Timothy C. Hain, MD.• Page last modified: August 22, 2021
Hydrocephalus literally means "water brain". It means that there is more spinal fluid than normal in the "ventricles" -- fluid containing chambers within the brain. Persons with hydrocephalus often complain of headaches and unsteadiness. They may also have visual disurbances (enlarged blind spot) due to papilloedma, tinnitus, aural fullness, and low frequency hearing loss, resembling Meniere's disease. The inner ear symptoms are also found in persons with low CSF pressure, such as CSF-leak.
Spinal fluid is generated mainly by the choroid plexus -- vascular structures within the lateral ventricles. Spinal fluid is transmitted through the 3rd and 4th ventricles, and is absorbed through the arachnoid granulations -- vascular structures in the lining of the brain.
Most commonly, hydrocephalus is due to a "plumbing problem" -- too much spinal fluid, narrowing of passages between the ventricles, or plugging up of the arachnoid granulations.
Surgeons, often break the causes down into two general categories --
- obstructive hydrocephalus -- a tumor or other structure is blocking fluid transmission -- for example, a tumor of the cerebellum or a colloid cyst (see below).
- non-obstructive hydrocephalus -- too much spinal fluid or poor drainage through arachnoidal granulations. For example, NPH or BIH
There are several possible sources:
- Stretching of central connections controlling the legs causes spasticity and difficult controlling leg motion
- Fluctuation of pressure in the spinal fluid can be transmitted to the inner ear
- Headache pain from hydrocephalus might trigger migraine associated vertigo.
Satzer and Guillaume (2016) discuss hearing loss in hydrocephalus and the "hydrodynamic theory". This idea is that CSF pressure that are transmitted directly to the inner ear perilymph through the cochlear aqueduct, and also to the endolymph via the endolymphatic sac. As the cochlear aqueduct is a "direct" connection, and the sac is a structure with a roof, one would think that the effect on the perilymph would be more prominent. While overpressure of a membranous structure in the inner ear could plausibly cause hearing symptoms, the classic cause of hearing loss from pressure fluctuations in the inner ear is from the endolymphatic system, not the perilymphatic system. A somewhat similar idea is that rapid fluctuations in inner ear pressure associated with malformations in the channels in the inner ear that transmit pressure from spinal fluid, might be associated with damage to hearing. This is thought to occur in EVAS (enlarged vestibular aqueduct syndrome).
Hearing symptoms, tinnitus and low frequency hearing loss are much more commonly found in persons with low CSF pressure. There are several publications concerning hearing loss following shunting (e.g. van Veelen-Vincent, M. L., et al. , 2001), and many publications describing low-tone hearing loss after procedures that lower CSF pressure.
Ellis and others (2020) discussed hearing loss from hydrocephalus, and advocated for the hydrodynamic theory. There are a few reports of hearing loss in patients with hydrocephlus that improved on shunting. (Dixon and Jones, 2012, Verma et al, 2019) Other potential mechanisms for hearing loss associated with hydrocephalus include compression on other structures by the source of hydrocephalus. Ellis et al (2020) reported a case of hearing loss from a dorsal midbrain tumor, adjacent to the inferior colliculus. Hoistad and Hain (2003) also reported a case of hearing loss and a lesion of the inferior colliculus.
|Coronal view (white in center is fluid)||Sagittal view (black in center is fluid)||Axial view (black in center is fluid).|
The diagnosis of hydrocephalus is mainly based on imaging studies -- CT scans or MRI scans. Someone with hydrocephalus should have large ventricles, as shown above on three views. Depending on the MRI sequence, fluid will be white (on T2) or black (on T1). Either method is sufficient to diagnose hydrocephalus.
Chen et al (2021) recently discussed other "incidentally detected" signs of intracranial hypertension. They reported that lumbar puncture does not need to be done with these signs, unless there is papilloedema. The signs they enumerated were empty sella, enlarged Meckel caves, increased perioptic CSF, tortuosity of the optic nerve, slceral flattening, cephalocels, and bilateral venous sinus stenosis. So the bottom line seems of this paper seems to be that one should pay close attention to papilloedema, but one can usually dismiss these other signs (for diagnosis of intracranial hypertension).
Sometimes there is a worry that the shunt is malfunctioning, and a shunt study is done. This involves injection of dye into the shunt tubing, and taking an X-ray to see where it went. There is a line of dye on the left side (right body side) of the image above.
|Colloid cyst itself (white structure in center)||Hydrocephalus from colloid cyst.|
Colloid cysts are an unusual cause of hydrocephalus. They are benign growths in the 3rd ventricle. These cysts can cause intermittent symptoms as they can obstruct the flow of CSF on an intermittent basis. The scans above are from a patient who presented with brief spells, lasting 5-10 seconds, of a jumbling sensation, accompanied by unsteadiness and trouble seeing to the left. She did not present with a headache at all. She was scanned because of the unusual nature of her symptoms, but with the thought she might have migraine. Of course, this turned out to be wrong. Because of the hydrocephalus, she was operated, as there is a danger of sudden death from these entities.
|Prior to shunt (NPH)||After Shunt (4 years)|
The treatment of hydrocephalus is largely through insertion of drains -- called "shunts". In essence, one drills a hole in the skull, inserts a tube into the ventricles, inserts another tube under the skin ending up most commonly in the belly, and has a valve/port at the top in the skull. (Pudenz, 1981)
At the the present writing, 2010, there is a preference for "programmable shunts", that allow one to adjust a valve in the shunt from the outside. Shunts can become infected or plugged up. There is a tendency to blame almost any head-related symptom on shunt malfunction. Shunts are frequently revised over and over again.
Some authors have suggested use of ventriculostomies, and endoscopic techniques. (Psarros and Coimbra, 2004; de Ribaupierre et al., 2007). It would seem to us that this method might be more difficult to regulate than the programmable shunt.
Not all hydrocephalus is treated -- for example, if hydrocephalus is discovered in adulthood, but it started in childhood, often no treatment is advocated.
Mechanical systems nearly always eventually fail, and shunts are no exception to this general rule.
One must also be realistic. Shunts are crude compaired to the normal brain that has feedback control mechanisms. In other words, no matter what method is used to treat hydrocephalus, lacking any intelligence (and we have no computerized shunts as yet), it cannot function as well as a normal brain.
It seems highly unlikely that the pressure fluctuations in the ventricles after a shunt, are as well controlled as pressure fluctuations in a normal brain. It follows that in a person with a shunt, there will likely be some gradual long-term damage to the brain associated with pressure fluctuation.
Of course brain neurosurgery of this type intrinsically involves making holes in the brain, and at least some local damage along the catheter "tract".
Shunt infections are common problems.
Overdrainage causes "slit like ventricles", and the "Low CSF pressure" syndrome. (Pudenz and Folz, 1991). Some patients with overdrainage develop low tone hearing loss.
A recent development in medicine is the training of many interventional radiologists or neurosurgeons who are capable of inserting "stents" into blood vessels. These individuals insert stents into cerebral veins, with the goal of increasing the size of cerebral veins, improving the drainage, and therebye pulling blood out of the brain. This procedure is used in patients with Ehlers-Danlos syndrome (a cause of highly flexible joints), Chiari, and idiopathic intracranial hypertension. (Patsalides et al, 2018; Kanagalingam and Subramanian, 2018). It does make sense that if there is significant stenosis of the venous sinuses, CSF pressure might be increased. Of course, stenting treatment is only intiated if there is narrowing of venous structures in the head, and thus this treatment is only considered after an MRV is done.
Logical questions remain however : It is very difficult to see why stenting would be used in Ehlers-Danlos in as much as there is no literature in Pubmed on increased intracranial hypertension and Ehlers-Danlos. One would think that EHD would cause increased flexibility of the posterior fossa, and symptoms perhaps of dizziness, but not increased CSF pressure. It is also difficult to see why this would be helpful in Chiari patients who have no reason to have venous disturbances.
Bottom line regarding caution and stents:
Overall, as of 2018, we think intravenous stenting is a promising approach for certain types of intracranial hypertension, but also that it may be a "growth" area in medicine that is being abused. There are certainly gigantic numbers of "treatments" for various dizzy conditions, that are simply wishful thinking. In the USA, our health care system is a pay "whatever it takes", which results in gigantic economic incentives and distortions.
We think that stenting is best is best reserved for individuals with papilloedema documented on OCT, or increased ICP on lumbar puncture. In other words, we don't think it is such a good idea for people with vague headaches and some thinking issues to "google" increased intracranial pressure and then go to visit a young and aggressive interventionalist at some academic medical center.
We also think that stenting decisions should not be made by the person/institutional system hoping to be paid to do the stenting, but rather by a Neurologist who is overseeing the case, located at another institution than the interventionalist planning to do the procedure. The Neurologist should agree that there is increased intracerebral pressure (either from OCT or lumbar puncture), and should also agree that there is sufficient intracranial venous stenosis to proceed. Without this oversight procedure, we would worry about inappropriate surgical procedures.