Evaluation of the patients with cerebrospinal fluid leaks: History and physical examination

Introduction

When evaluating a patient for a cranial base cerebrospinal fluid (CSF) leak, the history and physical examination are critical steps to determine the diagnosis, cause, and localization. Establishing the diagnosis of CSF rhinorrhea can be challenging because there is a wide range of causes and presentations, as well as many causes of rhinorrhea that can mimic a CSF leak. CSF rhinorrhea itself is caused by a defect in the skull base, resulting in a communication between the intracranial space and paranasal sinuses. However, this defect can result from many different traumatic and nontraumatic causes. This chapter outlines our approach to most efficiently and accurately establishing the diagnosis of CSF rhinorrhea.

Cause

The cause of CSF rhinorrhea can vary widely, and there is conflicting literature regarding the rates of various etiologies, likely because CSF rhinorrhea occurs so rarely. For the purpose of organization, the causes are often categorized as traumatic and non-traumatic, with the majority of CSF rhinorrhea causes being related to trauma ( Fig. 2.1 ).

Posttraumatic CSF leaks make up 80% to 90% of all CSF leaks and occur in the setting of blunt force head trauma or penetrating injuries to the skull base. Blunt head trauma makes up the majority of CSF leaks because it is far more common than penetrating trauma. CSF leaks are reported in 1% to 3% of all closed traumatic head injuries. Penetrating trauma involving the skull base is rare, but a greater percentage of penetrating trauma results in CSF leakage, with rates reported as high as 10%. It should be noted that not all patients with a skull base fracture will have CSF leak because this requires concurrent damage to the dura and sinus mucosa; it is estimated that 10% to 30% of patients with a skull base fracture on imaging will be diagnosed with a CSF leak. CSF leaks resulting from fractures of the anterior cranial fossa are more common than CSF leaks resulting from temporal bone fractures, perhaps because the dura is more adherent to the bone of the anterior cranial fossa and thus more likely to tear, and any extradural CSF in the anterior cranial fossa has a more direct route to the nasal cavity.

The majority of patients with a CSF leak are diagnosed within 48 hours of trauma, but it should be noted that a patient with a traumatic head injury may present with a delayed CSF leak that is diagnosed days to weeks after their trauma. A case series published in 2001 from our institution reviewed 51 traumatic CSF leaks and found that 8 patients (16%) presented months to years after the initial injury, with the great majority occurring within several days. It is unclear what causes this delay in diagnosis, but a few hypotheses have been proposed. Skull base fractures are often associated with many other high-velocity injuries that may cause intranasal bleeding, prolonged coma state, or prolonged intubation, all of which may mask and delay diagnosis of a more subtle cranial base CSF leak. Additionally, it has been proposed that delayed leaks occur when cerebral edema subsides and leakage of CSF through a fracture line can occur more freely, thus CSF rhinorrhea may not present immediately after the trauma.

In the era of endoscopic sinus and skull base surgery, there is concern that iatrogenic causes of CSF leak are becoming more common. However, the routine nature of these surgeries in combination with novel and reliable repair techniques have made endoscopic skull base surgery increasingly safer in the hands of an experienced surgeon. There are robust data published that showed a rate of CSF leak after primary functional endoscopic sinus surgery as low as 0.5%. The risk of a skull base defect does increase in revision sinus surgery. The areas of the skull base that are particularly thin and vulnerable during routine sinus surgery include the lateral lamella of the cribriform plate and the posterior table of the frontal sinus.

The most common skull base surgery, endonasal transsphenoidal pituitary resection, has an estimated postoperative CSF leak rate of 1% to 4%. Advances in skull base repair and reconstruction have greatly reduced this rate in the past 10 years. In a large multicenter retrospective review of 1108 patients undergoing transnasal endoscopic sellar surgery for pituitary adenoma or craniopharyngioma, 5.9% of patients had a postoperative leak. Preoperative factors predictive of intraoperative CSF leak included mild liver disease, craniopharyngioma pathology, elevated body mass index (BMI), and tumor extension into the anterior cranial fossa. Reconstruction with a pedicled, vascularized nasoseptal flap in the setting of intraoperative leak decreased the rate of postoperative CSF leak.

Inadvertent CSF leak can occur after endoscopic or open skull base surgery. Delayed CSF leak can be seen in the frontal or ethmoidal region after frontal craniotomy. More posteriorly, CSF leak can occur after clinoidectomy in the setting of a pneumatized clinoid. Similar to temporal bone fractures, surgical manipulation of the temporal bone resulting in CSF leak into mastoid air cells can present with CSF otorrhea or rhinorrhea via the eustachian tube in a patient with an intact tympanic membrane.

In addition to skull base surgery and sinus surgery, surgeries that can result in CSF leakage include endoscopic and endonasal septoplasty, nasal bone reduction, and endoscopic and external approaches to the orbit for decompression or tumor resection or surgery to the lacrimal complex. Regardless, if a patient has a history of skull base surgery or surgery near the skull base, a CSF leak should be considered if a patient develops clear fluid rhinorrhea or otorrhea. Thus, a thorough trauma and surgical history should be included in a patient history when CSF leak is being considered.

Nontraumatic causes of CSF leak can be more difficult to diagnose because they represent a wide array of diagnoses to consider when taking a history. A brief, nonexhaustive list to consider includes disease processes with increased intracranial pressure (ICP), erosive processes, skull base neoplasms, and congenital anomalies.

Regarding elevation in ICP, it is hypothesized that thinning of anatomically predisposed regions of the skull base can occur with chronic increase in ICP, leading to an eventual bony erosion, encephalocele, and CSF leak. Patients with elevated ICP can include those with idiopathic intracranial hypertension (IIH), hydrocephalus, or an intracranial neoplasm. It should be noted that a leak can act as a valve for pressure release, and these patients may not have elevated ICPs after a leak is detected. IIH and its connection with CSF rhinorrhea is discussed later in this chapter and will also be addressed in more detail later in this text.

Patients with skull base neoplasms located in the intracranial or sinonasal cavities rarely present with CSF leak, but a CSF leak must be considered in patients with these pathologies presenting with clear fluid rhinorrhea. Sinonasal malignancies represent a wide variety of histopathologies and include nasopharyngeal carcinoma, primary, and metastatic sinonasal tumors. Similarly, intracranial tumors at the skull base have the potential to erode through to the sinonasal cavity and result in a CSF leak. A patient with prior radiation to the skull base may also be at increased risk for CSF leak. The sinonasal mucosa has been shown to be more inflamed and friable after radiation therapy. Case reports of CSF leak from the middle cranial fossa after radiation of the pituitary suggest general weakening of the skull base may occur in the setting of radiation therapy. Additionally, there are reports of CSF leak after dramatic reduction in tumor size in the setting of prior radiation or medical therapy of skull base tumors such as after the use of dopamine agonist therapy for giant prolactinomas. These are all rare situations, and it is far more likely a patient with a skull base tumor has a CSF leak from surgical manipulation at the skull base rather than the tumor itself or radiation therapy.

Erosive processes of the skull base include vasculitis (granulomatosis with polyangiitis), osteomyelitis, severe fungal infections (invasive fungal or allergic fungal), and sinus mucoceles.

Allergic fungal rhinosinusitis (AFRS) is an immunoglobulin E (IgE)–mediated immune reaction to environmentally pervasive fungus that causes severe nasal inflammation with polyposis and thick mucus. AFRS has been found to have a higher rate of bony erosion of the skull base and orbit compared with other inflammatory rhinosinusitis disease processes. The incidence of AFRS skull base and orbital erosion is reported as high as 56% at the time of initial presentation. This bony erosion does not necessarily indicate a CSF leak but places a patient at far higher risk for a CSF leak, especially in the setting of surgical intervention and management of their disease.

Acute invasive fungal sinusitis is a far different and more devastating entity than AFRS, usually seen in immunocompromised patients and diagnosed based on vascular invasion of fungal species, resulting in necrosis of the sinonasal tissues. Invasive fungal disease has a mortality rate of nearly 50%, and intracranial involvement is an independent poor prognostic factor. There is a case report of a patient having a CSF leak and pneumocephalus in the setting of very advanced invasive fungal disease, but a greater concern is an overly aggressive surgical resection resulting in a CSF leak that cannot be repaired in an infected sinonasal cavity.

There are case reports of vasculitis-related skull base erosion and osteomyelitis-related CSF leaks, but these are very rare causes of CSF rhinorrhea. A CSF leak would be more likely to be observed after endonasal surgical intervention in patients with these disease processes rather than from the disease process itself.

Finally, congenital causes of spontaneous CSF leak include meningoencephaloceles and developmental defects at the skull base. Small defects in the skull base have the potential to remain asymptomatic or remain unidentified until adulthood. Sternberg’s canal refers to a persistent lateral craniopharyngeal canal in the lateral wall of the sphenoid. This was previously thought to be a common site of CSF leak caused by a persistent defect medial to V2 as it exits the skull base. However, it is now debated if this is truly a site of congenital defect or common area for IIH-associated CSF leak. In a large review of adult high-resolution computed tomography (CT) scans, only 0.8% of adults were found to have a persistent Sternberg’s canal, making it an unlikely source of CSF leak. Large transsphenoidal encephaloceles identified at birth can be associated with other midline craniofacial abnormalities and significantly distorted anatomy. These patients have prominent rhinorrhea with associated abnormalities of the face, optic system, and brain associated with median cleft face syndrome.

Cerebrospinal fluid rhinorrhea can be caused by a wide variety of causes; thus, a thorough history, including remote head trauma, recent head trauma, and prior surgical interventions, must be obtained. In nontraumatic causes, associated symptoms, physical examination, and additional testing are important to the patient history to determine the diagnosis of CSF rhinorrhea.