Intracranial Hypotension

What is Intracranial Hypotension?

The inside of your skull contains three main components: a fluid called cerebrospinal fluid (CSF), blood, and brain tissue. The CSF is found in a space between layers of brain coverings called the meninges. It is produced through a network of tiny blood vessels called the choroid plexus in each of the brain’s cavities, or ventricles. Special cells called ependymal cells that line the ventricles help to create a barrier between the blood and the CSF.

Your brain has a system of ventricles, including two on the side, one in the middle, and one enclosed by the brainstem and cerebellum, a part of your brain. These ventricles are connected by different channels, like the foramen of Monro and the cerebral aqueduct, which allow the CSF to move into the space around the brain and spinal cord. The CSF travels in this space until it is reabsorbed and sent back into your bloodstream.

The normal pressure of the CSF inside our brain ranges from about 65 to 195 mm of water. However, if it falls below 60 mm H2O, it is referred to as intracranial hypotension (ICH). ICH causes certain symptoms primarily because of low CSF volume, not just low pressure.

Back in 1891, a doctor performed the first lumbar puncture, a procedure to collect spinal fluid for testing. A few years later, another doctor observed that headaches after this procedure were likely due to leaking CSF. He suggested that the leak might be faster than the body’s production of CSF. Another researcher suggested that this kind of headache could be caused by a decrease in CSF production, an increase in its absorption, or a leak of the CSF.

What Causes Intracranial Hypotension?

Intracranial hypotension, a condition where there’s low pressure in the brain, can develop due to two main reasons: it can occur naturally or it can be a side effect of a medical procedure. The second type, known as iatrogenic intracranial hypotension, usually happens after a procedure like a lumbar puncture (LP). This is where a needle is inserted into the lower part of the spine to draw out cerebrospinal fluid (CSF), the clear fluid that cushions your brain and spinal cord. Removing about 10% of this fluid can cause a headache when you stand or sit up. This is known as a Lumbar Puncture Headache. Experts believe that decreasing the amount of spinal fluid increases the space it occupied, leading to an abnormal stretching of the cranial area. This causes further drop in brain pressure and vein enlargement when you’re upright.

On the other hand, spontaneous intracranial hypotension occurs naturally, often due to a cerebrospinal fluid leak. These leaks happen when the protective layers around your spinal cord get damaged or torn, usually from minor incidents like a twist or stretch. This can lead to a rupture of a cyst in your spinal area or a tear in the protective covering of your spinal nerves. This disruption is the second most common reason for CSF leaks, with the most common cause being protrusions from the meninges, called meningeal diverticula. This condition is often seen in people with disorders that affect their connective tissues, like Marfan’s syndrome.

In some cases, a connection forms between the spinal fluid and the veins, known as a spinal CSF-venous fistula, causing the CSF to leak into the venous system. These connections are the third most common cause of CSF leaks, although they only account for about 2.5% of cases.

Most of the time, CSF leaks happen in the spine, particularly in the thoracic or cervicothoracic junction. While they can sometimes occur at the base of the skull, it’s still a topic of debate whether these leaks contribute to spontaneous intracranial hypotension and the resulting headache when standing or sitting.

There is also a theory that low venous pressure could cause spontaneous intracranial hypotension. This could happen when blood is displaced to the lower parts of the body during physical activity, resulting in lower than normal pressure within the veins in the spine. This might decrease the flow of CSF in the spinal cavity, leading to more leaks from existing meningeal diverticula or cysts.

Risk Factors and Frequency for Intracranial Hypotension

From reviewing medical literature on Intracranial Hemorrhage (ICH), we learned that this condition affects about 5 out of every 100,000 people each year. It most commonly affects people around the age of 40, and is twice as common in women as in men. So, if a young or middle-aged adult experiences a headache that changes with their posture, it’s important to consider that they may be dealing with an ICH.

Signs and Symptoms of Intracranial Hypotension

Patients diagnosed with spontaneous or iatrogenic ICH often experience a specific type of headache known as a postural headache. This type of headache gets worse when the patient is standing upright and typically improves when they lie down. The headache is usually caused by the drainage of about 10% of the total CSF, the fluid in the brain. Some patients may also experience nausea, vomiting, and neck pain or stiffness. These symptoms generally start within 2 hours, often within the first 15 minutes. Additionally, a range of other symptoms has been reported, including:

• Changes in hearing
• Loss of appetite
• Dizziness or unsteadiness
• Blurred or double vision
• Light sensitivity
• Hiccups
• Unsteady walking

Testing for Intracranial Hypotension

Lumbar puncture, which measures changes in the cerebrospinal fluid (CSF) pressure within your spine, was originally the first method doctors used to identify benign intracranial hypertension (ICH), a condition where pressure in your brain is abnormally high. To determine this, doctors would typically need to see an opening pressure between 0 to 70 mmH2O. These days, the lumbar puncture isn’t typically the first test doctors will use to diagnose ICH, especially because many patients with this condition may have normal CSF opening pressures.

These days, an MRI (Magnetic Resonance Imaging) scan of the brain is commonly used instead to diagnose suspected ICH. Doctors look for certain signs in these MRI scans, typically summarized by the acronym SEEPS. SEEPS stands for Subdural fluid collections, Enhancement of the pachymeninges (the thicker, outermost layer of the meninges, the three layers of membranes that cover the brain and spinal cord), Engorgement of the venous structures, Pituitary enlargement, and Sagging of the brain. The most common symptom detected is the pachymeningeal enhancement, which is when the veins or overall fluid volume in the brain or spine appear to be larger than normal. But, these signs can also present in other health conditions like inflammation, infection, and tumour. The MRI may also detect significant levels of fluid collected around the brain, and the sagging of brain structures, including cerebellar tonsils. These may be reactions to a decrease in CSF. Occasionally, MRI scans show an abnormally thick outer layer of the brain and unusually large blood vessels in the outermost layer of tissue covering the brain and spinal cord in individuals with CSF leaks or headaches after a lumbar puncture.

If these tests aren’t enough, there’s a less common, but potentially useful technique called Radioisotope cisternography. This is often used when doctors suspect a spontaneous ICH and need to detect a CSF leak following an MRI that didn’t provide clear results. Performing this test involves injecting a radioisotope, a type of radioactive substance, into the lower part of your spinal area. This technique, however, isn’t generally the best for finding the precise location of a CSF leak due to a defect in the dura (the outermost layer of the meninges). This is when doctors would rely on another type of imaging test called a CT myelography, which is very effective in finding the exact location of the spinal leak.

Treatment Options for Intracranial Hypotension

Treating intracranial hypotension (low pressure inside the skull) depends on what’s causing it. In less severe cases and when brain fluid (CSF) is leaking, doctors usually start with simple, non-invasive treatments. Many patients get better with this approach without needing surgery. These treatments can include rest, drinking plenty of fluids, caffeine supplements, steroids, hormones that help balance your body’s fluids and salts, and abdominal binders (a type of medical belt).

If these simpler treatments don’t ease symptoms, doctors may need to use more invasive methods. One option is a lumbar epidural blood patch (EBP), where doctors inject a small amount of your own blood into your spine to seal the leak. This procedure has been successful for most patients but in some cases, symptoms can come back in a few days to weeks. Other options, though less common, are a continuous epidural saline infusion (injecting a salt-water solution into the space around the spinal cord) and surgery to repair the leak.

What else can Intracranial Hypotension be?

Headaches are a frequent health issue, and it’s possible for them to be a symptom of a more serious condition like an Intracerebral hemorrhage (ICH). However, because headaches are so common, they can sometimes be mistaken for more familiar problems like migraines, tension headaches, or even meningitis.

Additionally, there are other medical conditions that can cause headaches but may not show other significant neurologic signs during a physical exam, making it even harder to identify the true cause of the headache and diagnose an ICH. These conditions include:

• Subarachnoid hemorrhage
• Subdural hematoma
• Excessive drainage of cerebrospinal fluid due to a ventricular shunt
• Arteriovenous malformation
• Brain tumor

What to expect with Intracranial Hypotension

After being diagnosed and treated for ICH (Intracerebral Hemorrhage, which is a type of stroke caused by bleeding within the brain), symptoms usually get better on their own within two weeks. However, in rare cases, these symptoms can last for several weeks to months.

The information available to evaluate the long-term health status of patients after an ICH diagnosis is limited. Yet, a review of the existing scientific studies suggests that about 10% of patients might experience a return of the leakage of CSF (Cerebrospinal Fluid, which is a clear, colorless body fluid found in the brain and spinal cord), no matter what treatment approach they received.

Possible Complications When Diagnosed with Intracranial Hypotension

Aside from the usual symptoms, spontaneous intracerebral hemorrhage (ICH) can lead to serious brain-related complications. These severe conditions are believed to be the result of pressure causing deformities in brain structures. Rare but serious symptoms include milk production not related to breastfeeding (galactorrhea), abnormally high levels of a hormone called prolactin (hyperprolactinemia), lack of voluntary coordination of muscle movements (ataxia), weakness in all four limbs (quadriparesis), bleeding in the cerebellum (cerebellar hemorrhage), stroke in the back of the brain (posterior circulation infarction), movement disorders, reduced alertness, and clot formation in the brain’s veins (cerebral venous sinus thrombosis).

Serious Complications:

• Galactorrhea
• Hyperprolactinemia
• Ataxia
• Quadriparesis
• Cerebellar hemorrhage
• Posterior circulation infarction
• Movement disorders
• Decreased level of consciousness
• Cerebral venous sinus thrombosis

Preventing Intracranial Hypotension

Doctors should explain why patients are feeling the way they do and how they plan to treat them. At first, doctors typically recommend a non-aggressive treatment method, called conservative treatment, for a period of one to two weeks. During this time, patients can gradually return to their normal activities as they start to feel better. If symptoms do not improve, more treatment options will be discussed.

An epidural blood patch (EBP) is a commonly recommended next step. This method involves injecting a small amount of a patient’s own blood into the area around the spine to relieve pain. However, it’s necessary to know that this method may not work as well for idiopathic intracranial hypertension (ICH), a condition caused by high pressure in the fluid around the brain, as it does for headaches caused by a spinal tap or epidural anesthesia. Doctors will have an open conversation with patients about what they can expect from the treatment, so it’s important to be prepared for the possibility that it may not work as well for ICH and more invasive procedures may be needed if symptoms persist.