Topographic-Anatomic Substantiation of a Pterional Approach to Aneurysms of Middle Cerebral Artery

A.V. Prirodov, G.F. Dobrovolsky, V.V. Tkachev

Sklifosovsky Research Institute of Emergency Care, Burdenko Research Institute of Neurosurgery, Moscow, Russia

 

Development of new neurosurgical approaches and improvement of existing accesses are based on topographic-anatomic methods, being an important constituent of methodology of research, carried out by neurosurgeons.

There are different approaches, used in treatment of aneurysms of the middle cerebral artery (MCA). They include unilateral frontal, frontolateral, frontobasal, bifrontal or pterional trephinations of a skull and their modifications (Yasargil,1969, 1975; Anegava, 1987; Fox J.L., 1968; Ito, 1985; Vorkapic P. et al., 1985; Herose R.C. et all., 1982; Poppen J.L., 1960; Stoodley M.A., 1998; Suzuki J. et all., 1965; Fox J.L.,1983; Aiba T.,1975; Krylov V.V. et al., 1996, 2002; etc.).

The goal of the present study was to give topographic-anatomic substantiation of a pterional approach by studying peculiarities and versions of MCA, structural elements of a skull base and brain base, which are encountered during its performing.

Materials and Methods. This research was preceded by development of methods of preparing and use of block specimens (brain-skull base-cervical spine) with subsequent filling of the carotid system by dyed latex, stage-by-stage micropreparation, morphometry and taking photos of different areas of a specimen. The specimens under discussion were obtained in the following way. Removal of a skull fornix during autopsy of individuals, whose death had not been caused by CNS pathology, was followed by separation of dura of the anterior cranial fossa from orbital parts of the frontal and ethmoid bones up to the level of a posterior margin of the cribriform lamina. Then bones of the face were cut away with the help of a saw and chisel and a specimen was formed. It included cerebral hemispheres, stem, cerebellum, cervical areas of the spinal cord, structures of a skull base, cervical spine, Th1and Th2, all arteries of the carotid and vertebro-basilar systems. Transected intraorbital segments of ophthalmic arteries were ligated. The next step was exposure of internal carotid arteries and initial segments of vertebral arteries with subsequent introduction of catheters into their lumen and ligation. Both arterial systems were washed with water in succession. Then dyed latex was administered into arteries' lumens. Filling of arteries of the convexital area was controlled visually. Filled vessels were ligated once again. When filling of the carotid and vertebro-basilar systems was completed, specimens were fixed in 10% formalin solution. Modeling of a pterional approach to different segments of MCA by dissection of a roof of the Sylvian fissure cistern started on the next day. It is important to carry out modeling on the 1-5 day after brain fixation, when it is still soft and can be displaced in performing different micromanipulations. It allows to achieve maximum resemblance between an anatomic model and real intervention. Modeling of an approach was carried out with use of a surgery microscope (Opton OPMI 6.5 DEC, magnification of 4-14 times), retractors, microsurgical instruments. Modeling of a pterional approach was accompanied by stage-by-stage taking of microphotos and morphometry of vessels.

We prepared and studied 12 specimens on both sides in compliance with the above method.

Results. Our morphometric study showed, that ICA diameter varied from 2 up to 4.5 mm. A length of the ICA main trunk was constant and equal to 15±2 mm. The main arterial trunk was divided into two parts in 20 out of 24 cases and one could watch bifurcation. There was trifurcation in 3 cases. MCA was represented by clusters of small vessels, branching from the main trunk, in 1 case. Secondary trunks, formed by division of the main trunk, had a diameter of 1-2 mm and a mean length of 11-15 mm. Lenticulo-striatal arteries branched from a medial surface of MCA in proximal areas, located below that place, where the main trunk divided into secondary trunks. Their number varied from 3 up to 10. Their diameter was less than 0.5 cm. As well as other authors, we distinguished three groups of lenticulo-striatal arteries: medial, intermediate and lateral. A medial group was watched in 15 out of 24 cases. A number of arteries varied from 2 up to 4. An intermediate group was present in 16 cases. A number of arteries varied from 2 up to 6. A lateral group was observed in all 24 cases. A number of arteries varied from1 up to 8. We identified a temporo-polar artery; anterior, middle and posterior temporal arteries; an angular artery; an orbito-frontal artery; precentral and central arteries; anterior and posterior parietal arteries. The angular artery was the largest of them. Its maximum diameter was 1.5 mm. The rest arteries had a diameter of up to 1 mm. The research data allowed us to study versions and peculiarities of MCA, its anatomic interrelations with adjacent structures, as well as peculiarities of its blood supply in detail. This information is sure to be the basis of performing a less traumatic approach to MCA aneurysms and to improve operations' quality.

Conclusion. A proposed set of topographic-anatomic methods allows to lay the foundation of modeling a pterional approach, substantiation of its use in surgery of arterial aneurysms. It includes:

  1. Preparation of a block specimen, which can be described as "brain-skull base-cervical spine".
  2. Exposure of internal carotid and vertebral arteries.
  3. Filling of the carotid and vertebro-basilar arterial systems.
  4. Stage-by-stage micropreparation and taking microphotos of paracerebral structures and different segments of MCA.
  5. Morphometry of vascular structures.