Approach to headache
Patients suffering headaches will generally see a General Practitioner or a Neurologist for an assessment. This will involve taking a history, obtaining information about the headache, duration, family history and a physical examination may also be performed. Further investigations could include an MRI scan of the brain.
Ultimately, clinicians are trying to divide people into different types of categories. The two main categories being primary headache and secondary headache.
Primary headache, is a headache that does not have another medical cause for it. Migraine and tension-type headache are examples of a primary headache.
Secondary headaches have another underlying medical cause for them. Although primary headaches can be very debilitating and affect quality of life, they are usually not dangerous. Secondary headaches however can be very serious, and the management often differs significantly.
Basic anatomy of the brain
In order to understand high pressure and low pressure headache It helps to understand the basic anatomy of the brain.
As shown above, you can see the head, the skin and then the skull. The skull is essentially a tight box that does not have any flexibility. Within the skull is the brain and the spinal cord which comes out the bottom (as shown below).
The brain is covered by a very dense, fibrous sack, which is called the meninges. Inside this sack (the meninges) is a clear, colourless fluid called cerebral spinal fluid (CSF). Our CSF is made in the centre of the brain, in an area called the ventricles, by the choroid plexus. We have about 150mLs of CSF floating around our brain and spinal cord. The choroid plexus in make about half a litre a day. We also have an absorption system, which involves the little granulations shown at the top of the brain above.
Our brain weighs about a kilogram and floats in CSF, which performs an important function. If we focus on the brain itself and turn it upside down, there are lots of important structures.
At the bottom of the brain are vessels and nerves. If we did not have the fluid and the brain was not floating all of these structures could be compressed. The brain itself does not feel any pain however the meninges, which covers the brain, the nerves and the vessels are very sensitive.
Low-pressure headache
Low-pressure headache occurs when there is not enough CSF and there is not sufficient buoyancy to keep the brain floating.
This usually occurs when the CSF is being lost faster than it can be replaced. In terms of symptoms, the classic symptom experienced is a headache that is significantly worse when you are sitting or standing up, as opposed to laying down, referred to as an orthostatic headache.
The sensitive structures at the bottom of the brain can cause different symptoms as these nerves go out to the eye and the ear. With low CSF levels, people can experience double vision, also dizziness, tinnitus, ringing in their ears. In extremely severe situations confusion, reduced conscious state or potentially coma could be experienced.
Diagnosis of low-pressure headache
Clinicians may often request some imaging studies to help with the diagnosis.
Shown above are two MRI scans showing the brain cut through the middle as we look at the brain side on.
The first image occurred before any treatment was instituted. The second scan (scan B) is with treatment. In comparing the two images, the ventricle (marked by the triangle shape on scan A), is where our CS fluid is being made and is small in comparison to scan B.
The second thing is that the area of the brain which includes the brainstem and the cerebellum, which is the coordination centre of the brain, all look a bit squashed. In the second image we can see that there’s lots of space (marked by the black areas between brain structures) and that space is the CS fluid that is allowing everything to float and be separated.
The other observation between scan A and B is regarding the dotted line at the bottom. We can see that structures are falling below that line in scan A versus scan B.
Another type of scan is done with an injection of a contrast called gadolinium. This gives us information about whether a structure in the brain is inflamed or irritable.
Normally, the meninges, the surrounding part of the brain, doesn’t light up and isn’t white as shown above, but we can see that it’s quite irritated from the low level of CSF.
Causes of low-pressure headache
There are a number of different causes that can lead to a low-pressure headache. Trauma to the skull is one of the potential causes. We can see at the bottom of the scan shown below that there is a small fracture through the bone near the bottom.
A fracture through the bone also tears the sack that is keeping the fluid in place. Patients with low-pressure headache can experience clear spinal fluid coming out of their ear or out their nose.
Other potential causes include an iatrogenic cause, which means it’s related to medical treatment.
Sometimes in order to diagnose particular neurological conditions, a sample of the spinal fluid is needed. This sample is collected by injecting a needle in between the spinous processes in the back. This injection creates a small a hole and there’s the potential that the hole does not seal up. When the hole does not seal itself fluid can leak out. Clinicians use a small needle when performing this procedure. It is not common to experience this type of problem.
The other cause may occur from an epidural. Many women have them for pain management during labour. The idea of an epidural is they come very close to the dura and the spinal fluid, but do not cross that area. Anaesthetists are trained professionals who perform this procedure regularly, usually by feel. Occasionally they might go a little bit too far and puncture the dura. They have a much larger bore needle, so it’s a bigger hole, and people often experience a nasty headache.
Another less common cause are people who develop a spontaneous leak, usually from a tear in the meninges in the spinal column. This type of headache can be very sudden in onset, but can also be a gradual onset. These spontaneous leaks still have the orthostatic (pain severity changes with body posture) component to it.
There are many different theories around what causes a spontaneous CSF leak. Some clinicians think that it could be a small disc in the spine coming out and damaging the dura.
Interestingly, about two thirds of people who have this particular type of problem have abnormal connective tissue. Connective tissue is the tissue that holds everything together, it’s the structure between skin, fat, muscle and bone. Some people have hyper-mobility or abnormally flexible joints, which is usually due to a difference in connective tissue. Those with abnormal connective tissue or hypermobility may therefore be more prone to having these sorts of tears.
Management of low-pressure headache
Management is conservative with bed rest and fluids in the first instance, particularly after a recent lumbar puncture. There’s lots of different things that people recommend anecdotally, for example caffeine and other suggestions of this nature, but the evidence base for these are not particularly strong.
A blood patch is something that is used fairly often. This is where a sample of blood is taken and injected into the spine where the tear is, to seal the hole.
If symptoms persist, sometimes surgeons will be involved to surgically repair the tear.
High-pressure headache
As we know the skull contains the brain fluid called the CSF which acts as a cushion for the brain to sit in. In a high-pressure headache, there is either:
- Too much spinal fluid or
- Not enough space for the brain. The brain or something in the brain (such as a tumor) takes up too much space.
Symptoms of high-pressure headache
- Headache
- Double vision
- Blurred vision
- Pupil changes
- Hearing change
- Nausea and vomiting
- Confusion
- Drowsiness
- Coma
The symptoms are similar to a low-pressure headache. The headache itself was historically referred to as an early morning headache. It does not have the same postural, orthostatic symptoms. People can still experience double vision, tinnitus and/or hearing change. Nausea and vomiting are more common in high-pressure headache.
Diagnosis of high-pressure headache
There is a diagnostic marker when using an MRI scan that helps determine if high-pressure headache is present.
On the MRI scan shown above, the bright white is actually the clear spinal fluid. The white circles are the eyes at the front and the nerve behind them. The spinal fluid goes all the way along the path of that eye nerve. Clinicians can look through the pupil, with a device called an ophthalmoscope, to the back of the eye where the nerve enters the eye.
In the image shown above, image labelled 0 shows a normal and healthy optic disc, which has sharp borders and vessels going through it. The images labelled 1-5 show progressively worse stages of a more swollen disc. A swollen disc indicates that the pressure inside the brain is higher than it should be.
Causes of high-pressure headache
In terms of causes for high-pressure headaches, there can be too much CSF, which is called hydrocephalus.
The image above shows two different CT scans with the one on the left being a normal and healthy CT scan. The ventricles and the little choroid plexus which are making our spinal fluid can both be seen.
The scan on the right-hand side has significantly more areas of black. These black areas represent CSF. In the scan on the right there is too much CSF and the brain is literally being squashed.
This situation is often solved by surgeons inserting a small drain into the ventricle. This either drains into the abdomen or sometimes into the lining of the lung, to remove the extra fluid.
Extra fluid may be caused by a blockage from the fluid draining into the spinal cord. This can occur after an infection. Another cause may be due to a congenital abnormality someone is born with.
Re-absorption of the CSF can be affected by several factors. Infections such as meningitis may cause high-pressure headache. A bleed in the brain can also affect the reabsorption of the fluid. In these scenarios, CSF production may be normal and healthy, however the brain is unable to absorb it to maintain an equilibrium.
Another cause could be a blood clot in a vein. Arteries take oxygenated blood from the heart and deliver it to the brain and then the veins drain away that fluid. Veins help to absorb and remove spinal fluid.
Like a deep vein thrombosis in a leg, people can also get blood clots in the veins of the brain. These clots are more common in women who are postpartum, smokers or on hormonal contraception. They are also more common in people who have an active cancer which can make the blood sticky and more likely to clot.
This CT scan above, shows a fresh blood clot which looks like a slightly brighter grey compared to the rest of the brain scan. The red and blue arrows are pointing to a blood clot which is in the area of a vein in the brain.
Another situation that can occur is when high pressure is present but there is no excess CSF. This situation is referred to as idiopathic intracranial hypertension (IIH). It occurs more often in younger women and is usually more common in overweight women.
IIH often presents with headache and visual changes due to the high pressure. It can also result in pulsatile ringing in the ears.
IIH is an important condition to diagnose because if left untreated it can cause permanent vision loss.
Why IIH occurs is still not fully understood. Weight loss can help with management in those who are overweight. There are medications that can be utilised to lower CSF pressure and if necessary a shunt can be surgically inserted to help reduce the pressure.
Problems involving the brain such as a tumour, stroke, bleed or inflammation can also take up space and cause headache and symptoms associated with high pressure. This is why it’s important if someone experiences a new headache, imaging of the brain (usually an MRI) is performed.
