Incidence of Chronic IH
The Incidence of Chronic Idiopathic Intracranial Hypertension (IIH)
The incidence of chronic idiopathic intracranial hypertension for the general population is approximately 1 in 100,000. However, the incidence of chronic IIH for overweight women, 20-40 years old, is 20 in 100,000. By comparison, the incidence rate for invasive cervical cancer for the same group of women is only 9 in 100,000.
The Incidence of Chronic Secondary Intracranial Hypertension (SIH)
The incidence of chronic secondary intracranial hypertension (SIH) is not currently known because SIH is often recorded under a different diagnosis since no medical code exists for this form of chronic intracranial hypertension. It is also commonly misdiagnosed and has many causes, some confirmed and others unconfirmed.
IH and Related Disorders
IH and Chiari Malformations
A Chiari (kee-ar-ee) malformation is a neurological condition in which an area at the back of the brain, known as the cerebellar tonsils, is pushed down beyond the bottom of the skull into the spinal canal. As a result, the tonsils can physically block the circulation of cerebrospinal fluid in the sub-arachnoid space surrounding the brain and spine, and may cause secondary intracranial hypertension and other serious problems.
A Chiari Malformation
A Chiari malformation is often congenital. However, there is evidence that, over time, sustained increased intracranial pressure may cause an acquired Chiari malformation. While an acquired Chiari malformation can also be the result of overdrainage from an LP shunt or multiple spinal taps, some research suggests that an acquired Chiari malformation is eight times more common in chronic IH patients who have not had shunting procedures.
Additionally, for unknown reasons, certain people with congenital Chiari malformations develop chronic intracranial hypertension, even after neurosurgery (surgical decompression) to remedy any obstruction to CSF circulation.
There are many questions that need to be answered about the relationship between chronic intracranial hypertension and Chiari malformations. Does chronic intracranial hypertension play a role in the development of acquired Chiari malformations? What biological mechanism leads to increased intracranial pressure? With research, the answers to these questions can be found.
IH and Hydrocephalus
There is considerable confusion regarding intracranial hypertension and hydrocephalus. Both are disorders of abnormal cerebrospinal fluid dynamics. In other words, something goes wrong with the normal cycle of CSF production, absorption and drainage in both IH and hydrocephalus.
Intracranial pressure is determined by the three main components within the skull —brain tissue, blood and CSF— working together. Under normal circumstances, these three components maintain a dynamic equilibrium. In order for this balance to be maintained, it is believed that CSF, which is produced at approximately .3 cc per minute, must also exit the skull at the same rate.
However, since the skull is a fixed container, made of bone that cannot expand, changes in the volume of any one of these three components leads to abnormal intracranial pressure. Intracranial hypertension in adults is defined as CSF pressure at 250mmH2O or above. In chronic IH, the exiting (or egress) of CSF is thought to be impaired while simultaneously the CSF productions continues, which leads to elevated intracranial pressure.
In hydrocephalus, the ventricles (four small cisterns located within the brain) become enlarged and contain an excess of CSF. As part of the normal cycle of CSF production, CSF circulates through the ventricles before passing into the sub-arachnoid space surrounding the brain. If obstruction to CSF flow occurs within the ventricular system, then the ventricles up to the point of obstruction will become pressurized, fill with cerebrospinal fluid and in time, become enlarged. This is known as obstructive hydrocephalus.
Non-obstructive hydrocephalus occurs after CSF has left the ventricular system uneventfully. But, in this case, the CSF is either restricted in its flow over the brain surface (the sub-arachnoid space) or at the site of exiting or absorption (similar to chronic IH.) One question remains particularly puzzling: Why is there no ventricular enlargement in chronic IH (unlike non-obstructive hydrocephalus), if both disorders have the same site of absorption or CSF egress that is not adequately functioning?
IH and Hormonal Birth Control
There are many questions when it comes to hormonal birth control and chronic IH. While other side-effects and contraindications have been well-documented, the relationship between IH and hormonal birth control is still being examined. However, one form of hormonal birth control, levonorgestrel (Norplant), has been identified as a cause of secondary IH.
Estrogen, a common hormone in many birth control pills, has been linked to an increased risk of blood clots and is contraindicated in women with a history of blood clots or congenital thrombophilia. Cerebral blood clots (cerebral venous thrombosis) are a known cause of secondary IH, though more study is needed to determine whether estrogen also increases the risk of secondary IH through other mechanisms beyond clot formation.
IH and Pregnancy
Is pregnancy safe for me? What if my symptoms get worse when I’m pregnant?
Can I take medication during my pregnancy?
Since chronic IH strikes many young women, the issue of pregnancy can be complex. But it’s important to remember that each woman is an individual and her experience is uniquely her own.
Some women with chronic IH have uneventful pregnancies. Others have found that their symptoms became worse during their pregnancies, while still others have reported that their symptoms were better.
Pregnancy can also be a time when the symptoms of intracranial hypertension first appear. In certain cases, the disorder resolves or goes into remission after delivery. The sudden weight gain that accompanies pregnancy and its subsequent weight loss could be an important clue but more research is needed to determine the exact relationship between pregnancy and chronic intracranial hypertension.
Diamox (acetazolamide) is officially classified as a Class-C drug, which means its safety for use during pregnancy has not been established. However, many physicians have reported the use of Diamox to treat IH symptoms after the first 20 weeks of pregnancy. A limited amount of published medical literature suggests that Diamox may be safe even if used earlier, but additional information is needed to answer this question. Surgery is not usually a preferred treatment option because of the use of general anesthesia.
Most importantly, if you have chronic IH and are considering pregnancy, speak with your physician or physicians. Most physicians believe pregnancy in IH patients is a manageable situation. With their guidance, you will be able to make the best decision about pregnancy and your health.
Idiopathic IH and Weight
Idiopathic intracranial hypertension is sometimes characterized as a disorder affecting overweight women of childbearing age. The relationship between weight and elevated intracranial pressure is not known, though in many cases of IIH, losing weight helps reduce papilledema and sometimes, induces a remission. This is why weight reduction is very important for those who are overweight and have IIH. However, in some people, weight loss does not make a difference. So while weight can be a significant factor in IIH, it is clearly not the only factor. This is further reflected in the fact that only a small percentage of all obese women (and even fewer obese men) develop the disorder.
Additionally, if a person is not overweight or a young woman, an IIH diagnosis should not necessarily be dismissed. IIH has been found, though less frequently, in men and women of all body types, ages and races. In cases of IIH in children under ten, weight and gender are not significant factors.
It is also important to note that in secondary IH, unlike IIH, obesity, gender, age and race are not factors. Physicians should never rule out chronic IH–idiopathic or secondary–based on gender or body type.
IH and Blood Clots
Cerebral blood clots (also known as cerebral venous thrombosis) are a cause of secondary intracranial hypertension. A clot can be the result of an injury, head trauma, a blood-clotting disorder, or even the use of certain medications, including oral contraceptives containing estrogen.
Blood-clotting abnormalities have been documented in a number of women with chronic idiopathic intracranial hypertension. These women tend to share other common characteristics including the diagnosis of polycystic ovary syndrome (PCOS) and being overweight and insulin-resistant. This group could hold important clues to the biological mechanism behind chronic intracranial hypertension and merits more investigation.
It’s important to rule out cerebral venous thrombosis as a cause of secondary intracranial hypertension. Magnetic resonance imaging (MRI), especially Magnetic Resonance Arteriograms (MRA) and Magnetic Resonance Venagrams (MRV), provide detailed pictures of the head and brain’s blood circulation. Cerebral angiography (venography) measures the degree of narrowing or obstruction in a particular vein, vessel or artery. Common treatments of cerebral blood clots include the use of blood-thinning drugs (anti-coagulation therapy) and in some cases, the use of stents and balloon angioplasty.
Is Chronic IH Genetic?
Genes play a role in many diseases and disorders. Identifying whether chronic intracranial hypertension has a genetic component is of great interest to researchers since it could illuminate why this disorder occurs and spur the development of targeted treatments. It would also explain why some people are susceptible to chronic intracranial hypertension while others are not.
Understanding the genetics of chronic IH has been a key goal of the Intracranial Hypertension Registry. And each person with chronic IH holds important clues. If you have been diagnosed with chronic IH and have other family member/s who has/have also been diagnosed with chronic IH, we ask that both you and your family member/s consider enrolling in the IH Registry. Genetic research for chronic intracranial hypertension is in its infancy. With your help, we can learn vital knowledge about genetics that may ultimately lead to a cure. For more information on joining the IH Registry, please fill out the form below.
Signs of IH
Chronic IH is often characterized by an absence of clues. In idiopathic intracranial hypertension (IIH), there is no brain tumor, hemorrhage, cyst, lesion or blood clot found on a brain scan, no abnormalities of CSF and no localizing findings that point to injury of specific brain areas. In some cases of secondary intracranial hypertension (SIH), diagnosis may come long after the initial injury or trigger has occurred, leaving elevated intracranial pressure as the only evidence. Plus, a diagnosis of either IIH or SIH may be further complicated by the fact that a person does not exhibit all of the telltale symptoms.
However, there are some additional physical signs a physician may encounter that point to chronic IH. (A sign refers to something a physician can see, while a symptom is something a patient feels.)
Papilledema: Swelling of the optic nerves is probably the most common sign of IH. One sign of papilledema is an increased optic nerve diameter. An afferent pupil defect, in which the pupil in the eye is slow to react to light, can also indicate optic nerve swelling. Sixth nerve palsy due to elevated intracranial pressure may account for double vision and the eyes not tracking well together.
Visual field abnormality: Visual field abnormalities including peripheral and inferior nasal vision loss detected on a visual field test can be signs of chronic IH.
Empty sella: The pituitary gland, which is responsible for the body’s hormonal function, resides inside the sella turcica (cell-lah tur-sick-ah), a saddle-shaped space surrounded by the skull. Normally, the relatively round pituitary gland is visible within the sella turcica on imaging studies such as MRIs, CT scans and skull X-rays. Chronic IH can cause the pituitary gland to flatten against the skull bone, which gives the appearance that the sella turcica is empty.
Posterior scleral flattening: The sclera (the outer white covering of the eye) at the back of the eye can appear flattened on a CT or MRI scan, as a result of chronic IH.
The arrow points to an empty sella turcica.
An example of posterior scleral flattening (both eyes).