Arachnoid Cysts178

7/10/59Nicholas M. Wetjen

Marion L. Walker

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

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

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

Epidemiology

• 90 % supratentorial space

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

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

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

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

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.

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

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.

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

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

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

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

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

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

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

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

Treatment alternative

• Conservative• Surgery

Conservative

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

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

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

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