Editorial: Cerebrospinal fluid physiology No abstract available

Physiology of cerebrospinal fluid circulation Purpose of review This article describes the physiology of cerebrospinal fluid (CSF). We review current evidence and new concepts relating to CSF physiology with respect to CSF secretion, circulation and resorption and we highlight key pathophysiological associations including the relationship between CSF and intracranial pressure. Recent findings CSF secretion occurs primarily via the choroid plexus. Various transport mechanisms facilitate CSF secretion but the role Aquaporins play in this process is a recent discovery and an area of ongoing research. CSF circulation is a dynamic process but the importance of the perivascular ‘Glymphatic system’ and extraarachnoidal pathways of resorption are relatively new concepts. Summary CSF physiology is dependent on various interacting factors and is critical for normal brain development and function.

Trans-mastoid approach for cerebrospinal fluid leak repair Purpose of review To describe the technique and discuss the advantages and outcomes of the trans-mastoid approach (TMA) for temporal bone cerebrospinal fluid (CSF) leak. Recent findings TMA for CSF leak repair is an alternative to middle cranial fossa approach (MCFA) with less morbidity and good outcomes. Summary Persistent CSF leak in the temporal bone whether idiopathic, congenital or acquired, is an indication for surgery. TMA is a valid option for surgery, competing with MCFA in selected cases. Surgical technique consists of a standard mastoidectomy, exposure of the osteodural defect, and repairing it using multiple layers in an inlay and overlay fashion. Outcomes show low recurrence and complication rates with good hearing results. However, long-term follow-up should be made, as recurrences can be delayed.

Laboratory testing and imaging in the evaluation of cranial cerebrospinal fluid leaks and encephaloceles Purpose of review To summarize the current evidence on the diagnostic evaluation of cranial cerebrospinal fluid (CSF) leaks and encephaloceles, including laboratory testing and imaging studies. Recent findings The most sensitive and specific laboratory tests for CSF leak diagnosis are beta-2-transferrin and beta trace protein assays, the former more commonly used because of availability. Imaging studies used for localization of the leak site include high resolution computed tomography (HRCT) and magnetic resonance cisternography (MRC), often used in combination. Intrathecal contrast administration is reserved for complex cases with prior equivocal test results or for patients with multiple skull base defects to localize the leak site. Summary Diagnosis of CSF leaks and encephaloceles is aimed at both confirming the leak and localizing the leak site. Future advancements in testing techniques may shorten the diagnostic process, limit the need for invasive testing, and improve the safety of such testing in indicated cases.

The evolution of presenting signs and symptoms of lateral skull base cerebrospinal fluid leaks Purpose of review To review the presenting signs and symptoms of spontaneous cerebrospinal fluid (CSF) leaks of the lateral skull base. Recent findings Research continues to demonstrate that CSF leaks from the lateral skull base are insidious, and present with subtle signs and symptoms. Patients commonly present with symptoms of aural fullness, middle ear effusion, and otorrhea following tympanostomy tube insertion that can be confused for chronic otitis media. More recently headache, pulsatile tinnitus, and dizziness/vertigo are being recorded as symptoms at presentation, which is likely a reflection of the association of spontaneous CSF leak with obesity, intracranial hypertension, and superior canal dehiscence. The presence of these less common symptoms in the setting of middle ear effusion should raise suspicion for CSF leak. The rate of meningitis in spontaneous CSF leak is not negligible, and patients should be counseled on this life-threatening risk. Summary Spontaneous CSF leak from the lateral skull base presents with subtle signs and symptoms and remains a diagnostic challenge. Less common symptoms may represent associations with underlying comorbidities, and awareness of the increasing coincidence of diseases that accompany spontaneous CSF leak is essential to prompt diagnosis and management.

The role of obesity, sleep apnea, and elevated intracranial pressure in spontaneous cerebrospinal fluid leaks Purpose of review Spontaneous cerebrospinal fluid (sCSF) leaks often occurs in middle age, obese females. Here we investigate the role of obesity, idiopathic intracranial hypertension (IIH), and obstructive sleep apnea (OSA) in the pathophysiology of sCSF leaks. Recent findings The association of obesity and sCSF leaks has been well established in many studies. It has now been revealed that sCSF leak patients have thinner calvariums along with the skull base. An intracranial process likely leads to calvarium and skull base thinning in sCSF leaks patients since this occurs independent of extracranial bone thinning and independent of obesity. OSA, which is known to cause spikes in intracranial pressure (ICP), has been found to be significantly prevalent in the sCSF population and has been shown to lead to both calvarial and skull base thinning. Chronically elevated ICP (IIH) has also been shown to impact calvarial and skull base thicknesses. Summary The incidence of sCSF leaks has increased in recent decades along with an increasing rate of obesity. OSA and IIH, which are obesity-related factors and cause transient and chronic elevations in ICP, have now been implicated as critical factors leading to calvarial and skull base thinning and resultant sCSF leaks.

Middle fossa approach for spontaneous cerebrospinal fluid fistula and encephaloceles Purpose of review The aim of this article is to describe the middle fossa craniotomy (MFC) approach for the repair of cerebrospinal (CSF) fistula and encephaloceles. Recent findings The MFC approach has a greater than 93% success rate for managing CSF fistula and encephaloceles located along the tegmen tympani and tegmen mastoideum. Posterior fossa defects cannot be managed by an MFC approach. Multilayer repair with the combination of soft tissue and durable substances is preferred. Hydroxyapatite bone cement provides a durable repair of thinned or absent areas of bone with a low risk of infection. Concurrent management of symptomatic superior semicircular canal dehiscence may be readily performed. Small keyhole craniotomies with the utilization of the endoscope are possible as a means to minimize temporal lobe retraction. Summary MFC repair of CSF fistula and encephaloceles is a highly effective approach for the repair of tegmen mastoideum and tegmen tympani defects.

Postoperative management of patients with spontaneous cerebrospinal fluid leak Purpose of review To explore key management principles and outcomes following surgical intervention for spontaneous CSF leaks of the lateral skull base. Recent findings Outcomes following surgery for spontaneous CSF leaks of the lateral skull base depend on the surgical approach utilized. The approach reported most frequently in the literature is currently the middle fossa approach. Mean leak recurrence rates, regardless of approach, were approximately 6%. The lowest leak recurrence rates were associated with the combined middle cranial fossa-transmastoid approach. A multilayer closure was employed in all of the reviewed investigations, but the choice of reconstructive material did not significantly affect outcomes. Direct surgical complications rates, overall, were low at less than 2%. Meningitis, intracranial hemorrhage, and perioperative seizure activity were only rarely encountered. A concomitant diagnosis of idiopathic intracranial hypertension was found to be associated with increased rates of leak recurrence and sequential leak development at other skull base sites. Summary Postoperative management of patients with spontaneous CSF leaks of the lateral skull base has unique challenges. Observation of key treatment principles can lead to good outcomes and limit morbidity. A high index of suspicion should exist for concomitant idiopathic intracranial hypertension.

Diagnosis and management of spontaneous cerebrospinal fluid fistula and encephaloceles Purpose of review To describe the current state in the diagnosis and management of spontaneous cerebrospinal fluid (sCSF) fistula and encephaloceles. Recent findings The increased incidence of obesity has resulted in more cases of sCSF fistula and encephaloceles. Obesity results in increased intracranial pressure and a greater chance of developing a sCSF fistula or encephalocele. Obstructive sleep apnea can also result in transient increase in intracranial pressure and has been shown to be common in patients with sCSF fistula. Treatment of CSF fistula is usually necessary because of the increased risk of meningitis. The use of hydroxyapatite bone cements to repair the temporal bone defects has been described with a high success rate of closing the fistula and a low complication rate. Concurrent superior semicircular canal dehiscent can be seen in up to 15% of cases and should be suspected during the surgical approach to avoid potential sensorineural hearing loss and chronic imbalance. Summary sCSF fistula and encephaloceles are an uncommon cause of hearing loss, middle ear effusion, and otorrhea, but should be recognized and repaired because of the risk of meningitis.

OTOLOGY AND NEURO-OTOLOGY         Edited by Ravi N. Samy   Editorial: Cerebrospinal fluid physiology Ravi N. Samy Physiology of cerebrospinal fluid circulation Jonathan Shapey, A. Toma, S.R. Saeed Trans-mastoid approach for cerebrospinal fluid leak repair Alexandre Karkas, Edwina Khneisser Laboratory testing and imaging in the evaluation of cranial cerebrospinal fluid leaks and encephaloceles Noga Lipschitz, J. Michael Hazenfield, Joseph T. Breen, Ravi N. Samy The evolution of presenting signs and symptoms of lateral skull base cerebrospinal fluid leaks James G. Naples, Ravi R. Shah, Michael J. Ruckenstein The role of obesity, sleep apnea, and elevated intracranial pressure in spontaneous cerebrospinal fluid leaks Cyrus C. Rabbani, Mohamad Z. Saltagi, Rick F. Nelson Middle fossa approach for spontaneous cerebrospinal fluid fistula and encephaloceles Anthony M. Tolisano, Joe Walter Kutz, Jr. Postoperative management of patients with spontaneous cerebrospinal fluid leak Shawn M. Stevens, Cody J. Smith, Michael Lawton Diagnosis and management of spontaneous cerebrospinal fluid fistula and encephaloceles Joe Walter Kutz, Jr., Anthony M. Tolisano

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