What is CSF?
The brain is fully encased inside a lining called dura. Between this dura and the brain lies a clear and colourless liquid called the cerebrospinal fluid or CSF that acts as a cushion for the brain. The brain and the dura are positioned partly above the nose and the sinuses that are separated from them by a thin bone.
As the dura is separated from the nose and the sinuses by only a thin bone, any perforation in the bone and the dura can leak the CSF straight into the nasal or the throat cavities.
The CSF leak becomes visible when clear fluid starts draining from the nose (usually from one nostril) or into the back of the throat (tastes salty). This is felt especially when the patient changes position or strains himself. A CSF leak does not respond to medications that would otherwise clear up a runny nose.
The CSF leakage occurs when a hole forms in the dura and the thin bony partition that separates it from the sinuses and the nose. This can happen from any of the following reasons:
- There is an accident involving the head.
- There is a complication from sinus or brain surgery.
- It has happened (expectedly, we may add) due to tumour removal from inside a sinus.
- Some activity has increased pressure on the CSF to erode the thin bone between the dura and the sinuses to cause the CSF leakage. In some cases, a high CSF pressure situation (and a CSF leak) can occur spontaneously for no obvious reason.
First the surgeon will confirm that the clear drainage is in fact CSF only and not a simple nasal secretion. Then he will determine the reason behind the CSF leakage. Once the origin has been established, the surgeon will determine its management strategy. Here are some such strategies:
- If the CSF leak is due to head trauma, the surgeon is likely to put the patient on complete bed rest and place a lumber drain (a small tube placed in the back to allow limited CSF drainage) to divert the brain fluid and minimize pressure on injured areas for healing to occur. 9 cases out of every 10 respond satisfactorily to this CSF leak management and heal without needing any surgery.
- However, if the CSF is due to an injury sustained at the skull base which is noticed while being treated surgically, the surgeon may decide on an immediate surgical intervention to repair it.
- If the onset of a CSF leak from a skull base injury sustained during a surgery goes unnoticed, the surgeon will order a CT scan of the sinuses to identify the CSF leakage point. If the CT scan reveals a possibility of brain tissue falling as well as CSF leakage, the surgeon will also undertake an MRI of the skull base. If however, the MRI is not able to precision map the CSF leakage point at the defective skull base, the surgeon may have to do so first-hand in the operating room. The surgeon, in that case, will add a dye to the CSF through a lumber drain (a small tube placed in the back, as described earlier). After this, the site of leakage becomes easier to spot in the sinuses and repair work can be undertaken.
- Quite a few CSF leakage cases have their origins unexplained as they are not preceded by any significant trauma or surgery. It is assumed then that there is an increase in intracranial pressure leading to skull base bone erosion and causing a CSF leakage. In such a case, the surgeon will undertake CT and MRI scans of the sinuses and the skull base to pinpoint the leakage source site. Like above, if the site cannot be identified through imaging, he will place a dye in the spinal fluid at the start of the surgery. Once the dye reaches the brain fluid and comes out through the sinus, the surgeon will identify its origin point through direct observation and repair the leak thereafter.
While a CSF leak in itself is a perilous condition, there is also the added risk of an intracranial (within the skull) infection. Think of it, the sinuses are high on infection-causing microbes. When the leakage point takes CSF into sinuses, it may also pass on some of these microbes into the CSF space which can then infect the brain and the tissue around it.
There are two broad options for surgeons to undertake CSF leakage repair- operate on the defective dura and bone either through the side of the brain, or through the sinus close to the skull base.
- From the brain side- For CSF leak site repair through the brain side, the surgeon will cut through the skull, slightly pull the brain away from the skull to pinpoint the leak site and after identifying it, repair it. The brain-side CSF repair surgeries are conducted by neurosurgeons and have a high failure rate of around 25% i.e. 1 patient in every 4 is likely to suffer complications and compromised quality of life after the surgery.
- From the sinus side - Recent advances have enabled ENT surgeons to repair these CSF leakages from the sinus and nose side using an endoscope. While this surgery usually does not require any cuts on the face, if the leakage involves frontal sinuses above the eyes, the surgeon may be required to make a cut here as this region is difficult for endoscopic reach. If pre-operative images are unable to confirm CSF leakage site with precision or if the surgeon wants further confirmation, a dye can be added to the spinal fluid to pinpoint the leak site (as detailed above) right in the operating room. Once the site is clearly identified, the mucosa lining of nasal cavity and the sinus is removed in the region to reach the defect in the bone. The surgeon can also place in a support layer between the brain and the bony defect along with the layer on the sinus side. Once the repair has stopped the leakage, sealants are placed at the site to support it. What’s to be noted here especially is the fact that In contrast to the high-risk brain-side CSF repair that has a 25% failure rate, the endoscopic CSF leak repair is comparatively much more successful with just 10% failure rate. In other words, where a brain-side CSF repair is likely to deliver unsatisfactory results in 1 out of every 4 cases, an equivalent endoscopic repair work is likely to be successful for 9 patients out of every 10.
The potential risks of this surgery are similar to endoscopic sinus surgery risks wherein there is less than 1% risk of unexpected damage to the brain and the optic nerve. There is also some risk that the leakage can recur.