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Table of Contents
Terms Used In This Article
acetazolamide - also known as Diamox; medicine used to lower elevated
ICP
idiopathic - due to an unknown cause
idiopathic intracranial hypertension (IIH) - condition where a person
suffers from elevated intracranial pressure with no visible cause
intracranial pressure (ICP) - the pressure of the cerebrospinal fluid
in the skull
lumbar puncture (LP) - procedure where a needle is inserted into the
CSF space of the lower back region; can be used to remove CSF or insert
drugs
papilledema - swelling of the optic nerve due to increased
intracranial pressure.
posterior fossa volume - measurement of the size of the posterior
fossa, which is the space in the back of the skull where the cerebellum is
situated
pseudotumor cerebri (PTC) - another name for idiopathic intracranial
hypertension; not used as much anymore
Common Chiari Terms cerebellar tonsils -
portion of the cerebellum located at the bottom, so named because of their
shape
cerebellum - part of
the brain located at the bottom of the skull, near the opening to the spinal
area; important for muscle control, movement, and balance
cerebrospinal fluid (CSF) - clear liquid in the brain and spinal
cord, acts as a shock absorber
Chiari malformation I -
condition where the cerebellar tonsils are displaced out of the skull area
into the spinal area, causing compression of brain tissue and disruption of
CSF flow
decompression surgery -
general term used for any of several surgical techniques employed to
create more space around a Chiari malformation and to relieve compression
syringomyelia -
condition where a fluid filled cyst forms in the spinal cord
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May 31st, 2009 -- Pseudotumor cerebri (PTC), also known as idiopathic
intracranial hypertension (IH) is a condition characterized by an increase
in intracranial pressure (the pressure of spinal fluid in the head) with no
apparent cause. The most common symptom is a pressure headache, with
other symptoms including double vision, visual blurring, nausea, vomiting,
dizziness, and ringing in the ears. The most serious symptom
associated with PTC is vision loss. The sustained pressure associated
with PTC can eventually damage the optic nerve - the bundle of fibers which
connect the eye to the brain - and if not treated can lead serious vision
problems.
A growing body of research has shown what appears to be
a strong link between Chiari and PTC. Specifically a high percentage
of PTC patients also have Chiari. In addition, PTC has been identified
as a possible cause of failed Chiari surgeries (Fig 1). It is not
clear, however, if PTC causes Chiari, if Chiari causes PTC, if decompression
surgery can cause PTC, or if any or all of the above can come into play for
a given patient.
It could be that the sustained increase in pressure
associated with PTC
eventually leads the cerebellum to herniate out of the skull and creates a
Chiari malformation. If this were the case, then decompression surgery
would help symptoms associated with direct compression of the malformation,
but would not relieve the symptoms associated with the elevated pressure of
PTC.
It may also be the case that the blockage caused by a
Chiari malformation, which we know can elevate the intracranial pressure,
may lead to a fundamental change in the CSF system and eventually PTC.
In this case, even though the region around the Chiari malformation is
decompressed surgically, for unknown reasons, the intracranial pressure
remains high.
A third possibility is that both Chiari and PTC are
manifestations of a more fundamental problem, such as a too small posterior
fossa (the skull region where the cerebellum sits). Perhaps some
people with a small or abnormally shaped skull develop PTC, while others
develop Chiari, and still others develop both.
Finally, it may be that Chiari surgery itself plays a
role in the development of PTC. There appear to be some cases where
symptoms associated with PTC don't appear until after Chiari surgery.
How, and even if, decompression surgery could lead to PTC is not at all
clear.
Since the cause of PTC is unknown, treatments tend to
focus on the symptoms and can involve drugs or surgery. Unfortunately,
to date there have not been any rigorous studies comparing the effectiveness
of drug treatments versus surgery.
On the medicine side, acetazalomide is commonly one of
the first drugs tried. It is believed to act by reducing the
production of cerebrospinal fluid and thus leads to a decrease in ICP.
If the acetazalomide does not work, it is sometimes supplemented with a
second medicine, furosemide. Recently, an anti-convulsant, topiramate,
has been reported to be used to treat PTC, but more research is
required to determine its effectiveness. In addition to treating the
symptoms with medicine, if the patient is obese, weight loss has been shown
to be an effective approach to alleviating symptoms.
On the surgical side, a shunt can be inserted to divert
CSF and lower the pressure in the head. While shunting is very
effective in relieving symptoms, a patient then has to deal with potential
problems related to having a shunt inside of them; namely mechanical
malfunction and infection. Such problems are not uncommon can lead to the need for
additional surgeries to revise or replace the shunt.
For a patient whose vision is at risk, a surgeon may
elect to decompress the optic nerve by perforating the sheath over the nerve
bundle. This reduces pressure on the nerve and according to published
reports is usually successful in stabilizing or improving visual function.
However, this type of surgery does not address the problem of elevated
pressure directly and relief from other PTC symptoms is not as great.
One approach to treating PTC which may be falling out
of favor is to repeatedly drain CSF through lumbar punctures. Draining
a large quantity of CSF in this way usually provides temporary relief from
symptoms, but again does not really address the underlying problem.
Overall, treatments for PTC are effective for a
majority of people. Research has found that 70% or more of patients
experience symptom relief or resolution within a couple months of starting
treatment. However, there does appear to be a subset of patients,
perhaps as many as 25%, for whom PTC becomes a long, difficult battle.
In addition, much like Chiari, recurrence of symptoms, even years down the
road, has been noted.
Although the exact mechanism which leads to the
increased pressure in PTC is not known, from an abstract point of view there
are several possibilities: increased production of CSF, abnormal
absorption of CSF, increased brain mass, and obstruction of blood outflow
from the brain. However, and somewhat surprisingly, research has
failed to consistently find any of the above to be the problem in PTC
patients. Interestingly, studies have shown an increase in resistance
to CSF flow (much like exists with Chiari) in 75% or more of PTC patients.
In terms of PTC related to failed Chiari surgery, in
several research publications, Dr. Bejjani has identified a sub-group of
patients for whom decompression surgery provides temporary relief of
symptoms, which then return after a period of weeks or months. Lumbar
punctures on these patients have shown that they have elevated ICP, which is
the likely reason that the symptoms came back after a period of time.
Again, it is not entirely clear if the PTC was present, but undetected
before surgery, as the symptoms of PTC overlap such much with Chiari
symptoms.
A recent publication from surgeons in India (Furtado et
al) in Child's Nervous System provides more evidence that PTC should be
considered in cases where Chiari surgery appears to succeed initially, but
then symptoms return after a short period of time. The publication
details the cases of a 12 year old girl and a 24 year old man who both
developed serious symptoms associated with PTC after Chiari surgery.
In the girl's case, six days after surgery, she began to have
trouble walking and had a severe headache with vomiting. There was no
evidence of a CSF leak, but a lumbar puncture showed that her ICP was indeed
elevated. Medication was used to lower her pressure and her symptoms
resolved.
One week after surgery, the man was taken to an
emergency room in a coma and struggling to breathe. There were
indications that his intracranial pressure was so high that the doctors
could not do a lumbar puncture. Again, medication brought the pressure
down, but not before it had caused bleeding in his brain.
Interestingly, the researchers used the two patients
MRIs to measure their posterior fossa volume and found them to be small,
even as compared to other Chiari patients. However, the precise
meaning of this finding is not clear.
Although pseudotumor is by no means the only reason for
which Chiari surgery can fail (as detailed by Dr. Bejjani), it should
definitely be considered when symptoms initially go away for a period of
time and then come back. This is yet another example of the importance
of researching and identifying patient sub-groups, so that they may get the
proper treatment and improve their outcomes.
-- Rick Labuda
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Key Points
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Pseduotumor Cerebri is a condition
where the pressure of CSF in the brain is chronically elevated for unknown
reasons
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PTC appears to be somehow linked to
Chiari as a high percentage of PTC patients have Chiari
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PTC could cause Chiari, Chiari could
cause PTC, Chiari surgery could cause PTC, or some combination of the three
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PTC has been identified as a
possible cause of failed Chiari surgeries
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Report details two cases from India
where patients developed PTC symptoms a week after Chiari surgery
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In both cases, medicine was able to
control the PTC
Figure 1: Possible
Reasons For Failed Surgery (From Presentation By Dr. Ghassan Bejjani)
Sources: Pseudotumor cerebri: as a cause for early deterioration
after Chiari I malformation surgery. Furtado SV, Visvanathan K, Reddy
K, Hegde AS. Childs Nerv Syst. 2009 Mar 19. [Epub ahead of print] Skau M, Brennum J, Gjerris F, Jensen R.
What is new about idiopathic intracranial hypertension? An updated review of
mechanism and treatment.
Cephalalgia. 2006 Apr;26(4):384-99
Related C&S News Articles:
Idiopathic Intracranial Hypertension aka
Pseudotumor Cerebri
Failed Adult Chiari
Surgery
More Evidence That Pseudotumor Cerebri Plays A
Role In Failed Chiari Surgeries
Trying to identify why surgeries fail
Treatment options after failed surgery
High Rate Of Chiari Found In Pseudo-Tumor Patients |