A neurosurgical assessment of the blood supply in the optochiasmatic system: a cadaveric-anatomic study.

The chiasmal and subchiasmal surfaces are of critical importance in connection with the performance of surgical procedures owing to the critical blood supply to these areas. Recently, the perforating arteries providing the blood to the optic nerves and chiasm have gained attention as they significantly affect the morbidity from surgical approaches. Intraoperative preservation of these perforating arteries is considered critical to prevent further visual loss. Thirty autopsy specimens, including the optic apparatus, were examined for their perforating arteries feeding the optic chiasm and optic nerves. The optic nerves and chiasmal surfaces were divided into four zones based on the presence and numbers of perforating arteries as anterior superior-posterior superior surfaces and anterior inferior-posterior inferior surfaces. The superior surface of the optic chiasm was supplied by the A1 segments of the bilateral anterior cerebral arteries and by the perforating arteries originating from the anterior communicating artery. On the other hand, the inferior surface of the optic chiasm was fed by the bilateral posterior communicating arteries and by the supraclinoidal segments of the bilateral carotid arteries. We demonstrated the anatomical involvement of a large number of nourishing arteries in feeding the optic apparatus related to the perforating arteries by classifying them into zones based on the surgical approaches, which has been rarely reported in the literature.

Assessment of the Circle of Willis with Cranial Tomography Angiography.

BACKGROUND: The circle of Willis is a major collateral pathway important in ischemic conditions. The aim of our study was to assess the structural characteristics of the circle of Willis within the Turkish adult population, along with variations and arteries involved in the measurement of diameters and lengths on cranial computed tomography angiography (CTA). MATERIAL AND METHODS: One hundred adult patients who underwent CTA images were evaluated retrospectively. RESULTS: Results of the study revealed 82% adult, 17% fetal, and 1% transitional configurations. A complete polygonal structure was observed in 28% of cases. Variations of the circle of Willis were more common in the posterior portion. Hypoplasia was found to be the most common variation and was observed as a maximum in the posterior communicating artery (AComP). CONCLUSIONS: The patency and size of arteries in the circle of Willis are important in occlusive cerebrovascular diseases and cerebrovascular surgery. Although CTA is an easily accessible non-invasive clinical method for demonstrating the vascular structure, CTA should be evaluated taking into account image resolution quality and difficulties in the identification of small vessels.

An in vitro assessment of the cerebral hemodynamics through three patient specific circle of Willis geometries.

The Circle of Willis (CoW) is a complex pentagonal network comprised of fourteen cerebral vessels located at the base of the brain. The collateral flow feature within the circle of Willis allows the ability to maintain cerebral perfusion of the brain. Unfortunately, this collateral flow feature can create undesirable flow impact locations due to anatomical variations within the CoW. The interaction between hemodynamic forces and the arterial wall are believed to be involved in the formation of cerebral aneurysms, especially at irregular geometries such as tortuous segments, bends, and bifurcations. The highest propensity of aneurysm formation is known to form at the anterior communicating artery (AcoA) and at the junctions of the internal carotid and posterior communicating arteries (PcoAs). Controversy still remains as to the existence of blood flow paths through the communicating arteries for a normal CoW. This paper experimentally describes the hemodynamic conditions through three thin walled patient specific models of a complete CoW based on medical images. These models were manufactured by a horizontal dip spin coating method and positioned within a custom made cerebral testing system that simulated symmetrical physiological afferent flow conditions through the internal carotid and vertebral arteries. The dip spin coating procedure produced excellent dimensional accuracy. There was an average of less than 4% variation in diameters and wall thicknesses throughout all manufactured CoW models. Our cerebral test facility demonstrated excellent cycle to cycle repeatability, with variations of less than 2% and 1% for the time and cycle averaged flow rates, respectively. The peak systolic flow rates had less than a 4% variation. Our flow visualizations showed four independent flow sources originating from all four inlet arteries impacting at and crossing the AcoA with bidirectional cross flows. The flow paths entering the left and right vertebral arteries dissipated throughout the CoW vasculature from the posterior to anterior sides, exiting through all efferent vessels. Two of the models had five flow impact locations, while the third model had an additional two impact locations within the posterior circulation caused by an additional bidirectional cross flows along the PcoAs during the accelerating and part of the decelerating phases. For a complete CoW, bidirectional cross flows exist within the AcoA and geometrical variations within the CoW geometry can either promote uni- or bidirectional cross flows along the PcoAs.

Simulation of cerebral hemodynamics for preoperative risk assessment.

BACKGROUND: An important part of the medical treatment of many cerebrovascular diseases is the occlusion of brain supplying arteries. Until now, the risk of this intervention can only be estimated by invasive diagnostics including the risk of cerebrovascular accidents. METHODS AND RESULTS: As a supporting tool, a computer model of the circle of Willis was designed. The model is based upon linear differential equations describing electrotechnical circuits extended non-linearly. By these means, time continuous simulations of different states and the online observation of all calculated state variables such as blood pressure and blood flow in every modeled vessel became feasible. For individual simulations, model parameters were determined by MR-angiography and boundary values by simultaneous Duplex-measurements in both carotid and vertebral arteries. State variables generated by the model behaved physiologically and the reaction of individual cerebrovascular systems in critical situations could be investigated by special scenarios. Inaccuracies concerning the determination of model parameters and boundary values of the used differential equations are likely to be resolved in the near future through a more careful and technically improved determination of these values. CONCLUSIONS: Computer models of subjects were created taking in account the individual anatomical and non-linear physical properties of real vascular systems supplying the brain. Thereby information could be obtained concerning the hemodynamic effects of an iatrogenic vascular occlusion.

Microneurosurgical training model in fresh cadaveric cow brain: a laboratory study simulating the approach to the circle of Willis.

BACKGROUND: Residents of neurosurgery need many years to develop microneurosurgical skills, and laboratory training models are essential for developing and refining surgical skills before clinical application of microneurosurgery. A simple simulation model is needed for young residents to learn how to handle microneurosurgical instruments, and to perform safe dissection of intracranial vessels and nerves. METHODS: The material consists of a 2-year-old fresh cadaveric cow cranium. A 4-step approach was designed to dissect the internal carotid artery and its proximal branches, the optic nerve, the optic chiasm, and the pituitary stalk. RESULTS: The model simulates standard microneurosurgery using a variety of approaches to vessels and neural structures in and around the circle of Willis of the human brain. CONCLUSION: The cadaveric cow brain, besides being cost-effective, represents a fairly useful method to accustom residents of neurosurgery, especially junior residents, to dissecting intracranial vessels and nerves, and it simulates intracranial microneurosurgical procedures performed in the human brain.