A disruption in the brain lining (known as the dura) and the bone separating the brain and the sinuses will result in the drainage of fluid that normally surrounds the brain into the sinuses. This fluid is known as cerebrospinal fluid or “CSF.” Drainage of CSF into the sinuses can result in a multitude of problems, not to mention the often times annoying constancy of nasal dripping.
Cerebrospinal fluid consists of a mixture of water, electrolytes, glucose, amino acids and various proteins. Cerebrospinal fluid is colorless, clear, and typically devoid of cells. CSF leaks fall into two basic categories: spontaneous CSF leaks and CSF leaks that occur because of a defect or injury in the bone separating the brain and the sinuses (known as the skull base). These include CSF leaks that are traumatic, caused by surgery and by tumors.
Penetrating and closed-head trauma cause 90% of all cases of CSF leaks. Cerebrospinal fluid rhinorrhea following a traumatic injury can occur immediately or up to three months later.
Surgical trauma can occur during endoscopic sinus surgery or during neurosurgical procedures. These injuries occur along the skull base. These injuries vary from simple cracks in the bony architecture to large defects with potentially injury to the brain.
In uncommon cases, aggressive tumors and cancers either erode or invade the bone of the skull base. The breakdown or destruction of the bone results in disruption of these barriers.
Spontaneous CSF leaks occur in patients without any of the previous causes discussed. Recent evidence has led us to realize that spontaneous CSF leaks are probably due to elevated intracranial pressure. The causes of elevated ICP can be multiple; nevertheless, once elevated ICP develops, the pressure exerted on areas of the anterior skull base result in thinning of the bone. Ultimately, the bone is weakened until a defect if formed and a leak begins. The dura or part of the brain may actually protrude through the weakened until a defect is formed and a leak begins. The dura or part of the brain may actually protrude through the weakened part of the bone.
The presentation of a CSF leak is typical: Clear, watery discharge that often occurs only on one side of the nose. Often the discharge is continuous, but it may be sporadic and related to certain activities. This drainage may be reproducible by bending over or by straining. Patients may report a metallic or salty tast. Many patients with spontaneous leaks often are diagnosed with allergies or sinus infections and are unsuccessfully treated, often for many months, with antihistamines, nose sprays, and antibiotics.
Patients with recurrent meningitis should be evaluated for CSF leaks, regardless of the presence of active clear nasal discharge.
A history of headache, ringing in the ears and blurry vision may suggest increased intracranial pressure. In these patients, MRI and CT may reveal signs of increased ICP.
Physical exam includes a complete head and neck examination. Nasal endoscopy is very helpful, especially in a patient who has undergone sinus surgery. Examination may reveal clear discharge, a skull base defect or a mass, such as a neoplasm or encephalocele. In many cases, however, physical examination and nasal endoscopy, are normal and the physician must base his or her decision on history alone.
There are a number of laboratory and imaging studies that can be ordered to confirm the presence of a CSF leak. Testing the drainage for Beta-2 transferrin, a protein found exclusively in CSF, is the most common laboratory test. A high-resolution CAT scan is the best form of diagnostic imaging for identifying a CSF leak. By injecting contrast into the spinal canal, CT cisternography can show the precise location of a CSF leak in most patients who have active clear nasal drainage.
Management of CSF leak is determined in part by the cause of the leak. A leak that is the result of trauma to the head usually is managed with placement of a lumbar drain and bed rest. When a CSf leak develops from inadvertent injury to the skull base at the time of surgery, but its recognition or onset is delayed, a CT sinus is typically requested in order to identify the defect site. On occasion, the defective skull base site may not be obvious on imaging studies and has to be identified in the operating room using a dye added to the CSF via a lumbar drain. Once identified, the leak can usually be repaired endoscopically. The benefit of the surgery is to not only stop the CSF leak, but also to remove the risk of an intracranial infection. The success of endoscopic repair of CSF leaks is generally over 90%.