Youmanns

1. Arachnoid Cysts
178
7/10/59
Nicholas M. Wetjen
Marion L. Walker

2. Outline
• Epidemiology
• Pathology
• Embryology
• Clinical presentation
• Imaging
• Treatment alternative

3. Arachnoid Cysts
• Benign
• Non-neoplastic
• Extra-axial
• Intra-arachnoid lesions filled with fluid similar to or exactly like
cerebrospinal fluid
• 60% to 80% discovered in children
• Male-to-female : 2 : 1

4. Arachnoid Cysts
• Primary arachnoid cysts
• congenital cysts
• loculated, compartmentalized, or freely communicating with the surrounding
CSF cisterns
• Secondary arachnoid cysts
• result of another condition : meningitis, trauma, or hemorrhage
• signs of previous inflammatory changes : gliosis or hemosiderin
• cyst fluid may be xanthochromic, proteinaceous, or hemorrhagic

5. Epidemiology
• 90 % supratentorial space

6. Pathology
• Appearance
• membranes of the cyst : delicate, filmy, translucent
• islands of mesenchymal cells,meningoepithelial cell positive for epithelial
membrane antigen(EMA)
• underlying cortex is usually normal
• distinguishing features of the arachnoid cyst wall versus a
normal arachnoid membrane
• split of the arachnoid layer at the margin of the cyst
• the increased thickness of the collagen layer
• the absence of the cobweb-like trabeculations of normal arachnoid

7. Embryology
• Result from abnormal embryologic development of the
subarachnoid space
• 15 weeks’ gestation
• meninx primitiva, or perimedullary mesh : precursor to the pia mater
and arachnoid
• the rhombic roof ruptures, CSF pulses through this mesh, and the pia
mater and arachnoid separate incompletely

8. Clinical Presentation
• Headache : local mass effect
• High intracranial pressure (ICP)
• Hydrocephalus
• Asymptomatic throughout life
• Infants : macrocephaly, enlarged tense fontanelle, and splayed sutures with
irritability, failure to thrive, and developmental delay

9. Supratentorial Arachnoid Cysts
• Unilateral headache in the supraorbital or temporal region that may
be exacerbated with physical exertion
• Focal, complex-partial, or generalized seizures
• Arachnoid cysts of middle fossa and sylvian fissure
• Arachnoid cysts of parasellar intra-arachnoid
• Arachnoid cysts of the cerebral convexities
• Arachnoid cysts of the Interhemispheric
• Arachnoid cysts in the quadrigeminal cistern

10. Middle fossa and sylvian fissure cysts
• Type I
• small, lenticular, biconvex collections
• located at the anterior pole of the middle fossa directly posterior to the
sphenoid ridge
• communicate freely with the adjacent cisterns
• little associated mass effect
• do not have associated calvarial deformities
• do not require treatment.

11. Middle fossa and sylvian fissure cysts
• Type II
• Larger triangular- or quadrangular-appearing cysts
• Involve the proximal to mid aspect of the sylvian fissure with a medial border
along the margin of the insula
• They are less likely to communicate with adjacent basal cisterns with delayed
contrast uptake on cisternography
• More likely than type I cysts to require treatment

12. Middle fossa and sylvian fissure cysts
• Type III
• Large, rounded cysts that involve the entire length of the sylvian fissure
• Marked mass effect and midline shift with thinning, scalloping, and expansion
of the middle fossa cranial bones (thinning of temporal squama or
displacement of the wings of the sphenoid bone) or splaying of cranial
sutures in younger children.
• They usually do not have communication with adjacent cisterns and often
require surgical treatment.

14. Parasellar intra-arachnoid cysts
• Suprasellar
• common, almost exclusively in children
• hydrocephalus by extending into the third ventricle and obstructing the
aqueduct of Sylvius
• visual abnormalities, including hemianopia or decline in acuity. Gait ataxia
and opisthotonos
• bobble-head doll syndrome
• Endocrinopathy
• Precocious puberty
• growth hormone deficiency
are the most common

15. Parasellar intra-arachnoid cysts
• Intrasellar
• uncommon
• typically present in the fourth or fifth decade of life
• headache,visual abnormalities or endocrinopathy
• Ddx : craniopharyngioma or Rathke’s cleft cyst

16. Other type
• Arachnoid cysts of the cerebral convexities
• headaches or seizures
• Arachnoid cysts in the quadrigeminal cistern
• Hydrocephalus, Progressive macrocephaly
• Parinaud’s syndrome, nystagmus, hearing deficits
trochlear nerve palsy, and apneic spells

17. Other type
• Interhemispheric cysts
• often associated with agenesis of the corpus callosum
• macrocephaly and asymmetric growth of the calvaria
• increased ICP, developmental delay,
• hypertonia or hypotonia, hemiparesis
• ocular changes, and epilepsy

18. Infratentorial Arachnoid Cysts
• tinnitus, vertigo, facial weakness, facial sensory loss, hearing loss, or ataxia
• trigeminal neuralgia and hemifacial spasm
• obstructive hydrocephalus
• ataxia, nystagmus
• cranial nerve dysfunction
• progressive quadriparesis
• Ddx : mega cisterna magna
Dandy-Walker malformation
epidermoid cyst, and large cystic tumors

19. Imaging
• Plain radiographs
• nonspecific thinning and deformity of the adjacent bone
• Angiograms
• show shifts of the adjacent vasculature and venous phase
• Ultrasound
• prenatal ultrasound has detected arachnoid cysts as early as 13 weeks’
gestation
• sonolucent with enhanced transmission of the ultrasound beam through the
collection and are thus hypoechogenic to surrounding brain

20. Imaging
• CT
• sharply circumscribed, smoothly marginated lesions
• arachnoid cyst walls are so thin that they are not visible on CT and not
enhance, whereas the walls of cystic tumors may be visible
• the fluid of an arachnoid cyst is identical to CSF
• CT with intrathecal or intraventricular injection of metrizamide can
simultaneously provide anatomic detail of the subarachnoid and
intraventricular space
• communicating arachnoid cysts : cyst fills with metrizamide, but the clearance of
contrast from the cyst is delayed
• noncommunicating cysts : no early entry of contrast into the cyst (2 to 6 hours), but
contrast accumulates around the cyst

21. Imaging
• MRI
• better detection of smaller cysts and cysts adjacent to bony structures
• DWI : differentiate epidermoids from arachnoid cysts
• Electrocardiogram-gated cine-mode MRI sequences : demonstrate
communication between intracranial arachnoid cyst and CSF spaces

22. Treatment alternative
• Conservative
• Surgery

23. Conservative
• asymptomatic patients
• middle fossa arachnoid cysts : Chronic subdural hemorrhage 
surgery
• Single FU 6-8 wk for rule-out any change

24. Surgery
• Increased ICP or hydrocephalus
• Headache : most common in sylvian fissure arachnoid cysts

25. Surgery
• Craniotomy for Cyst Excision and Fenestration
• with or without marsupialization as the first-line approach
• Shunt Placement
• craniotomy and cyst fenestration subsequently required cystoperitoneal
shunting for either cyst recurrence or no improvement in symptoms
• patients with arachnoid cysts and associated hydrocephalus may require
ventriculoperitoneal shunts in addition to cystoperitoneal shunts
• ventricular decompression may increase the risk for subdural hematoma :
High-pressure valves or flow-control valves to avoid drainage
• Neuroendoscopic Management

27. Intraspinal Arachnoid Cysts
• Congenital lesions
• Associated with vertebral anomalies, neural tube defects,
syringomyelia, and trauma
• Most commonly thoracic
• Compression of the spinal cord, nerve roots, or cauda equina and
become symptomatic
• Surgical decompression