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Congenital anomalies are the product of errors in "embryogenesis"
(malformations consequent to errors in the developmental stages of the embryo)
or the result of intrauterine events that affect embryonic and fetal
growth (deformations and disruptions).
As a general rule, it is apparent that the more complex the formation of
a structure, the more opportunities for malformation. Some of the most serious
neurological abnormalities (e.g., anencephaly [no Brain], encephalocele
[part of the Brain is exterior to the Skull) develop in the first two months
of gestation and represent defects in neural tube (the embryonic precursor
of the entire central nervous system) formation. The medical term
for this is "dysraphia". Other defects (e.g., hydranencephaly,
porencephaly [conditions where the Brain is severely malformed]) occur
later and appear to be secondary to destructive processes after the Brain has
formed.
Modern investigative methods, such as amniocentesis and ultrasonography
may provide an accurate in utero detection of many malformations.
Genetic counseling for parents of a child with a major neurological
abnormality is important, since the risk of a subsequent child's having
such a defect is high. These parents frequently also need psychological
help and support. Women who have had a pregnancy resulting in an infant or
fetus with a neural tube defect should be advised that folic acid supplementation
(4 mg/day) before conception and during early pregnancy may substantially reduce
the risk of neural tube defects in subsequent pregnancies.
This section will elaborate on those abnormalities in which the Neurosurgeons
of Neurosurgical Consultants have a focused interest. Most of the other
abnormalities involve defects in Skull structure the majority of which are
managed by
Craniofacial Plastic Surgeons
and/or Pediatric Neurosurgeons.
Basilar impression: When the Base of the Skull and the Cervical Spine are
pushed too closely together.
Brainstem auditory evoked potential (BAER): An electrical test to examine
the hearing abilities of the Brainstem.
Brainstem: The base of the Brain which controls many basic functions such
as breathing, swallowing, eye movement and other basic functions.
CT (Computed Tomography) scan: A special type of radiograph ("x-ray")
which is especially useful to look at bone structure. It also shows the Brain
and Spinal Cord, but not in the detail that can be obtained with MRI.
Central Canal: A tubular cavity in the center of the Spinal Cord which
is normally not dilated.
Cerebellum: The portion of the Brain which is in the Posterior Cranial
Fossa. It is involved in coordination of all our movements.
Dura Mater: The leather-like covering over the surface of the Brain and
Spinal Cord.
Electroencephalogram (EEG): A test to evaluate the patterns of the Brain's
"electrical waves".
Electromyography (EMG): An electrical test used to evaluate the function
of different muscles, nerves, and groups of nerves. It is often combined with a
measurement of the Nerve Conduction Velocity (NCV).
Foramen Magnum: The opening at the Base of the Skull through which the
Spinal Cord passes.
Hydrocephalus: Often called "water on the Brain". In this condition, the
fluid spaces of the Brain (Ventricles) are larger than normal because of an
abnormal accumulation of the Cerebrospinal Fluid (CSF).
Hydromyelia: See Syrinx.
MRI (Magnetic Resonance Imaging): A study which uses sophisticated
technology and a magnetic field to produce high quality images of the Brain,
Spinal Cord or other body parts.
Myelogram: A test which involves a spinal puncture to inject dye into the
Cerebrospinal Fluid space around the Spinal Cord. This dye can be moved into the
Cervical Spine and Base of the Skull. Both plain x-rays and CT scans can be used
to help define problems in the spine.
Shunt: A tube system which drains Cerebrospinal Fluid (CSF) from
one space to another body structure.
A Ventriculo-peritoneal Shunt is created by placing a
special catheter into one of the Brain's Lateral Ventricles, connecting
it to a "one-way" pressure valve (a concept similar to the valve that
controls a "pressure cooker" used in food preparation) and then passing
beneath the skin towards the abdominal cavity where the "distal" portion
of the shunt catheter "floats" within the peritoneal space from which the
shunted CSF can be absorbed back into the circulatory system.
A Ventriculo-atrial Shunt is created by placing the "distal"
catheter through the Jugular Vein (in the neck) into the Right Atrium of
the Heart.
A Lumbar Subarachnoid-Peritoneal Shunt is used in some
unusual circumstances by placing the first ("Proximal")
portion of the Shunt into the subarachnoid space in the lower lumbar
region and passing it beneath the skin and inserting it into the
Peritoneal Cavity.
A Cyst-Peritoneal Shunt is used in conditions such as
Dandy-Walker Cyst
by placing the "Proximal" catheter into the cyst and draining that CSF
into the Peritoneal Cavity.
Somatosensory evoked potentials (SSEP): An electrical test that gives
some information about spinal cord function.
Spasticity: Increased tightness or tone in the arms and/or legs, making
the patient less flexible; the arms and/or legs seem stiff.
Syrinx (syringomyelia; hydromyelia): These terms all refer to an
abnormally dilated fluid filled cavity in the Spinal Cord.
Tonsils: The lower portion of the Cerebellum which can be pushed down
into the Cervical Spinal Canal in the
Arnold Chiari Malformation.
Ventricles: Fluid filled cavities within the Brain. The Cerebrospinal
Fluid (CSF) is made by a "gland-like" apparatus (the "Choroid
Plexus") lying within the Ventricle (about 2 pints each day) and
circulates through the Ventricles, over the surface of the Brain and Spinal
Cord and to then be reabsorbed into the Arachnoid Granulations (special
structures that drain into the Brain's veins.) If there is a blockage to
either the flow or reabsorbtion within the system, the fluid can build up
and cause Hydrocephalus.
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:
- Headache
- Nausea/vomiting
- Lethargy
- Seizures
- Mass protrusion in the skull
- Focal neurological signs secondary to pressure of surrounding structures
- Developmental delay
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:
- 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
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.
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 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
costs.
Videos of these procedures are
available on this website.
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This page last edited on 5/9
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