A CONTRALATERAL PTERIONAL APPROACH IN SURGERY OF ANEURYSMS OF THE ANTERIOR CEREBRAL - ANTERIOR COMMUNICATING ARTERIES

Svistov D.V.

Department of Neurosurgery, Russian Military-Medical Academy, St.Petersburg

 

Aneurysms of anterior cerebral (ACA) – anterior communicating (ACoA) arteries are the most frequent form of saccular aneurysms of anterior segments of the arterial circle and account for 30% of their number. Development of operative microsurgery has a history of many years’ standing. Despite it, some problems of surgical treatment of these aneurysms still demands profound consideration because of poor results, in particular in an acute period of their rupture. One of them is a choice of an approach side.

It is known [1], that the anatomy of ACA-ACoA complex in patients with aneurysms of this localization is characterized by asymmetry in the majority of cases. Angiography is indicative of asymmetric filling of anterior segments of the arterial circle in 70.3%; a diameter of dominating ACA is greater than that of contralateral ACA (90.6%); thus, there is a more or less marked anatomic version of the arterial circle, i.e. anterior trifurcation of one of the internal carotid arteries (ICA). Aneurysm is supplied with blood by ACA with a greater diameter in 89.3% of cases. These facts are an indirect proof of bifurcation-and-hemodynamics theory of pathogenesis of this disease.

If to take into account asymmetric anatomy of segments of arteries supplying aneurysm with blood and usually median localization of its neck and cupola, then a question of a preferable side of a surgical approach if left open. There are at least four competitive approaches: pterional (a standard approach), unilateral subfrontal, hemispheric and transcallosal. A problem of preference given to this or that type of craniotomy is not a subject for discussion in the present work; however, only a pterional approach commits a surgeon to making a precise choice of one out of two possible sides of an operation.

Usually a right-side pterional approach is considered to be preferable. Nonetheless, there are some situation when a left-side approach is more expedient:

  1. Large aneurysm of ACoA directed to the right.
  2. Aneurysm is supplied with blood by the dominating left ACA.
  3. Multiple aneurysms on the territory of left-side vessels.

Considerations usually taken into account in making a choice of an approach side are as follows:

Conventional succession of manipulations allows to achieve a desirable final result in the majority of cases. However, this approach is inconvenient in some anatomic forms of aneurysms. In case of marked asymmetry of A1 segments of ACA and filling of both A2 segments on one side, a cupola of aneurysm is directed laterally and to the depth of an operative wound (a side opposite to the approach) as well as upwards and to the back (into the interhemispheric fissure). These are anatomic conditions when a neck of aneurysm is covered by loops of A2 segments of ACA. The front segment is ipsilateral and the back segment is contralateral; thus its control in applying a clip in the front-to-the back direction or between A2 segments is practically impossible even if endoscopic technique is used.

We used a contralateral approach in a consecutive series of 10 patients with aneurysms of ACA-ACoA.

The indications for its choice included marked asymmetric anatomy of ACA (an approach was performed on the side of ACA affected by hypoplasia) and a cupola directed to the back and upwards. Diagnostic angiography was a means of supporting a choice of a contralateral approach as examination was carried out both in standard and atypical positions. Centering of an X-ray corresponded to a path of an operative approach performed along the right lesser wing of the sphenoid bone. An image of aneurysms was projected on orbits or the infratemporal fossa. In this case a neck and cupola of aneurysm looked like a continuation of the A1 segment of dominating ACA and were either within “an oven fork” formed by A2 segments or perpendicular to their path.

Succession of manipulations was as follows:

A compulsory component of an operation was endoscopic technique and a microvascular Doppler device (16 MHz). Succession of dissecting segments of arteries of ipsi- and contralateral carotid basins in conventional and contralateral approaches is compared in the table given below.

Stages

Traditional Craniotimy

Contralateral Craniotomy

Ipsipateral

Contralateral

Ipsipateral

Contralateral

1

Ñ1

 

Ñ1

 
2

À1

 

À1 origin

 
3

À1-ÀÑîÀ

   

Ñ1+À1

4

À2

À2

À1+ÀÑîÀ

 
5  

À1

À2

À2

When a conventional approach is used, a proximal segment of contralateral ACA is exposed in the last turn. In a contralateral approach it is done before an exposure of ipsilateral A1 (usually effected by hyperplasia). It allows to ensure temporary clipping at an early stage of an approach to aneurysm.

Advantages of the modified approach are as follows:

As for disadvantages, they are:

During 1999-2001 the above method was used in 10 consecutive patients who were operated in an acute period of subarachnoid hemorrhage (from the onset up to 14 days after it). Operations for aneurysms of the same localization were performed in 12 cases during the same period of time and irrespective of the main group. A choice of an approach in these patients was conditioned by a side of filling, i.e. it was performed on a side of the dominating ACA.

A group

IOR

Aneurysm
clipped

Ischemic
complications

Mortality

I (n=10)

1 (10%)

10 (100%)

1 (10%)

1 (10%)

II (n=12)

4 (33%)

8 (66%)

3 (25%)

2 (16.7%)

The results of interventions are given in the table (IOR – intraoperative ruptures). It can be seen that total results in use of the modified approach for surgical treatment of aneurysm with the most complicated localization are not in the least worse than those received in application of the conventional approach. The only fatal outcome was conditioned by massive parenchymal-ventricular hemorrhage which was a direct cause of death. As for the second group, one patient died from ischemic stroke as a sequela of operative trauma of the ACA-ACoA complex. It should be also noted that all the cases, in whom the conventional approach resulted in a failure of clipping, belonged just to that very anatomic group of patients who were treated successfully when the modified approach was used. The only case with augmentation of psychoorganic symptoms in application of the modified approach was connected with trauma due to abnormality of the middle cerebral vein which entered the sphenoparietal sinus too low.

The results of preoperative angiographic examination of a female patient with aneurysm of ACA-ACoA fed by the left ACA under conditions of disconnection of the arterial circle and the anterior trifurcation of the left ICA are given as an example (Fig. 1). Left-side (a) and right-side (b) anterior semiaxial oblique views of left-side carotid angiograms taken before an operation. Aneurysm looks like a continuation of A1 and is directed laterally and to the back. The projection of aneurysm and its neck is not “in conflict” with A2 segments on the right side in contrast to the ipsilateral projection (aneurysm is projected on the ACA bifurcation). The operation (right-side pterional approach) consisted in stage-by-stage preparation of A1 of the left ACA, an area of its bifurcation and the aneurysm neck and then a straight clip was applied without any technical difficulties. Postoperative angiograms (Fig. 1c, d) are indicative of exclusion of aneurysm and preservation of patency of A1 of the left and A2 of the right ACA.

One of the problems, demanding special discussion, is a risk of an intraoperative rupture of aneurysm. According to published reports, the rate of intraoperative ruptures is rather high and varies from 18% in the cooperative study (1963-1987) [4] up to 36% in operations without application of a surgery microscope [8]. Besides the rate of IOR may be higher in interventions performed in an acute period of hemorrhage [3]. Mortality and invalidism in patients who suffered IOR makes 30-35% (in contrast to 10% in the absence of this complication) [3]. IOR can take place at any of three stages of surgical intervention [9]:

  1. During a preliminary approach (before aneurysm exposure).
    1. It is a rare phenomenon. As a rule, there is brain swelling watched even in case of uncomplicated subarachnoid hemorrhage. Usually such cases are characterized by unfavorable prognosis.
    2. Possible causes.
      1. Vibration during trepanation.
      2. An increasing transmural gradient of pressure in opening of the dura mater.
      3. Hypertension caused by release of catecholamines in response to pain.
    3. Treatment.
      1. Quick reduction of blood pressure.
      2. Control of hemorrhage by clipping of supraclinod segments of ICA or compression of vessels on a neck.
      3. In case of necessity – resection of the frontal pole.
  2. During dissection of aneurysm (it is a cause of the majority of IOR, there are two mechanisms).
    1. Ruptures in blunt dissection.
      1. Bleeding from such ruptures is profuse, close to a neck and difficult for control.
      2. Temporary clipping of a major vessel with prescription of neuroprotectors.
      3. If ruptures spread on carrying arteries defect is sutured.
    2. Damage in sharp dissection.
      1. Usually it has a punctate character and is distal in relation to a neck; it is controlled by application of a suction device.
      2. It can be eliminated with the help of tamponade.
      3. A defect can be done away with by use of bipolar coagulation.
  3. Ruptures during clipping.
    1. Insufficient exposure of aneurysm; a clip’s branch can perforate one of invisible chambers of aneurysm.
      1. Removal of a clip, control of bleeding by two suction devices and temporary clipping.
      2. Repeated dissection and clipping of aneurysm.
    2. Damage of a neck in incomplete clipping of aneurysm.
      1. It is necessary to ensure a proximal position of a clip; tips of branches should project above a neck margin, the second clip should be applied in parallel with the first one.
      2. Applying several or special clips (they are used for fixing standard clips).

Measures, promoting prevention of IOR, include:

  1. Limitation of brain retraction by resection of the wing of the sphenoid bone, reduction of brain volume (drainage of the ventricular system, lumbar drain, hyperventilation, use of barbiturates).
  2. Decreasing a risk of a neck or cupola rupture (sharp dissection, full mobilization of aneurysm before its clipping, preventive temporary clipping of a carrying vessel).

The majority of measures, promoting prevention of IOR in the contralateral approach, can be used successfully. They include thorough resection of the wing of the sphenoid bone up to the anterior clinoid process, “proximal control” of a major vessel, feeding aneurysm, at early stages of the approach, dissection of aneurysm beginning from its neck. A greater degree of brain traction is compensated by the following circumstance: a cupola of aneurysm faces a side of traction but not the skull base.

Thus, our clinical study demonstrates validity and safety of the contralateral pterional approach in surgery of ACA-ACoA aneurysms under conditions of anterior trifurcation of ICA, carrying aneurysm, when a body of the latter is directed laterally, to the back and upwards.

References

  1. Evzikov G.Yu. Surgical treatment of arterial aneurysms of the anterior communicating artery in an acute period of hemorrhage. Author’s abstract of thesis for a degree of a Candidate of Medical Science. – M., 1996. – 37 P.
  2. Krylov V.V., Gelfenbein M.S. Use of a contralateral pterional approach in surgery of cerebral aneurysms//Zhurnal Voprosy Neirokhirurgii imeni N.N. Burdenko.- 1998. - N4. – P. 9-16.
  3. Batjer H, Samson D S: Management of Intraoperative Aneurysm Rupture. Clin Neurosurg 36: 275-288, 1988.
  4. Graf C J, Nibbelink D W: Randomized Treatment Study: Intracranial Surgery. In Aneurysmal Subarachnoid Hemorrhage - Report of the Cooperative Study, Sahs A L and Nibbelink D W, (eds.). Urban and Schwarzenburg: Baltimore, 1981, pp 145-202.
  5. Lynch JC, Andrade R Unilateral pterional approach to bilateral cerebral aneurysms. Surg Neurol 1993 Feb;39(2):120-127
  6. de Oliveira E, Tedeschi H, Siqueira MG, Ono M, Fretes C, Rhoton AL Jr, Peace DA Anatomical and technical aspects of the contralateral approach for multiple aneurysms. Àcta Neurochir (Wien) 1996;138(1):1-11; discussion
  7. Oshiro EM, Rini DA, Tamargo RJ Contralateral approaches to bilateral cerebral aneurysms: a microsurgical anatomical study. J Neurosurg 1997 Aug;87(2):163-169
  8. Pertuiset B: Intraoperative Aneurysmal Rupture and Reduction by Coagulation of the Sac. In Cerebral Aneurysms - Advances in Diagnosis and Therapy, Pia H W and Langmaid C, (eds.). Springer-Verlag: Berlin, 1979, pp 398-401.
  9. Schramm J, Cedzich C: Outcome and Management of Intraoperative Aneurysm Rupture. Surg Neurol 40: 26-30, 1993.