Intracranial Hyper/Hypotension
Intracranial Hypertension (IHyper)
Also known as Pseudotumor Cerebri, is a condition where there is a high-pressure surrounding the brain and spinal cord due to excess cerebrospinal fluid (CSF). CSF acts as a cushion for the brain and is a transport for nutrients and waste around the brain and spine. As the skull is inflexible and excess CSF puts pressure on the brain tissue. The causes of this are usually unknown (idiopathic) but some comorbid conditions include Chiari Malformation and Craniocervical Instability.
It occurs mostly in women who are of child-bearing age but can occur in all ages and genders. There is some debate about whether weight has an impact on developing IHyper, but research has yet to support this or find statistical difference between those who are classified as normal or overweight.
Common symptoms include:
- Headache (worse in the morning or lying down)
- Vision Loss
- Pulsatile tinnitus
- Visual disturbances (blond spots, poor peripheral vision)
- Nausea/Vomiting
IH can not be diagnosed via imaging but can show some consequences of IH such as small/slit-like ventricles and/or empty or partially empty sella. Imaging is mainly used to rule out causes. Diagnosis is performed using tools like Lumbar Punctures or Invasive Intracranial Pressure (ICP) monitoring. In-depth eye examinations by Ophthalmologists, are also performed due to the impact IH has on the optic nerve looking for issues like optic nerve swelling and/or papilledema.
Treatment ranges from medications such as Diamox (Acetazolamide) and/or Topomax (Topiramate) or the use of a surgically implanted shunts. There are several types of shunts used and they divert CSF away to other areas of the bodies to be absorbed. Shunts can be positioned to start at either the ventricles or an area in the lumbar and end in either the peritoneal area or atrium. The common shunts include the ventriculoperitoneal (VP) shunt and lumbar-peritoneal (LP) shunt. Some shunts are adjustable by the specialists through a device with magnets to change the amount of fluid flowing. Shunt settings can be moved by MRIs so one needs to check whether their shunt is compatible or needs re-setting after imaging. Another surgical treatment is the implant of a stent into the venous sinus when these are narrowed. This allows the normal passage of the blood and CSF to move from the brain to the jugular veins and into the heart to resume.
Intracranial Hypotension (Ihypo)
This condition is the opposite where there is a negative pressure around the brain due to low amounts of CSF. This can occur when a leak in the lining of the brain/spine occurs and allows CSF to drain out. It can also be an issue for those who have a shunt that is over-draining.
IHypo/CSF leaks occur for many reasons including defects in the dura, after lumbar punctures or surgeries that pierce the dura and sometimes spontaneously (usually seen associated with Ehlers-Danlos). Some of these cause temporary leaks that will seal with time and CSF regeneration. Others require surgical intervention to fix the leak through blood patches, surgical repair of defects or adjusting shunts.
It's often very hard to identify when CSF leaks occur, but imaging is important as there are enough cases where pockets of CSF fluid are seen. Continuous ICP monitoring and dynamic myelograms can help identify a leak, but the absence of a leak does not rule them out.
Those with low CSF can have symptoms such as headaches that get worse on being upright, nausea, double vision, tinnitus etc. Leaks or over-draining of LP shunts can cause cerebellar herniation/cerebellar slump/acquired Chiari.
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