Neuroanatomical Study Anatomic and radiologic analysis of the atlantal part of the vertebral artery Sahika Liva Cengiz a, * , Aynur Cicekcibasi b , Demet Kiresi c , Yalcın Kocaogullar a , Onur Cicek a , Alper Baysefer a , Mustafa Buyukmumcu b a Neurosurgery Department, Selçuk University, Meram Faculty of Medicine, A/5 Meram Akyokus ß 42080, Konya, Turkey b Anatomy Department, Selçuk University, Meram Faculty of Medicine, Konya, Turkey c Radiology Department, Selçuk University, Meram Faculty of Medicine, Konya, Turkey article info Article history: Received 19 February 2008 Accepted 27 May 2008 Keywords: Cadaver External landmarks Horizontal part Paramedian suboccipital craniectomy Posterior fossa surgery Third segment of the vertebral artery Vertebral artery abstract The horizontal third segment (V3h) of the vertebral artery (VA) in 7 cadavers (14 sides) was dissected and the anatomical measurements recorded. Measurements from 24 healthy individuals (48 sides) were taken for comparison using multislice CT scanning. The distance between the medial tip of the VA V3h and the line passing through the mid point of the posterior tuberculum of the atlas was marked as length A. The distance between the medial tip of the VA V3h and the point penetrating the dura mater was clas- sified as length B. The angle between these lines was the alpha (a) angle. Measurements were taken when the head was in a neutral position, as well as in maximum right and left rotation, extension and flexion. In cadavers, the mean a angle (±S.D.) was 82.42 ± 10.34° and 83.21 ± 10.81° on the right and left side, respectively. On multislice CT scanning, the mean a angle was 81.64 ± 10.15° on the right and 83.77 ± 10.65° on the left. These angles varied with the position of the head. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction A potential hazard of the far lateral approach in a posterior fossa craniectomy is injury to the horizontal third segment (V3h) of the vertebral artery (VA), located in the superior aspect of the atlas. The VA is classically divided into four parts: its origin (from the subclavian artery in the root of the neck) to the sixth cervical ver- tebra (first part); its course through the foramina transversaria of the sixth to the first cervical vertebrae (cervical/second part); from the foramen transversarium of the atlas vertebra to its passage through the dura mater at the foramen magnum (suboccipital/ third part); and its course within the cranium to the pontomedul- lary border (intracranial/fourth part). 1–12 The V3h portion of the VA lies close to the floor of the posterior fossa and damage to the VA may be fatal. 13,14 Therefore, before attempting surgery at the pos- terior fossa and craniocervical junction, a thorough anatomical study of the path of the VA is mandatory. Here, we describe the normal anatomy and variations, as well as the surgical approach needed to expose the VA V3h segment, with the intention of devel- oping a safe and effective technique for the far lateral approach in a posterior fossa craniectomy. 2. Methods Seven cadavers (14 sides), with no history of craniocervical pathology, and 24 healthy individuals (48 sides), who were ana- tomically normal, were examined. The procedures were based on the guidelines of Selçuk University’s Ethical Committee on the Care and Use of Cadaveric Specimens. All of the healthy individuals who took part in the study were volunteers and were notified of the po- tential implications of radiation exposure. Dissections of the left and right V3h segments of the VA were performed in all cadavers. Each cadaver was placed in a prone po- sition. The head was slightly extended in the neutral position, as the position of the head can greatly influence the structures that the surgeon will encounter. A midline incision was made through the inion and foramen magnum. After the blunt dissection of the trapezius, splenius capitis, and semispinalis capitis muscles, the suboccipital trigonum was exposed. The V3h portion of the VA was measured using an electronic caliper and goniometer. All length measurements were in centime- ters. The distance between the medial tip of the VA V3h and the line passing through the mid point of the posterior tuberculum of the atlas was recorded as length A. When the head was in the neutral position (N), length A was labelled as NAR on the right (R) side and NAL on the left (L) side (Table 1). The distance between the medial tip of the VA V3h and the point penetrating the dura mater was recorded as length B. When the head was in the neutral position, length B was defined as NBR on the right side and NBL on 0967-5868/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.jocn.2008.05.033 * Corresponding author. Tel.: +90 33 2223 6449; fax: +90 33 2223 6181. E-mail address: livacengiz@yahoo.com (S.L. Cengiz). Journal of Clinical Neuroscience 16 (2009) 675–678 Contents lists available at ScienceDirect Journal of Clinical Neuroscience journal homepage: www.elsevier.com/locate/jocn