeal, accessory men- major meningeal arteries originating from this cleavage give ingeal, and ascending pharyngeal arteries. In an anterior-to- rise to a rich anastomotic network that may enlarge after posterior direction, it receives contributions from the recurrent various insults (22) and play a role in the genesis of dural branches of the ophthalmic and lacrimal arteries as well as AVMs. This anastomotic network divides progressively into from the medial tentorial artery (Figs. 1 and 3). Medially, those primary, secondary, and penetrating vessels. arteries anastomose with the intracavernous branches of the The primary anastomotic vessels change little in diameter as internal carotid artery. The sellar dura has a bilateral supply they course over the dural surface and anastomose frequently from the paired capsular, inferior hypophysial, medial clival, with each other. They cross the superior sagittal sinus, con- and dorsal meningeal arteries that anastomose across the mid- necting the dura over the paired cerebral hemispheres into a line on the anterior and posterior surfaces of the dorsum sellae single vascular unit. Crossing