Giant intracranial aneurysms: Diagnosis with special reference to computerised tomography

uinical Radiology (1980) 31, 27- 39

0009-9260/80/01320027502.00

© 1980 Royal College of Radiologists

Giant Intracranial Aneurysms: Diagnosis=with Special Reference to Computerised Tomography MICHAEL O ' N E I L L , T E R E N C E H O P E and G O R D O N T H O M S O N

Departments of Neuroradiology and Neurosurgery, Frenchay Hospital, Bristol The clinical presentation, radiological investigations and surgical m a n a g e m e n t o f 11 patients with giant intra cranial aneurysm (> 2.5 cm) have been reviewed. Most patients had signs and s y m p t o m s caused by the mass effect of the aneurysm. Only two presented with subarachnoid haemorrhage. The m o s t helpful plain film finding was intracranial calcification. This varied f r o m a mere fleck to the classical curvilinear variety. Computerised t o m o g r a p h y (CT) scans were available on all l 1 patients. All showed a space-occupying lesion o f high density. Two types o f e n h a n c e m e n t were seen following intravenous contrast m e d i u m , (a) h o m o g e n e o u s and (b) rim e n h a n c e m e n t w i t h or w i t h o u t a p a t c h y increase in density centrally. The CT appearances in s o m e of the cases resembled those shown by other lesions such as n e o p l a s m . Arteriography in almost all cases demonstrated the aneurysm but o f t e n under-estimated its size. On t w o occasions the aneurysm did n o t fill and the nature o f the lesion d e m o n s t r a t e d on the plain CT r e m a i n e d u n c o n f i r m e d . Direct surgical attack rather than carotid ligation was t h e o p e r a t i o n o f choice. Most patients r e s p o n d e d very well to this t r e a t m e n t .

The classification o f intracranial aneurysms by size is an arbitrary one. Five groups are recognised with diameters ranging from less than 3 m m in group 1, to more than 25 m m in group 5 (Locksley, 1966). The group 5 aneurysms have also been t e r m e d giant aneurysms (Morley and Barr, 1968). In the last two and a half years, 11 cases o f giant aneurysms have been e n c o u n t e r e d at this Regional Centre, and all o f them have been e x a m i n e d by c o m p u t e r i s e d t o m o graphy (CT). An analysis o f the clinical, radiographic and CT appearances has been u n d e r t a k e n to illustrate the varied presentation and fmdings that can arise. Seven of the cases are described in greater detail and illustrated. It is stressed that such lesions need to be constantly borne in m i n d w h e n analysing scans showing mass lesions a r o u n d the base of the brain. CASE R E P O R T S Case 1. B.C., a 29-year-old housewife, presented with a six weeks history of loss of limb control, paroxysmal headaches, ataxia and episodes of incontinence. On examination she was found to have papilloedema, an ataxic gait, and a slightly aggressive manner. Her blood pressure was normal. The plain skull radiographs were normal. A C T scan showed a large space-occupying lesion between the frontal horns of the lateral ventricles, mostly isodense in appearance, but in parts more dense than the adjacent brain tissue (Fig. la) and showing a clear-cut marginal enhancement after 50 ml of intravenous Conray 420 (Fig. lb). A right carotid angiogram showed in the lateral view a displacement of the anterior cerebral artery around the mass, and in the AP view a displacement of the artery to the left of the mid-fine (Figs lc, d). No aneurysm was shown, but in retrospect a small bulbous loop close to the anterior communicating

artery region in the AP view could possibly represent the stump of a thrombosed aneurysm. A burr hole biopsy of the lesion was undertaken, but abandoned when a firm mass of uncertain nature was encountered. Three days later, the lesion was formally approached through a bone flap, and an 8 cm aneurysm t'tlled with organised thrombus was removed from what appeared to be the right pericallosal artery. The patient has done well following surgery. Case 2. E.T., a 16-year-old schoolgirl, complained of dizziness for three months and more recently the onset of morning headache, vomiting, dysarthria and dysphagia. On examination there was ataxia of gait and of the left arm, with a severe dysarthria, left palatal weakness and nystagmus of gaze in all directions. There was sensory loss on the right side of her scalp in the trigeminal distribution. Skull radiographs were normal, but tomograpby showed some evidence of bone thinning in the posterior fossa and an adjacent fleck of calcification. A C T scan showed a large ovoid mass centrally in the posterior fossa, of increased density, and with marked homogeneous enhancement throughout the area after intravenous injection of 50ml of Conray 420 (Figs 2a, b). The appearances were thought to be those of a tumour, and although an aneurysm was considered a possibility, the lesion was thought to lie too near the mid-fine for that to need further exclusion. Hence a posterior fossa exploration was undertaken, to reveal a bluish pulsatile mass between the tonsils, producing a jet of arterial blood at needle puncture. The operation was therefore postponed, and vertebral angiograpfiy later revealed a 4 cm aneurysm filling from a large left vertebral artery, with a displaced basilar artery filling from the right vertebral artery (Figs 2c, d). At a further operation the aneurysm was dissected off the vertebral and basilar arteries and removed. The patient had a partial bulbar palsy which has now recovered and she is well. Case 3. K.R., a 46-year-old female, developed a gradual deterioration with headaches over several years. Over the recent year the vision in the right eye had also deteriorated and she had become incontinent of urine. On examination she was orientated in place but not in time. She had shown

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CLINICAL RADIOLOGY

Fig. la - Case 1, CT. A large central space-occupying lesion is s h o w n between the frontal horns of the lateral ventricles,

Fig. lb - Case 1, CT. Intravenous Conray produces rim enh a n c e m e n t of the lesion.

Fig. lc - Case 1_ Right carotid angiogram. The anterior cerebral and pericallosal arteries sweep widely around the lesion,

Fig. l d Case 1. Note bulbous loop close to the anterioI c o m m u n i c a t i n g artery region.

GIANT INTRACRANIAL

Fig. 2a - Case 2, CT. Large ovoid density in the posterior fossa_

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Fig. 2b - Case 2, CT. Intravenous Conray produces generalised e n h a n c e m e n t of the whole lesion.

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Fig. 3a - Case 3. Curvilinear calcification shown in the frontal region.

Fig. 3b - Case 3, CT. Large rounded lesion with a calcified margin above the anterior clinoid. Movement artefact,

Fig. 3c - Case 3. Intravenous Conray produces slight enh a n c e m e n t centrally and of the rim also.

anosmia, blindness in the right eye with optic atrophy, and papilloedema on the left. A plain skull film showed curvilinear calcification in the right frontal region (Fig. 3a), and a right carotid angiogram showed a bifurcation aneurysm about 1 cm in length, with marked displacement o f the anterior cerebral artery to the left of the mid-line. A C T scan showed

a large rounded mass above the right anterior clinoid with a calcified rim which showed a little e n h a n c e m e n t of the margin after intravenous Conray 420 (Figs 3b, c). A diagnosis o f right-sided bifurcation aneurysm, with a calcified rim and a mainly thrombosed l u m e n was made. As the lateral ventricles were dilated, a ventriculo-atrial s h u n t was inserted,

GIANT INTRACRANIAL

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Fig. 4a - Case 4. Patchy calcification with a curviUnear margin in the frontal region.

Fig. 4b - Case 4, CT.' A large rounded density with calcification in it is shown in the left frontal region,

Fig. 4c - Case 4, CT. After intravenous Con.ray there is enhancement of the lesion particularly posteriorly.

With improvement in her general mental state and headache. She is now well but has a blind right eye. Case 4. H.J., a 57-year-old male, presented with deterioration of personality and epilepsy, with severe headaches o f about five yeats duration. There was also a progressive loss of vision in the left eye and urinary incontinence. On exami-

nation he was depressed, normotensive, and with a left optic atrophy. The skull radiograph showed patchy calcification in the left frontal region with a curvilinear margin (Fig. 4a). A C T scan showed a large rounded density in the left frontal region, containing calcification (Fig. 4b). After intravenous Cortray 420 some slight generalised increase in density

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Fig. 4d - Case 4. Left carotid angiogram. Anterior communicating artery a n e u r y s m 2 cm across.

occurred b u t the change was n o t uniformly marked (Fig, 4c). A left carotid angiogram showed a 2 cm anterior c o m m u n i cating artery a n e u r y s m projecting forwards and upwards (Fig. 4d). At operation an aneurysm 8 cm across was encountered following incision of the left frontal lobe. The bulk of t h e a n e u r y s m was removed being alternate layers o f clot and fibrous tissue. The p a t e n t sac was encased in acrylic. Postopcratively he did well until hydrocephalus supervened one m o n t h later with an akinetic state. This responded well to a ventriculo-atrial shunt. He was well and free from fits when seen at follow-up. Case 5. S.N., a 41-year-old female, was referred with a three-year history of epilepsy which h a d become worse recently. A provisional diagnosis of multiple sclerosis had been made in the past as a result of tingling in the lower limbs four years previously. On examination she was normotensive and h a d a mild left upper m o t o r n e u r o n e facial palsy. A C T scan showed a rounded area of increased density low down and to t h e right o f the third ventricle. It enhanced markedly after intravenous Conray 420 (Figs 5a, b). A carotid arteriogram showed a large middle cerebral artery aneurysm 3 cm across, projecting upwards and ., backwards (Fig. 5c). The a n e u r y s m was excised and t h e patient m a d e a good recovery. : Case 6. P.F., a 17-year-old girl, p r e s e n t e d . w i t h a ninem o n t h history o f falling attacks. These were preceded on each occasion by a feeling of sickness and an u n u s u a l taste in

t h e m o u t h . During these episodes she became dysphagic but remained orientated in time and place. Physical examination was normal. A diagnosis of temporal lobe epilepsy was made. A skull radiograph showed curvilinear calcification in the right temporal lobe (Fig. 6a). A C T scan showed a bilocular calcified space-occupying lesion in the right middle fossa (Fig. 6b). At carotid a n g i o g a p h y a middle cerebral artery occlusion was demonstrated, and no filling of the aneurysm occurred (Fig. 6c). Nevertheless, it was considered to be a t h r o m b o s e d giant middle cerebral artery a n e u r y s m involving the main t r u n k of the artery, which was also t h r o m b o s e d . At operation via a right fronto-temporal craniotomy the Sylvian fissure was opened and a large t h r o m b o s e d a n e u r y s m encountered. This was clipped and excised. The patient made an excellent recovery and remains well and free of fits at follow-up. Case 7. M.B., a 56-year-old female catering officer, presented with a two-year history of falling vision, mainly and at fftrst in the left eye but also affecting the right eye to the point of total hemianopia at the time o f arrival in hospital. On examination, she was noted to have a well-controlled hypertension of 150/90 m m H g and total right h o m o n y m o u s hemianopia with large headline print vision only. A left carotid angiogram carried o u t at the referring hospital had s h o w n a large ophthalmic artery a n e u r y s m (Figs 7a, b) projecting above the sella into the midline. A C T scan showed a central suprasellar mass, enhancing densely throughout

GIANT INTRACRANIAL

Fig. 5a - Case 5, CT. Rounded density to the right of the thkd ventricle.

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Fig. 5b - Case 5. After intravenous Conray there is marked enhancement of the whole area. anterior cerebral artery aneurysm. The last case had presented with blindness, the plain radiographs were normal, and the CT scan had shown a large rounded density in the anterior fossa with mild generalised enhancement after Conray. The patient with the bifurcation aneurysm had presented with temporal l o b e attacks, and the sac projected upward into the brain substance, enhancing markedly with Conray on CT. Of the two other middle cerebral artery aneurysms, one presented with a subarachnoid haemorrhage, and a calcified lesion on plain radiographs, whilst the last presented with a large intracerebral haemorrhage around the fundus of the sac. A summary of all 11 cases is included in Table 1.

b

;

i

g

.

5c - Case 5. Right carotid angiogram. Middle cerebral artery aneurysm 3 cm across. following intravenous Conray 420 (Figs 7c, d). A good cross circulation was later demonstrated from the right side to the left so that the left common carotid artery was ligated, and improvement has akeady occurred one month after operation. The other four cases included two middle cerebral artery aneurysms, a bifurcation aneurysm and an

DISCUSSION Incidence Giant aneurysms are rare. In the series of 658 intracranial aneurysms quoted by Morley and Barr (1968), there were 28 cases of giant aneurysm giving an occurrence rate of about 5%. Our incidence of 11

CLINICAL RADIOLOGY

34 Table 1 - Patient details

Patient

Clinical presentation

B.C., 29 years, F

Six weeks loss of limb control. Headache. Papilloedema Three months ataxia vertigo. Then headache, vomiting, dysphagia

E.T., 16 years, F

K.R., 46 years, F

H.J., 57 years, M

S.N., 41 years, F

P.F., 19 years, F

M.B., 56 years, F

J.B., 60 years, M

A.W., 46 years, M

B.M., 48 years, F

G.N., 60 years, M

Radiographs

CT

Plain film, RIP Angio. Avascular area. Possible aneurysmal stump in retrospect Plain film. Fleck of caleification in posterior fossa Angio. Giant aneurysm on vertebral artery Headaches. Loss of Plain film. Rim calcificavision in right eye. tion. Evidence of RIP Memory loss above anterior clinoids. Angio. Bifurcation aneurysm Twenty years loss of Plain film. Curvilinear vision in left eye calcification in the high and personality frontal region with change. Fits more patchy calcification recently within the area Anglo. Anterior communicating artery aneurysm, 2em across Three yeats - fits and Plain film. Normal ataxia. Mild left Angio. Bifurcation facial weakness aneurysm, 3 cm across

Operation. Removal of Rounded density. Rim aneurysm. Clinically enhancement after Conray. Hydrocephalus improved Operation. Removal of Oval density in posterior aneurysm. Clinically fossa with marked enexcellent hancement after Cortray Rounded density above anterior eilnoids. Minor enhancement centrally after Conray. Marginal rim. Hydrocephalus Rounded density in left frontal region. Rim calcification. Minor enhancement

Rounded density to the right of the thalamus. Marked enhancement after Conray One year - focal Plain film. Rim of calcifiOvoid calcification in right epilepsy. Recent cation in fight temporal middle fossa headaches region with patchy calcification within the area Angio. Middle cerebral artery occluded Months - increasing Plain film. Pressure effect Central density above the loss of vision. on sella sella with dense enFound to have a Anglo. Ophthalmic artery hancement after Corttay homonymous aneurysm projecting field defect above the sella Several years increas- Plain film. Normal Rounded density in left ing blindness, fits Previous angio, had shown anterior fossa. Generaand general confua serpiginous aneurysm lised enhancement with sion. Optic atrophy of the anterior cerebral Conray artery Recent severe headPlain film. Calcified rim Rounded density right ache with initial right middle fossa middle fossa, enhancing unconsciousness. Anglo. Giant right middle with Conray CSF bloodstained cerebral artery aneurysm 3 cm across Eighteen months of Plain film. Normal Rounded density in the temporal lobe Angio. Large bifurcation right middle fossa en(uncal.) attacks aneurysm 2.5 cm in hancing markedly after length, projecting upComay wards Rounded density in right Sudden onset of stib- Plain film. Normal arachnoid haemor- Anglo. Large right middle middle fossa. Thought rhage with a]eft cerebral artery aneuto be mainly haemorhemiparesis rysm 2.5 cm across rhage

cases in a b o u t 180 cases o f i n t r a c r a n i a l a n e u r y s m s i n v e s t i g a t e d in t h e last t w o and a h a l f years gives a similar i n c i d e n c e o f a b o u t 6%. Bull ( 1 9 6 9 ) r e p o r t e d 2 2 cases c o l l e c t e d over a p e r i o d o f 2 2 years.

Outcome

Operation. Ventriculoatrial shunt inserted. Clinically improved Operation. Removal of aneurysm. Clinically improved

Operation_ Removal of aneurysm. Good recovery Operation. Removal of aneurysm. Good recovery

Operation. Carotid artery ligation. Patient improving No operation_ Death two months later from cerebrovascular accident Operation. Clipping of the right common carotid artery. Good recovery Operation. Clipping and partial removal of aneurysm. Hemiplegia following operation Operation. Clot evacuated. Aneurysm clipped_ Improvement continues after operation [

Age a n d Sex Ratio T h e age of our p a t i e n t s o n p r e s e n t a t i o n rangeO f r o m 16 to 60 years w i t h a m e a n o f 4 3 . 4 years. This is slightly y o u n g e r t h a n t h e m e a n age o f 51 years in

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ANEURYSMS

35

Fig. 6a - Case 6. Patchy calcification with a curvilinear margin in the middle fossa.

Fig. 6c - Case 6. Right carotid angiogram. Middle cerebral artery occlusion. No ffiring of the aneurysm.

Fig. 6b - Case 6, CT. Calcified lesion in the right middle fossa.

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Fig. 7a - Case 7. Left carotid angiogram. L~ge ophthalmic artery aneurysm,

Fig. 7b - Case 7. The aneurysm lies above the seUa in the midline.

Fig. 7c - Case 7. Rounded density above the sella.

Fig. 7d - Case 7. After intravenous Conray there is marked enhancement of the lesion above the sella.

the 13 cases described by Sonntag et al. (1977). Only four o f the patients were aged 50 years or m o r e whereas in the series q u o t e d by Bull (1969) over twothirds o f his 22 cases were m o r e than 50 years old.

The almost 2:1 ratio o f female to male is in good agreement with the other series (Morley and Barr, 1968 ; Bull, 1969; S o n n t a g e t al., 1977), w h e r e a total o f 43 o u t o f 63 patients were female.

GIANT INTRACRANIAL

Clinical Presentation Only two of our patients presented with subarachnoid heamorrhage. This leads us to support those authors whose series indicate that such a presentation is rare (Bull, 1969; Jain, 1965; Morley and Barr, 1968; Sarwar et al., 1976). The 70% incidence quoted by Sonntag et al. (1977) is unusually high. Large aneurysms may lead to the presence of intracranial space-occupying lesions being suspected (Jain, 1965). The case histories outlined above largely support this view. Four of the patients had visual defects; three had fits; two focal epilepsy and three dementia. In Bull's series the most frequent complaint was some disturbance of vision, and the same ratio (6/22) as in our series had permanent mental changes. It is interesting that Jefferson (1937) postulated that large aneurysms lead to insanity when commenting on the high incidence of aneurysms at necropsies in asylums.

Radiological Presentation The plain skull radiograph was normal in four patients. On five occasions, calcification was noted, and in two patients, there was evidence of local pressure changes on the sella. The calcification was of the classical curvilinear variety in four of the cases, and in two of these, patchy calcification was also present within the area. The appearances of the calcification were such that the possibility of a giant aneurysm was included in the initial differential diagnosis, on the plain films alone. In another case, tomography showed a fleck of calcification in the posterior fossa, and this was shown to be associated with some bone erosion, so that a meningioma was initially considered to be the likely diagnosis. The incidence of calcification on the plain films was similar to that quoted by Bull (1969) and Morley and Barr (1968), being five out of 22, and eight out of 28 cases, respectively. It is important to remember that calcification in a giant aneurysm is not necessarily curvilinear in outline, and may be patchy in nature or even represented by merely a fleck. CT scanning has now established itself as the investigation of choice in the present day diagnosis of intracranial lesions. It is usually requested following plain skull radiographs. It is interesting that in Bull's series, collected over many years, air encephalography was the next investigation requested, following plain skull radiographs, in half of the patients. Air encephalography was not undertaken in any of our patients. This underlines the debt we owe to CT scanning. The decline in the more traditional neuroradiological procedures as evidenced by this change

ANEURYSMS

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of approach is one of the factors helping to make CT scanning economic (Thomson, 1977). Its reliability in this series is shown by the fact that all 11 patients had abnormal scans. The giant aneurysms showed as areas of increased density mostly with sharply defined margins, and some with calcification in their edge and substance. There was no evidence of surrounding oedema. Ten of the 11 patients had enhanced scans (50ml of Conray 420i.v.). In one patient evaluation of enhancement was impossible due to haemorrhage. In the other nine patients two types of enhancement were seen. In six patients there was marked homogeneous enhancement of the whole lesion. In two patients there was partial enhancement of the lesion, but the edge appeared to increase in density, an appearance designated as rim enhancement. In the other there was rim enhancement alone. The differing appearances of the main lesion would be consistent with the varying amount of thrombus around the wall, and the size of the remaining lumen. Homogeneous enhancement of the whole lesion occurs when no clot is present and the whole lumen is patent. :Patchy enhancement occurs when layers of clot are present (Byrd et al., 1978). Rim enhancement is said to be explained by the presence of small vessels which have been demonstrated in the adventitia of giant or serpiginous aneurysms (Terao and Muraoka 1972). Diagnostic difficulties may arise in interpreting the CT fmdings. This is shown in our series by the fact that one case was biopsied (Case 2) and an attempt was made to biopsy a second (Case 1). Although arteriography may under-estimate the size of an aneurysm (e.g. Case 4), it is claimed to be diagnostic (Morley and Barr, 1968). This has not been our experience. In two cases the aneurysm did not fill at all. This did not matter to patient management in Case 6 as curvilinear calcification on the skull radiograph initially made the diagnosis of aneurysm very likely. However, in Case 1 although the possibility of an aneurysm was considered on CT its non-filling at arteriography led to an attempted burr hole biopsy. At operation later thrombus was found in the neck of the aneurysm. The particular features of a giant aneurysm are that they occur around the base of the brain, they are usually clear-cut entities, sometimes containing and/or edged with calcification and unaccompanied by surrounding oedema. Enhancement may be total and marked when the lumen is full of circulating blood or may be only partial and rim-like when varying quantities of thrombus interfere with the size of the available lumen. Differential diagnosis is commonly that of meningioma which has a typically granular appearance with a clean-cut edge, and in which generalised enhancement usually occurs

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after Conray. Some surrounding oedema is usually present. The plain skull films often help, but in cases o f doubt an arteriogram should be carried out to make the differentiation. A glioma m a y cause difficulties especially when the more solid slow-growing type o f t u m o u r is present. A craniopharyngioma or pituitary tumour immediately above the sella m a y also cause some confusion, requiring arteriography. Echinococcal cysts have been quoted (Maxwell and Chou, 1977), being cystic lesions with clear-cut partly calcified margins. They may need to be considered in any patient arriving from an area where such a lesion is known to be prevalent. Neurinomas in the posterior fossa in particular may also cause confusion, and an abscess m a y produce a similar rim enhancement but the appearances are usually much more pronounced and readily differentiated. In any case of a localised haemorrhage, the possibility o f a giant aneurysm underlying the lesion may need to be remembered, but arteriography is likely to be carried out anyway in such a situation, thus revealing the true underlying cause.

Surgical Aspects It has been claimed that direct surgical attack is seldom possible or effective, and that carotid ligation is perhaps the treatment of choice (Morley and Barr, 1968). This has not been our experience, and in this series no patient was made worse following direct attack upon the aneurysm and most were greatly improved. The danger o f rupture in giant aneurysms is controversial. Jain (1965) claims that it is rare. Laminated thrornbus in the aneurysm may act as a protective exoskeleton (Sadik et al., 1965). Two cases only presented with subarachnoid haemorrhage and both o f these were middle c e r e b r a l - a r t e r y aneurysms (Cases 9 and 11). Thus the need for surgery in giant aneurysms is not associated with the danger o f rebleed, but rather with the necessity for removal of the mass. We have shown that operating has relieved headache, fits, hemiparesis and progressive dementia. Case 2 demonstrated the urgent need for relief from brain stem compression by this large posterior fossa tumour. It was felt that the patient was about to succumb from a progressive bulbar palsy, y e t complete removal was likely to be extremely hazardous. Fortunately surgery was successful. The surgeon should ask himself the question, is there any likelihood of this lesion on the CT scan being an aneurysm? A close scrutiny o f the skull radiograph and a request for an angiogram prior to biopsy will in most cases elucidate the problem.

CONCLUSIONS 1. Giant aneurysms are rare but we have seen 11 cases over a two and half year period. 2. The clinical presentations are variable tending to be a consequence of a mass effect. Subarachnoid haemorrhage is uncommon in this series. 3. Plain skull radiographs should not be omitted although they may be normal. Giant aneurysms m a y be suspected from the presence of curvilinear calcification or flecks of calcium. Bony erosion may occur. 4. Angiography may fail to outline the full extent o f the aneurysm due to the presence o f mural thrombus. Rarely the aneurysm may not fill at all. 5. CT scanning is a reliable technique in demonstrating the presence of giant aneurysrns. It gives rise to a granular appearance due to patchy areas o f increased density. Enhancement occurs following the injection o f intravenous contrast and may be homogeneous, or ring-like in nature, varying in degree corresponding with the thickness o f the aneurysm wall and the amount of thrombus contained. If the whole aneurysm is thrombosed, no enhancement will occur in its substance although rim enhancement may be seen. Acknowledgements. We are indebted to the neurosurgical consultants of the SW Regional Unit, A. Hulme, H. Griffith, B. Cummins and M. Torrens for permission to refer to their case notes. Also to Miss Sandra Sketchley for typing the manuscript.

REFERENCES Bull, J. (1969). Massive aneurysm at the base of the brain. Brain, 92, 535-570, Byrd, S. E., Bentson, J. R., Winter, J., Wilson, G. H., Joyce, P. W. & O'Connor, L. (1978). Giant intracranial aneurysms simulating brain neoplasms on computed tomography_ Journal of Computer Assisted Tomography, 2, 303 -307. Jain, K. K. (1965)- Surgery of intracranial berry aneurysms. Canadian Journal of Surgery, 8, 172-187. Jefferson, G. (1937). Compression of the chiasma, optic nerves and optic tracts by intracranial aneurysms. Brain, 60, 444-497. Locksley, H. B. (1966). Report on the cooperative study of intracranial aneurysms. Journal of Neurosurgery, 25, 321-368. Maxwell, R. E. and Chou, S. N. (1977). Journal of Neuro, surgery, 46,438-445_ Morley, T. P. & Barr, H. W. K_ (1968). Clinical Neurosurgery, 16, 73-94. Sadik, A. R., Budzilovich, G. N. & Shulmon, K. (1965). Giant aneurysm of middle cerebral artery. A case report. Journal of Neurosurgery , 22, 177-181.

GIANT I N T R A C R A N I A L A N E U R Y S M S Sarwar, M., Batnitzky, S. & Schechter, M. (1976). Tumorous aneurysms.Neuroradiology, 12, 79-97, Sonntag, V. K. H., Yuan, R. H. & Stein, B. M. (1977). Giant intracranial aneurysms. A review of 13 cases. Surgical Neurology, 8, 81 89.

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Terao, H. & Muraoka, I. (1972). Giant aneurysm of the middle cerebral artery containing an important blood channel. Case report. Journal of Neurosurgery, 37, 3 5 2 356. Thomson, J. L. G. (1977). Cost effectiveness of an EMI brain scanner. Health Trends, 9, 16-19.