Arachnoid cysts - Springer Link

Neurosurg. Rev, 21 (1998) 14-22

Arachnoid cysts: how do postsurgical cyst size and seizure outcome correlate? Christian A. Koch 1, J. Layne Moore 2, and Dieter Voth 3

Departments of 1Medicine and 2Neurology, Ohio State University Hospitals, Columbus, Ohio, USA, and Department of 3Neurosurgery, Johannes-Gutenberg-University Mainz, Fed. Rep. of Germany

Abstract Arachnoid cysts (ACs) are congenital cystic brain malformations associated with epilepsy. The purpose of this study was to determine the effect of surgical intervention of ACs on cyst size and seizure outcome. We reviewed the world's medical literature dealingwith surgically treated ACs in epilepsy patients. Our study included only cases, in which the relationship between pre- and postoperative CT-size of the AC and seizure outcome was described. We also includedsixpatients with ACs and epilepsy treated surgically at the University of Mainz. We analyzed postoperative AC size and seizure outcome with respect to mode of operation, cyst location, and patients' age. A total of 76 patients was reviewed. Sixty (79 % ) patients had a smaller AC postoperatively. Forty-six of those 60 (76.6 % ) experienced seizure improvement. Thirteen patients (21.6 %) remained unchanged and one patient (1.8 %) worsened. In 16 of the 76 patients (21%) the postoperative AC size was unchanged. Eight of those 16patients improved. Six patients (37.5 %) remained unchanged and two (12.5 %) worsened. A positive correlation between postoperative AC size and seizure outcome was well demonstrated among patients treated by cystfenestration,needle aspiration, or internal shunting. Among patients treated by cystoperitoneal shuntingthis direct correlation was less clear. Seizure outcome correlates directly with postoperative AC size. Seizure reduction is associated with decreased AC size postoperatively and depends on the mode of operation. Based on these data we would expect that patients with epilepsy secondary to ACs would demonstrate improved seizure control with lower AC volume. Conversely, we might expect increasing AC size to correlate with worse seizure control. This relationship may guide physicians in efficacy and timely patient management. Keywords: Arachnoid cyst, cyst fenestration, cystoperitoneal shunt, cyst size, epilepsy surgery, seizures.

© 1998 by Walter de Gruyter & Co. Berlin- New York

1 Introduction

Intracranial ACs are believed to be congenital malformations occuring in relation to an intracranial cistern, most commonly in the middle cranial fossa [23]. Origin, pathophysiology, symptoms, and therapy of these cerebrospinal fluid (CSF) filled brain cavities are controversial. ACs are now increasingly an incidental finding on neuroimaging and the relationship between these cysts and epilepsy and headaches has been challenged. Many reports exist about reduction of seizures and headaches in patients with ACs treated surgically [4, 34, 57]. We conducted the following study to determine the effect of surgical intervention of ACs on cyst size and seizure outcome. This information may influence the decision making in patient management.

2 Patients and methods

We reviewed the worldwide medical literature dealing with surgically treated ACs in epilepsy patients and included in our study only cases, in which the relationship between pre- and postoperative CT-size of the AC and seizure outcome was described. A total of 70 patients could be identified [7, 10, 13, 16, 24, 25, 27, 29, 33, 36, 38, 39, 43, 46-49, 53, 54, 56, 59, 60, 63]. We also included six patients with ACs associated with epilepsy, who were treated surgically at the University of Mainz between 1984 and 1992. Modes of operation in those six patients included cystoperitoneal shunting (CPS, 1 patient), needle aspiration (2 patients), and cyst fenestration (3 patients). The patients' age at surgery ranged from 3 years (yr) to 60 yr (mean 26 yr). There were three

Koch et al., Arachnoid cysts:postsurgical cyst size males and three females. All patients received preoperative scalp electroencephalograms (EEGs) which were normal in only one patient. Distinct EEG abnormalities were identified in five patients. The follow-up varied from 1 yr to 7 yr (mean 3.5 yr). We analyzed postoperative AC size and seizure outcome of all 76 patients with respect to mode of operation, cyst location and preoperative cyst size, and patient's age. Modes of operation consisted of cyst fenestration (32 patients), CPS (18 patients), needle aspiration (7 patients), internal shunting (6 patients), and others (13 patients) such as cyst fenestration combined with CPS (7 patients), cystoventriculo-shunt (2 patients), cystoatrial-shunt (1 patient), arachnoidplasty (1 patient), ventriculoperitoneal shunt (1 patient), and cysto-cisternal shunt (1 patient). All 76 patients had pre- and postoperative head CTs. Postoperative AC sizes were reported as decreased or unchanged. Only a few authors mentioned the precise preoperative cyst size, seizure type, EEG findings, and whether a communication between AC and subarachnoid space (SAS) existed [7, 16, 24, 25, 27, 39, 46, 47, 59, 60, 63]. Seizure outcome was reported as seizure freedom, improvement, no change, or deterioration. We simplified our outcome analysis by classifying seizure outcome into three categories: improvement, no change, and deterioration. The age range of the 76 patients was from 2 months (too) to 70 yr. Follow-up ranged from 4 mo to 11 yr. The gender of 19 patients was not reported. Of the remaining 57 patients, twenty-one were female and 36 male. In 16 patients no precise information about AC location was given. Thirty-four of the remaining 60 patients (57 %) had an AC in the middle cranial fossa (MCF). In 11 patients (18 %) the AC was at the convexity, in five patients (8 %) in the posterior cranial fossa, in four patients (7 %) suprasellar, and in six patients (10 %) interhemispherically.

3 Results

Sixty of the 76 patients (79 %) had a smaller AC postoperatively. Forty-six of those 60 patients (76.6 %) experienced seizure reduction. Thirteen patients (21.6 %) remained unchanged and one patient (l.8 %) worsened. In 16 of the 76 patients (21%) the AC size on postoperative CT was unchanged. Eight of those 16 patients improved. Six patients (37.5 %) remained unchanged and two (12.5 %) worsened. Neurosurg. Rev. 21 (1998)

15 Postoperative AC enlargement did not occur in any patient. Of the 54 patients who experienced seizure improvement postoperatively, forty-six (85 %) had a smaller AC. Eight patients (15 %) had an unchanged AC. The seizures of 19 patients remained unchanged. Thirteen of those 19 patients (68 %) had a smaller AC and six patients (32 %) an unchanged AC. Three patients of the 76 (4 %) worsened postoperatively. In one patient the AC was smaller and in two patients unchanged. A positive correlation between postoperative AC size and seizure outcome was well demonstrated among patients treated by cyst fenestration (Table I). In patients treated by needle aspiration of the AC the direct relationship between postoperative cyst size and seizure outcome was best shown, although the study size was small (Table II). An association between cyst size and seizure outcome also appears in patients treated by internal shunting, although not as clearly as in the group treated by needle aspiration (Table III). Postsurgieal cyst size and seizure outcome correlated least clearly among patients treated by CPS (Table IV). Among the procedures listed as "other procedures", a positive correlation seems demonstrated in patients treated by fenestration in combination with CPS (Table V). The precise preoperative AC size was reported in 22 patients. We stratified those patients according to preoperative cyst size. Those with cysts 3 cm and smaller were analyzed separately from those with cysts larger than 3 cm. We then compared pre- and postoperative cyst size to seizure outcome for both groups. Fourteen patients had a preoperative AC smaller than 3 cm. Eleven of these patients improved with nine patients (90 %) having postoperatively a smaller AC and two having an unchanged AC. Three patients remained unchanged. Two of them had a smaller AC and one an AC unchanged in size. Eight patients had a preoperative AC larger than 3 cm. All eight patients improved postoperatively with seven (88 %) having a smaller AC and one having an unchanged AC. Based on these data the correlation between postoperative cyst size and seizure outcome does not depend on the preoperative AC size.

16

Koch et al., Arachnoid cysts: postsurgical cyst size

Table I. Cyst fenestration

Table VI. Fenestration of MCF ACs

Postoperative AC size on CT

Total

Seizures Improved Unchanged Worsened


Total


Decreased

26

18+2"

5+1"

-

Decreased

12

11

1

-

Unchanged

6

1

4

1

Unchanged

5

2

2

1

* = own patients Table VII. Cystoperitoneal shunting of MCF ACs Table II. Needle aspiration Postoperative AC size on CT

Total


Decreased

5

4+1"

-

-

Unchanged

2

1"

1

-

* = own patients


Total


Decreased

5

4

1

-

Unchanged

1

1

-

-

Table IV.. Cystoperitoneal shunting Total


Decreased

13

7

6

-

Unchanged

5

4+1"

-

-

*= own patient Table V. Other procedures Postoperative AC size on CT

Seizures Total Improved Unchanged Worsened

Decreased

11

6 FC+I CV 1A+1 Ci +1 VP

1 CV

Unchanged

2

-

1 FC

FC CV CA Ci A VP

= = = = = =

Total


Decreased

7

7

-

-

Unchanged

3

3

-

-

fenestration or CPS. Of the 32 patients treated by cyst fenestration, seventeen h a d an A C in the M C E

Table HI. Internal shunting



1 CA

Fenestration plus CPS Cystoventriculo-shunt Cystoatrial-shunt Cystocisternal-shunt Arachnoidplasty Ventrieuloperitoneal-shunt

Table V I a n d V I I illustrate the correlation b e t w e e n the postoperative size of middle cranial fossa ( M C F ) A C s a n d seizure o u t c o m e in patients t r e a t e d by cyst

O f the 18 patients treated by CPS, ten h a d a n A C in the M C F (Table VII). As previously mentioned, the positive correlation b e t w e e n postoperative cyst size and seizure o u t c o m e is b e t t e r d e m o n s t r a t e d in patients treated by fenestration t h a n in those treated by CPS. O f the 32 patients treated by fenestration, t h e patients' age was r e p o r t e d in 22 cases. Eleven patients were younger t h a n 21 yr a n d 11 were at least 21 yr old. Eight of the 11_patients (73 % ) younger t h a n 21 yr improved. Seven of those eight (88 %) h a d a smaller A C a n d one patient an u n c h a n g e d AC. O n e child worsened a n d h a d an u n c h a n g e d AC. Two children r e m a i n e d u n c h a n g e d while having a smaller A C postoperatively. Six of the 11 patients (55 %) older t h a n 20 yr improved. Five of those six (83 %) h a d a smaller A C a n d one patient an u n c h a n g e d AC. Five of the 11 patients (45 % ) r e m a i n e d u n c h a n g e d with two having a smaller A C a n d t h r e e having an u n c h a n g e d AC. T h e fenestration p r o c e d u r e could not be c o m p a r e d with CPS concerning younger a n d older patients, because CPS was p e r f o r m e d mainly in patients younger t h a n 21 ys. T h e patients' age was n o t rep o r t e d in one case of the 18 patients treated by CPS. Fifteen patients were younger t h a n 21 ys. Eleven of those 15 (73 % ) improved. Six of those 11 patients (55 %) h a d a smaller A C and five a n u n c h a n g e d AC. Four patients (27 %) r e m a i n e d u n c h a n g e d while showing a smaller A C postoperatively. Only two patients were older t h a n 20 ys.

Neurosurg. Rev.21 (1998)

Koch et al., Arachnoid cysts: postsurgical cyst size According to the above results there was a trend for patients younger than 21 ys. to have a better seizure outcome after treatment by cyst fenestration than those older than 20 ys. The positive correlation between postoperative cyst size and seizure outcome of patients younger than 21 ys. is better demonstrated after cyst fenestration than after CPS. 4 Discussion

The first described AC [11] had an intraarachnoidal location created by a duplication of the arachnoidea which was interpreted as embryonal malformation. The etiology of intracranial ACs, however, is in fact unclear. Many ACs are present at birth or in childhood [2, 3, 9] with some cysts showing a delay in the clinical presentation until adult life even as late as the seventh decade [21, 37]. A review of autopsies in newborns revealed an AC incidence of 0.17 % [1]. ROBINSON[51] reported ACs represented i % of allintracranial lesions. This is probably an underestimate, because current neuroimaging techniques are much more sensitive than those in the past. STARKMAN[55] defined ACs as closed compartments situated within the arachnoid and segregated from the subarachnoid space (SAS). ACs, however, may or may not communicate with the SAS [37] and may increase in size [6] even in the face of communication (which is in that case inadequate) while behaving like true cysts.

17 ture. Neurological symptoms usually correlate with cyst location and depend more on the rate of cyst growth than cyst size. However, even very slowly growing or small ACs can become s3qnptomatic by pressure on certain adjoining structures. ACs have been discovered in surgical specimens from patients undergoing resective surgery for medically refractory epilepsy (19, 20) and in autopsies from patients with intractable seizures [26, 41]. Seizure improvement in patients with surgically treated ACs occurred in ma W cases supporting the relationship between these cysts and epilepsy [34]. One goal of surgery is to reduce pressure and obstructive forces of ACs on adjoining structures. Another objective of surgery is to minimize complications of cyst rupture or hemorrhage [2].

4. A pulsatile pump mechanism in ACs which communicate with the SAS. Enlargement in this case occurs by pressure waves of venous origin during valsalva maneuver etc. [18, 64].

Of the numerous options for surgical treatment of ACs, craniotomy for cyst fenestration and CPS are most commonly used. Part of the controversy about whether to shunt or to fenestrate [48] is based on the postoperative cyst size. According to VAN DER MECHE [58] postoperative cyst size should not be a consideration in procedure choice. Many patients, however, improved postoperatively along with a reduction of cyst volume [3, 7,10,13,16, 23-25, 27, 29, 33, 36, 38, 39, 43, 45-49, 53, 54, 56, 59, 60, 63]. Only a few authors report the relationship between pre- and postoperative cyst size and seizure outcome [7,10,13, 16, 24, 25, 27, 29, 33, 36, 38, 39, 43,46-49, 53, 54, 56, 59, 60, 63]. Seizure types varied including partial, complex-partial, and generalized seizures. Although mainly associated with convex located ACs, seizures have also been described with atypical cyst locations such as suprasellar [27, 29, 47, 49], interhemispheric [13, 38], and posterior cranial f0ssa [7, 43, 47]. PUNZO [47] reported posterior fossa ACs which did not communicate with the SAS. The ideal procedure for patients with ACs and epilepsy remains uncertain. One successfull past approach consisted in removing as much as possible from the outer wall of the cyst and in creating an adequate communication with the ventricle and/or SAS to reduce epileptogenic irritation of the adjacent structures, mainly the cortex. A positive association is expected with postoperative seizure improvement and reduction of cyst volume or postoperative seizure deterioration along with cyst enlargement (Figure 1).

Only 5-9 % of ACs are reportedly asymptomatic [4, 23, 58]. However, symptomatic ACs may be overrepresented in the predominantly neurosurgical litera-

In this study the direct correlation between postoperative cyst size and seizure outcome was best demonstrated in patients treated by cyst fenestration. This

It is not yet understood, why ACs become symptomatic in different age groups. The following four mechanisms are postulated and may lead to AC enlargement: 1. Active secretion from the cyst wall [28] possibly exacerbated when the AC does not communicate with the SAS or when there is a coexisting 2. Slit-valve mechanism between the AC and the SAS allowing easier ingress into than egress from the cyst [5,12, 32, 52]. This principle may support the theory about the congenital origin of ACs. 3, An increase in the osmotic gradient of the cyst fluid [21, 65].

Nem-osurg. Rev. 2I (2[998)

18

Koch et al., Arachnoid cysts: postsurgical cyst size Figure 1A. Head CT of a 28-yr-old man with a left temporal AC (8 x 6 x 6 cm). The patient suffered right sided Jacksonian motor seizures treated unsuccessfully with phenytoin, then by fenestration of the cyst with postoperative seizure improvement. B. Postoperative head CT of the same patient showing a reduction in cyst size.

Figure 2A. Head CT of a 43-yr-old woman with a right frontal AC (5 × 3 x 3 cm). She suffered generalized seizures treated unsuccessfully with phenytoin, then by fenestration of the AC with subsequent seizure-freedom for 1.5 years. Then, however, she developed complex-focal seizmes. B. Postoperative head CT of the same patient showing a reduction in cyst size.

finding may be partly due to a more efficient procedure and/or lower rates of complications with fenestration compared with CPS or other techniques. Shunt malfunction and infection are well described complications [3, 9, 29, 33, 38, 45, 48]. No data about postoperative complications in the present study of 76 patients were available in 11 cases. Malfunction and/or infection occurred in four of the 18 patients (22 %) treated by CPS. This may partly explain, why the direct correlation between postoperative cyst size and seizure outcome in the shunt group was least clear. Conversely, of the 32 patients treated by cyst fenestration, only two (6 %) suffered postoperative complications.

Figure 3. Head CT of a 19-yr-old man with a left frontal AC (6 × 5 x 3 cm). The patient suffered generalized seizures treated successfully by phenobarbital. (From Ref 35: KOCHCA, JL MOORE,JA ROt3YN:Intracranial arachnoid cysts. Hospital Physician, Vol. 33, August 1997 pp 52-59 1997, with permission "Copyright Turner White Communications, Inc.")

Arachnoidplasty [54] which consists of a cyst fenestration foltowed by reclosing the outer cyst wall to prevent CSF leakage, demonstrated a good result and also a clear positive correlation between postoperative cyst size and seizure outcome. This is unexpected with respect to the previously mentioned postulated pathophysiology for A C enlargement. Neurosurg. Re,z21 (1998)

19

Koch et al., Arachnoid cysts: postsurgical cyst size Table VIII. Seizure outcome and AC size in medically treated patients Author

EEG findings Seizuretype

Seizureoutcome

AC size

Follow-up

BELTRAMELLO 14 yr, m 1985 [8]

Age/gender Location L temporal

Diffuse abnormalities

Generalized

Free on phenobarbital

Decreased

5 yr

WESTER 1991 [62]

21 yr, m

L sylvian

Abnormal changes at age 4

Partial since childhood

Deterioration*

Decreased*

10 yr

PUNZO 1992 [47]

26 yr, m

R temporal communication (C)

ND

ND

Improved

Unchanged

6 yr

MOKRI 1994 [42]

40 yr, f

R frontal, 0 6 cm

Grade I Partial d y s r h y t h m y motor L, ca. 2 X/week

Initially seizure reduction, then freedom on phenytoin/ mephobarbital

Decreased 3 yr after AC was discovered

11 yr

KocH, present study

19 yr, m

Normal L frontal, O 5 crn, no communication (MRI)

Seizure-free for 2 yr on phenobarbital, then for 4 yr without medication

Unchanged

6 yr

Generalized

L Left m = male R = right f = female O = diameter yr = years C = by cisternography ND = no data available * = patient had for 7 years an unchanged AC and unchanged seizures;he then developedworsening seizures in association with a decreasing AC over a short period with finally improving seizures (WEsTERhypothesizes a recent cyst rupture as explanation)

Also surprisingly, a direct correlation between postoperative cyst size and seizure o u t c o m e is well demonstrated in patients treated by needle aspiration or internal shunt. However, small study sizes may limit validity of those observations. It appears necessary to remove at least part of the cyst wall to reduce the potential of cyst growth and of epileptogenic forces. A s expected a n d shown for patients treated by cyst fenestration, seizure o u t c o m e depends on the patients' age at surgery T h e earlier (epilepsy) surgery is performed, the b e t t e r the seizure o u t c o m e [40]. However, the direct correlation between cyst size and seizure o u t c o m e seems age-independent. The p h e n o m e n o n of early postoperative seizure imp r o v e m e n t followed by late seizure worsening in the face of reduction of cyst volume may be explained by the creation of a new surgically induced epileptogenic focus such as postoperative scar formation (Figure 2). This may influence the interpretation of the correlation b e t w e e n cyst size and seizure outcome. Limitations of our retrospective study include bias by heterogeneity This applies mainly for different Neurosurg. Rev.21 (1998)

follow-up periods varying from 4 m o to 11 yr. Also, cyst location was heterogeneous. We tried to limit this factor by subdividing into patient groups with the same cyst location such as middle cranial fossa. Modes of operation differed. We therefore analyzed each m o d e separately T h e same accounts for the patients'age. Thus, we divided patients into two groups, one group consisting of patients younger t h a n 21 yr, and one c o m p o s e d of patients at least 21 yr old. A n o t h e r source of bias may b e the quality of published studies selected for this paper. It is unclear w h e t h e r authors selected only patient groups with more successfull o u t c o m e for publication. Unfortunately, patients with ACs treated medically for epilepsy are rarely d o c u m e n t e d a n d n o t available for comparison with the surgical group. In review of the literature only four patients could be identified, in which the relationship between A C size on followup CTs and seizure o u t c o m e was r e p o r t e d [8, 42, 47, 63]. We added one of o u r own patients (Figure 3). Four of the five patients improved over a follow-up period between 5 a n d 11 yr (Table VIII). T h e patient r e p o r t e d by WESTER [62] improved finally along with cyst reduction. It remains unclear, w h e t h e r a micro-

20

Koch et al., Arachnoid cysts: postsurgical cyst size MRI q 1 yr or 1,2

enlarged AC

unchanged AC [

SZ worse

surgicaltx

unchanged

improved

SZ worse

medical tx with MRI q 6 me 1

surgical tx

~im~pro

unchanged

smaller A ~ ved

medical tx with MRI q 1 yr

SZ worse

surgicaltx

unchanged

medical tx with MRI q I yr

improved

medical tx with MRI q 2 y r z

if no SZ improvement after 2 yr medical tx, consider surgery

Figure 4. Algorithm for management of patients with ACs and epilepsy. AC = Arachnoid cyst; SZ = seizures, tx = treatment; q = every, yr=year(s) trauma and subsequent cyst rupture with cyst drainage into the SAS occurred in some cases [42] as it has been shown in other patients with spontaneous diminution or disappearance of an A C [17, 31,44, 61, 66]. Based on the presented data we recommend the following approach for patients with ACs associated with epilepsy (Figure 4): Treatment should first be conservatively with annual MRIs. If there is no enlargement of the A C or exacerbation of symptoms, medical treatment should extend over a period of two years. In the case of medical intractability, surgical treatment of the A C should be considered on an individual basis. If enlargement of the A C on M R I follow-up exams is noted without clinical deterioration, medical therapy should be continued, but M R I follow-up exams shortened to every six months, because of the potential risk of cyst rupture and subdural hematoma. Rarely, a situation may arise with worsening seizures in the face of decreasing cyst volume. This case may require surgical intervention. On the other hand, pa-

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Acknowledgment: This article is dedicated to JAMIE A. ROBYN,MD, PhD. We thank DEBRA S. MASSUROS for her secretarial assistance. Remarks: This paper has been presented as a poster at the 50th Meeting of the "American Epilepsy Society", San Francisco, December 10, 1996, at the 1997 AANS Annual Meeting in April, Denver, Colorado (Board Number 1241), and also at the llth International Congress of Neurological Surgery, July 10,1997, in Amsterdam, Netherlands, and was published as an abstract in EPILEPSIA, Vol. 37, Suppl 5, 1996.

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