Journal of Neurology, Neurosurgery, and Psychiatry 1983;46:1102-1107

Arachnoid cysts in the middle cranial fossa: cause andtreatment of progressive and non-progressivesymptomsFGA VAN DER MECHE,* R BRAAKMANtFrom the Departments ofNeurology* and Neurosurgeryt, University Hospital Rotterdam-Dijkzigt,Rotterdam, the Netherlands

SUMMARY Ten consecutive patients with arachnoid cysts in the middle cranial fossa, diagnosed byCT, were studied. They were divided into three clinical groups: (1) four patients with progressivesymptoms caused by secondary bleeding, (2) five patients with non-progressive symptoms ofheadache or epilepsy, and (3) one asymptomatic patient. The nine symptomatic patients wereoperated upon and eight showed clinical improvement. Measurements of the CT scans revealedequal brain volumes on the affected and normal sides, refuting the hypothesis that the cyst is causedby agenesis of the temporal lobe. The hemicranium on the affected side was larger, accommodatingboth the cyst and a normal brain volume. The progressive symptoms after bleeding were caused bybrain shift and increased CSF pressure. The cause of the non-progressive symptoms has not yetbeen established: two mechanisms are suggested: (1) expansion of the cyst accompanied bycompression of surrounding structures, and (2) disturbed CSF dynamics without increasedintracystic pressure. Removal of the membranes of the cyst with an opening to the basal cisternsshould resolve both problems. After surgery a residual cyst may remain.

Arachnoid cysts in the middle cranial fossa areusually considered to be developmental in nature.They seem to occur predominantly in children andadolescents, especially males, and more often on theleft than on the right side.' Temporal lobe agenesissyndrome is another name given to this condition,because during surgery it was discovered that thetemporal lobe was absent or only partly developed.'

In the past, patients presented with either asymp-tomatic bulging of the head or with progressivesymptoms, suggestive of a space-occupying lesion,usually caused by a secondary subdural bleeding.Many cases, however, remained undetected asrevealed by an unsuspected incidence of 5 per 1000 ina systematic necropsy study.2 As a result of increasingavailability of CT, arachnoid cysts are now morefrequently diagnosed in relation to headache andepilepsy. If the association with these non-progres-sive conditions is not coincidental, symptoms might

be caused by (1) a space-occupying effect withpressure on surrounding structures, (2) a change inCSF dynamics, (3) agenesis or dysgenesis of thetemporal lobe, especially in the case of epilepsy.

If the cause is identified, then the appropriatetherapy can be applied: that is decompression by cystdrainage to the peritoneal cavity or right cardiacatrium, or regulation of CSF flow by membranec-tomy and opening of the suprachiasmatic cisterns, orno surgical treatment at all if epilepsy is caused bydysgenesis of the temporal lobe.

In a first attempt to solve this problem we studiedretrospectively ten consecutive patients diagnosed byCT. They were divided into groups according to theirsymptoms: (1) progressive symptoms defined asheadache combined with nausea, vomiting, diplopiaor papilloedema suggestive of raised intracranialpressure, and (2) non-progressive symptoms: head-ache or epilepsy.

Patients and methods

Address for reprint requests: FGA van der Meche, UniversityHospital Rotterdam-Dijkzigt, 40 dr. Molewaterplein, 3015 GDRotterdam, the Netherlands.

Received 10 April 1983Accepted 2 June 1983

Between June 1977 and August 1981, an arachnoid cyst inthe middle cranial fossa was diagnosed in 10 patients by CT.Nine patients were surgically treated; one patient wasasymptomatic. Six patients were male; in seven cases thecyst was located on the left side; the median age was 12-5

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Arachnoid cysts in the middle cranialfossa: cause and treatment

Table 1

Clinical data CTscan data Follow-up

Pt no. Sex Age Srmptoms (duration) Cyst size Bleedinig Midlinie Duirationi(yr) (cm-?) shift (moniths) Reslults

Patients with non-progressive symptoms1 m 30 headache (6 months) 3 - - 6 free of symptoms

epilepsy (1 wk) (no medication)2 f 9 epilepsy (6 months) (numerous 10 - _ 9 verv much improved

generalised convulsions) onlv 1 focal fit withmedication. as before

3 m 37 headache (>4 yrs) 22 - - 21 unchanged4 m 9 headache (6 vrs) 31 - - 54 free of headache

epilepsy (1 month) fits from a focuscontralateral to the cyst

5 m 4 headache during walking (months) 29 - + 16 free of symptomsdevelopment accelerated'?

Patients with progressive symptoms6 m 16 headache nausea 63 subdural + 16 free of svmptoms

vomiting, apathy (2 wks) haematoma7 m 7 headache, diplopia 28 subdural + 24 free of symptoms

apathy. papilloedema (3 months) haematoma8 f 10 headache. nausea 182 subdural + 18 free of svmptoms

vomiting, apathy (1 mnth) haematoma9 f 15 headache, nausea 118 intracvstic + 6 free of symptoms

vomiting. papilloedema (1 mnth) hacmatoma

Patient without symptoms10 f 24 - 46 -

years (range 4 to 37 years). These figures are in accordancewith those in the literature.3 4 Table 1 presents furtherdetails.The operation consisted of removal of the outer mem-

brane of the cyst and opening the inner membrane to createa connection with the suprachiasmatic cisterns. Histology-not performed in patients 2 and 5-showed arachnoidmembranes in all others. At the end of 1981 all patients wereseen by the first author. They were interviewed following astandard protocol and examined in detail for any minorfocal deficitCT scan measurementsIn order to confirm or disprove the hypothesis of agenesis ofbrain tissue, the volumes of the left and right hemisphereswere compared. To avoid measuring temporary volumechanges, for example, those caused by secondary bleeding,a postoperative CT scan obtained at the time of follow-upwas used. Two procedures were followed: (1) direct volumemeasurement, and (2) measurement of the skull "radius" asan indirect method. For direct volume measurements, onlythe scans with three or more slices above the lateralventricles were used, in order to include as much braintissue as possible. The scan of patient 1, with the smallestcyst, was accordingly excluded. Tissue of the brain-stem andthe cerebellum was excluded if it could be clearly distin-guished on both sides. All scans were analysed by re-drawing on paper the cyst and brain tissue from both sides.Subsequently the pieces of paper were cut out, weighed andtheir weights compared with the weight of a standardsurface area. The weight of re-drawn and cut standardsurface areas of 100 cm2 showed a variation of < 1% (n = 5).Knowing the thickness of the CT slice the volume could becalculated from these surface areas. The scan of patient 8could be measured with an off-line computer-assisted CTscan analyser (Philips). The manual analysis of this patientdiffered by only 3% from the computer-assisted analysis

(see results). The second, indirect method assumes anincrease in skull diameter on the affected side comparedwith the normal side, if it has to contain both the cyst and thenormal volume of brain tissue. Therefore, the skull"radius" was measured on both sides at the level of thepineal gland perpendicular to the midline.

Results

Nine patients were symptomatic. Four patientspresented with progressive symptoms related to raisedCSFpressure or brain shift (patients 6, 7, 8, 9). Theydeveloped headache combined with nausea, vomit-ing, double vision or general malaise, all after minortrauma. All had a secondary bleeding: in three thiswas due to a subdural haematoma, and in one anintracystic bleeding. In retrospect, three of the fourpatients had at an earlier stage complained of non-progressive symptoms: headache, general malaiseand deteriorating academic performance. After sur-gery all patients were free from symptoms.

Five patients presented with non-progressivesymptoms. Four of them had complained of head-ache for months (patients 1, 5) or even years (patients3, 4). In patient no 4 only, was this related to minortrauma six years previously. In three of them, thepain was not localised; in the fourth (patient 3) thepain was usually on the side of the cyst, butoccasionally contralateral. He was the only patientwho did not benefit from the operation. None ofthese patients showed signs of haemorrhage atoperation nor on histological examination of themembrane. Three patients suffered from epilepsy(patients 1, 2, 4; for patient 2 it was the only

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van der Meche/, Braakman

............

Figl1CTscan ofpatient 8: (a) preoperatively aleft-sided cyst is present with acomplicating subdural

haematoma; (b) postoperatively no haematoma is visible; note that the cyst has re-expanded; the patient is,

however free ofsymptoms.

symptom). In two patients the side of the cyst wasconsistent with focal characteristics of either theconvulsion or the EEG. In the third patient (no 4) thefocal epileptic signs were consistent with the EEGfocus, but inconsistent with the side of the cyst; thiswas the only patient whose epilepsy did not improveas a result of operation; his chronic headache,however, disappeared.

CT SCAN MEASUREMENTSThe case of patient no 8 makes it clear that the cystwas formed by a space-occupying lesion rather thanagenesis of the temporal lobe. The large cyst becamesymptomatic because of a complicating subduralhaematoma following minor trauma (fig la): 18months after the operation a large cyst was stillpresent (fig lb). It is evident, however, that the lossof brain space had been compensated for. Thecomputer-aided volume measurements were as fol-lows: cyst: 182 ml; both left and right supra-tentorial brain volume: 530 ml. Hence, there was no

Table 2 Cyst and brain volume of the affected sideexpressed as the percentage ofthe brain volume on thenormal sidePt. No. Brain volume Cyst volume (%)

affected side (%)1 not measured < 12 97 23 106 34 106 55 102 66 105 127 103 58 97 329 98 2110 99 10

loss of brain tissue. The volume measurements madeby hand are summarised in table 2; the cyst volumesand the brain volumes on the affected side wererelated to the normal side. Irrespective of the size ofthe cyst, the brain volumes on both sides wereapproximately equal, the mean value on the affectedside being 101-4 ± 3 8%. This is not significantlydifferent from the normal side (Student's t test forpaired observations).The results of the indirect method, measuring the

skull "radius" on both sides at the level of the pinealgland, are presented in fig 2. The difference betweenthe affected and the normal side is proportionallylarger in skulls with larger cysts.

15

Eu

.2 10-.V

.2

4,

C 0*54,._

0

0

00 0

* *:0

O 50 160 150Cyst volume (cm3)

200

Fig 2 Relationship between volume ofcyst and differencein 'radius' between the affected and the normal side.

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Arachnoid cysts in the middle cranialfossa: cause and treatment

DEXTERITY AND PSYCHOLOGICAL

FUNCTIONINGConsidering temporal lobe agenesis as a possibility,we looked for signs of functional impairment. Theintellectual function in all patients but patient no 5was average or even above average with regard toeducational or occupational level. For instance, thegirl with the largest cyst (fig 1) had excellent schoolresults and was socially fully integrated. Patient no 5differs from the others in that he was born with a skullcircumference in excess of the 98th percentile; thisindicates growth of the cyst before birth. Hepresented with headache during walking, but othercomplaints were delayed development of speech andenuresis. After the operation a considerable cyst stillexisted (29 ml). Despite this, his developmentfollowing operation had, according to his parents,accelerated to near-normal level.

Seven of the cysts were located on the left side.Five of these patients, including those with the largestcysts, were nevertheless right-handed.

Discussion

Developmental cysts in the middle cranial fossa are

sometimes considered to be primary arachnoidmalformations,'122 but more often they are believedto be secondary fluid collections' I I`

23 in theabsence of a part of the temporal lobe. Absence ofbrain tissue should lead to a difference in brainvolume between the two sides. Volume measure-ments of the CT scans of these ten patients, however,led to the opposite conclusion: there was no loss ofbrain tissue, not even when the cysts were very large(table 2). In addition, it could be demonstrated thatthe affected hemicranium was larger, the increasebeing proportional to the size of the cyst, andtherefore able to harbour both the cyst and thenormal brain volume (fig 2). Shaw24 demonstratedthe same phenomenon in a postmortem study of twobrains with temporal cysts; he could not detect anyleft/right difference in brain volume or weight. It can,therefore, be concluded that there was no loss ofbrain tissue. Consequently the cyst has to be theprimary developmental disorder with secondarydisplacement of the brain. This conclusion alsoexplains why, in the great majority of cases, no motordeficit, not even a shift of handedness, and nointellectual loss has been found in this series or inothers.3 4

Progressive symptoms suggestive of increased CSFpressure or brain shift are caused by a decompensa-tion of the intracranial contents, usually by subduralor intracystic bleeding. This complication occursmost frequently before the age of 20.4 Four suchpatients are included in this series (numbers 6, 7, 8,

9). The surgical therapy consists of releasing thehaematoma and removing the cyst. The results wereexcellent and comparable to those in the literaturelisted in table 3; only the series that specified theirresults according to complaints have been includedhere.Non-progressive symptoms such as headache or

epilepsy can occur with cysts uncomplicated bybleeding. Sometimes this is attributed to expansionof the cyst; a valve mechanism" or active secretion19has been suggested. An indirect argument forexpansion could be a large rounded cyst showingsigns of compression on the CT scan.22 Patients 4 and5 fulfil this radiological criterion. If expansion occurs

before birth, it should result in skull enlargement,possibly with some brain damage (patient 5). Aicardiand Bauman,' however, reported macrocrania of asevere degree without any neurological signs or

abnormalities in development, in accordance withthe conclusion that there is no loss of tissue.More often non-progressive symptoms are found

in patients with angular cysts without signs ofexpansion (patients 1-3). The cause of this has notyet been clarified. It has, however, been known forsome time that many cysts are in fact diverticula.Surgery has revealed an opening to the basalcisterns4 2 23 and on cisternography the cyst can beshown to fill with air,26 isotope'3 27 or

metrizamide.3 14 28 In these instances increasedintracystic pressure is unlikely to play a role.Nevertheless, operation has been reported to cause

relief of headache in three patients withdiverticula.'2-14 An explanation other than intracysticpressure could be a local change in the functions ofthe subarachnoidal space: (1) Disturbance of themechanical buffer for brain movement based on a

smooth redistribution of CSF and fine trabeculationwithin the subarachnoid space is certainly presentand could lead to abnormal traction and compres-sion. (2) Obliteration of the temporal subarachnoid

Table 3 Result of operation in patients with progressivesymptoms caused by haemorrhageAuthors No. of No. of Result

patients bleedingsAicardi and 2 2 1 goodBauman, 19755 1 sudden death

Smith andSmith, 19766 1 1 good

Leo et al, 19797 1 0 improvedHeimans et al,

19798 2 0 goodGalassi et al,

19803 12 7 goodAueretal, 19819 5 5 goodVarmaetal, 1981"' 6 6 goodThis series 4 4 good

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Table 4 Result ofoperation in patients withnon-progressive symptoms: headache

Authors No. of Result Durationpatients follow-up

Tiberin andGruszkiewicz, 196111 1 good 9 months

Torma andHeiskanen, 196212 2 good 1 and 7 years

Seur and Kooman, 197613 1 goodSmith and Smith, 19766 1 good 3 yearsHanda et al, 197714 1 good ?Anderson et al, 6 "good 8 months-

19791 results" 18 yearsLeo et al, 19797 1 "improved" ?This series 4 3 good 6-54 months

1 unchanged

space could also block the lateral CSF route to thesite of absorption with intermittent rises in CSFpressure as has been found with solid tumours.29 Katoet aP6 indeed found blockage of the lateral route intwo patients, and Stein27 even described an infantwith a diverticulum associated with communicatinghydrocephalus.The post-operative results of both groups, angular

cysts and round "expanding" cysts have been com-bined. Three of four patients who suffered fromchronic headache were cured. The one patient whodid not benefit from operation suffered fromlocalised headache over the cyst, but sometimesidentical pain on the other side. Two years after theoperation an open connection between the cyst andthe basal cisterns was demonstrated. In this case, it ispossible that the headaches were not related to thecyst.Two of three patients with epilepsy benefited from

operation. The third had an epileptic focus on theopposite side from the cyst. The epilepsy did notimprove but his chronic headache disappeared afterthe operation.

Previous studies have also shown that chronicheadache and epilepsy can be improved or cured byoperation (tables 3 and 4). One may argue that onlypositive results are published. The original authors,however, selected the patients in these tables not on

van der Meche, Braakman

the basis of non-progressive symptoms, but solely onthe existence of a cyst, irrespective of the presentingcomplaint. Therefore, the high rate of postoperativeimprovement suggested by the tables is probablyvalid. Further confirmation comes from our patients6, 7 and 9. They all had secondary haemorrhage afterminor trauma. In retrospect, they also had chroniccomplaints. In all three, these disappeared aftersome time. Non-progressive symptoms have there-fore a good prognosis after operation.Two different surgical approaches have been

advocated: removing the outer membrane andopening the inner membrane giving drainage to thebasal cisterns3 6 8 10 12 15 3034 and cystocardial or

cystoperitoneal drainage.26 35 36Since intracystic pres-

sure is not necessarily related to the symptoms,pressure regulation with drainage of the cyst does notseem to be a logical first choice. Restoration of CSFdynamics by removing the membranes should beeffective in all cases. Furthermore, the effectivenessof different operations should not be judged by thedisappearance of the cyst on the CT scan. Because ofthe early developmental displacement of the brain,one should expect a residual cyst after surgery. This isclearly demonstrated in figures la and b: afterremoval of the subdural haematoma the cyst even re-

expanded, while the patient became symptom-free.To summarise, the course of events may be as

follows: During development, a cystic arachnoidmalformation displaces the temporal lobe withoutany functional loss. Symptoms, if any, are caused (1)by secondary haemorrhage, (2) by expansion of thecyst, or (3) by disturbed CSF dynamics withoutincreasing intracystic pressure. Surgery should aim toevacuate the mass and restore the CSF dynamics;postoperatively, a residual cyst can be expected.

We thank G Blaauw, J van Dongen and J van Gijnfor their valuable comments, Mrs J Doornbosch forsecretarial help and Mrs BS Vollers-King forlanguage editing of the text.

Table 5 Result ofoperation in patients with non-progressive symptoms: epilepsyAuthors No. ofpatients Result Medication Duration follow-upRoger et al, 196416 1 good ? ?Vigouroux et al, 196617 2 good ?Bhandari, 197218 1 good -?Aicardi & Bauman, 19755 1 good ? 5 yearsSmith & Smith, 19766 1 good ? 5 yearsHeimans et al, 19798 1 improved + ?Galassie et al, 19803 5 improved + 6 months-9 yearsAuer et al, 19819 3 good + 1-3 yearsThis series 3 no change + 41 years

improved + 9 monthsgood - 6 months

good = free from fitsimproved = significant reduction of fits

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Arachnoid cysts in the middle cranial fossa: cause and treatment

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