What it is
A thin bone separates the ear from the intracranial cavity above. If the bone becomes thin or if weak holes develop in the bone, the cerebrospinal fluid (CSF) can leak down into the middle ear and mastoid cavity. A brain hernia, referred to as an encephalocele, could also develop over time.
Because these CSF leaks usually develop slowly, symptoms can go unnoticed for years before a diagnosis is made. Most patients will experience hearing loss due to having fluid behind the eardrum. If a tympanostomy tube is inserted to drain the fluid, the patient will generally notice that the drainage is clear and persistent. There may be wetness on a pillow or enough to moisten a tissue. Some patients, however, may develop an acute case as a result of an intracranial infection, or meningitis, if bacteria travel from the ear into this fluid surrounding the brain. In either case, once CSF or a brain hernia is suspected, the diagnosis will be confirmed with a laboratory test of the fluid. A CAT scan or MRI confirms the diagnosis and helps to localize the source of the leak or hernia.
What causes it
Head trauma is one cause of CSF leaks, but CSF more commonly occurs from an increase in intracranial pressure. That pressure results most commonly from obesity. Belly fat increases abdominal pressure, which causes a backup of spinal fluid that would normally drain into the abdomen. The backed-up spinal fluid increases the intracranial pressure, which eventually thins the bone, resulting in a small hole that allows fluid or brain tissue to drain into the ear.
How it is treated
Surgical repair is required for a CSF leak and/or encephelocele. Surgery not only corrects the immediate problem, but also prevents further complications, such as meningitis. Options for surgical repair include the transmastoid approach, which goes through the mastoid bone behind the ear and repairs the defect from below, or the middle fossa approach (craniotomy), which repairs the site from above. A surgeon often combines these two approaches because it provides better visualization of the repair site and improves the chances for a permanent repair. Limited activity for six weeks after surgery helps ensure a successful repair.
To reduce the risk of future leaks, the patient may be encouraged to lose weight in order to reduce intracranial pressure. Medications to reduce the production of CSF or shunting of the fluid may also be required in recurrent or severe cases.