Kevin C. Welch, MD
A disruption (a hole or tear) in the brain lining (called 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.
This article discusses current concepts in the causes and diagnosis as well as treatment of CSF leaks.
Anatomy and Physiology
Cerebrospinal fluid consists of a mixture of water, electrolytes, glucose, amino acids and various proteins. Cerebrospinal fluid is colorless, clear, and usually does not contain any cells. The primary site of CSF production is the choroid plexus (an area within the brain), which is responsible for 50-80% of its daily production.
All these sites produce CSF at a rate of approximately 20 mL/hr for a total of approximately 500 mL daily. At any given time, there is approximately 90-150 mL of CSF circulating throughout the central nervous system (CNS, which includes the brain and spinal cord). Cerebrospinal fluid circulates around the brain and spinal cord within the subarachnoid space.
In the adult patient, it is helpful to broadly classify CSF leaks into two categories: spontaneous CSF leaks and CSF leaks that are caused by injury to the bone separating the brain and the sinuses (known as the skull base: you can read the Patient Education topic Skull Base Anatomy for more information about this region). These include CSF leaks that are traumatic, caused by surgery (a.k.a. iatrogenic), and by tumors.
Accidental Trauma: Penetrating and closed-head trauma cause 90% of all cases of CSF leaks. Cerebrospinal fluid rhinorrhea (CSF leaking out of the nose) following a traumatic injury is classified as immediate (within 48 hours) or delayed. Of patients with delayed CSF leaks, 95% present within 3 months after the injury. Most patients with an injury causing CSF leaks are identified within 48 hours.
Surgical Trauma: Surgical trauma can occur during endoscopic sinus surgery or during neurosurgical procedures. These injuries occur along the bone separating the sinuses from the brain, or skull base and through the lining of the brain. Skull base injuries vary from simple cracks in the bone to large holes with potential injury to the brain.
Tumor-related CSF Rhinorrhea: It is uncommon for the growth of benign tumors to result in CSF rhinorrhea. However, aggressive benign tumors (such as inverted papilloma) and cancers can either erode or invade the bone of the skull base. The breakdown or destruction of the bone results in disruption of these barriers. If a leak is not present before surgery, very frequently the removal of these tumors results in an immediate CSF leak that is typically repaired at the time of the surgery.
Spontaneous CSF Rhinorrhea: 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 (ICP). Intracranial pressure is a different pressure from blood pressure, which most patients are familiar with, and is measured in a completely different way. 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 (hole) is formed and a leak begins. The dura (brain lining) or a part of the brain may actually protrude through the weakened part of the bone (this is known as an encephalocele).
History: A thorough history is the first step toward accurate diagnosis. 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 taste. 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 (multiple episodes), especially pneumococcal meningitis, should be evaluated for a CSF leak, regardless of the presence of active clear nasal discharge.
A history of headaches, ringing in the ears and blurry vision may suggest increased intracranial pressure. In these patients, MRI and CT may reveal signs of increased intracranial pressure, such as empty sella syndrome or arachnoid pits, radiologic findings which can be shown and described to you by your surgeon.
Physical Exam: Physical examination includes a complete head and neck examination. Nasal endoscopy (looking into the deeper portion of the nose and sinuses with an endoscope) is very helpful, especially in a patient who has undergone sinus surgery. Examination may reveal clear discharge, a skull base defect (if traumatic or surgically caused) or a mass, such as a tumor or encephalocele. In many cases, however, physical examination and nasal endoscopy are normal and the physician must base his or her decisions on history alone.
In patients with head trauma, the mixture of blood and CSF may make the diagnosis difficult. Cerebrospinal mixed with blood forms a "halo sign" when dripped on filter paper. However, the presence of a halo sign is not exclusive to CSF and can lead to false-positive results. The clinical findings most frequently associated with CSF rhinorrhea are meningitis (30%) and pneumocephalus (30%).
There are a number of laboratory and imaging studies that can be ordered to confirm the presence of a CSF leak. The ones listed here are the most common.