REVIEW TOPIC REVIEW Anatomy and Pathology of the Cranial Emissary Veins: A Review With Surgical Implications Martin M. Mortazavi, MD* Emissary veins connect the extracranial venous system with the intracranial venous R. Shane Tubbs, MS, PA-C, sinuses. These include, but are not limited to, the posterior condyloid, mastoid, oc- PhD* cipital, and parietal emissary veins. A review of the literature for the anatomy, Sheryl Riech, BS* embryology, pathology, and surgery of the intracranial emissary veins was performed. Ketan Verma, BS* Detailed descriptions of these venous structures are lacking in the literature, and, to the authors’, knowledge, this is the first detailed review to discuss the anatomy, pathology, Mohammadali M. Shoja, MD‡ anomalies, and clinical effects of the cranial emissary veins. Our hope is that such data Anna Zurada, MD, PhD§ will be useful to the neurosurgeon during surgery in the vicinity of the emissary veins. Brion Benninger, MDk KEY WORDS: Anatomy, Cranial, Neurosurgery, Venous system Marios Loukas, MD, PhD¶ Aaron A. Cohen Gadol, MD, Neurosurgery 70:1312–1319, 2012 DOI: 10.1227/NEU.0b013e31824388f8 www.neurosurgery-online.com MSc# *Section of Pediatric Neurosurgery, Child- “ f there were no emissary veins, injuries and fossil records indicate that there is an ren’s Hospital, Birmingham, Alabama; and diseases of the scalp would lose half increasing frequency of some emissary veins, ‡Neuroscience Research Center, Tabriz I their seriousness.”—Sir Frederick Treves such as the mastoid and parietal vessels in University of Medical Sciences, Tabriz, Iran; 1 3 §Department of Anatomy, Medical Faculty, (1853-1923) humans. University of Varmia and Masuria, Olsztyn, Emissary veins connect the veins outside the Because information regarding these special- Poland; kDepartments of Surgery, Oral cranium with the intracranial venous sinuses ized structures is scant, we reviewed the anatomy Maxillofacial Surgery, Integrated Bioscien- 2-6 ces, Oregon Health & Science University, (Figure 1A). These structures are more com- and clinical and surgical implications of the Portland, Oregon; ¶Department of Ana- monly found in children, and not all of the emissary veins. Standard search engines (eg, tomical Sciences, St. George’s University, various emissary veins are identified in every PubMed) and anatomy textbooks were reviewed Grenada; #Goodman Campbell Brain and individual.7 These veins serve an important for the term “emissary vein.” Spine, Indiana University Department of Neurological Surgery, Indianapolis, Indiana function of equalizing intracranial pressure and can act as safety valves during cerebral conges- ANATOMY Correspondence: tion or in patients with lesions of the neck or Aaron A. Cohen-Gadol, MD, MSc, cranium such as obstruction of the internal Posterior Condyloid Emissary Vein Goodman-Campbell Brain and Spine, 5-10 Department of Neurological Surgery, jugular veins. The foramina for these vessels The posterior condyloid emissary vein con- 6 Indiana University, tend to be larger during childhood and may nects the lower end of the sigmoid, marginal or 1801 North Senate Blvd., Suite 610, communicate with the diploic veins.10 occipital sinuses with the internal vertebral Indianapolis, IN 46202. Emissary veins are also considered an impor- venous plexus (Figure 1A).3,6,10,12 Irmak et al4 E-mail: [email protected] tant component for selective brain cooling.2,4 noted that a posterior condylar emissary vein 7 Received, November 10, 2010. These veins are valveless, so, technically, blood may connect the sigmoid sinus with the sub- 10 Accepted, November 9, 2011. can flow bidirectionally, thereby allowing cooler occipital plexus of veins. Observations have Published Online, November 29, 2011. blood from the evaporating surfaces of the head shown that the posterior condylar foramen is the to cool the brain.4 Louis et al5 found that largest emissary foramen in the retromastoid Copyright ª 2011 by the 8 Congress of Neurological Surgeons emissary veins act as the primary outflow route region. for venous drainage in the upright position and may serve to cool venous blood circulating Mastoid Emissary Vein through the head. The mastoid emissary vein passes through the Emissary veins can often be seen on magnetic mastoid canal and connects the transverse or resonance imaging, computed tomography, and sigmoid sinus to the posterior auricular or angiography, and the various types are named occipital veins, which then join the vertebral according to their position on the cranium.5,8,11 plexus of veins (Figure 1A and B).3,4,8,10,13,14 Interestingly, an enlarged emissary foramen does Lang and Samii15 observed that the mastoid not necessarily transmit a large emissary vein,8 emissary foramen exists less frequently in females 1312 | VOLUME 70 | NUMBER 5 | MAY 2012 www.neurosurgery-online.com Copyright © Congress of Neurological Surgeons. Unauthorized reproduction of this article is prohibited. EMISSARY VEINS FIGURE 1. A, schematic drawing of the major emissary veins and their internal connections. B, posterior view of a cadaver cranium noting a large injected (blue) right-sided mastoid emissary vein. C, schematic drawing illustrating the anterior condylar vein (AC) traveling through the hypoglossal canal. For reference, also note the right sigmoid sinus (SS) and superior petrosal sinus (SPS). Also note the basilar venous plexus applied to the dorsal surface of the clivus. D, cadaveric dissection revealing the left mastoid and occipital emissary veins. than males, although the reason for this is unclear. It is reported that the occipital vein may drain to the confluence controversial whether mastoid foramina are more common of sinuses. on the right or left side.5 Cheatle13 noted an infrequent Parietal Emissary Vein association between the mastoid emissary vein and the petros- quamosal sinus. The parietal emissary vein connects the superior sagittal sinus with the occipital vein that then joins the vertebral venous plexus (Figure 1A).3,6 Parietal emissary veins also interact with the Occipital Emissary Vein diploic veins within the cranial bones, which as mentioned The occipital emissary vein connects the transverse sinus to the previously, may allow for the cooler blood to spread through the occipital vein, which then drains blood to the vertebral venous cranium to the meninges.4 Both the parietal and mastoid plexus (Figure 1A).3,6 On occasion, the occipital emissary vein emissary veins are found at high frequencies in Homo sapiens joins the transverse–sigmoid sinus complex.16 Okudera et al17 compared with other hominid species.2 NEUROSURGERY VOLUME 70 | NUMBER 5 | MAY 2012 | 1313 Copyright © Congress of Neurological Surgeons. Unauthorized reproduction of this article is prohibited. MORTAZAVI ET AL Petrosquamosal Sinus Anterior Condylar Vein Although it serves as the primary cerebral drainage site in many The anterior condylar vein accompanies the hypoglossal nerve lesser primates and quadrupeds, the petrosquamosal sinus is a rare through the hypoglossal canal (Figure 1C) and joins the anterior emissary vein in humans that typically disappears before birth in condylar confluent.23 humans. The petrosquamosal sinus ranges from 2 to 4 mm in diameter and originates at the junction between the transverse and Temporal Emissary Vein sigmoid sinuses, coursing laterally above the superior border of the This venous structure may connect the remnant of the temporal bone. petrosquamosal sinus with the deep temporal vein and likely represents the dorsal cerebral vein seen in some mammals. Ophthalmic Veins The ophthalmic veins are considered by some to be emissary Superficial Petrosal Emissary Vein veins (Figure 1A) because they may perform a similar function as This vein connects the vessel(s) traveling along the superficial the emissary veins by connecting the exterior with the interior petrosal vein in the middle cranial fossa to the vein traveling with cranium (angular vein to cavernous sinus) and are valveless. The the facial nerve within the stylomastoid foramen. Such vessels may ophthalmic veins travel through the orbit and traverse the supe- be remnants of the primary head sinus. rior orbital fissure to reach the most anterior portion of the cavernous sinus.18 Significance of Emissary Veins During Surgery Open Procedures Sphenoidal Emissary Vein (Vesalius) The cranial emissary veins provide surgical advantages. For Sphenoidal emissary veins (Vesalian veins) connect the cavernous procedures such as the transcondylar and far lateral approaches, sinus with the pterygoid or pharyngeal plexuses (Figure 1A).18-20 the emissary veins act as landmarks for the deeper lying venous These veins are not constant and are found in only approximately 1 sinuses.24-28 In the retrosigmoid approach to the posterior cranial in 3 cases.18 The foramen for this vessel is found just medial to the fossa, emissary veins should be freed from the bone to avoid foramen ovale. avulsion of the vein or lacerations of the underlying sinuses to which they are connected; otherwise, hemorrhage or air embo- 25 Emissary Veins of the Foramen Ovale lism may occur (Figure 1D). Bleeding from emissary veins may 29,30 Just like the sphenoidal emissary veins, the emissary veins of the result in postoperative epidural hematoma formation. foramen ovale connect the cavernous sinus to the pterygoid plexus Although the most appropriate amount of material, including (Figure 1A).18,19 fibrin glue used to put into a bleeding emissary foramen, is not known, care should be used when applying