Benign intracranial hypertension is a condition wherein there is intracranial hypertension with no demonstrable mass or any other abnormality. Three names are in use today, pseudotumor cerebri, idiopathic intracranial hypertension and benign intracranial hypertension. 

It is a diagnosis of exclusion. There is no single test or procedure leading to the correct diagnosis of this syndrome.

Historically BIH was referred to, as brain swelling of unknown cause, otitic or toxic hydrocephalus, pseudoabscess, hypertensive meningela hydrops or serous meningitis.

Epidemiology: 

BIH is a rare disease.  There are no reliable epidemiological data.  It occurs in any age group including children and infants; but is most common in obese young females between 25 and 35 years of age.  The mean age at onset of symptoms is about 30 years. 80-90% is woman, and most of them are obese (mean weight 90 kg). Some studies suggest an annual incidence rate of 1 per 100,000.  In the high-risk group of obese woman in the reproductive age-group, the annual incidence rate is suggested to be about 20 per 100,000 people. 

Etiology: 

The etiology of BIH remains obscure.  Because of the different pathophysiology and prognosis BIH is considered separate from conditions producing symptoms identical to benign intracranial hypertension, such as chronic meningoencephalitis venous sinus thrombophlebitis, congestive intrathoracic lesions, polyradiculitis and spinal cord tumors.

The most consistent finding in patients with BIH is obesity (40-80% of all patients). Mostly a marked weight gain has been observed several months before the symptoms occurred.  Hormonal changing periods (menarche, pregnancy, oestrogen therapy) and signs of hormonal dysfunction (hypertrichiasis, sometimes galactorrhoea) are often associated with BIH.  Therefore it has been supposed that endocrine dysfunction may be a cause of BIH but up to now there is little supporting evidence.  Occasionally drugs are suggested to cause BIH, e.g. tetracycline, nalidixic acid or vitamin A (usually to treat acne in adolescents or young women).  Vitamin deficiency may also be involved in the development of BIH, especially vitamin A and B12. 

Pathophysiological considerations:

We know little about the pathophysiological mechanism leading to the symptomatology.

The pathophysiology of genuine BIH is still discussed controversially.  Increased brain water content, increased cerebral blood volume and increased outflow resistance to CSF have all been suggested.

Increased brain water content of about 4% was found in a study.  It is attributed to intracellular and/or extracellular swelling and leads to a decrease in craniospinal compliance which counteracts ventricular dilatation.  The increased brain water content renders the brain less compressible.  Thus there will be in case of increased resistance to CSF outflow a high pressure but no enlargement of the ventricles.  The result is a diminished total CSF volume and a ventricular size that is even smaller than normal.  In the pathophysiological concept of Malm  extracellular edema causes partial compression of the major venous sinus with consequent rise in sagittal sinus pressure as one mechanism for the development of increased CSF pressure. 

Increased cerebral blood volume (CBV), according to the current knowledge, is found in the majority of cases.  It is the result of cerebral vasodilatation or increased intracranial pressure, which leads to an increase in pressure in the veins traversing the sub arachnoid space with a consequent rise in total CBV. 

Increased resistance to outflow of CSF is according to the current pathogenic hypothesis the basic defect in the development of BIH. The increased resistance may be caused by congenitally fewer arachnoid absorptive channels or acquired structural changes in the arachnoid villi.  Now the symptoms of intracranial hypertension may develop by:                

 Further increase in resistance at the level of the villi (e.g. caused by steroid withdrawal, female sex hormone changes, pituitary-adrenal dysfunction, hypo para-thyroidism, tetracycline or nalidixic acid therapy), leading to interstitial brain water accumulation and elevation of CSF pressure.

 Intracellular brain water accumulation caused by agents or events interfering with membrane structure or function and brain water permeability (e.g. head injury, anemia, vasopressin, or other endocrine dysfunctions). 

Both mechanisms will bring about a rise in intracranial pressure until the CSF absorptive level for the new equilibrium of CSF dynamics is reached. 

In some, the BIH syndrome may represent a response to some exogenous factors and endogenous physiological alterations.

Such conditions include:

Intracranial venous drainage occlusion (mastoiditis and lateral sinus obstruction, paranasal sinus and phayngeal infections, congenital atresia or stenosis of venous sinuses, extracerebral mass lesions, head injury, polycythemia vera).

Cervical or thoracic venous drainage obstruction (intrathoracic mass lesions and postoperative obstruction of venous return).

Endocrine dysfunction (pregnancy, menarche, oral contraceptives, obesity, Addison's disease, hypothyroidism).

Hematological disorders (acute iron deficiency anemia, pernicious anemia, thrombocytopenia).

Vitamin metabolism (hyper/hypo vitaminosis A, vitamin D deficiency).

Reaction to drugs such as tetracycline, penicilin, sulfamethoxazole, indomethacin, nalidixic acid, and  prophylactic antisera.

Galactosemia, galactokinase deficiency, sydenham's chorea, sarcoidosis, and Turner's syndrome are some of the rarer associated conditions.  

Symptoms: 

Suggested criteria for BIH include, the  symptoms of increased intracranial pressure (ICP), papilledema and ICP values of more than 20 mmHg, and absence of focal neurological signs, except those typically for raised ICP, such as a sixth nerve palsy. There is no symptomatic epilepsy and no impairment of consciousness; normal composition of cerebrospinal fluid (CSF); no mass lesion or hydrocephalus on CT scan.

The typical clinical picture of BIH is that of a young or middle aged obese woman with headache and sometimes impaired vision. Dizziness, nausea, vomiting, tinnitus and hearing loss are occasional associated symptoms. rarely there is CSF rhinorrhoea. The symptoms of increased intracranial pressure are often intermittent but usually with a history of less than one year.  In contrast to space-occupying lesions the symptoms of patients with BIH are usually less pronounced.  In addition patients with BIH are characterized by greater daily variations of their complaints, i.e. every day they feel different.  Signs of lethargy, decreased activity or disturbances of consciousness are usually missing.  Patients with BIH often do not see the doctor until they suffer from marked visual impairment. 

Children present with diplopia due to 6th nerve paresis which is a secondary sign due to increased ICP.

In infants, progressive increase in the size of the head with bulging fontanels is is presenting symptom.

Diagnostic evaluation: 

BIH is a diagnostic syndrome and no single test leads to the correct diagnosis.

Fundi examination reveals papilledema. Neurological examination usually reveals no focal neurological signs except those which are typical for raised intracranial pressure such as  sixth nerve palsy (10%), slight gait disturbance and ataxia mostly due to dizziness. The  IIIrd and the Vth cranial nerve involvement and visual field defect can be observed rarely.

Chronic meningoencephalitis, venous sinus thrombophlebitis, congestive intrathoracic lesions, polyradiculitis and spinal cord tumors may produce symptoms identical to BIH.  These conditions must be ruled out before the diagnosis  of benign intracranial hypertension can be established.  

CT & MRI:

The symptoms of increased intracranial hypertension demand a CT or MRI to exclude a mass lesion or hydrocephalus.  The typical finding is a ventricular system of normal or diminished size (Evans ratio < 0.25 the width of the frontal horns divided by the maximum internal skull diameter).  Enlarged optic nerve sheaths can be observed on the computed tomograms of the orbit.  Attention must be paid to the patency of the sinus thrombosis and thus symptomatic intracranial hypertension.  In about 10-40% of patients with BIH an empty sella is diagnosed , and occasionally a neurodegenerative disease can be revealed.  CT or MRI must be performed before a lumbar puncture is considered. 

Lumbar puncture:

The examination of CSF is compulsory to exclude symptomatic forms of intracranial hypertension.  In BIH the typical findings are completely normal values of protein, glucose and cells.  The diagnosis requires the demonstration of significantly increased ICP > 20 mmHg.

Normally it is sufficient to measure ICP by Lumbar pressure measurement over a period of 30-120 min.  This minimally invasive procedure enables one to recognize steady state increased ICP and abnormal pressure waves.  In BIH lumbar pressure correlates very well with pressure values recorded on other sites, provided that a strictly flat lateral recumbent position is maintained.  If there is any doubt of the quality of the recorded pressure, other forms of pressure measurements with overnight recording of ICP must be used.   

Visual assessment:

Visual fields, intraocular pressure measurement, fundus photographs and visual acuity are performed, since the most serious sequel of BIH is permanent visual loss due to the chronic papilledema.  BIH is a cause of progressive visual loss in children and young adults.  

Papilledema (95% <10% unilateral, dioptres mostly ranging from 1.0 to 4.0), visual obscurations or blurring of vision (80%), double vision (20%), partial visual field loss (20%), enlarged blind spots (90%) and loss of central vision are common. The results of these investigations determine the therapeutic procedure and the urgency of treatment . 

Measurement of CSF outflow resistance (R): 

Provides specific diagnostic information in BIH. It can be performed by means of lumbar infusion.  Computerized infusion tests should be preferred to reduce duration and plateau pressure as well as to increase accuracy.  R is found to be increased up to 50 mmHG/min/ml.  Mean R ranges are 12 to 35 mmHg/min/ml.  However, there is no correlation between ICP and R. 

ICP recording: 

ICP overnight recording reveals an increased intracranial pressure (>15 mmHg) with plateau-waves in 30% of patients and B-waves in 90% of patients. There is also a suggestion of transient episodes of raised ICP due to nocturnal hypoxia and hypercarbia in some patients which may contribute to symptoms such as papilledema and visual failure. 

Management:

BIH is self limiting with no sequelae in most.

Management of patients with BIH should be based on the presence and progression of visual loss. 

BIH must be treated, if rapid or progressive visual impairment occurs.  Hence, treatment and follow-up must be performed together with an ophthalmologist.

Treatment is directed at the associated  cause, if any (such as steroids in Addison's, and iron in anemia).  Elimination of exogenous factors and endogenous physiological alterations, promptly gives relief.

Acetazolamide and/or  Frusemide is given for a period of 6-24 months to lower CSF production.

Steroids for about 2.4 weeks may be effective, but the bodyweight of obese young women is frequently increasing, so that it should not be recommended as a therapeutic measure of first choice. Many physicians question the role of steroids.

Drug therapy provides temporary improvement but fails in approximately one third of cases.  Despite all the measures above, impress upon the patient the necessity to lose weight.

Lumbar puncture is also only a temporary measure, but it can easily be performed to relieve the symptoms in the acute phase.  Furthermore it is compulsory for diagnostic evaluation, i.e. to exclude pathological composition of CSF as a possible cause of intracranial hypertension and to measure outflow resistance.

Shunting provides long lasting CSF pressure reduction.  It can be carried out as a lumboperitoneal shunt, or ventriculo-peritoneal/atrial shunt.

Decompressive procedures to prevent further visual loss are frequently needed.

Presently, optic nerve sheath decompression is the treatment of choice in patients with visual loss, but this does not alleviate the increased ICP or its other symptoms of increased ICP.  However it improves visual function in about 70% of all operated eyes in acute papilledema and 30% in chronic papilledema. Repeated optic nerve sheath decompression or optic nerve fenestration should be considered in cases of persistent recurring symptoms.

CSF draining into the orbit has been hypothesized as its mechanism of action. But orbit can not accommodate all the CSF. pulse pressure damping may have a role. resultant scarring around the nerve may protect the nerve; but this can not explain the improvement of the opposite nerve.  Sub temporal decompression is less commonly performed nowadays. Bilateral decompression may be required. It does not always prevent further visual loss, and may result in contra-lateral partial seizures, mostly beginning 6-12 months post-operatively.