computerized tomography (the emai scanner): a comparison ... · computerized scans reliably...

Journal of Neurology, Neurosurgery, and Psychiatry, 1976, 39, 203-211

Computerized tomography (the EMAI Scanner): acomparison with pneumoencephalography and

ventriculographyJ. GAWLER, G. H. DU BOULAY, J. W. D. BULL, AND J. MARSHALL

From The National Hospital for Nervous Diseases, Queen Square, London

SYNOPSIS Computerized tomography, using the EMI Scanner, allows the diagnosis of cerebralatrophy or hydrocephalus to be made with the same degree of accuracy as conventional neuro-radiological methods. Ventricular measurements made on EMI scans have been compared withthose from pneumoencephalograms and ventriculograms. A range of normal ventricular measure-ments for the EMI scan is suggested.

Because the small difference in tissue densitybetween cerebrospinal fluid and brain tissue isresolved by computerized tomography theventricular system, subarachnoid cisterns, andcortical sulci can be visualized without recourseto contrast media. Focal or generalized ventricu-lar enlargement is readily seen and widening ofcortical or cerebellar sulci can be detected.Obstructive hydrocephalus can generally be dis-tinguished from cerebral atrophy and angio-graphy or pneumoencephalography are oftenavoided.One problem which attends the introduction

of new diagnostic equipment is to establish thenormal. Before the EMI Scanner became avail-able, encephalography or ventriculography werethe only means of demonstrating the ventricularsystem and subarachnoid space clearly duringlife. It is thus of value to compare the EMI scanwith a conventional ventricular contrast proce-dure when both are undertaken in the samepatient, for nearly 60 years of experience hasaccumulated in relation to the latter method.

METHODS

We have reviewed 80 by 80 matrix EMI scans andconventional ventricular contrast procedures frompatients investigated by both. As ventricular size andthe appearance of the subarachnoid space were to be

(Accepted 8 October 1975.)203

compared, those with mass lesions involving thecerebral hemispheres were excluded.Comparison was made between the EMI scan

and either a pneumoencephalogram or pneumo-ventriculogram in 78 patients whose ages rangedfrom 8 months to 73 years. EMI scanning had alwaysbeen undertaken before the ventricular contrastprocedure but the investigations were never separ-ated by more than 21 days. Seventy-five percent ofthe contrast procedures had been undertaken duringgeneral anaesthesia.Our original intention was to correlate EMI scans

and pneumoencephalograms, in a prospective man-ner, among patients with dementia referred for bothinvestigations. It soon became clear, however, thatcomputerized scans reliably demonstrated cerebralatrophy and subsequent contrast investigations werenot justified. The initial EMI system, using the 80 by80 matrix picture, was improved by a high resolu-tion 160 by 160 matrix scan which provided aclearer image of the intracranial anatomy (Fig. 1).As a result, the number of pneumoencephalogramsundertaken each month at The National Hospitalhas fallen from 50 to less than 10 since the EMIScanner became available and it is now hard to findcontrast studies which are normal or show onlyatrophy to correlate with high resolution EMI scans.All the 80 by 80 matrix examinations with com-parable ventricular contrast procedures were there-fore studied to ascertain the reliability of scanningand to establish normal limits for the technique.

EVALUATION OF COMPUTERIZED TOMOGRAMS Theintracranial content is displayed by a contiguous

Protected by copyright.

on May 31, 2020 by guest.

http://jnnp.bmj.com

/J N

eurol Neurosurg P

sychiatry: first published as 10.1136/jnnp.39.3.203 on 1 March 1976. D

ownloaded from

http://jnnp.bmj.com/

J. Gawler, G. H. du Boulay, J. W. D. Bull, and J. Marshall

FIG. 1 (a) Normal 80 by 80 matrix EMI scan. (b) Normal 160 by 160 matrix EMI scan. Comparison of theseexaminations demonstrates the greater clarity with which the ventricular system and subarachnoid space areseen on the high resolution scan.

series of six or eight transverse tomograms. Eachtomogram represents those structures within a trans-verse 'slice' of the head 13 mm in depth. Thevertical dimension of an individual 'slice' is lost bysuperimposition but a three-dimensional impressionis obtained from the series. An 80 by 80 matrixtomogram is composed of 6 400 cells each measuring3 mm by 3 mm in the transverse plane and having a

depth of 13 mm. The x-ray absorption coefficientregistered at each cell represents the average absorp-tion from all the tissues within it. Cells containingonly cerebrospinal fluid have a value of 0 or 1,while those encompassing only cerebral tissue givevalues between 11 and 30. At the ventricular margincells will contain both fluid and brain tissue and anumerical gradient is likely here (Fig. 2).

204



http://jnnp.bmj.com

/J N

eurol Neurosurg P


ownloaded from


Computerized tomography: a comparison with pneumoencephalography and ventriculography

80x80CELLS

12111098 742000 7 0 3 6 9 11CELL ABSORPTION VALUES

FIG. 2 Computerized tomograms represent a tissue 'slice' 13 mm in depth so that the ventricular marginsoccupy several cells. A numerical gradient of x-ray absorption values therefore exists at the ventricularperimeter.

FIG. 3 Ventricular measurements taken from computerized scans. For description see text.

FIG. 4 Ventricular measurements taken from conventional ventricular contrast procedures. For descriptionsee text.

205



http://jnnp.bmj.com

/J N

eurol Neurosurg P


ownloaded from



When the ventricular extremity lies within cellsthat contain principally cerebral tissue a reduction indensity may not be apparent and the ventricle wouldthen appear smaller than its true size. Conversely,when a cell contains sufficient fluid to lower itsdensity the whole cell is registered as ventricle, even

when only a segment of ventricle projects into it.This would increase apparent ventricular size.

Appropriately adjusted, the oscilloscope displaywill show the ventricular margins fairly well, but asthe display can be varied in size and the focal lengthof the Polaroid camera altered, absolute measure-ments are best taken from the numerical printout ofabsorption values. Cells having a value less than 1

were considered to contain cerebrospinal fluid andthe ventricular margins have been constructed on

this basis.All measurements given in this communication

have been obtained by counting 3 mm by 3 mm cellson the numerical printout and the following havebeen obtained from each EMI scan (Fig. 3).A. The greatest width between the lateral aspects

of the cellae mediae. (The lateral ventricles divergeposteriorly, especially as the cellae mediae approachthe trigones. Care was therefore taken to restrictthis measurement to the cellae mediae and not toinclude the superior aspects of the trigones.)

B. The width between the lateral extremities of thetips of the frontal horns.

C. The distance between the lateral aspects of thefrontal horns measured halfway along their antero-posterior length.D. The maximum width of the third ventricle.E. The anteroposterior extent of the fourth

ventricle measured in the midline.The ratio described by Evans (1942), the distance

between the tips of the frontal horns divided by thewidth of the skull measured between its inner tables,was calculated for each patient. Scans were scrutin-ized for evidence ofcerebral or cerebellar atrophy anda record made of widened sulci, enlargement of theinterhemispheric fissure, or dilatation of the insularcisterns. All the EMI scans were evaluated withoutreference to the contrast procedures by one ob-server (J.G.) and a conclusion-normal, atrophy(cerebral or cerebellar), or hydrocephalus-wasreached.

EVALUATION OF CONVENTIONAL STUDIES A secondobserver (G.H. du B) reviewed all the ventricularcontrast procedures without knowledge of the EMIscan findings and the following measurements weretaken (Fig. 4).

A. The width of the cellae mediae measuredacross the superior aspects of the lateral ventricles.

B. The distance between the lateral extremities ofthe tips of the frontal horns.D. The maximum width of the third ventricle.E. The greatest distance between the roof and

floor of the fourth ventricle.F. The height of the lateral cleft of the larger

temporal horn.Evans's ratio was calculated from the contrast

procedure and evidence of cerebral or cerebellaratrophy noted. The width of the largest corticalsulcus was recorded and those 4 mm or more inwidth were regarded as abnormal.

Using the criteria set out by Engeset and Skraastad(1964) in their review of ventricular measurements, aconclusion about each radiological procedure wasreached in the manner described for the EMI scan.

RESULTS

In 59 of the 78 patients in this series the conclu-sions drawn from both methods of investigationwere identical (Table 1). In the remaining 19 thefindings differed (Table 2) and will be describedin detail. Seven pneumoencephalograms provedincomplete; four showed no ventricular filling,and three had one lateral ventricle unfilled. Thehigh incidence of technically unsuccessful con-trast procedures reflects the referral of suchpatients for EMI scans to exclude a structural

TABLE 1COMPARISON OF EMI SCAN AND VENTRICULAR

CONTRAST PROCEDURE (78 PATIENTS)

Full agreement between techniques No. Total(59 patients) no.

Cerebral atrophya. Ventricles and sulci enlarged 20b. Sulci only enlarged 4c. Ventricles enlarged, sulci equivocal 3

Total 27 27

Borderline cerebral atrophya. Ventricles and sulci equivocal 2b. Sulci equivocal 3

Total 5 5

Hydrocephalus 12Normal I 1Normal ventricular system but posterior

fossa tumour 3Postoperative cavity and generalized

cerebral atrophy I

Total 59

206



http://jnnp.bmj.com

/J N

eurol Neurosurg P


ownloaded from


Computerized tomography: a comparison with pneumoencephalography and ventriculography

cause for nonfilling. In this group no cause wasfound, five EMI scans being normal and twoshowing cerebral atrophy.Two patients had normal ventricular dimen-

sions on both the computerized scan and con-trast study but the latter showed distension ofthe anterior recesses of the third ventricle(ballooning). One of these patients had cerebellarectopia and the other a small acoustic neuroma.Four EMI scans were normal when the pneumo-encephalogram showed either slight lateralventricular enlargement or equivocal sulcalwidening. Six patients showed enlargement of

FIG. 5 Cerebral atrophy. 80 by 80 matrix.

TABLE 2COMPARISON OF EMI SCAN AND VENTRICULAR

CONTRAST PROCEDURE (78 PATIENTS)

Differentfindings between techniques No. Total(19 patients) no.

Ventricular contrast procedure inadequatea. EMI scan normal 5b. EMI scan cerebral atrophy 2

Total 7 7

EMI scan normala. AEG third ventricle ballooned 2b. AEG lateral ventricles dilated 2c. AEG cortical sulci enlarged 2

Total 6 6

Ventricular dilatation on both studiesa. Enlarged sulci seen on EMI scan only 3b. Enlarged sulci seen on AEG only 3

Total 6 6

19

the ventricular system on both studies butwidening of the cortical sulci was seen only onthe scan in three and only on the pneumo-encephalogram in three. Enlarged sulci weremissed on the contrast procedure because theyfailed to fill with air and on the EMI scan be-cause tomograms were not obtained at theappropriate level.The lateral, third, and fourth ventricles could

always be identified on EMI scans when technic-ally adequate tomograms had been obtained atappropriate levels. The temporal horns of thelateral ventricles however, were seen on the EMIscan only when they were enlarged. Cleardemonstration of the cortical sulci on the scanimplied that they were dilated (Fig. 5). Wideningof the interhemispheric fissure and deepening ofthe subarachnoid space overlying the island ofReil (circular cistern) were helpful signs ofcerebral atrophy on computerized scans. Un-doubted widening of the interhemispheric fissurewas present in 10 and enlargement of the insularcistern in 15 of the 33 patients of this series withdefinite cerebral atrophy.

Enlargement of cerebellar sulci was present in17 of the patients with cerebral atrophy. This wasdetected by both investigations in 13, bypneumoencephalography alone in two, and byEMI scan alone in two. When cerebellar atrophy

207P

rotected by copyright. on M

ay 31, 2020 by guest.http://jnnp.bm

j.com/

J Neurol N

eurosurg Psychiatry: first published as 10.1136/jnnp.39.3.203 on 1 M

arch 1976. Dow

nloaded from



was present, the cisterns surrounding the brainstem, especially the ambient cisterns, were oftenstrikingly prominent on the EMI scan.

Ventricular measurements have been selectedfrom those in which both studies were un-

equivocally normal, showed cerebral atrophyor hydrocephalus. Directly comparable dimen-sions from the two studies are given in tabularform for each of these groups (Tables 3-5).

In all three groups, the ventricular parametersmeasured directly on the EMI scan were on

FIG. 6 (a, left; b, above) (a) Hydrocephalus due toaqueduct stenosis. 80 by 80 matrix. (b) After the in-sertion ofa shunt there has been a dramatic reduction inventricular size. The radial artefact seen on 'slice' 3Ais due to the metal component of a Holter valve; suchaberrations have been almost eliminated by the 160by 160 system.

average less than the equivalent dimensions onthe contrast procedures. Among normal sub-jects, the mean value for Evans's ratio was alsoless on the scan. In those with cerebral atrophyor hydrocephalus, however, Evans's ratio was onaverage slightly greater on the EMI scan.The temporal horn of the lateral ventricle was

seen on the EMI scan only when its lateral cleftwas 6 mm or more in height on the contraststudy (measurement F). Similarly, cortical sulciwere visible on the scan when they measured

208



http://jnnp.bmj.com

/J N

eurol Neurosurg P


ownloaded from


Computerized tomography: a comparison with pneumoencephalography and ventriculography 209

FIG. 7 Cerebral atrophy. 160 by 160 matrix.

FIG. 8 Cerebellar atrophy. 160 by 160 matrix.

TABLE 3COMPARISON OF VENTRICULAR DIMENSIONS

(11 NORMAL SUBJECTS)

Range Mean

EMI Contrast EMI Contrastscan study scan study(mm) (mm) (mm) (mm)

A. Width of cellae mediae 24-39 28-41 33.0 35.5B. Width to tips of frontal

horns 21-36 32-50 29.7 40.5C. Width of third ventricle 3-6 3-9 4.6 5.6D. Height of fourth

ventricle 6-15 10-18 10.8 15.8Evans's ratio 0.18-0.30 0.23-0.30 0.24 0.27

TABLE 4COMPARISON OF VENTRICULAR DIMENSIONS(20 SUBJECTS WITH CEREBRAL ATROPHY)

Range Mean



horns 33-60 40-65 43.1 53.4C. Width to third ventricle 6-15 5-22 9.0 10.2D. Height of fourth


TABLE 5COMPARISON OF VENTRICULAR DIMENSIONS

(12 SUBJECTS WITH HYDROCEPHALUS)

Range Mean



horns 36-93 50-103 58.7 68.9D. Width of third ventricle 6-42 8-32 17.7 17.6E. Height of fourth


4mm or more in width on the contrast procedure.Several hydrocephalic patients were subse-

quently managed by ventricular shunting opera-tions and serial computerized scans thereafterhave proved of value in monitoring progress



http://jnnp.bmj.com

/J N

eurol Neurosurg P


ownloaded from



(Fig. 6). A number of cases from this series havebeen re-examined using the high definition 160by 160 matrix and a significant improvement inresolution was apparent (Figs 7 and 8).

FIG. 9 EMI scan of a patient whose ventricularsystem contains some air after encephalography. Theright frontal horn which contains the air appears

distended.

Several patients, not included in this series,have undergone computerized scanning whileresidual air, usually from encephalography, waspresent in the ventricles. An illustration of such a

case has been included (Fig. 9) to show that thesegment of ventricle containing air may belocally expanded.

DISCUSSION

The diagnosis of cerebral or cerebellar atrophycan be made from the EMI scan with the same

degree of accuracy as pneumoencephalography.When searching for evidence of cortical atrophyon computerized tomograms it is essential toobtain appropriate 'slices' toward the skullvertex and, likewise, adequate 'slices' incorpora-ting the superior cerebellar vermis are needed todisclose cerebellar atrophy.

Hydrocephalus is also reliably detected butcertain disadvantages should be noted in thiscontext. Pneumoencephalography allows thepassage of contrast medium to be followed along

the cerebrospinal fluid containing pathways andthe level of obstructive lesions may be so deter-mined. Computerized tomography yields astatic record and, when the entire ventricularsystem is dilated, the level of obstruction maynot be apparent. An EMI scan alone, forexample, could not distinguish hydrocephalusdue to atresia of the exit foramina of the fourthventricle from basal cistern block. When thescan shows only diffuse ventricular enlargement,in the absence of cortical atrophy, a con-trast procedure-pneumoencephalography, ven-triculography, or RIHSA encephalographydepending on the clinical circumstances-willbe required.Two patients in this series showed ballooning

of the anterior recesses of the third ventricle onpneumoencephalography, although ventricularsize was otherwise normal. Both patients, onewith a small acoustic neuroma and the otherwith cerebellar ectopia, had normal EMI scans.In this context, the continued need for contrastprocedures in those where the clinical suspicionof a posterior fossa or perisellar lesion is strongbut the EMI scan negative, must be emphasized.Measurements taken directly from the EMI

scan printout were all somewhat smaller thanthe equivalent dimensions taken from contrastprocedures. There are three possible explana-tions. First, the ventricles may be magnified byconventional radiographs; second, the ventricu-lar system may be inflated by the introduction ofair (Probst, 1973); and, third, ventricular sizemay be underestimated by computerized tomo-graphy.

Evans's ratio eliminates the problem ofmagnification, and in normal subjects the lateralventricles still appeared smaller on EMI scans.Returning to the consideration of ventricularmeasurement based on the cell size of computer-ized tomograms, it is likely that narrow seg-ments of the ventricular system will be under-estimated as their extremities would be lost incells containing principally cerebral tissue. Thisconclusion is supported by the greater dis-crepancy in size on measuring the tips of thefrontal horns on the one hand and the lessmarked discrepancy between measurements ofthe cellae mediae on the other.

Inflation of the ventricular system by airwould also seem likely in normal subjects, for

210



http://jnnp.bmj.com

/J N

eurol Neurosurg P


ownloaded from


Computerized tomography: a comparison with pneumoencephalography and ventriculography 211

computerized scans showing air in the ventriclesoften illustrate expansion of the segments con-taining gas.Among patients with either hydrocephalus or

cerebral atrophy, Evans's ratio was, on average,a little larger from the EMI scan than from thecontrast procedure, the reverse of the situationin normal subjects. Analysis of individual casesshowed that, in some patients with a markedlydilated ventricular system, the lateral ventricleswere larger when measured on the EMI scan.This suggests that either ventricular inflationafter the introduction of air is less marked whenthe ventricles are dilated or that contrast pro-cedures in some of these cases actually deflatethe ventricular system. While deflation might beexpected in those with obstructive hydrocephalus,it is surprising that it also appears to occur insome patients with berebral atrophy.

Bearing in mind the limitations of measure-ment on EMI scans and noting the apparentreduction in ventricular size seen in normal sub-jects when scans are compared with contrastprocedures, a normal range of ventricular

TABLE 6MEASUREMENTS FROM EMI SCAN

Normal Borderline Enlarged(mm) (mm) (mn)

A. Width of cellae mediae 36 or less 39 42B. Width to tips of frontal

horns 39 or less 42 45C. Width at midpoint of

frontal horns 18 or less 21 24D. Width of third ventricle 6 or less 9 12E. Height of fourth ventricle 12 or less 15 18Evans's ratio 0.29 or less 0.30 0.31

parameters for the EMI scan is suggested(Table 6).The EMI scan is a harmless, painfree method

of diagnosing cerebral atrophy or hydrocephaluswhich removes the need for conventional con-trast procedures in many cases. Scanning may beundertaken to provide a firm diagnosis amongpatients in whom contrast procedures are notjustified and, because the exposure to x-rays islow, serial examination is also feasible. Thetechnique is therefore ideal for monitoring theprogress of disease or the effects of treatmentand for screening those, such as the survivors ofsubarachnoid haemorrhage, who run the risk ofdeveloping hydrocephalus. The EMI scan is per-formed under physiological conditions, so thatartefacts which might result from anaesthesia orcontrast substances are avoided and the identi-fication of fluid-containing structures does notdepend upon their adequate filling by contrastmedia. As computerized tomography becomesmore sophisticated, it would seem likely that theindications for conventional ventricular con-trast procedures will decline still further.

We should like to thank EMI Limited for their support ofour research programme. Invaluable radiographicassistance was provided by Miss V. Fullom, secretarialassistance by Miss S. Andrews, and photographic help byMr H. Prentice.

REFERENCES

Evans, W. A. (1942). An encephalographic ratio for estima-ting ventricular enlargement and cerebral atrophy.Archives of Neurology and Psychiatry, 47, 931-937.

Engeset, A., and Skraastad, E. (1964). Methods of measure-ment in encephalography. Neurology (Minneap.), 14,381-385.

Probst, F. P. (1973). Gas distension of the lateral ventriclesat encephalography. Acta Radiologica, Diagnosis, 14, 1-4.



http://jnnp.bmj.com

/J N

eurol Neurosurg P


ownloaded from


computerized tomography (the emai scanner): a comparison ... · computerized scans reliably...

Documents