Arachnoid Cysts are congenital lesions that arise during Brain and Skull
development from a splitting of the Arachnoid membrane, one of the
covering layers of the Brain. This splitting results in the formation of a cyst.
Cerebrospinal Fluid (CSF), the fluid that bathes and protects the
Brain, circulates within the Subarachnoid space. With the
"splitting" of the Arachnoid membrane CSF appears to "flow" into the
split region forming the cyst since the CSF cannot escape the region
at the same rate that it enters the cyst. This process results in a slow
increase in the size of the cyst over a time frame that varies from one patient to
the next. As a consequence the Brain is slowly compressed.
Most Arachnoid Cysts become symptomatic in childhood. The
exact symptoms depend upon the location, size and rapidity of growth of the
cyst. These cysts can become quite large and yet only cause mild
symptoms. In many cases of "giant" Arachnoid cysts that are not identified until
adulthood, the increase in size is sufficiently slow and the compression of
adjacent Brain so gradual that symptoms do not develop until the Brain's capacity
to accommodate to any further compression/distortion is exhausted.
Unfortunately this is actually late in the course of the disease process.
Typical symptoms include:
Suprasellar Cysts (a variety of Arachnoid Cyst that lie above the
"Sella Turcica" - which is the bone compartment at the base of the skull that
houses the Pituitary Gland may have the following additional features:
- Mass protrusion in the skull
- Focal neurological signs secondary to pressure of surrounding structures
- Developmental delay
Almost all Arachnoid Cysts occur in relation to an Arachnoid Cistern
(anatomically named spaces within the subarachnoid system). The most
common locations are the Middle Cranial Fossa (near the Temporal
Lobe) and Suprasellar (near the Third Ventricle). However, cysts may be
found anywhere within the intracranial compartment, including the
Posterior Cranial Fossa.
Routine evaluation with CT or MRI scan is usually satisfactory.
CT Scans usually show a smooth bordered cystic mass composed of a density
similar to Cerebrospinal Fluid. There is no "enhancement" with
contrast administration. Expansion of the nearby bone by remodeling is usually
seen, confirming their chronic nature. MRI Scans demonstrate the CSF filled mass
together with its "mass" (or pressure) effect upon the Brain.
- Hydrocephalus due to obstruction of normal cerebrospinal fluid circulation
- Endocrine symptoms occur in up to 60% of patients (such as early
development of puberty)
- Head bobbing
- Visual impairment
Arachnoid Cysts that do not cause significant mass effect or symptoms
(Figures 3A & 3B), regardless of their size and location, generally do not
require treatment. If there is significant or severe mass effect on surrounding
structures, or if there are symptoms, then surgical treatment is
The following table summarizes the treatment options:
Arachnoid Cysts are an area of specific interest for the Neurosurgeons and
staff of Neurosurgical Consultants. Their successful treatment in most cases
involves the use, where applicable, of highly advanced
Minimally Invasive Microendoscopic Techniques.
This revolutionary concept in Neurosurgery greatly limits the amount of surgical
exposure required and therefore, limits the amount of tissue that is touched
and retracted during the operation. Most of these Endoscopic procedures are
conducted through very small holes in the Skull. This results in less
post-operative pain, earlier mobilization, diminished hospital stay, less risk
for complications, an earlier return to activities as well as lower overall
Videos of these procedures are
available on this website.
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This page last edited on 2/19