![]() It is a partial protrusion or a complete ring formation of bone connecting the dorsal surface of the lateral mass and the rostral surface of the posterior arch. CT angiogram shows PP of the atlas ( arrow). In the present study, PP was defined as a partial protrusion or a complete ring formation of bone at the dorsal surface of the atlas ( Fig. In addition, we investigated the frequency of the ponticulus posticus (PP) of the atlas. ![]() 2), and VA fenestration (a circular arterial network around the posterior arch of the atlas) ( Fig. At the same time, 4 other VA variations were investigated: laterality (asymmetry) of the VA caliber between the right and left sides (defined as a difference ≥ 2 mm), PICA end (VA ending at the PICA without anastomosis to the contralateral VA), persistent first intersegmental artery (FIA) at the atlantoaxial junction ( Fig. and M.Y.) to evaluate whether a PICA originating from the V 3 segment existed at the atlantooccipital junction ( Fig. The imaging data of the patients was transferred in DICOM format to a workstation (Shade Quest version 1.22, Yokogawa Electric Corp.), and a reconstructed image of each patient was reviewed by the first and second authors (T.I. None of the patients had previously been diagnosed with atherosclerotic stenosis, traumatic dissection, or other pathologies of the VA. The amount of contrast medium was properly adjusted to the patient’s body weight and renal clearance. Nonionic iodinated contrast medium was injected into the antecubital vein using a bolus-tracking method with an automatic injector. This clinical study was a retrospective analysis of 3D CT angiography (CTA) data from a series of 153 consecutive patients who visited our department between January 2013 and March 2015 and underwent 3D CTA on a 64-slice CT system (SOMATOM Definition AS, Siemens AG) for the screening or evaluation of the intracranial arteries and/or the extracranial carotid and vertebral arteries. We then performed a statistical analysis to elucidate the relationship between VA variations, including PICAs originating from V 3, and atlas variations. Enhanced CT images were reviewed to clarify their incidence, along with other VA variations and skeletal variations of the atlas. In the present study, we focused on PICAs originating from V 3 as observed on CT. It is essential to know if radiological examinations are applicable to the evaluation of PICAs originating from V 3. Although some cadaveric investigations have reported extradural PICAs originating from V 3, the precise incidence and anatomical nature of this variation have not been studied on clinical images. It is important to understand the course of the PICA on imaging studies before surgery. Because of the abundant venous plexus covering the epidural space in this region, it is hard to visualize the extradural part of the PICA. In such cases, the PICA may be damaged during extradural surgical dissection. 25 In this variation, the PICA branches off the extradural space between the occiput and the atlas. 14 Rhoton reported on extradurally originating PICAs from the V 3 segment, which is the extradural portion from the transverse foramen of the atlas to its dural penetration close to the foramen magnum. However, among the cerebellar arteries, the course of the PICA shows the most variation. The PICA is generally thought to originate from the intradural (V 4) segment of the VA thus, surgeons pay careful attention to the artery after dural opening. Great care should be paid to this artery in operations that involve the craniovertebral junction (CVJ). It also results in serious sequelae, including difficulties in swallowing, saliva clearance, and articulation, as well as hemiparesis. Occlusion of this vessel may cause serious ischemic conditions, such as Wallenberg syndrome, cerebellar infarction, and, in the worst cases, acute tonsillar herniation due to neural edema. It perfuses important neural structures, including the lateral posterior area of the medulla oblongata, the inferior half of the anterior surface of the cerebellum, and the inferior half of the vermis. T he posterior inferior cerebellar artery (PICA) is considered to be the first branch from the vertebral artery (VA).
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