The Lateral Mesencephalic Vein: Surgical Anatomy and Its Role in the Drainage of Tentorial Dural Arteriovenous Fistulae Delia Cannizzaro 1 , Stylianos K. Rammos 2 , Simone Peschillo 3 , Adel M. El-Nashar 4 , Andrew W. Grande 4 , Giuseppe Lanzino 1 - BACKGROUND: The lateral mesencephalic vein (LMV) represents an important connection between the infra- tentorial and supratentorial compartments. It joins the basal vein of Rosenthal and the petrosal system. In our experience with management of tentorial dural arteriove- nous fistulas (DAVFs) we have often noted involvement of the lateral mesencephalic vein (LMV) in the venous drainage of these fistulas. - METHODS: We reviewed the clinical and angiographic findings of 26 patients with tentorial DAVFs to study the incidence and pattern of drainage through the LMV. In addition, we reviewed the pertinent literature on the anatomy of the LMV. - RESULTS: The LMV was involved in the venous drainage of 31% (8/26) of patients with tentorial DAVFs. The direction of venous drainage through the LMV is more commonly from the infratentorial to the supratentorial compartment. There were no specific clinical symptoms/signs associated with tentorial DAVFs involving the LMV compared with those without LMV involvement. When involved in DAVF drainage, the LMV could be invariably identified on noninvasive imaging studies. We present illustrative clin- ical/angiographic cases and provide a detailed review of the pertinent clinical anatomy of this important but often neglected intracranial vein. - CONCLUSIONS: The LMV is a constant venous anasto- mosis between the supratentorial and infratentorial com- partments. Detailed knowledge of the most common variations of the LMV surgical and radiological anatomy has important clinical implications. The vein is an impor- tant anatomic landmark during surgery of midbrain lesions. It is often involved in the tentorial DAVF drainage, and it is critical in understanding some “unexpected” venous complications during surgery for posterior fossa lesions. INTRODUCTION T he mesencephalic veins and the lateral mesencephalic trunk, in particular, constitute an important venous anastomosis between the infratentorial and supratentorial compartments. Because of numerous anatomic variations, mesencephalic veins have been subjected to various classification schemes and their terminology can be confusing at times. More- over, their role in pathologic conditions is not well-defined. Over the years, we have noticed involvement of mesencephalic veins, especially of the lateral mesencephalic trunk in a number of tentorial dural arteriovenous fistulas (DAVFs). In this study, we review the descriptive and surgical anatomy of the lateral mesencephalic trunk and illustrate its role in a subgroup of pa- tients with tentorial DAVFs. MATERIALS AND METHODS This study consists of 2 parts: 1) a detailed and illustrated review of the anatomy of the mesencephalic veins with specific focus on the lateral mesencephalic trunk; and 2) a retrospective review of the pattern of drainage in a consecutive series of patients with ten- torial DAVFs. Key words - Basal vein - Intracranial arteriovenous dural fistulas - Lateral mesencephalic vein - Petrous vein - Tentorial arteriovenous dural fistulas Abbreviations and Acronyms DAVF: Dural arteriovenous fistula ICA: Internal carotid artery LMV: Lateral mesencephalic vein MRI: Magnetic resonance imaging From the 1 Department of Neurological Surgery, Mayo Clinic, Rochester, Minnesota, USA; 2 Arkansas Neuroscience Institute, Little Rock, Arkansas, USA; 3 Department of Neurology and Psychiatry, Endovascular Neurosurgery/Interventional Neuroradiology, Sapienza University of Rome, Rome, Italy; and 4 Department of Neurosurgery, University of Minnesota, Minneapolis, Minnesota, USA To whom correspondence should be addressed: Giuseppe Lanzino, M.D. [E-mail: lanzino.giuseppe@mayo.edu] Citation: World Neurosurg. (2016) 85:163-168. http://dx.doi.org/10.1016/j.wneu.2015.08.060 Journal homepage: www.WORLDNEUROSURGERY.org Available online: www.sciencedirect.com 1878-8750/$ - see front matter ª 2016 Elsevier Inc. All rights reserved. WORLD NEUROSURGERY 85: 163-168, JANUARY 2016 www.WORLDNEUROSURGERY.org 163 Original Article