The Management of Cranial and Spinal CSF Leaks
G. Michael Lemole Jr., MD
Jeffrey S. Henn, MD
Joseph M. Zabramski, MD
Volker K. H. Sonntag, MD
Division of Neurological Surgery, Barrow Neurological Institute, St. Joseph's Hospital and Medical Center, Phoenix, Arizona
The term cerebrospinal fluid (CSF) leak refers to any disruption of the arachnoid and dura that allows CSF to escape to an extradural space. CSF leaks can occur anywhere along the craniospinal axis. The most common clinical manifestation of cranial CSF leaks is rhinorrhea or otorrhea. Leakage along spinal pathways can cause severe postural headaches such as those that complicate spinal puncture. Occasionally, recurrent bouts of bacterial meningitis are the only clue to diagnosis. Treatment options range from bedrest and drainage of CSF to direct surgical repair by a variety of approaches. Management depends on the suspected location, cause, and presenting symptoms of the CSF leak. The details of the senior authors' approach to the evaluation and treatment of cranial and spinal CSF leaks are reviewed.
Key Words: cerebrospinal fluid (CSF), CSF fistula, CSF leak
The diagnosis and management of the patient with a cerebrospinal fluid (CSF) leak depend on the location of the leak, its etiology, and the patient's presenting symptoms. When a leak is associated with external drainage of CSF via the paranasal sinuses, external ear, or a cutaneous tract, it is more appropriately referred to as a CSF fistula. In the literature, however, the distinction between these terms has become blurred, and CSF fistula and CSF leak are used interchangeably.
CSF leaks can result from diverse etiologies, including trauma, hydrocephalus, tumor, infection, and iatrogenic and idiopathic causes. Clinical manifestations range from frank drainage of CSF that is easily recognized to slow, intermittent leakage that can be difficult to diagnose. Localization of a CSF leak can also prove challenging. The pertinent anatomy and mechanisms of formation of cranial and spinal CSF leaks must be understood to diagnose and treat these lesions properly. A clear understanding of their natural history is also mandatory for making sound management decisions.
This article examines the natural history, diagnosis, and treatment of CSF leaks involving the skull base and spinal column. The first section concentrates on cranial CSF fistulas; the second section addresses spinal CSF leaks, including their relationship to symptomatic intracranial hypotension.
In the second century A.D. Galen described the leakage of CSF after cranial trauma, but it was not considered a pathologic process until the mid17th century. In 1826 Miller noted nasal flow of spinal fluid in a child with hydrocephalus. In 1899 St. Clair Thomson coined the term rhinorrhea in a report describing a group of patients with spontaneous nasal CSF leaks. In 1923 Grant first proposed closing a traumatic dural defect. He reported a 19-year-old male with rhinorrhea and pneumocephalus following an automobile collision. He stated, "We felt that an attempt should be made to find and close the tear in the dura through which the air had entered." Profuse bleeding from the dura foiled Grant's proposed surgical intervention. In 1926 Dandy reported the first successful operative repair of a CSF leak. He closed a traumatic dural tear over a frontal sinus fracture using muscle and fascia lata.
During the next several decades, a better understanding of the natural history of traumatic and spontaneous CSF fistulas was obtained. The earliest efforts to identify the site of a leak included instilling dyes into the CSF space. The dyes, however, were found to be neurotoxic and are no longer recommended.[5,60,85]
Other intrathecal markers for documenting CSF leakage were developed. In the 1950s, radioactive isotopes were first used and injected into the CSF space for diagnostic purposes. Since then refinements in the radioactive tracers used for these procedures have improved the overall efficacy of the technique.
The development of computed tomography (CT) and the introduction of water-soluble contrast agents for intrathecal use, such as metrizamide, greatly improved the diagnosis and localization of CSF leaks. Diagnostic techniques are still evolving, and recent successes with magnetic resonance (MR) imaging suggest that it too may become a valuable tool.
Normal CSF Physiology
Figure 1. Cerebrospinal fluid is produced within the ventricular system by the choroid plexus and transependymal flow. It then circulates (arrows) through the foramina of Luschka and Magendie, around the basal cisterns and spinal cord, and up and over the cerebral
convexities to be reabsorbed into the superior sagittal sinus through arachnoid granulations.
CSF is formed in the cerebral ventricles by the choroid plexus and through transependymal flow of parenchymal fluid. CSF communicates directly with the basal subarachnoid cisterns through the foramina of Magendie and Luschka in the posterior fossa. The subarachnoid space is defined by the potential volume between the pial lining over the neural parenchyma and the arachnoid layer of the meninges. Multiple trabeculae traverse the space between these two layers. The arachnoid layer does not directly follow the conformations of the underlying brain parenchyma and thus forms pockets or cisterns through which the CSF percolates. CSF exiting the fourth ventricle flows freely through the basal cisterns down around the spinal cord and up and over the cerebral convexities to be reabsorbed into the venous blood stream through arachnoid granulations in the superior sagittal sinus (Fig. 1).
CSF is thought to act as a physiological shock absorber that buffers the neuroparenchyma from direct trauma. It has also been proposed that CSF is analogous to lymph for the nervous system. The process of the formation, flow, and reabsorption of CSF is dynamic. The entire volume of the CSF space is about 150 ml, and almost 500 ml of CSF are produced each day. Therefore, the volume of CSF is replaced about three times a day.
Classification of Cranial CSF Leaks
Figure 2. Ommaya’s classification scheme for cerebrospinal fluid leaks. From Ommaya AK, Di Chiro G, Baldwin M et al: Nontraumatic cerebrospinal fluid rhinorrhea. J Neurol Neurosurg Psychiatry 31:214-225, 1968. With permission from the British Medical Association.
In 1937 Cairns offered the first classification of CSF rhinorrhea, dividing CSF fistula into acute, delayed, traumatic, operative, and spontaneous groups. This scheme was further refined by differentiating between primary spontaneous or idiopathic rhinorrhea and secondary spontaneous rhinorrhea (i.e., rhinorrhea with an underlying etiology such as a tumor or hydrocephalus). Ommaya classified all CSF leaks as traumatic or nontraumatic, dividing each based on whether the underlying CSF dynamics reflected high or low pressure. Traumatic etiologies included accidental trauma to the cranium or spinal axis as well as iatrogenic injuries. Nontraumatic CSF leaks included those caused directly or indirectly by tumors, those caused by hydrocephalus, those initiated by infection, and those thought to arise from congenital anomalies or focal atrophy (Fig. 2). Groups within Ommaya's classification scheme overlap (e.g., when occult traumatic fractures of the skull manifest with delayed CSF leaks), but the system is useful when the natural history of each group is considered.