Although Arachnoid Cysts are actually Congenital in
origin and not really Tumors, we have included
them among the Benign lesions since they can become major
intracranial "Space Occupying Lesions" that cause
symptoms by virtue of their size and compression of normal
Brain just as happens with many of the other lesions included
in this section.
Arachnoid Cysts 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
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
- 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
- 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 recommended.
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
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 costs.
Videos of these
procedures are available on this website.
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This page last edited on 2/19