The delicate tissue of the human brain is shielded from the dense skull surrounding it by a clear fluid called cerebrospinal fluid, enclosed in a three-layer sack called the meninges. When there is an imbalance between production and resorption of the fluid people can develop increase or decrease pressure of the fluid around the brain. In cases of slow progressive increase of pressure on the brain, the fluid might find a pathway of lower resistance to draine. This commonly happens through the bone that separates the nose from the brain or the ear from the brain.
In cases of where the temporal bone is involved, the fluid will go through the mastoid cavity and middle ear down the Eustachian tube and drain into the back of the nose. Most times patients will present with clear fluid behind the eardrum which turns into continuous clear drainage from the ear when a ventilation tube is placed in the eardrum by the surgeon. This is called CSF otorrhea.
Management of CSF otorrhea is very important since the pathway can become a conduit for air and bacteria to enter around the brain and cause severe infection known as meningitis. To treat this process the surgeon has to both correct the defect where the fluid is coming through and address the reason patient has increased CSF pressure around the brain.
In most cases the cause of increased CSF pressure, also known as intracranial hypertension, is unknown. This condition used to be called pseudotumor cerebri but now, more correctly is called idiopathic intracranial hypertension. It is associated with the female gender, childbearing age, and obesity. However the condition can be seen in males and people who are not obese. The exact cause of the condition is not known at this time. In certain cases the condition appears years later after an episode of meningitis, brain tumors, brain surgery, or other causes that can contribute to poor resorption of CSF.
Treatment of the surgical defect can be done through the mastoid bone, through a middle fossa approach, or combination of the two. Dr. Monfared’s preferred method is to use a middle cranial fossa approach which would allow primary closure or patching of the dura as well as resurfacing of the middle fossa bone which naturally divides the brain and dura from middle ear and mastoid cavity. When the area of the leak is large a muscle flap is also used to reinforce the barrier. A lumbar drain is placed at the time of surgery to allow for low-pressure drainage of the CSF to prevent the fluid leaking through the surgical area. The drain is usually left in place for 3 days which is long enough for the patched area to seal. The patient will be started on a medication that decreases the production of CSF to prevent creation of further leaks down the line.
At times the brain tissue can herniated through the bone of the middle fossa, known as the tegmen, into the middle ear and mastoid. This condition is called an encephalocele and is repaired through a similar approach. The brain tissue that has herniated into the middle ear and mastoid cavity is not viable and usually causes hearing loss and possibly chronic infections.