1. science
2. medicine
3. surgery

CHAPTER 3
Thomas Westermaier,* Tilmann Schweitzer and Ralf‑Ingo Ernestus
Department of Neurosurgery, University of Wuerzburg, Wuerzburg, Germany
*Corresponding Author: Thomas Westermaier—Email: [email protected]‑wuerzburg.de
Abstract:
Arachnoid cysts are fluid‑filled duplications or splittings of the arachnoid layer with
a content which is similar but not equal to the cerebrospinal fluid. Arachnoid cysts
are not actual neurodegenerative disorders, rather the underlying defect of the texture
of the arachnoid layer is probably congenital in nature. They can occur sporadically
or can be associated with other malformations or diseases. Arachnoid cysts may be
discovered in early childhood. However, they can develop de novo, grow or decrease
in size. They may be diagnosed by ultrasound screening in the fetal period or be
discovered during childhood or adulthood. Many arachnoid cysts are asymptomatic.
Treatment strategies are discussed controversially. If they are diagnosed
incidentally or are correlated with only very mild symptoms, a conservative
management with follow‑up imaging may be favored. If they grow, they can cause
headaches, seizures or other neurological symptoms and require neurosurgical
treatment. This chapter addresses aspects of pathogenesis, clinical symptoms,
indication for neurosurgical treatment and treatment options.
INTRODUCTION
Cystic malformations of the arachnoid layer had first been reported about 180 years
ago.1 In 1979, the English anatomist Cunningham published an autopsy report on a young
acromegalic patient who had died from diabetes insipidus. He described the coincidence
of a right hemispheric arachnoid cyst (AC) with a pituitary adenoma.2 During the opening
of the cyst, a “large quantity of sero‑sanguilent fluid escaped”. This autoptic finding and
a previous episode of strong headache, suggested intracystic hemorrhage. In the first half
of the 20th century, after X‑ray and cerebral angiography had been introduced, further
reports on this pathological entity were published.3 Since this time, the nature and most
favorable treatment of these space‑occupying lesions has been discussed controversially.
Neurodegenerative Diseases, edited by Shamim I. Ahmad.
©2012 Landes Bioscience and Springer Science+Business Media.
37
©2011 Copyright Landes Bioscience. Not for Distribution.
ARACHNOID CYSTS
38
NEURODEGENERATIVE DISEASES
Cystic fluid retentions within the arachnoid layer, which may develop secondary to
intracranial hemorrhage or meningitis, have to be differentiated from true, primary AC.
In addition, they have to be distinguished from other cystic lesions which involve the
outer part of the cerebral cortex and the meninges, like glioependymal cysts or cystic
lesions of infectious or neoplastic origin.4,5 True AC are benign lesions and considered to
be developmental or at least based on a congenital mistake of the arachnoid architecture.
It has to be noticed that, particularly in the area of the skull‑base and the Sylvian
fissure, arachnoid septations of varying strength are woven through the subarachnoid
space. A variety of inner arachnoid membranes can be defined which physiologically
form the subarachnoid cisterns.6
Ultrastructurally, AC walls are similar to the normal arachnoid membrane. Analyzing
operatively resected AC walls, by light and electron microscopy, Miyagami and Tsubokawa
found that the inner surface of the AC wall consisted of one or several layers of arachnoid
cells with slender processes and large extracellular spaces.7 Rengachary and Watanabe
observed structural differences from the normal arachnoid: (1) the splitting of the arachnoid
membrane at the margin of the cyst, (2) a thicker layer of collagen in the cyst wall, (3) the
absence of traversing trabecular processes within the cyst and (4) the presence of hyperplastic
arachnoid cells in the cyst wall, which presumably participate in collagen synthesis.8
The pathogenesis of AC is still not entirely known. Meningeal tissue is of
mesectodermal origin and derives from the neural crest. AC, as well as meningeomas,
may be located intraventricularly, which indicates that mesectodermal tissue may be
dislocated into the neural tube during the folding of the latter, which begins around
embryonic day 20. A network of mesenchymal cells develops between the brain and
the epidermis and eventually differentiates into a dense outer layer and a reticular inner
layer to form the meninges. The inner layer further differentiates to form the dura mater
and the leptomeninges.9
The improvement of ultrasound technology and the practice of routine prenatal
ultrasound diagnostic provided new insight regarding the time of appearance of AC, their
in utero development and the co‑incidence with other brain malformations. Intracranial
cysts now can be detected as early as in the first trimester of pregnancy.10 AC may occur
together with anomalies of the corpus callosum,11 Chiari malformations,12 skeletal
malformations,13 and complex vascular malformations.14 Furthermore, they may appear
in the frame of syndromes and genetic disorders such as neurofibromatosis Type 1,15
Pallister‑Hall‑Syndrome or Aicardi’s syndrome.4 Their frequent occurrence in early
childhood, histological features with absent postinflammatory or posthemorrhagic changes
and the occurrence together with genetic disorders strongly suggest a developmental
nature. Therefore, it is the current opinion that AC are congenital malformations.
However, this opinion has recently been challenged. In children and adults, temporal
and Sylvian location is highly predominant16,17 while in a prenatal analysis most AC
are located interhemispherically and temporal AC are extremely rare11 (Table 1). This
observation raises some doubt on the hypothesis that the formation of AC is strictly
congenital. This might be confirmed by the observations, that they may develop de novo
in adults,18 may grow over time and, the cyst size on first diagnosis is larger with increasing
age.19 In fetuses, the subarachnoid spaces covering the temporal lobes are very deep.
Under normal circumstances, these spaces regress in size from the end of gestation until
the first few months of life. It may be hypothesized that any peri‑ or postnatal event, such
©2011 Copyright Landes Bioscience. Not for Distribution.
Pathogenesis
ARACHNOID CYSTS
39
Table 1. Distribution of arachnoid cysts
Supratentorial
Middle fossa
Interhemispheric
Hemispheric
Suprasellar
Skull base
Intraventricular
Infratentorial
CPA
Hemispheric
Other
Tentorial incisure
Prenatal (n = 54)11
Pediatric (n = 67)16
Elderly (n = 23)17
34
1
16
1
5
7
5
12
1
1
10
8
31
13
9
5
4
20
11
31
1
22
8
5
3
9
Distribution of arachnoid cysts discovered by (a) routine ultrasound screening in pregnancy, (b) in
children and (c) in patients older than 65 years. Arachnoid cysts rarely become symptomatic in old patients.
Published cases were collected and reviewed by Caruso et al.17 One of the infratentorial cysts was located
within the fourth ventricle causing symptoms of normal pressure hydrocephalus. The differences in the
distribution between pre‑ and postnatally diagnosed arachnoid cysts is apparent. Arachnoid cysts in the
middle cranial fossa do practically not appear in the prenatal period but make up the majority of lesions
in the pediatric and adult age. On the contrary, the predominant localization in prenatal diagostics is
interhemisheric. These lesions are less frequently found in infants and rare in adults.
as even minor hemorrhage or inflammatory processes, could lead to the formation of a
cyst by inhibiting this process of regression.11
In summary, most reports suggest that there is at least a congenital mistake in the
texture of the arachnoid layer. Minor irregularities of the developing CSF flow through
the mesenchymal network can result in a splitting of the developing arachnoid in the fetus.
The development or filling of these arachnoid pockets, however, seems to be dynamic
and further changes can occur at any stage of life.
NATURAL BEHAVIOUR OF ARACHNOID CYSTS
The knowledge about the spontaneous behaviour of AC is not only essential for
assessing the indication for surgical treatment but also, in case of prenatal diagnosis, in
order to counsel parents on the further course of pregnancy. Pierre‑Kahn et al thoroughly
analyzed the outcome of 56 fetuses in whom AC were diagnosed by routine ultrasound
screening. In that study, 55% of the cysts were diagnosed between gestational week 20
and 30 and 45% after gestational week 30. Interestingly, the latter had normal ultrasound
examinations between week 20 and 30, supporting that AC are developing dynamically.
After their detection, serial follow‑up ultrasound and MRI examinations were performed.
In utero, the cysts grew in 20% of the cases, remained stable in 76% and decreased in 4%.
After delivery, the cysts grew in 24%, remained stable in 52% and decreased in 24%.11
Focussing on AC of the middle cranial fossa and the Sylvian fissure, Galassi
et al classified the lesions into three categories, class 1 and 2 representing small
and medium‑sized cyst with none or only little mass effect and a more or less open
©2011 Copyright Landes Bioscience. Not for Distribution.
Localization
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NEURODEGENERATIVE DISEASES
©2011 Copyright Landes Bioscience. Not for Distribution.
communication to the subarachnoid space. Class 3 represented voluminous cysts with a
distinct mass effect and dislocation of midline structures and no communication to the
subarachnoid space as assessed by intracisternal contrast application.20 (Fig. 1) Becker
et al found that only in class 3 cysts there is a positive correlation between the age at
which a patient becomes symptomatic and the size of the cyst. This observation suggests
that there is an obvious growth of these large lesions. Smaller lesions, however, do not
show a correlation of size and age at first admission.19 In the same study, a subgroup of
Figure 1. Coronar (T2 TSE) and transverse (T2 TIRM) MRI of a large left temporal/Sylvian anrachnoid
cyst of an 8‑year‑old boy. An asymmetric bulging of the skull was the only symptom of the otherwise
normally developed child who was not surgically treated.
ARACHNOID CYSTS
41
patients (11 patients) was not operated on but followed by CT‑scans. In 3 of these, the cyst
grew in follow‑up CT‑scans, 6 remained unchanged while 2 decreased in size. There are
several reports on a decreasing AC’s volume without surgical intervention. This may
occur during traumatic brain injury, allegedly by a rupture of the cyst wall with consecutive
drainage into the subarachnoid space. In some cases, however, spontaneous reduction
or even disappearance of AC has been observed without a history of head injury.21,22 In
summary, the spontaneous course of an AC is uncertain. This has a direct implication
for treatment decisions. If the finding is truly incidental or the symptoms are only mild, a
conservative management might be preferred at first to observe the further development.
In a number of patients, the therapeutical strategy changes with the growth of the
cyst. If this occurs, it may produce neurological symptoms. In 1964, Robinson reported a
different consistence of the content of the cyst and the normal cerebrospinal fluid.3 Berle
and coworkers systematically analyzed the intracystic fluid and found different contents
of phosphate, protein, ferritin and lactate dehydrogenase as compared to normal CSF.
Possible mechanisms of cyst‑growth, therefore, have to be consistent with these findings.23
A variety of mechanisms has been proposed. Active secretion by the cells of the cyst‑wall,
expansion following an osmotic gradient or a unidirectional valve‑mechanism may be
possible mechanisms.
Active Fluid Secretion
In an ultrastructural and cytochemical study, Go et al analyzed the resected walls of
AC. They observed similarities between the neurothelial lining of arachnoid granulations
such as intercellular clefts and sinusoid dilatations and desmosomal intercellular junctions,
pinocytic vesicles, lysosomal structures and a basal lamina. On the luminal surface, the
cyst wall is densely covered with microvilli, thus, suggesting active secretion.24 Enzyme
cytochemistry demonstrated Na‑K‑ATPase at the luminal plasma membrane and alkaline
phosphatase at the opposite membrane. This architecture might indicate fluid transport
towards the lumen. Different consistence compared to CSF may be explained by this theory.
Osmotic Gradient
The hypothesis that AC grow by osmotic gradients has been proposed due to the
minor differences of substance concentrations compared to CSF. A thin arachnoid wall
with loose connective tissue could allow a penetration of water. However, the formation
of an osmotic gradient has to be triggered. In secondary cysts, hemorrhage with products
of blood degradation or inflammatory reactions could act as osmotic triggers. In primary
AC, there is no evidence that these mechanisms exist.25
Valve Mechanism
Small and medium‑sized cysts have been found to remain constant in size and
to communicate readily with the normal subarachnoid space.19,20 In larger cysts or in
growing cysts, a valve‑mechanism may develop with unidirectional fluid transport. Under
©2011 Copyright Landes Bioscience. Not for Distribution.
MECHANISMS OF CYST‑GROWTH
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NEURODEGENERATIVE DISEASES
circumstances with a positive extra‑/intracystic pressure, the cyst may increase in volume.
In fact, valve‑like foldings of the cyst wall or intracystic membranes have actually been
observed during endoscopic or open operative procedures.26,27
Other Mechanisms Leading to Clinical Symptoms
CLINICAL SYMPTOMS
The clinical symptoms are determined by the location of the cyst. AC can occur at any
location in the cranium and spine where an arachnoid layer is present. In addition, they can
be found in the ventricular system. In this case, it has to be noted, that tight adherance to the
choroid plexus has been observed intraoperatively. It has been proposed that intraventricular
AC arise from arachnoid tissue which has been displaced into the ventricles by in‑growing
vascular mesenchyma at the time of formation of the choroid plexus.34‑37 The prevalence
of AC in a group of healthy adults has been found to be 1.1‑1.5%.38,39 Familial cases of
AC have been described with40,41 or without association to other hereditary diseases.42‑44 A
predominance of the male gender for temporal AC is highly significant while cerebellopontine
angle AC more often occur in females.45 To date, there is no firm explanation for this sex
distribution. Typical symptoms due to AC are described below.
Temporal and Sylvian Arachnoid Cysts
The middle fossa is the most common location of AC. In larger series of pediatric and
adult patients, approximately two third of them sustain AC in the middle fossa or in the
Sylvian fissure. Rarely, temporal AC are found bilaterally; these patients may suffer from
glutaric aciduria.46 In general, however, there is a predilection for the left hemisphere.45
Symptoms either result from a mass effect causing increased intracranial pressure or from an
irritation of the temporal or frontal cortex. Most often, these patients present with headache
and seizures as well as contralateral motor deficits.47,48 Developmental delay and retardation
are more common in patients with AC.48 An asymmetry of the skull may develop as well as
a facial asymmetry or exophthalmus due to a misdevelopment of the sphenoid ridge.3,49,50
There has been an ongoing debate about the association of temporal AC with
psychiatric disorders and neuropsychiological deficits. Various cases of psychiatric
disorders have been reported to be associated with AC. These include attention deficit
hyperactivity syndrome, depressions, hallucinations, dementia, schizophrenia, anorexia
nervosa, insomnia and other psychotic disorders. Some of those patients were surgically
treated for their AC and an improvement after surgery was reported in some cases.51
Systematic pre‑ and postoperative evaluation of cognitive function has been
performed by Wester et al. They found that many patients with left temporal AC show
©2011 Copyright Landes Bioscience. Not for Distribution.
Apart from symptoms due to an enlargement of the cyst, several other mechanisms
like spontaneous intracystic hemorrhage due to aneurysm rupture or traumatic brain
injury have been reported to cause clinical symptoms.28‑30 Patients with AC appear to be
prone to develop chronic subdural hematomas even after minor head trauma which can
make the previously asymptomatic AC clinically apparent.31,32 Clinical symptoms due to
a spontaneous or traumatic rupture of the cyst and consecutive formation of a subdural
hygroma have also been described.33
ARACHNOID CYSTS
43
significant deficits in various cognitive functions such as verbal perception, memory
function, complex verbal tasks, visuospatial functions and visual attention. These
deficits were, in fact, ameliorated in follow‑up neuropsychological testing after surgical
treatment. In many of these patients, however, these cysts did not cause complaints and
neuropsychololgical deficits had not been clinically apparent until specific testing had
been performed. These cysts can be interpreted as true incidental findings.
Intraventricular Arachnoid Cysts
Cerebellopontine Angle and Retrocerebellar Arachnoid Cysts
Infratentorial location accounts for approximately 10% of all AC. The majority of
these are located in the cerebellopontine angle or in retrocerebellar location.53,54 Symptoms
of retrocerebellar cysts include hydrocephalus and compression of cerebellar or brainstem
structures. Patients predominantly present with headaches or gait disturbances.
Figure 2. Intraoperative view after median suboccipital craniotomy and retraction of the cerebellar
tonsils. The inferior vermis was slightly incised to allow sufficient overview of the fourth ventricle.
A complex network of intracystic septations was found intraoperatively allowing free CSF flow after
complete resection of the cyst.
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Intraventricularly located AC are rare. They have been found in the lateral, third and
fourth ventricles (Fig. 2). Classically, these cysts become clinically apparent by development
of an acute or chronic hydrocephalus in case of increasing cyst size. Symptoms due to
a compression of the surrounding structures have also been reported. AC in the fourth
ventricle, for example, may cause cerebellar dysfunction27 or by depression‑like symptoms.52
44
NEURODEGENERATIVE DISEASES
Cerebellopontine angle AC may occlude the CSF circulation in the posterior fossa
and cause obstructive hydrocephalus. Cerebrllopontine angle structures may be directly
compressed or affected in terms of a neurovascular compression. Cranial nerve symptoms
may evolve, including hearing loss, trigeminal neuralgia, hemifacial spasm, diplopia,
hoarseness, dysphagia or diplopia.55‑61
Intra‑ and suprasellar AC arise in the basal subarachnoid space in close vicinity to
the optic nerve, pituitary gland and stalk, hypothalamus and mesencephalon. In case of
massive suprasellar extension, they may obstruct the physiological drainage of cerebrospinal
fluid at the level of the third ventricle or Foramen of Monroi, thus causing obstructive
hydrocephalus. Visual impairment may be caused by compression of the optic nerve and
endocrine disturbances by a compression of the pituitary gland or stalk. A compression of
hypothalamic structures may cause developmental abnormalities like precocious puberty.62
A bobble‑head doll syndrome with an involuntary back and forward movement of the
head at a frequency of 2‑3 per second may be due to a compression of third ventricle
structures or thalamic nuclei. It is a clinical feature highly suggestive for suprasellar AC.
However, this typical feature can only be found in a minority of these patients.
Spinal Arachnoid Cysts
Similar to cranial AC, spinal AC typically cause symptoms due to a compression
of the spinal cord and nerve roots. Myelopathic symptoms like ataxia, re‑appearance of
primitive reflexes or progressive paralysis may occur due to cord compression. Radicular
symptoms due to involvement of exiting nerve roots may include pain, sensory deficits
or weakness of the effector muscles (Fig. 3).
DIAGNOSTIC PROCEDURES
In many patients with intracranial and spinal AC, it is a challenging to evaluate the
indication for surgical treatment. The success of the treatment strategy is based on the
correlation of the lesion with the clinical symptoms. A detailed interview of the patient
or the patient’s parents and a thorough neurological examination are indispensable in
order to correlate signs and symptoms with the radiological finding. This particularly
counts for presumably incidental cysts.
If headache is the only symptom, its course should be documented and be brought
in line with the results of serial imaging studies, if a conservative and observing strategy
with follow‑up imaging studies is chosen. The studies of Wester et al have demonstrated
that patients with AC might have distinct cognitive deficits. In adult patients or older
children, a neuropsychological testing should be recommended in order to detect more
obscure clinical symptoms. Laboratory investigations for screening of glutaric aciduria
must be recommended in patients with bilateral AC.46 In fetuses with AC detected by
routine ultrasound screening, karyotype evaluation and fetal MRI should be performed
to rule out a possible association with other malformations.11
Electroencephalography is essential in patients with supratentorial AC in order to
determine the necessity for antiepileptic medication. In spinal AC a cord compression may
©2011 Copyright Landes Bioscience. Not for Distribution.
Supra‑ and Intrasellar Arachnoid Cysts
45
Figure 3. T2‑weighted sagittal (A) and axial (Th 8) (B) magnetic resonance images of a large spinal
arachnoid cyst in a 20‑year‑old female who presented with a progressive paraparesis. The spinal cord
is thinned and shifted anteriorly by the space occupying cyst. After hemilaminectomy, fenestration and
excision of intracystic membranes, the patient recovered completely.
be further evaluated by somatosensory and motor evoked potentials. Magnetic resonance
imaging (MRI) is the mainstay of radiological diagnostics. Due to their worse imaging
quality and because of X‑ray exposure, computed tomography scan (CTS) is, especially in
children, not acceptable as a diagnostic tool. Modern phase contrast MRI and functional
MRI are not only capable of demonstrating structural abnormalities but also able to depict
CSF‑flow patterns and functional organization of the brain respectively. Cisternography
with contrast filling of the subarachnoid space followed by CTS, sometimes at more than
one time‑point to evaluate the time‑course of contrast‑filling of CSF‑compartments, is
reserved for very few cases of diagnostic uncertainty.
©2011 Copyright Landes Bioscience. Not for Distribution.
ARACHNOID CYSTS
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NEURODEGENERATIVE DISEASES
As discussed above, the successful treatment of AC depends on a thorough patient
evaluation and determination of the appropriate treatment strategy. Rarely, patients present
with signs of an acute obstructive hydrocephalus or compression of vital structures caused
by an expansion of an AC requiring emergent decompression.52,63 Hemorrhage into an
AC, e.g., by rupture of an intracranial aneurysm, might be another emergent situation,
requiring rapid surgical intervention.28 The obvious association of AC with chronic subdural
hematomas necessitates evacuation of the hematoma but not primarily a treatment of
the asymptomatic AC.31 In contrast, subdural hygroma associated with an AC has been
reported to disappear by a therapy with acetazolamind, avoiding surgery.64,65 In cases of
progressive chronic hydrocephalus and focal neurological deficits like aphasia, motor
deficits, cranial nerve deficits, spinal cord compression, surgery is to be recommended if
the AC is the obvious cause of the respective deficit. Concerning epilepsy, the benefit of
surgery is not clear. Most patients seem to improve as the frequency of seizures decreases.
However, medical therapy might be as effective hence is the first choice of treatment.47
Headaches are the most frequent complaint of patients with an AC. However, the origin
of headaches is manifold and in many patients with headaches, AC must be regarded as an
incidental finding. The results of surgical treatment are discussed controversially. Some
authors are restrictive to operate on patients with headaches as the sole symptom,47 others
report very good results of surgery for headaches as the leading symptom.66,67 Headaches
might be a sign of an intermittent elevation of intracranial pressure. The diagnostic challenge
is the diagnosis of elevated ICP. In some patients, clear signs are visible on imaging studies.
In cases of doubt, invasive ICP monitoring might be performed as reported by di Rocco
et al.68 For patients with only moderate and infrequent headaches, responding to medication,
a non‑operative strategy is adequate since the fate of AC is uncertain and a decrease in
size is possible.19 Continuous follow‑up examinations with assessment of the course of
complaints, neurological symptoms and intake of analgetics are necessary in these cases.
In systematic assessment of cognitive functions, patients with AC have been found to
have reproducible deficits. Moreover, these deficits have been reported to improve after
surgical therapy.69 However, many of the patients assessed did not report specific subjective
complaints. A too aggressive surgical strategy bears the danger to impose operative risks on
the patient without improving the quality of life. In addition, the cysts may spontaneously
decrease in size. Similar to patients presenting with headaches, a follow‑up strategy may
be chosen including imaging studies, neurological and neuropsychological examinations.
TREATMENT
There are several options for treatment of AC. Resection of the cyst‑walls requires
open surgery. Fenestration of the cyst with creation of an opening to the subarachnoid
cisterns can be performed endoscopically or in an open microsurgical technique. Various
shunting techniques have been reported including cystoperitoneal and cystosubdural
shunts. There is an ongoing debate on the optimal surgical strategy. The form of treatment
which is individually chosen, depends on various factors: The patient’s symptoms, the
location and shape of the cyst, the extent of intracystic septations, the vicinity to relevant
neural and vascular structures and the surgeon’s experience with different techniques. For
patients without relevant symptoms and without related neurological deficits, observation
©2011 Copyright Landes Bioscience. Not for Distribution.
INDICATION FOR TREATMENT
ARACHNOID CYSTS
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©2011 Copyright Landes Bioscience. Not for Distribution.
may be recommended. If there is an indication for treatment, endoscopic fenestration can
be recommended as the treatment of first choice for many AC, in particular if there are
no relevant intracystic septations. For suprasellar arachnoid cysts, very good results have
been reported. Ventriculocystostomy and ventriculocystocisternostomy seem to be the most
successful long‑term treatment. Temporal and temporobasal AC appear to be more difficult
to be treated by endoscopic techniques.70 If there are intracystic septations or multiple fine
neural structures like in the cerebellopontine angle, the recurrence rate might be higher
if treatment only consists of cyst‑fenestration. Complete or near‑complete excision of the
cyst wall or adherences supplies the most successful treatment at this locations (Fig. 4).53
For small or medium‑sized temporal cysts, excision or fenestration supplies a good
chance of complete disappearance of the cyst and complete re‑expansion of the adjacent
temporal lobe. For large cysts, an only incomplete expansion of the adjacent brain has been
Figure 4. Preoperative (A) T2‑weighted sagittal MRI depicting a large septated arachnoid cyst in the
fourth ventricle containing multiple septations. Those were confirmed intraoperatively (see Fig. 4).
Brainstem structures are displaced anteriorly. The lateral ventricles appear slightly enlarged as compared to
postoperative imaging (B). Postoperative MRI shows a regular flow‑void in the aquaeductus mesencephali.
48
NEURODEGENERATIVE DISEASES
demonstrated. Additional shunt placement may be required.71 Shunting procedures are only
little invasive, supply good control of the cyst volumes by pressure‑controlled drainage,
but may have a relatively high recurrence and revision‑rate.72 Fenestration or excision
of the cyst may bear a higher operative risk, but leaves the patient shunt‑independent.
A long‑term success‑rate of 76‑90% has been reported for these ways of treatment.70,72
The necessity to treat and the choice of the optimal way of treatment have to be chosen
deliberately. All forms of treatment have more or less operative risks and recurrence
rates. Retreatment, again, imposes a recurrent treatment‑risk on the patient and patients
may eventually become discontented.
Arachnoid cysts are benign malformations of the arachnoid texture. They can occur
in any location in the cranium or spinal canal with an arachnoid layer. They can become
symptomatic by growth causing a mass effect or by intracystic hemorrhage. The clinical
symptoms mainly depend on the location of the cyst. With increasing availability of
diagnostic facilities, in particular MRI, many arachnoid cysts are discovered incidentally.
Therapeutically, endoscopic fenestration of the cyst, open resection of the cyst‑walls or
permanent drainage of the intracystic fluid via a cystosubarachnoid or cystoperitoneal shunt
are possible. The most challenging task is to evaluate the indication and the appropriate
way of surgical treatment.
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Conclusion
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