Abstract

Background: CSF fistula involves abnormal leakage of cerebrospinal fluid (CSF) from its normal pathways, typically from high- to low-pressure areas at the base of the skull. It requires an osteomeningeal breach, causing discomforts such as headaches and abnormal drainage. Temporal bone CSF leakage often results from trauma or chronic otitis media, and its surgical treatment is often delayed. The application of endoscopes in skull base procedures has become increasingly common, offering new ways to improve visualization during performance. Endoscopic tools provide a broad view, sharp image quality, enhanced magnification, and the advantage of visualizing areas that are typically hard to see directly.

Methods: CSF leaks in the temporal bone can be challenging to diagnose, with subtle symptoms that can go undetected for years. Imaging techniques such as computed tomography (CT) and magnetic resonance imaging are used for diagnosis, with CT cisternography being the most reliable. Surgical repair may be necessary in certain cases. Most patients do not require surgery, as conservative management is effective. Surgery is considered for severe symptoms. Absolute contraindications include conditions that prevent general anesthesia, while relative contraindications include vestibular issues and migraines. Endoscopic surgery involves a light source, rigid endoscope, and high-definition camera. The defect is repaired using materials such as bone wax, fat, and fibrin glue. Surgery is performed under general anesthesia with a small incision behind the ear, and the skull base is reconstructed.

Results: Once the patient can ambulate and tolerate a diet, they can be discharged (average hospital stay is 2 days) on 60 mg of oral prednisone daily for 2 weeks followed by a 1-week taper. During postoperative course, patient’s course was uncomplicated and there was no evidence of CSF leakage at 24 h, nor at the review 2 weeks later in the outpatient clinic.

Conclusion: CSF leaks of temporal bone origin are rare and should be considered in patients with non-resolving outer ear effusion or meningitis. Temporal bone CT represents the most valuable imaging modality for diagnosis and preoperative surgical planning. Isolated dural defects of the tegmen tympani may be repaired through subtemporal approach through a craniotomy. Endoscope-assisted surgery leads to an elevated efficacy of defining precisely the site of the bone defect.

Keywords: Cerebrospinal fluid leakage, Middle fossa, Neurosurgery, Osteomeningeal breach, Skull base, Subtemporal craniotomy

INTRODUCTION

A cerebrospinal fluid (CSF) leakage refers to the abnormal escape of CSF from its normal ventricular, cisternal, and subarachnoid pathways. In this way, CSF moves from a higher-pressure system to a lower-pressure one, which generally corresponds to the cavities located at the base of the skull. For a CSF fistula to occur, an osteomeningeal breach (OMB) must necessarily take place, where the bony and dural barrier surrounding the brain and spinal cord loses its continuity. The loss of CSF causes a series of discomforts, both from the decrease in its intracranial amount (headache) and from its abnormal path (rhinorrhea and otorrhea). However, the primary significance of a CSF fistula and its corresponding OMB is that it constitutes an entry point to the central nervous system for a series of microorganisms that colonize the mucosa of cavities adjacent to the base of the skull, which can lead to meningitis with life-threatening risks.[ 1 ]

CSF leakage from the temporal bone is an uncommon condition with multiple potential etiologies. It most often occurs in the context of traumatic fractures of the temporal bone and, less frequently, can arise spontaneously, secondary to erosive chronic otitis media, or due to surgical injury. The incidence of CSF leakage affecting the temporal bone has not been clearly established, although it is believed to be less common than those involving the anterior base of the skull. A large series of traumatic temporal bone fractures found that the incidence of CSF leakage is 17%.[ 3 ]

Since the best way to clearly observe a defect in the arcuate eminence is from a superior angle, most high-volume centers favor using a microscope-assisted middle fossa craniotomy (MFC) for treatment.

That said, about 30% of cases involve defects located more medially along a sloped portion of the tegmen, making access more challenging.

These medially situated defects often require a more extensive surgical opening, the removal of bony ridges on the lateral skull base, and/or extended periods of brain retraction to be properly seen. In particular, the inner or nonampullated edge of the defect tends to be the hardest to access, and if it’s not fully repaired, there is a higher risk that symptoms will persist or return after surgery.

The application of endoscopes in skull base procedures has become increasingly common, offering new ways to improve visualization during performance.

Endoscopic tools provide a broad view, sharp image quality, enhanced magnification, and the advantage of visualizing areas that are typically hard to see directly.

We consider endoscopic techniques at the skull base to be both reliable and efficient for detecting and correcting medial defects, especially when combined with a MFC. The angled design of the endoscope helps to illuminate and expose the dehiscence more clearly, minimizing the need for extended manipulation of the temporal lobe.

This method allows for complete visualization of the arcuate eminence defect, showing besides skull base anatomy in a high-quality image, ensuring accurate identification and correction of the defect.

PREOPERATIVE EVALUATION

CSF leaks of the temporal bone pose certain diagnostic and management challenges. Symptoms can be subtle and can be present for years before diagnosis. In some cases, patients may present acutely with potentially fatal intracranial infection. Once a leak is determined to be present, available imaging methods may not localize the source. There are several options for surgical repair, which include transmastoid, middle fossa, or combined approaches.[ 5 ]

Numerous techniques, including plain skull radiography, high-resolution tomography, intraoperative injection of fluorescein dye, positive contrast studies, radionuclide cisternography, and dynamic film magnetic resonance (MR), are all helpful in a limited way. For over a decade, computed tomography (CT) cisternography has been considered the most reliable and accurate method of diagnosing CSF fistula; however, this technique is invasive and time-consuming and is contraindicated in patients with active meningitis. MR cisternography is a noninvasive technique that can detect a CSF fistula by the inherent bright signal of CSF on T2-weighted images. High-resolution CT is highly effective in the demonstration of small defects in bone at the site of a CSF fistula. Both these techniques are safe, less time-consuming than CT cisternography, and have a high patient compliance rate[ 6 ] [ Figures 1 and 2 ].

Figure 1:

Anatomic location of inner ear cerebrospinal fluid (CSF) leakage on preoperative magnetic resonance scans can help anticipate the need for the endoscope during middle fossa craniotomy repair (Panel a): Preoperative axial magnetic resonance image film ponderation shows hyperintense image suggestive of CSF column extending through the mastoid cells and inner ear (red circle). (Panel b): Preoperative coronal magnetic resonance image film ponderation shows hyperintense image suggestive of CSF column extending into the mastoid cells and inner ear (red circle). (Panel c and d): Preoperative axial magnetic resonance image T2 ponderation shows hyperintense image suggestive of CSF column extending through a defect into the mastoid cells and inner ear (Red circle).

Figure 2:

High-resolution computed tomography (CT): Axial and coronal views of temporal bone. (Panel a and b): Plain high-resolution axial CT scan reveals a cerebrospinal fluid (CSF) fistula at the right tegmen tympani into mastoid air cells. (Panel c): Plain high-resolution coronal CT scan, 1-mm thick, reveals a bone defect in the right tegmen tympani with a CSF-density column extending extracranially.

INDICATIONS AND CONTRAINDICATIONS

Most patients are symptomatic and do not necessitate surgical intervention because conservative management is effective.[ 2 ] Conservative treatment includes avoidance of triggers, as well as otologic examination and interval audiometric testing.

In patients with incapacitating auditory and/or vestibular symptoms, however, surgical repair is a reasonable option.

Patients that meet the diagnostic criteria for ear fistula require documentation of a high-resolution CT, comprehensive audiometric testing, and a cine MR.

Absolute contraindications for ear fistula repair include comorbid conditions that would preclude general anesthesia and intracranial pathology that would increase the risk of a lateral skull base approach. Should be avoided in patients where the bony defect affects the only hearing ear.

In these cases, surgical approaches may best be done using a transmastoid or MFC approach or with angled endoscopy.

Additional relative contraindications include vestibular hypofunction in the contralateral ear, migraines, and Meniere’s disease. In such cases, conservative management is most reasonable.[ 4 ]

SURGICAL EQUIPMENT AND TECHNIQUE

Equipment needed for MFC assisted with endoscopic surgery includes a light source and rigid endoscope coupled to a 3 charge-coupled, high-definition (HD) camera, and HD video monitor. A 3 mm diameter 0 angle endoscope is used for assisted lateral skull base surgery. Surgical ergonomics are critical. The HD monitor should be positioned at on the side-up contralateral to the craniotomy. A craniotome and basic craniotomy is used.

Occluding the defect is achieved with bone wax, fascia, bone pate, hydroxyapatite cement, fat tissue, fibrin glue or a combination of 2 or more of these materials, plugging the defect. As the defect is usually very small, achieving a durable resurfacing outcome may be challenging and combination of these materials is used to settle into the defect.

Finally, plugging approaches have been associated with a lower recurrence rate of symptoms. Bone wax, fat tissue, and fibrin glue are used in a plugging approach.[ 2 ]

General anesthesia is routinely performed. Patient is preoperatively given levetiracetam, ceftazidime, and dexamethasone. A Foley urinary catheter should be placed following intubated. A minimal hair shave, a 6 cm linear incision is drawn, extending from 1 cm above and superior to the postauricular skin crease and along the floor of the middle fossa and superiorly over the temporalis into the hairline superiorly. Next, about 15 cc of 1% lidocaine with 1:100,000 epinephrine is infiltrated into the planned surgical field. The ear is prepped and draped in the usual sterile fashion. The skin incision is then made perpendicular to the hair follicles even though the risk of alopecia along the surgical scar. The incision is made approximately 1 cm above the attachment of the pinna superiorly to avoid pain with wearing glasses that fall on the scar line postoperatively. Care is taken to not extend the incision past the anterior hairline.

The skin flaps are retracted superficial along ways to the temporalis fascia sharply. Bipolar cautery is used for hemostasis as monopolar cautery is avoided. A temporalis fascia graft is harvested centrally, allowing for a peripheral rim of fascia to facilitate closure.

An anteriorly based muscle and periosteal flap is designed, carried down to the bone, and elevated anteriorly, as well as inferiorly, to expose the middle fossa cranial base. Then, the rigid 0 angle endoscope is introduced, and the bone defect of 0.5 cm and a CSF leak is clearly seen at tegmen tympani, so after is taped with bone wax, fat tissue, fibrin glue in multiple layers plugging, absence of liquid output is evidenced, and an inferiorly based temporalis muscle flap provides a pedicled flap for reconstructing the skull base, and a closure by plans is made [ Figure 3 ].

Figure 3:

Intraoperative images during surgery using a 0° rigid endoscope, right ear in the region of the tegmen tympani following middle fossa craniotomy. (Down at the right we can observe a four point arrow view of the skull orientation). (Panel a): In the right ear, improved view of the middle cranial fosa at the tegmen tympani zone, making evident a bone defect of approximate 5 mm. (yellow star: Arcuate eminence, purple circle: Tegmen tympani) (Panel b): A middle fossa retractor is used to maintain surgical exposure. Fibrin glue is collocated at the defect site at tegmen tympani. (Panel c): A fat tissue flap is collocated at the defect site under direct view of rigid 0° endoscope. (Panel d): A second fibrin glue flap through plugging technique is collocated at the defect site. (Panel e): A second fat tissue flap is collocated at the bone defect site to ensure water tight closure. V: Ventral, D: Dorsal, Ce: Cephalic, Ca: Caudal.

POSTOPERATIVE CARE

Patients are monitored in a setting for 24 h. If there is any concern about efficacy of the repair, a heavily weight T2 MRI of the cranial skull base may be obtained for confirmation. Headache and vertigo are managed with minimal pain medications to avoid masking neurological change and vestibular suppressants. Intravenous steroids are continued. Once the patient can ambulate and tolerate a diet, which can be discharged (average hospital stay is 2 days) on 60 mg of oral prednisone daily for 2 weeks followed by a 1-week taper.

Patients should be encouraged to ambulate without straining or lifting heavy objects for at least 2 weeks.

Further hearing loss (1%), CSF leak (1%), temporal lobe injuries and hemorrhage, facial weakness, meningitis, persistent headaches, and persistent disequilibrium (worse in patients with a migraine history) are complications of this procedure.[ 2 ]

During postoperative course, the patient’s course was uncomplicated and there was no evidence of CSF leakage at 24 h, nor at the review 2 weeks later in the outpatient clinic.

DISCUSSION

The MFC through a subtemporal approach has the advantage of allowing localization of the dural defect in the temporal bone while avoiding brain intradural retraction and potential neurological complications. The case presented suggests that the success of the repair, and diminished risk of hearing loss through the MFC as an effective treatment for this condition. Its advantages include a direct route and improved exposure of the entire middle fossa cranial base and a secure extracranial repair with little chance of recurrence.

In addition, here in the presented case, the use of the endoscope allows to visualize the defect along the tegmen tympani that would no longer be visualized trough a microscope with that high-resolution image. Besides, in cases of nonampullated or medial defects, the use of the retractor along with the use of a skull base endoscope allows clear and high-resolution visualization of the defect even though through a small craniotomy, without the need of extension of craniotomy in cases where the defect cannot be found.

CONCLUSION

CSF leaks of temporal bone origin are rare and should be considered in patients with non-resolving outer ear effusion or meningitis. Temporal bone CT represents the most valuable imaging modality for diagnosis and preoperative surgical planning. Isolated dural defects of the tegmen tympani may be repaired through subtemporal approach through a craniotomy. Endoscope-assisted surgery leads to an elevated efficacy of defining precisely the site of the bone defect.

Ethical approval:

The Institutional Review Board approval is not required.

Declaration of patient consent:

Patient’s consent was not required as there are no patients in this study.

Financial support and sponsorship:

Nil.

Conflict of interest:

There are no conflicts of interest.

Use of artificial intelligence (AI)-assisted technology for manuscript preparation:

The authors confirm that there was no use of artificial intelligence (AI)-assisted technology for assisting in the writing or editing of the manuscript and no images were manipulated using AI.

Disclaimer

The views and opinions expressed in this article are those of the authors and do not necessarily reflect the official policy or position of the Journal or its management. The information contained in this article should not be considered to be medical advice; patients should consult their own physicians for advice as to their specific medical needs.

References

1. Gonzalo NMRodrigo ISRodrigo IC. Fistula of cerebrospinal fluid in the ear. Available from: https://www.sochiorl.cl/uploads/61_2-09.pdf [Last accessed on 2025 Feb 06].

2. Kozin ED, Lee DJ. Endoscopic-assisted surgical repair of superior canal dehiscence using a keyhole middle fossa craniotomy approach. Oper Tech Otolaryngol Head Neck Surg. 2019. 30: 223-30

3. Kutz JW, Husain IA, Isaacson B, Roland PS. Management of spontaneous cerebrospinal fluid otorrhea. Laryngoscope. 2008. 118: 2195-9

4. Pappas DG, Hoffman RA, Holliday RA, Hammerschlag PE, Pappas DG, Swaid SN. Evaluation and management of spontaneous temporal bone cerebrospinal fluid leaks. Skull Base Surg. 1995. 5: 1-7

5. Pelosi S, Bederson JB, Smouha EE. Cerebrospinal fluid leaks of temporal bone origin: Selection of surgical approach. Skull Base. 2010. 20: 253-9

6. Shetty PG, Shroff MM, Sahani DV, Kirtane MV. Evaluation of high-resolution CT and MR cisternography in the diagnosis of cerebrospinal fluid fistula. AJNR Am J Neuroradiol. 1998. 19: 633-9