posterior fossa aneurysms simulating · posterior fossa aneurysms simulating tumours w. f. michael...

Journal of Neurology, Neurosurgery, and Psychiatry, 1974, 37, 218-223

Posterior fossa aneurysms simulating tumours

W. F. MICHAEL

From the Department of Neurology, St. Bartholomew's Hospital,and The National Hospital, Queen Square, London

SYNOPSIS Seven cases of aneurysm of the vertebral and basilar arteries, in which the clinicalfeatures suggested a diagnosis of posterior fossa tumour, are presented. Their clinical manifestationsand the difficulties of diagnosis are discussed. These lesions may mimic cerebellopontine angletumours or brain-stem gliomas, or, less commonly, the picture is one of a compressive lesion at theforamen magnum. The need for vertebral angiography is emphasized. Exploratory surgery carriesa high risk, and is to be avoided.

Posterior fossa aneurysms are uncommonlesions, and partly because of this continue topresent considerable problems in diagnosis.With modern techniques of angiography, aneur-ysms of the vertebrobasilar system can usually bedemonstrated unequivocally; however, vertebralangiography is still a procedure not without risk,and clinicians are rightly hesitant in advisingthis in circumstances where its relevance orhelpfulness seems uncertain. This is particularlyso where the clinical picture suggests a slowlyexpanding tumour, and the possibility of avascular pathology may be overlooked.A number of authors have discussed the diffi-

culties of diagnosis of basilar aneurysms thathave not bled and, even before the era of angio-graphy, reports appeared of aneurysms foundunexpectedly at operation or postmortem inpatients supposedly suffering from posteriorfossa tumours. Yaskin and Alpers (1944) col-lected a series of 21 such cases from the literaturewith symptoms of a mass lesion, and both theyand Alajouanine et al. (1948) concluded that thediagnosis could not usually be made on clinicalgrounds alone. Denny-Brown and Foley (1952)felt that they could delineate a sufficiently clear-cut syndrome resulting from arterioscleroticbasilar aneurysms to make angiography un-necessary; however, their six cases were elderlyhypertensives with histories of sudden brain-stem or posterior cerebral episodes, some ofwhich subsequently improved and do not reallyfit in to the group under discussion. More

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recently Duvoisin and Yahr (1965) discussed theclinical features of posterior fossa aneurysmssimulating tumours and also concluded that onlyvertebral angiography can give a definitivediagnosis. Jannetta et al. (1966) claimed thataneurysms could be differentiated from non-vascular tumours in this situation by pneumo-encephalography, but as their criteria wereselected with hindsight from two cases diagnosedby vertebral angiography and necropsy re-spectively, this was unconvincing.

This paper describes seven cases of largeaneurysm of the vertebrobasilar system whichsimulated tumours, and discusses their clinicalmanifestations and management.

SOURCES

The case notes were studied of all patients seen at St.Bartholomew's Hospital and at the NationalHospital, Queen Square, on whom the diagnosis ofaneurysm of the vertebrobasilar system had beenestablished angiographically. The earliest of thesedated from 1953, and 46 cases were recorded up to1972. Of these, 38 cases presented with subarachnoidhaemorrhage and will not be further discussed. Onefurther case with a small basilar aneurysm was alsoexcluded as the clinical picture was clearly producedby a very large carotid aneurysm. The other sevencases are described below.

CASE 1

(SBH 510584.) A previously fit woman of 41 yearswas first seen in November 1970 complaining of

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double vision and was found to have a partial 6thnerve lesion. A carotid angiogram failed to show anyabnormality. One year later she began complainingof deafness in the left ear. In August 1972 she wasseen again having noticed a progressive weakness ofthe left side of the face for the past two months.Examination showed impairment of sensation onthe left side of the face with an absent cornealreflex, a left 6th nerve palsy, and a lower motorneurone weakness of the left side of the face, but noobjective hearing loss. The blood pressure was130/70 mmHg. Plain radiographs of the skullshowed some asymmetry of the internal auditory

FIG. 1. Left vertebral angiogram, lateral view, incase 1, showing a large aneurysm of the basilar artery.

FIG. 2. The brainfrom case 1, as seen atpostmortem,viewedfrom the side and below. Note the deep indenta-tion of the brain-stem produced by the aneurysm.

meati, the left appearing larger than the right. Thecerebrospinal fluid (CSF) contained 88 mg/100 ml.protein. A pneumoencephalogram was reported asshowing swelling of the brain-stem in both thelateral and PA views, with encroachment upon thepontine cistern and backward displacement of the4th ventricle and aqueduct; the cerebellopontineangle cisterns on both sides were filled but were verynarrow. It was felt that the diagnosis was a brain-stem glioma and deep x-ray therapy was arranged.By way of confirmation before the start of treatment,a vertebral angiogram was done which demon-strated a large basilar aneurysm, shown in Fig. 1.She remained well until six months later when shesuddenly died from subarachnoid haemorrhage. Theaneurysm was found at postmortem examination tobe deeply indenting the brain-stem (Fig. 2).

CASE 2

(NHQS 87790.) This 67 year old woman wasadmitted in 1959. She had had hypertension for manyyears, and had been getting increasingly deaf, par-ticularly on the right side. For nine months she hadhad severe occipital headaches made worse bycoughing and sneezing. She gave a history of diplopiaon looking to the right for about five months. Arelative felt that there had been a gradual deteriora-tion in mental function, and had observed a grandmal seizure a few months previously. On examina-tion, there was evidence of impaired mental func-tion, nystagmus on gaze to either side, a reducedcorneal reflex on the right, and a right facial weak-ness. There was perceptive deafness, more on theright than the left. In the limbs, there were mildpyramidal tract signs and a terminal tremor mainlyaffecting the right arm and leg. The blood pressurewas 180/110 mmHg and the retinal vessels showedarteriosclerotic changes. It was felt that she pre-sented a picture of scattered lesions, but with definitesigns pointing to a posterior fossa lesion, and thatthese features could best be explained by a basilaraneurysm with arteriosclerotic changes elsewhere.The CSF contained 100 mg/100 ml. protein. Apneumoencephalogram showed a small lesion fillingthe right cerebellopontine angle, and a vertebralangiogram showed a tortuous left vertebral arterywith aneurysmal dilatation of the basilar artery. Thepatient was not disturbed by these investigations.She was transferred to another hospital and diedthree months later.

CASE 3

(NHQS A17599.) This 58 year old woman was firstadmitted to the National Hospital in April 1964

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having had a subarachnoid haemorrhage producingcoma without localizing signs. Bilateral carotidangiograms and a right vertebral angiogram werenegative. She was readmitted in June 1967 com-plaining of occipitocervical headaches for six months,progressive weakness of the left arm and leg, anddifficulty in distinguishing temperature with the righthand. Examination then revealed tenderness in theupper part of the neck, more on the left than theright. There was severe weakness of upper motorneurone type in the left arm and leg, and impairmentof temperature sensation on the right side belowthe level of the 4th cervical dermatome. A clinicaldiagnosis of upper cervical cord compression pro-ducing a Brown-Sequard syndrome, possibly due tocervical spondylosis or spinal cord tumour wasmade. Plain radiographs of the skull were normaland plain radiographs of the cervical spine showedspondylotic changes only. A myelogram demon-strated a filling defect of 2 cm at the level of theforamen magnum on the left side. The CSF proteinwas 167 mg/100 ml. A left vertebral angiogramshowed this to be an aneurysm. She was treatedconservatively but subsequently she suffered in-creasing left-sided weakness and pain on movementof her neck, and died six months later.

CASE 4

(NHQS A24214.) This man, aged 58 years, was firstseen in May 1965 with a year's history of increasingapathy and forgetfulness. Ten days before admissionhe woke with a severe headache, followed the nextday by some weakness of his right arm and difficultywith speech which improved after about two days.Examination showed a moderately severe dementia,slight right facial weakness, and minimal pyramidaltract signs in the right arm and leg. His blood pres-sure was normal. Skull radiograph and electro-encephalogram (EEG) were normal and a pneumo-encephalogram showed a large mid-line surprasellarspace occupying lesion. The CSF contained 20lymphocytes per cu. mm and protein 90 mg/100 ml.Bilateral carotid angiography showed two smallaneurysms, one on each internal carotid artery, anda vertebral arteriogram demonstrated a largeaneurysm at the termination of the basilar arterywhich was thought to be causing the filling defectseen on the pneumoencephalogram. It was felt thatthis lesion was causing some intermittent obstructionto the flow of CSF, thus contributing to the dementia.The recent headache and transient weakness werethought to be the result of a slight leakage of bloodfrom the aneurysm. He was readmitted two yearslater for increasing dementia and incoordination,now with bilateral pyramidal tract signs. An intra-

thecal isotope scan suggested some degree of obstruc-tive hydrocephalus. Repeat pneumo-encephalogramshowed that the basilar aneurysm was larger thanpreviously, and there was evidence of increasinghydrocephalus due to obstruction at the foraminaof Monro and also at the tentorial hiatus. A shuntingoperation to reduce the intraventricular pressureproduced a considerable subsequent improvement inhis walking and balance and possibly also in hisintellectual function. However, a year later hesuddenly became stuporose and died. Necropsyshowed subarachnoid and intraventricular haemor-rhage, and an aneurysm of the upper part of thebasilar artery indenting the third ventricle andextending to the foramen of Monro.

CASE 5

(NHQS A28382.) This 60 year old woman was firstadmitted to the National Hospital in January 1966,when she gave a six month history of headaches.Four months beforehand she had noticed droopingof the left eyelid and double vision on upward gaze.The ptosis quickly became complete and wasaccompanied by a severe throbbing pain in theregion of the left orbit. The ptosis and the diplopiahad partially cleared by the time she was admitted.On examination, there was a partial left 3rd nervepalsy. She was moderately hypertensive with a bloodpressure of 200/110 mmHg. A left carotid angiogramshowed an area of dilatation in the region of theanterior communicating artery and also someirregularity of the origin of the internal carotidartery in the neck. It was felt that the 3rd nerve palsywas the result of arteriosclerosis rather than a localgross vascular abnormality. She was discharged andmade a steady improvement, with the ocular palsyfinally disappearing. However in April 1967 she hadan exacerbation of the left frontal headache whichextended into the left side of the neck and inside theear on that side. With this, the left eyelid graduallydrooped more and then closed completely. Onexamination there was a complete left 3rd nervepalsy and bilateral extensor plantar responses. A leftvertebral angiogram showed an aneurysm arisingfrom the terminal part of the basilar artery and pro-jecting posteriorly. Once again it was not felt thatsurgical intervention was indicated.

CASE 6

(NHQS A29677.) This 61 year old man was admittedto the National Hospital in March 1966 with ahistory of unsteadiness on standing for 18 months.For one year he had had increasing deafness in theleft ear with tinnitus. He had noticed some difficulty

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in swallowing for the past six months and occasion-ally early morning headaches. For four monthsthere had been a progressive weakness of the legs,such that he was now having difficulty in getting outof a chair. Examination showed early bilateralpapilloedema. There was marked nystagmus in alldirections of gaze. The left corneal reflex was de-pressed and he had impaired pain sensation over thefirst division of the left trigeminal nerve, thoughappreciation of light touch seemed unimpaired. Inaddition, there was evidence of lesions of the left8th, 9th, 10th, and 12th cranial nerves, the last men-tioned producing wasting and fasciculation of thetongue on that side. In the limbs, there was a mildright hemiparesis and left sided cerebellar signs. Theblood pressure was 180/100 mmHg.A diagnosis of left cerebellopontine angle tumour

was made; an acoustic neuroma seemed possible butthe lack of a facial nerve lesion was unusual, and thislesion was clearly a very long one to involve the 12thnerve. It was decided to proceed straight to aventriculogram, and this revealed a large mass lyingin the left cerebellopontine angle. Surgical explora-tion showed this to be a large aneurysm of thevertebral artery with extensive intramural thrombo-sis. Nothing further was done and the patient madean uneventful recovery. However, he died ninemonths later in another hospital, the cause beinggiven as thrombosed vertebral aneurysm. Nonecropsy was carried out.

CASE 7

(NHQS A52569.) This was a man aged 59 years whopresented to the National Hospital in February 1970.For the past 10 years he had suffered from head-aches, and three months before admission he de-veloped a progressive unsteadiness of gait and diffi-culty in swallowing. On admission, he had nystagmuson lateral and upward gaze, mild bilateral 7th nerveweakness, bilateral palatal weakness with dimin-ished pharyngeal sensation, and atrophy and fascicu-lation of both sides of the tongue. Gait was severelyataxic and the left plantar response was extensor. Itwas felt that he was suffering from an infiltratingspace occupying lesion in the posterior fossa,possibly a pontine glioma. A lumbar punctureshowed a CSF protein of 400 mg/100 ml. Ventriculo-graphy revealed a filling defect in the floor of the 4thventricle. The posterior fossa was therefore explored;the lower part of the medulla and upper part of thespinal cord were markedly expanded and displacedposteriorly, apparently due to an intramedullarylesion. Further inspection showed an extracerebralmass extending upwards into the cerebellopontineangle. Needling this failed to produce any fluid, and

an incision into it showed the contents to be areddish brown material. A brisk arterial haemorrhagethen occurred and it was then realized that the lesionwas an aneurysm, largely filled with thrombus. Thebleeding was eventually stopped and the feedingvessel to the aneurysm clipped. Bilateral vertebralangiograms were done soon after the operation,when it appeared that the clips were effective as theaneurysm was not visualized. The patient's con-dition remained critical, and he died three dayslater. At postmortem examination an enormousaneurysm was found arising from the left vertebralartery, equivalent in bulk to the medulla. Thepatient's demise was attributed to brain-steminfarction.

DISCUSSION

These cases are generally in accord with those ofearlier series, both in their clinical features and inthe difficulties experienced in coming to acorrect diagnosis. As Yaskin and Alpers (1944)pointed out, a considerable variety of symptomsand signs is to be expected in view of the largenumber of important structures related to thevertebral and basilar arteries, but several syn-dromes seem to result fairly frequently from post-erior fossa aneurysms. In the 21 cases ofaneurysmsimulating a mass lesion reviewed by Yaskinand Alpers (1944), palsies of cranial nerves 3 to10, ataxia and long tract signs, and an organicmental syndrome all occurred, and similarfeatures were seen in the smaller series ofAlajouanine et al. (1948) and Duvoisin andYahr (1965). Particularly commonly involvedwere the 7th and 8th cranial nerves, often pro-ducing a picture resembling that of a cerebello-pontine angle tumour. Trillet et al. (1970) de-scribe a typical case of this sort. In the presentseries, cases 1, 2, and 6 all had signs pointing toa lesion in this location, though case 2 alsoshowed evidence of hypertension and arterio-sclerosis, to which were attributed the intellec-tual deterioration and the grand mal fit. Case 6had much more extensive cranial nerve involve-ment than would be usual with an acousticneuroma. Lower cranial nerve palsies are not un-common in the literature, but it is interestingthat both cases 6 and 7 showed wasting of thetongue as involvement in earlier series seemsmore usually to have extended only down to the10th nerve. Incoordination, ataxia, and pyra-

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midal tract signs, either alone or with cranialnerve palsies, are frequent and point to involve-ment of the cerebellum and brain-stem. Symp-toms and signs of raised intracranial pressurewere seen only in case 6, but are well docu-mented in earlier series; case 4, however, withintermittent obstructive hydrocephalus, is muchmore unusual.

TABLE 1INCIDENCE OF HEADACHES AND CSF

PRESENT SERIESPROTEIN LEVELS IN

Case Headaches CSF protein(mg/100 ml.)

1 No 882 Severe occipital 1003 Intermittent 1674 Sudden headache at start 90

of illness only5 Yes Not done6 Occasional early morning Not recorded7 Yes 400

Usually therefore the physical signs are thoseof a cerebellopontine angle mass or brain-stemcompression. Much less common is the picture ofa lesion at the level of the foramen magnum orbelow, illustrated in the present series by case 3.Yaskin and Alpers (1944) report one such case oftheir own who had both brain-stem and spinalcord signs and include one other case from theliterature. Perhaps the most fully describedexample of this syndrome is the case ofSymondset al. (1937) in which a vertebral aneurysm pro-duced compression of the spinal cord at theforamen magnum (their case 6).The anatomical site of these lesions is generally

clear and it is defining the pathology that tendsto present the problem. It will be noticed thatcase 2 was the only one of this series in which thediagnosis of basilar aneurysm was made onpurely clinical grounds, but a pneumoencephalo-gram was still thought advisable to exclude asmall tumour in the cerebellopontine angle. Incase 3, even with the clue provided by the pre-vious subarachnoid haemorrhage, the diagnosisof vertebral aneurysm was not clearly anticipated.Clues to the aneurysmal nature of the tumouremphasized by earlier authors have been an

episodic history, suboccipital headache andnuchal pain aggravated by movement of the head(Yaskin and Alpers), and elevation of the CSFprotein with or without xanthochromia (Du-voisin and Yahr). Table 1 shows the incidenceof headaches and the CSF protein levels in thepresent series; the headaches of case 6 were pre-sumably those of raised intracranial pressure,and otherwise only in case 2 were the headacheshelpful diagnostically. The CSF protein on theother hand was elevated in all cases in which itwas recorded, although, of course, this also is anon-specific finding.

In cases 6 and 7, the true nature of the prob-lem came to light only as a result of surgicalexploration. In case 6 the patient made a satisfac-tory recovery, but case 7 died soon after theoperation. There seems no doubt that explora-tion in patients who prove to have posterior fossaaneurysms is highly dangerous; this was pointedout by Alajouanine et al. (1948), both of whosecases were explored surgically and died withinthree days, while of the seven cases from the

TABLE 2LENGTH OF HISTORY AND FINAL OUTCOME IN PRESENT SERIES

Case Length of history till admission Progress afteradmission

I Twenty-one months 6th nerve Died six monthspalsy later

2 Nine months headaches and Died three monthsdiplopia. Many years deafness later

3 1964 subarachnoid haemorrhage; Died six months1967 six months headaches, one after admissionmonth hemiparesis

4 Two years dementia Died one year laterof subarachnoidhaemorrhage

5 Two years headaches and diplopia6 Eighteen months unsteadiness and Died nine months

deafness later of 'throm-bosed vertebralaneurysm'

7 Three months unsteadiness and Died three daysdifficulty swallowing post-op.

literature that they reviewed, four were operatedon and all succumbed within a few hours. Deathwas equally rapid in Symonds and Meadows'scase. Case 7 also illustrates another grave dis-advantage of posterior fossa surgery, in that,even by direct observation, it may prove difficult

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or impossible to discover with certainty thenature of the lesion, because of the distortion ofthe anatomy and sometimes from the tendencyof aneurysms to burrow deep into nervous tissue.This last feature is visible in Fig. 2. This problemwas encountered in both of the cases of Ala-jouanine et al. (1948), the second case of Dandy(1944), and a case described by Guillain et al.(1930), in all of which the aneurysm was eithernot seen or not correctly identified, and thediagnosis was made at the necropsies that fol-lowed soon afterwards.

However, although surgery is clearly highlyunsatisfactory as a means ofdiagnosing vertebro-basilar aneurysms, this is not necessarily to saythat it may not be successful as a means oftreating those patients already known to besuffering from these lesions, as a planned pro-cedure. With advances in anaesthetic and surgicaltechnique this may become more feasible, andSundt et al. (I 972) report the successful removalof a large basilar aneurysm under conditions ofprofound hypothermia and circulatory arrest.Jannetta et al. (1966) also describe the ligation ofa vertebral aneurysm without mishap, apparentlywithout the use of special techniques.The prognosis of these large vertebrobasilar

aneurysms seems to be poor. Table 2 shows thelength of history of each of the present cases andthe final outcome, and these results correspondto earlier ones. Only one of the five cases de-scribed by Duvoisin and Yahr (1965) was alivetwo years after the onset of symptoms. In con-trast with this, Troupp (1971) found that, out of20 cases presenting with subarachnoid haemor-rhage, only eight had died 52 months afterdiagnosis. It appears therefore that basilaraneurysms that present with pressure symptomshave no better prognosis than those that come tolight because of bleeding.

In conclusion, it is clear that large vertebro-basilar aneurysms are dangerous lesions. Theyare difficult or impossible to distinguish fromother space occupying lesions on clinical grounds,and vertebral angiography is the only certain

way of making the diagnosis. This is essential ifsurgery is contemplated.

The author wishes to thank Dr. J. W. Aldren Turnerfor permission to publish case 1, and for much help-ful advice and discussion. Permission from theMedical Committee of the National Hospital topublish cases 2 to 7 is gratefully acknowledged. Dr.G. du Boulay greatly facilitated this study by kindlymaking available his private radiological records.Dr. H. C. Grant of the Department of Neuro-pathology, Middlesex Hospital, carried out thepostmortem examination on case 1, and generouslyprovided the photograph for Fig. 2. Dr. A. P.Hopkins kindly read the manuscript and providedmuch helpful discussion.

REFERENCES

Alajouanine, T., Le Beau, J., and Houdart, R. (1948). Lasymptomatologie tumorale des volumineaux anevrysmesdes arteres vertebrales et basilaires. Revue Neurologique, 80,321-337.

Dandy, W. E. (1944). Intracranial Arterial Aneurysms.Comstock: Ithaca, N.Y.

Denny-Brown, D., and Foley, J. M. (1952). The syndromeof basilar aneurysm. Transactions of the American Neuro-logical Association, 77, 30-34.

Duvoisin, R. C., and Yahr, M. D. (1965). Posterior fossaaneurysms. Neurology (Minneap.), 15, 231-241.

Guillain, G., Schmite, P., and Bertrand, I. (1930). An6vrysmedu tronc basilaire ayant determine la symptomatologied'une tumeur de I'angle ponto-cer6belleux. Revue Neuro-logique, 1, 795-802.

Jannetta, P. J., Hanafee, W., Weidner, W., and Rosen, L.(1966). Pneumoencephalographic findings suggestinganeurysm of the vertebral-basilar junction. Journal ofNeurosurgery, 24, 530-535.

Sundt, T. M., Jr., Pluth, J. R., and Gronert, G. A. (1972).Excision of giant basilar aneurysm under profound hypo-thermia. Report of case. Mayo Clinic Proceedings, 47, 631-634.

Symonds, C. P., Meadows, S. P., and Taylor, J. (1937). Com-pression of the spinal cord in the neighbourhood of theforamen magnum. Brain, 60, 52-84.

Trillet, M., Eyssette, M., and Schott, B. (1970). Histoirenaturelle d'un an6vrysme de I'angle ponto-cerebelleuxgauche. Journal de Medecine de Lyon, 51, 877-882.

Troupp, H. (1971). The natural history of aneurysms of thebasilar bifurcation. Acta Neurologica Scandinavica, 47,350-356.

Yaskin, H. E., and Alpers, B. J. (1944). Aneurysm of thevertebral artery. Report of a case in which the aneurysmsimulated a tumor of the posterior fossa. Archives ofNeurology and Psychiatry (Chic.), 51, 271-281.

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