intracranial aneurysm encasement - jnnp’s ambition...

J. Neurol. Neurosurg. Psychiat., 1968, 31, 524-527

Intracranial aneurysm encasement

WILLIAM M. HAMMON

From the Neurosurgery Service, Walter Reed General Hospital, Washington, D.C.,U.S.A.

As improvements in neurosurgical techniquesapplied to intracranial surgery for prevention ofbleeding from arterial saccular aneurysms are morewidely appreciated, understood, and utilized bymore neurosurgeons throughout the world, theparticular problems encountered in each patientwith an intracranial aneurysm become more readilysolved. Better general pre-operative evaluation andcare, including total intracranial dynamic vascularcontrast studies, the pre-operative, operative, andpost-operative use of corticosteroids to combatcerebral oedema, and the effects of operativetrauma, the utilization of controlled respirationneuro-anaesthetic techniques, the improvement inoperative field visibility by utilizing magnificationand improved lighting techniques, along with theuse of a variety of special instruments specificallydesigned for intracranial aneurysm surgery, haveall aided in improving the over-all operative results.When the surgeon finds he can safely apply a clipor ligature to the neck of the aneurysm and notimpair vessel patency, he can thus eliminate theaneurysm from the vascular stream and preventpossible fatal haemorrhage, yet maintain continuityof normal blood flow to the cerebral tissues distally.Intentional sacrifice of a vessel should be avoidedwhere possible.

There are.circumstances, however, that precludesafe, elective aneurysmal neck occlusion. Specificsituations all too frequently encountered includethe following:

(1) The aneurysm arising from the middlecerebral artery complex with efferent vesselsexiting from the walls or dome of the aneurysm,whereby obliteration of the aneurysm neck wouldinterfere with some distal blood flow.

(2) The aneurysm arising from the anteriorcommunicating artery complex, rather than solelyfrom the anterior communicating artery itself,when present, such that attempted neck clippingcould cause impairment of distal anterior cerebralblood flow.

(3) The aneurysm which arises from an unequalor asymmetrical first portion (A-I) of the anterior

cerebral artery whereby a 'trap' procedure wouldsignificantly impair either or both of the moredistal anterior cerebral arteries' blood flow aswell as the 'trapped' anterior cerebral perforatingbranches.

(4) The aneurysm the neck of which is toobroad for a conventional clip and which, when aligature is tied snugly, would cause impingementupon the parent vessel lumen due to distortion,kinking, or indentation by the mass within theligature.There are other specific situations that individual

neurosurgeons with experience can also cite asexamples peculiar to a given patient which couldmake occlusion of an aneurysm neck relativelyunsafe or unwise. These problems are becomingmore evident in the vertebral-basilar artery circu-latory distribution as well.An additional problem being recognized more

frequently and accurately as the result of the use ofoperative and post-operative angiography (Drakeand Vanderlinden, 1967), is that of the aneurysmthe neck and dome of which were thought to havebeen successfully obliterated surgically, but wherea portion of the weak aneurysm-vessel junction areacan be shown to be still in direct continuity with thepassing blood stream (Figs. 1 and 2). It was fromthis weakened junctional area that the aneurysmoriginally arose (Sahs, 1966). This situation is notalways immediately apparent. At a later angiographyor on necropsy examination, it has been noted thata clip or ligature is no longer in absolute juxtaposi-tion to the parent vessel, but has been displaced andis now part of the dome or wall of what is essentiallya new aneurysm formation, having arisen at theremaining weakened site in the vessel wall (Hayes,1967; Sahs, 1966).These varied situations do not afford a safe or a

total permanent isolation of the aneurysm from themain arterial stream to prevent further possibleintracranial haemorrhage. As a result, additionalmethods for solving these problems have beensought.

It has been apparent to some (Dutton, 1956;524

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FIG. 1. Pre-operative angiogram showing aneurysmarising from middle cerebral artery approximately I cmfrom its origin.

FIG. 2. Post-operative angiogram which reveals onlypartial aneurysm occlusion due to improper application ormigration of clip.

Selverstone and Ronis, 1958; Dutton, 1959; Hayesand Leaver, 1966), that the encasing or investing ofthe non-clippable aneurysm or aneurysm complex,and also of the successfully clipped or ligatedaneurysm with a material to prevent rebleedingor reformation of the aneurysm would add signi-ficantly to the immediate and long-term results ofcorrective and curative intracranial aneurysmsurgery.A major step has been taken in this direction by

the use of an easily applied material which com-pletely encases the aneurysm complex, rapidlysolidifies, and prevents the possibility of haemorrhageyet maintains parent vessel continuity (Dutton,1956, 1959; Hayes and Leaver, 1966). This thusaffords the aneurysm and its associated afferent andefferent vessels a reinforced exterior wall, preventingeither rupture of the aneurysm or regrowth of theaneurysm from its weakened site of origin.

METHOD

A somewhat detailed operative approach is describedto emphasize simplicity yet completeness.

Utilizing controlled respiration ('hyperventilation')endotracheal general anaesthesia (Hayes and Slocum,1962) with an increase of 30-50% above estimated normalminute volume1, a small modified Dandy frontotemporalosteoplastic craniotomy is performed, being carriedwell down along the lateral sphenoid ridge, and the duraopened as it crosses the sylvian fissure anterolaterally.The prechiasmatic cistern is then approached by gentlyretracting the frontal lobe along the sphenoid ridge,entered and cisternal fluid thoroughly aspirated. If theaneurysm is located at or near the anterior communi-cating region cisternal fluid is removed from between theinternal carotid artery and the optic nerve, rather thanfrom the pre-chiasmatic cistern, to avoid possible ruptureof the aneurysm. The aspiration of this cisternal fluid isusually all that is necessary to gain excellent operativeexposure when using the controlled respiration technique.In cases with significant hydrocephalus, a lateral ven-tricular tap can be performed through the operative area.The bridging veins from the temporal tip to the spheno-parietal sinus are identified, coagulated, and dividedwhen indicated-that is, when the temporal lobe is to beretracted. The internal carotid artery is then identifiedand it or its appropriate branch is followed out to theaneurysm location, thus always having proximal vesselcontrol available. When the aneurysm is from the basilarartery region, the internal carotid artery usually neednot be dissected free.When the aneurysm complex (including afferent and

efferent arterial vessels) is identified it is then carefully,but completely, separated from its surrounding cerebraltissues. In areas such as the anterior or posterior per-forated substance, or where the aneurysm is particularly

'The Radford Nomogram (Radford, Ferris, and Kriete, 1954), is usedto calculate this percentage increase.

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William M. Hammon

long or may be under the tentorial edge-as may occurwhen arising from the area of junction of the internalcarotid and posterior communicating arteries-appli-cation of a clip or ligature to the completely visualizedneck may be performed before or in lieu of furtherdissection of the dome. This can then be followed byamputation of the aneurysm dome from its neck, or itsaspiration by needle and syringe, thus collapsing thedome. When the entire aneurysm complex or its residualis then free of its investing tissues, the surrounding areais kept as dry as possible, using suction to prevent thefast-setting methyl methacrylate1 from being floatedaway during its application. If the parent vessel appearsto be in spasm, topical application of a phentolaminemesylatel soaked cotton patty for approximately fiveminutes has been found to be advantageous in reducingthe spasm.

Achieving optimal exposure of the aneurysm complex,the methacrylate liquid and powder are then mixed inapproximately a 1:2 ratio and stirred until a consistencysimilar to that of thick syrup is attained. Using a smallmedicine dropper, a few ml. of the mixed methacrylateare injected beneath and behind the aneurysm complex,and then additional methacrylate is applied by the dropperto the sides and presenting surface of the entire aneurysmcomplex, again noting that the immediate afferent andefferent vessels as well as the entire aneurysm must beimmersed in and covered by the methacrylate. Thehardening time is approximately two to three minutesin situ. The heat of polymerization2 (up to 1150 F if notirrigated) can be felt in a small ball of the acrylic thesurgeon may wish to roll between his gloved fingers(Dutton, 1959). When he feels either an increase inwarmth or a hardening of this ball, the operative field isthen irrigated continuously for five minutes with room-temperature sterile saline to dissipate the heat of reaction.It should be noted that retracting spatulae, cotton pattiesand other instruments should be removed from theoperative field before the hardening of the methacrylate.Inclusion of ligatures, clips, gelatin foam, muscle stamps,or fine mesh gauze applied to the immediate area of theaneurysm complex is totally acceptable. A routinecraniotomy closure is then performed. Antibiotics arenot routinely administered prophylactically.

If during dissection the aneurysm should ruptureinadvertently, appropriate clipping of the dome and/orneck can be performed if necessary, but if the parentvessel's or an efferent vessel's patency might be jeopar-dized, the application of a small muscle stamp and gentlepressure will usually be effective in controlling thebleeding. The dissection can then be continued and theadherent muscle stamp tamponade will be included inthe encasement procedure.An attempt is usually made not to apply the metha'-

crylate directly to the optic nerve or other cranial nerves,but at times this has not been found to be either possibleor practical. There have been no recognized instanceswhere optic nerve damage has been clinically apparent

'Aneuroplasty (Codman and Shurtleff, Inc., Randolph, Massa-chusetts, U.S.A.)'Regitine (Ciba Pharmaceutical Co., Summit, New Jersey, U.S.A.)

or of other cranial nerves which the methacrylate mayhave either touched or even encompassed.

DISCUSSION

Since 1957, when Hayes began using methyl metha-crylate to encase intracranial aneurysms at WalterReed General Hospital, 63 patients with 78aneurysms have had definitive encasement pro-cedures on 72 of these aneurysms. The author hastreated similarly 30 additional aneurysms in 22patients while at the U.S. Army Hospitals inLandstuhl and Frankfurt, Germany. A total of 85patients have had 102 aneurysms encased in fastsetting methyl methacrylate. The first 40 patientshave been reported previously by Hayes and Leaver(1966). Table I shows the location of the various

TABLE ILOCATION OF ANEURYSMS ENCASED

Middle cerebral arteryInternal carotid arteryAnterior communicating arteryBifurcation internal carotid arteryProximal anterior cerebral arteryDistal anterior cerebral arteryVertebral-basilar artery

4529137332

102

aneurysms encased. It is of interest that 20 of these85 patients (23-5 %) had multiple aneurysms, twopatients had four. There were eight deaths in thepost-operative period, a surgical mortality of 9-4%.When treating surgically aneurysms of the middle

cerebral artery and anterior communicating-anteriorcerebral artery complex, maintaining a normalvascular flow while preventing rebleeding is bestachieved by the encasement procedure when this ispossible.The only known post-operative haemorrhages

from 'encased' aneurysm areas have occurred as aresult of incomplete encasement. There have beentwo such cases and both were at the trifurcation ofthe middle cerebral artery. In one the rebleedingcaused death and in the other an intracerebralhaematoma with resultant permanent hemiplegia.In both cases the operative areas were directlyre-examined and incomplete encasement noted, bothencasement defects being on the most inferiorsurface. No other cases of bleeding from the encasedaneurysm complexes have occurred.

In two instances where the author has re-exploredthe operative field where methacrylate had beenapplied previously-one case as the result of re-bleeding as cited above, and the second case wherea surgeon at another hospital applied methacrylateto a contiguous area, but not to the actual aneurysm

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FIG. 3. Photograph of an encased internal carotid arteryaneurysm complex showing the general relationship to theentire carotid-vertebral-basilar tree.

FIG. 4. Wall of aneurysm shown in Fig. 3 with plasticremoved showing minimal surface response.

complex-it was apparent that there was no adhe-rence of the methacrylate to the surrounding cerebraltissue, and no gross evidence of an increased glialreaction greater than would have been anticipatedfrom the previous operative dissection. Dutton(1959) has also noted this previously.

There have been no necropsy examinations wherepathological examination of the encased aneurysmcomplex could be performed at a time more than 30days after application of the methacrylate.

It is to be noted again that this material is neitheran adherent nor a glue. It forms only a rigid externalcasing for the aneurysm (Fig. 3) and causes minimal,if any, thickening of the adventitia (Fig. 4).

SUMMARY

A specific method for the prevention of intracranialhaemorrhage from cerebral aneurysms is againpresented and its use suggested. The methacrylatecompound is a relatively non-irritating reinforcementfor the weakened vessel-aneurysm complex, main-taining vascular patency and preventing possiLblerecurrent haemorrhage due to faulty clip or ligatureapplication or migration.

I wish to thank Brigadier General George J. Hayes andColonel Ludwig G. Kemp for permission to includetheir personally supervised cases. Also a special note ofappreciation to Mrs. Dolores Hipsley for preparing thismanuscript at a particularly difficult time.

REFERENCES

Drake, C. G., and Vanderlinden, R. G. (1967). The late consequencesof incomplete surgical treatment of cerebral aneurysms. J.Neurosurg., 27, 226-238.

Dutton, J. E. M. (1956). Intracranial aneurysms. A new method ofsurgical treatment. Brit. med. J., 2, 585-586.

-(1959). Acrylic investment of intracranial aneurysms. Ibid.,2, 597-602.

Hayes, G. J., and Slocum, H. C. (1962). The achievement of optimalbrain relaxation by hyperventilation technics of anesthesia.J. Neurosurg., 19, 65-70.and Leaver, R. C. (1966). Methyl methacrylate investment ofintracranial aneurysms. A report of seven years experience.Ibid., 25, 79-80.

-(1967). Personal communication.Radford, E. P. Jr., Ferris, B. G. Jr., and Kriete, B. C. (1954). Clinical

use of a nomogram to estimate proper ventilation duringartificial respiration. New Engi. J. Med., 251, 877-884.

Sahs, A. L. (1966). Observations on the pathology of saccular aneu-rysms. J. Neurosurg., 24, 792-806.

Selverstone, B., and Ronis, N. (1958). Coating and reinforcement ofintracranial aneurysms with synthetic resins. Bull. Tufts-NewEngl. med. Cent., 4, 8-12.

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