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Idiopathic intracranial hypertension

September 11, 2019


Idiopathic intracranial hypertension, sometimes
called by the older names benign intracranial hypertension or pseudotumor cerebri, is a
neurological disorder that is characterized by increased intracranial pressure in the
absence of a tumor or other diseases. The main symptoms are headache, nausea, and
vomiting, as well as pulsatile tinnitus, double vision and other visual symptoms. If untreated, it may lead to swelling of the
optic disc in the eye, which can progress to vision loss. IIH is diagnosed with a brain scan and a lumbar
puncture; lumbar puncture may also provide temporary and sometimes permanent relief from
the symptoms. Some respond to medication, but others require
surgery to relieve the pressure. The condition may occur in all age groups,
but is most common in women aged 20–40, especially those with obesity. Signs and symptoms
The most common symptom of IIH is headache, which occurs in almost all cases. It is characteristically worse in the morning,
generalized in character and throbbing in nature. It may be associated with nausea and vomiting. The headache can be made worse by any activity
that further increases the intracranial pressure, such as coughing and sneezing. The pain may also be experienced in the neck
and shoulders. Many have pulsatile tinnitus, a whooshing
sensation in one or both ears; this sound is synchronous with the pulse. Various other symptoms, such as numbness of
the extremities, generalized weakness, loss of smell, and loss of coordination, are reported
more rarely; none are specific for IIH. In children, numerous nonspecific signs and
symptoms may be present. The increased pressure leads to compression
and traction of the cranial nerves, a group of nerves that arise from the brain stem and
supply the face and neck. Most commonly, the abducens nerve is involved. This nerve supplies the muscle that pulls
the eye outward. Those with sixth nerve palsy therefore experience
horizontal double vision which is worse when looking towards the affected side. More rarely, the oculomotor nerve and trochlear
nerve are affected; both play a role in eye movements. The facial nerve is affected occasionally
–- the result is total or partial weakness of the muscles of facial expression on one
or both sides of the face. The increased pressure leads to papilledema,
which is swelling of the optic disc, the spot where the optic nerve enters the eyeball. This occurs in practically all cases of IIH,
but not everyone experiences symptoms from this. Those who do experience symptoms typically
report “transient visual obscurations”, episodes of difficulty seeing that occur in both eyes
but not necessarily at the same time. Long-term untreated papilledema leads to visual
loss, initially in the periphery but progressively towards the center of vision. Physical examination of the nervous system
is typically normal apart from the presence of papilledema, which is seen on examination
of the eye with a small device called an ophthalmoscope or in more detail with a fundus camera. If there are cranial nerve abnormalities,
these may be noticed on eye examination in the form of a squint or as facial nerve palsy. If the papilledema has been longstanding,
visual fields may be constricted and visual acuity may be decreased. Visual field testing by automated perimetry
is recommended as other methods of testing may be less accurate. Longstanding papilledema leads to optic atrophy,
in which the disc looks pale and visual loss tends to be advanced. Causes
“Idiopathic” means “of unknown etiology”. Therefore, IIH can only be diagnosed if there
is no alternative explanation for the symptoms. Intracranial pressure may be increased due
to medications such as high-dose vitamin A derivatives, long-term tetracycline antibiotics
and hormonal contraceptives. There are numerous other diseases, mostly
rare conditions, that may lead to intracranial hypertension. If there is an underlying cause, the condition
is termed “secondary intracranial hypertension”. Common causes of secondary intracranial hypertension
include obstructive sleep apnea, systemic lupus erythematosus, chronic kidney disease,
and Behçet’s disease. Mechanism
The cause of IIH is not known. The Monro-Kellie rule states that the intracranial
pressure is determined by the amount of brain tissue, cerebrospinal fluid and blood inside
the bony cranial vault. Three theories therefore exist as to why the
pressure might be raised in IIH: an excess of CSF production, increased volume of blood
or brain tissue, or obstruction of the veins that drain blood from the brain. The first theory, that of increased production
of cerebrospinal fluid, was proposed in early descriptions of the disease. However, there is no experimental data that
supports a role for this process in IIH. The second theory posits that either increased
blood flow to the brain or increase in the brain tissue itself may result in the raised
pressure. Little evidence has accumulated to support
the suggestion that increased blood flow plays a role, but recently Bateman et al. in phase
contrast MRA studies have quantified cerebral blood flow in vivo and suggests that CBF is
abnormally elevated in many patients with IIH. Both biopsy samples and various types of brain
scans have shown an increased water content of the brain tissue. It remains unclear why this might be the case. The third theory suggests that restricted
venous drainage from the brain may be impaired resulting in congestion. Many patients with IIH have narrowing of the
transverse sinuses. It is not clear whether these stenoses are
the pathogenesis of the disease or a secondary phenomenon or both. It has been proposed that a positive biofeedback
loop may exist, where raised ICP causes venous narrowing in the transverse sinuses, resulting
in venous hypertension, decreased CSF resorption via arachnoid granulation and further rise
in ICP. Diagnosis
The diagnosis may be suspected on the basis of the history and examination. To confirm the diagnosis, as well as excluding
alternative causes, several investigations are required; more investigations may be performed
if the history is not typical or the patient is more likely to have an alternative problem:
children, men, the elderly, or women who are not overweight. Investigations
Neuroimaging, usually with computed tomography or magnetic resonance imaging, is used to
exclude any mass lesions. In IIH these scans typically appear to be
normal, although small or slit-like ventricles, dilatation and buckling of the optic nerve
sheaths and “empty sella sign” and enlargement of Meckel’s caves may be seen. An MR venogram is also performed in most cases
to exclude the possibility of venous sinus stenosis/obstruction or cerebral venous sinus
thrombosis. A contrast-enhanced MRV scan has a high detection
rate for abnormal transverse sinus stenoses. These stenoses can be more adequately identified
and assessed with catheter cerebral venography and manometry. Buckling of the bilateral optic nerves with
increased perineural fluid is also often noted on MRI imaging. Lumbar puncture is performed to measure the
opening pressure, as well as to obtain cerebrospinal fluid to exclude alternative diagnoses. If the opening pressure is increased, CSF
may be removed for transient relief. The CSF is examined for abnormal cells, infections,
antibody levels, the glucose level, and protein levels. In IIH, by definition all of these are within
their normal limits. Occasionally, the CSF pressure measurement
may be normal despite very suggestive symptoms. This may be attributable to the fact that
CSF pressure may fluctuate over the course of the normal day. If the suspicion of problems remains high,
it may be necessary to perform more long-term monitoring of the ICP by a pressure catheter. Classification
The original criteria for IIH were described by Dandy in 1937. They were modified by Smith in 1985 to become
the “modified Dandy criteria”. Smith included the use of more advanced imaging:
Dandy had required ventriculography, but Smith replaced this with computed tomography. In a 2001 paper, Digre and Corbett amended
Dandy’s criteria further. They added the requirement that the patient
is awake and alert, as coma precludes adequate neurological assessment, and require exclusion
of venous sinus thrombosis as an underlying cause. Furthermore, they add the requirement that
no other cause for the raised ICP is found. In a 2002 review, Friedman and Jacobson propose
an alternative set of criteria, derived from Smith’s. These require the absence of symptoms that
could not be explained by a diagnosis of IIH, but do not require the actual presence of
any symptoms attributable to IIH. These criteria also require that the lumbar
puncture is performed with patient lying sideways, as a lumbar puncture performed in the upright
sitting position can lead to artificially high pressure measurements. Friedman and Jacobson also do not insist on
MR venography for every patient; rather, this is only required in atypical cases. Treatment
The primary goal in treatment of IIH is the prevention of visual loss and blindness, as
well as symptom control. IIH is treated mainly through the reduction
of CSF pressure and, where applicable, weight loss. IIH may resolve after initial treatment, may
go into spontaneous remission, or may continue chronically. Lumbar puncture The first step in symptom control is drainage
of cerebrospinal fluid by lumbar puncture. If necessary, this may be performed at the
same time as a diagnostic LP. In some cases, this is sufficient to control
the symptoms, and no further treatment is needed. The procedure can be repeated if necessary,
but this is generally taken as a clue that additional treatments may be required to control
the symptoms and preserve vision. Repeated lumbar punctures are regarded as
unpleasant by patients, and they present a danger of introducing spinal infections if
done too often. Repeated lumbar punctures are sometimes needed
to control the ICP urgently if the patient’s vision deteriorates rapidly. Medication
The best-studied medical treatment for intracranial hypertension is acetazolamide, which acts
by inhibiting the enzyme carbonic anhydrase, and it reduces CSF production by six to 57
percent. It can cause the symptoms of hypokalemia,
which include muscle weakness and tingling in the fingers. Acetazolamide cannot be used in pregnancy,
since it has been shown to cause embryonic abnormalities in animal studies. Also, in human beings it has been shown to
cause metabolic acidosis as well as disruptions in the blood electrolyte levels of newborn
babies. The diuretic furosemide is sometimes used
for a treatment if acetazolamide is not tolerated, but this drug sometimes has little effect
on the ICP. Various analgesics may be used in controlling
the headaches of intracranial hypertension. In addition to conventional agents such as
paracetamol, a low dose of the antidepressant amitriptyline or the anticonvulsant topiramate
have shown some additional benefit for pain relief. The use of steroids in the attempt to reduce
the ICP is controversial. These may be used in severe papilledema, but
otherwise their use is discouraged. Venous sinus stenting
Venous sinus stenoses leading to venous hypertension appear to play a significant part in relation
to raised ICP, and stenting of a transverse sinus may resolve venous hypertension, leading
to improved CSF resorption, decreased ICP, cure of papilloedema and other symptoms of
IIH. A self-expanding metal stent is permanently
deployed within the dominant transverse sinus across the stenosis under general anaesthesia. In general patients are discharged the next
day. Patients require double antiplatelet therapy
for a period of up to 3 months after the procedure and aspirin therapy for up to 1 year. In a systematic analysis of 19 studies with
207 cases, there was an 87% improvement in overall symptom rate and 90% cure rate for
treatment of papilloedema. Major complications only occurred in 3/207
patients. In the largest single series of transverse
sinus stenting there was a 11% rate of recurrence after one stent, requiring further stenting. Due to the permanence of the stent and small
but definite risk of complications, most experts will recommend that patients with IIH must
have papilloedema and have failed medical therapy or are intolerant to medication before
stenting is undertaken. Consultation with a neurologist, neurophthalmologist
and/or ophthalmologist in combination with a neurointerventionalist who performs the
procedure is generally recommended. Surgery
Two main surgical procedures exist in the treatment of IIH: optic nerve sheath decompression
and fenestration and shunting. Surgery would normally only be offered if
medical therapy is either unsuccessful or not tolerated. The choice between these two procedures depends
on the predominant problem in IIH. Neither procedure is perfect: both may cause
significant complications, and both may eventually fail in controlling the symptoms. There are no randomized controlled trials
to guide the decision as to which procedure is best. Optic nerve sheath fenestration is an ophthalmological
operation that involves the making of an incision in the connective tissue lining of the optic
nerve in its portion behind the eye. It is not entirely clear how it protects the
eye from the raised pressure, but it may be the result of either diversion of the CSF
into the orbit or the creation of an area of scar tissue that lowers the pressure. The effects on the intracranial pressure itself
are more modest. Moreover, the procedure may lead to significant
complications, including blindness in 1–2%. The procedure is therefore recommended mainly
in those who have limited headache symptoms but significant papilledema or threatened
vision, or in those who have undergone unsuccessful treatment with a shunt or have a contraindication
for shunt surgery. Shunt surgery, usually performed by neurosurgeons,
involves the creation of a conduit by which CSF can be drained into another body cavity. The initial procedure is usually a lumboperitoneal
shunt, which connects the subarachnoid space in the lumbar spine with the peritoneal cavity. Generally, a pressure valve is included in
the circuit to avoid excessive drainage when the patient is erect. LP shunting provides long-term relief in about
half the cases; others require revision of the shunt, often on more than one occasion—usually
due to shunt obstruction. If the lumboperitoneal shunt needs repeated
revisions, a ventriculoatrial or ventriculoperitoneal shunt may be considered. These shunts are inserted in one of the lateral
ventricles of the brain, usually by stereotactic surgery, and then connected either to the
right atrium of the heart or the peritoneal cavity, respectively. Given the reduced need for revisions in ventricular
shunts, it is possible that this procedure will become the first-line type of shunt treatment. It has been shown that in obese people, bariatric
surgery can lead to resolution of the condition in over 95%. Prognosis
It is not known what percentage of people with IIH will remit spontaneously, and what
percentage will develop chronic disease. IIH does not normally affect life expectancy. The major complications from IIH arise from
untreated or treatment-resistant papilledema. In various case series, the long-term risk
of ones vision being significantly affected by IIH is reported to lie anywhere between
10 and 25%. Epidemiology On average, IIH occurs in about one per 100,000
people, and can occur in children and adults. The median age at diagnosis is 30. IIH occurs predominantly in women, especially
in the ages 20 to 45, who are four to eight times more likely than men to be affected. Overweight and obesity strongly predispose
a person to IIH: women who are more than ten percent over their ideal body weight are thirteen
times more likely to develop IIH, and this figure goes up to nineteen times in women
who are more than twenty percent over their ideal body weight. In men this relationship also exists, but
the increase is only five-fold in those over 20 percent above their ideal body weight. Despite several reports of IIH in families,
there is no known genetic cause for IIH. People from all ethnicities may develop IIH. In children, there is no difference in incidence
between males and females. From national hospital admission databases
it appears that the need for neurosurgical intervention for IIH has increased markedly
over the period between 1988 and 2002. This has been attributed at least in part
to the rising prevalence of obesity, although some of this increase may be explained by
the increased popularity of shunting over optic nerve sheath fenestration. History
The first report of IIH was by the German physician Heinrich Quincke, who described
it in 1893 under the name serous meningitis. The term “pseudotumor cerebri” was introduced
in 1904 by his compatriot Max Nonne. Numerous other cases appeared in the literature
subsequently; in many cases, the raised intracranial pressure may actually have resulted from underlying
conditions. For instance, the otitic hydrocephalus reported
by London neurologist Sir Charles Symonds may have resulted from venous sinus thrombosis
caused by middle ear infection. Diagnostic criteria for IIH were developed
in 1937 by the Baltimore neurosurgeon Walter Dandy; Dandy also introduced subtemporal decompressive
surgery in the treatment of the condition. The terms “benign” and “pseudotumor” derive
from the fact that increased intracranial pressure may be associated with brain tumors. Those patients in whom no tumour was found
were therefore diagnosed with “pseudotumor cerebri”. The disease was renamed “benign intracranial
hypertension” in 1955 to distinguish it from intracranial hypertension due to life-threatening
diseases; however, this was also felt to be misleading because any disease that can blind
someone should not be thought of as benign, and the name was therefore revised in 1989
to “idiopathic intracranial hypertension”. Shunt surgery was introduced in 1949; initially,
ventriculoperitoneal shunts were used. In 1971, good results were reported with lumboperitoneal
shunting. Negative reports on shunting in the 1980s
led to a brief period during which optic nerve fenestration was more popular. Since then, shunting is recommended predominantly,
with occasional exceptions. References External links
Idiopathic intracranial hypertension at DMOZ

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