Introduction
Cerebrospinal fluid (CSF) leakage may be observed in inner ear malformations (IEMs), particularly in cases of incomplete partition type I (IP-I) and cochlear hypoplasia type II (CH-II).Reference Sennaroğlu and Bajin1 If unrecognised, this condition may lead to recurrent episodes of meningitis.Reference Zwierz, Masna and Burduk2
In patients with IP-I and CH-II, a defect may be present in the endosteal layer.Reference Sennaroğlu3 This defect may occasionally manifest as a cyst or a leaking fistula, which can be readily identified on imaging studies.Reference Sennaroglu and Bajin4 However, when the defect is covered by mucosa without a cystic configuration, diagnosis becomes more challenging and may mislead the clinician. Such concealed defects increase the risk of recurrent meningitis owing to delayed or missed diagnosis.
A cerebrospinal fluid ‘gusher’ may occur following cochleostomy in cases of IEM.Reference Berrettini, Forli, De Vito, Bruschini and Quaranta5, Reference Suk, Lee and Lee6 The reported incidence is approximately 50 per cent in IP-I, 8 per cent in IP-II and 100 per cent in IP-III anomalies.Reference Sennaroglu7 In IP-III, the complete absence of the modiolus results in gusher formation. In contrast, in IP-II and IP-III, as there is no defect in the otic capsule endosteum, a spontaneous CSF fistula at the level of the stapes footplate is not typically expected.
In patients who experience a CSF gusher during cochlear implantation and subsequently develop meningitis, the initial suspicion frequently focuses on recurrent CSF leakage from the implanted side. Although this is a reasonable assumption, the contralateral ear should always be carefully evaluated.
In this case series, we present three patients with IP-I malformation who experienced an intra-operative CSF gusher during cochlear implantation and subsequently developed meningitis due to a CSF fistula located in the contralateral ear.
Case 1
A female patient born in September 1999 has been followed up for congenital hearing loss. She was diagnosed with bilateral profound sensorineural hearing loss associated with an IP-I anomaly. In September 2005, a cochlear implant (Advanced Bionics®) was inserted into the right ear. During cochleostomy, a CSF gusher occurred, which was controlled by packing temporal fascia into the cochleostomy site adjacent to the electrode array. An intra-operative lumbar drain was inserted, and the patient was monitored for 7 days before the drain was removed and she was discharged.
In 2008, approximately two years after surgery, the patient experienced two episodes of meningitis occurring five months apart. Following the second episode, she was referred to our clinic. Initially, the CSF leak was assumed to originate from the implanted side because of the intra-operative gusher. Initial computed tomography (CT) imaging demonstrated normal middle ear and mastoid aeration on the left side. However, at the time of meningitis, CT imaging revealed the presence of fluid within the middle ear on the contralateral side (Fig. 1). Otoscopic examination showed a dull tympanic membrane without vascularity.
Computed tomography of the patients before cerebrospinal fluid fistula surgery.
In June 2008, surgical exploration of the left ear demonstrated a CSF leak arising from the stapes footplate, which was sealed using temporal fascia. To improve exposure, the incus and stapes were removed. Owing to recurrence of the leak during follow-up, the ear was re-explored four months later, and the CSF leak was again identified at the level of the footplate. The fistula was closed using temporal fascia and fibrin glue. Despite this, the patient experienced another episode of meningitis three months later.
As persistent CSF leakage was confirmed, a subtotal petrosectomy was performed on the left ear, and the cavity was obliterated with fat. Since this procedure, the patient has had no further episodes of CSF leakage or meningitis. She is currently 25 years old and continues to attend regular follow-up visits (Table 1).
Demographic and clinic features of the three patients
Table 1 Long description
The table compares three female patients by demographics, imaging findings, fistula characteristics, cochlear implant details, and surgical approach. All three have the same inner ear malformation type and the cerebrospinal fluid fistula is located at the oval window in every case. CT shows opacity and MRI shows a cyst for all patients, indicating consistent imaging findings across cases. The fistula occurs at ages 9, 5, and 2 years, showing a wide spread in onset. Implantation occurs at 72, 16, and 23 months, and the interval between implant and fistula is 36, 39, and 5 months, with Case 3 having the shortest interval. Implant side is right for Cases 1 and 2 and left for Case 3, while fistula side is left for Cases 1 and 2 and right for Case 3, so implant and fistula sides do not match in any case. Surgery uses an endaural approach in all cases, with Case 1 requiring two endaural procedures and a subtotal petrosectomy. The table summarizes three cases only, so patterns may not generalize beyond this small sample.
CI = cochlear implant; CSF = cerebrospinal fluid; CT = computed tomography; IEM = inner ear malformation; MRI, magnetic resonance imaging.
Case 2
A female patient born in 2011 was diagnosed with bilateral IP-I inner ear malformations and profound sensorineural hearing loss. At the age of 18 months, a right-sided cochlear implant (MED-EL FORM 24®) was performed. During cochleostomy, an intra-operative CSF gusher occurred. The electrode entry site was sealed using temporal fascia and fibrin glue. An intra-operative lumbar drain was inserted, removed on post-operative day 7, and the patient was subsequently discharged.
At the age of five years, the patient was involved in a non-vehicular traffic accident. She sustained minor trauma and was observed for two days before discharge. No skull fractures were identified at that time. Subsequently, she presented with severe headache, fever and vomiting and was diagnosed with meningitis. Over the following six months, she experienced three further episodes of meningitis and was referred to our clinic.
On otoscopic examination, the left tympanic membrane appeared dull. Computed tomography (CT) imaging demonstrated soft-tissue density within the left middle ear consistent with CSF; however, no temporal bone fracture was identified (Figure 1). During surgical exploration of the left ear, the middle ear was found to be filled with CSF. Inspection of the stapes footplate revealed a fistula with visible CSF leakage. The fistula site was carefully widened using a small diamond burr, and a temporal fascia graft was placed in a plug-like manner. The incus and stapes were preserved, and fibrin glue was applied over the graft. An intra-operative lumbar drain was inserted, and the patient was discharged following removal of the drain on post-operative day 7.
The patient is currently 14 years old and continues to attend regular follow-up appointments (Table 1).
Case 3
A female patient born in 2023 has been followed up for congenital hearing loss after failing the newborn hearing screening test. Following referral to our clinic, bilateral profound sensorineural hearing loss was identified. Radiological imaging demonstrated a bilateral IP-I anomaly.
Behavioural audiological testing using insert earphones yielded responses only from the left ear. Magnetic resonance imaging (MRI) showed the presence of the cochlear nerve on the left side, with absence on the right. On the basis of these findings, left-sided cochlear implantation was performed at the age of 18 months (January 2025).
Intra-operatively, a CSF gusher was observed following cochleostomy. A MED-EL FORM 24® electrode array, introduced through a piece of temporal fascia, was inserted into the cochlea. Once CSF leakage had ceased, the procedure was completed.
The patient was monitored as an inpatient for one week post-operatively and was discharged without complications. At the first post-operative week follow-up, the patient was clinically normal. The cochlear implant was activated at the one-month follow-up, and the patient began regular use of the device.
Five months later, the patient presented to the emergency department in her hometown with headache, fever and irritability. Physical examination revealed nuchal rigidity and clear nasal discharge. A diagnosis of meningitis was made, and empirical antibiotic therapy with vancomycin and ceftriaxone was initiated. On day 10, persistent CSF rhinorrhoea was noted, and the patient was referred back to our clinic.
Given the history of an intra-operative CSF gusher, recurrent CSF leakage from the implanted side was initially suspected. However, otoscopic examination demonstrated a dull tympanic membrane on the contralateral side. Contrary to this initial assumption, CT imaging revealed opacification of the middle ear and mastoid on the right side, with no evidence of CSF leakage on the cochlear implant side (Fig. 1).
In June 2025, the patient underwent surgical exploration of the right ear via an endaural approach. Intra-operatively, a cystic lesion was identified on the oval window footplate with active CSF leakage. The cyst was excised, and a 0.5-mm fenestration was created in the oval window using a diamond burr. With preservation of the incus and stapes, a temporal fascia graft was fashioned into a plug and inserted into the fenestration, followed by application of fibrin glue. The procedure was concluded once CSF leakage had ceased.
An intra-operative lumbar drain was inserted, and CSF drainage was gradually tapered over six days. On post-operative day 7, the lumbar drain was removed, and the patient was discharged without neurological sequelae or further CSF leakage.
On retrospective review of the patient’s pre-implant imaging, a cystic lesion at the level of the oval window was identified on MRI. However, temporal bone CT did not demonstrate middle ear opacification suggestive of pre-existing CSF leakage (Table 1).
Discussion
Recurrent meningitis is a significant concern in patients with IEMReference Chen, Shi, Gong, Chen and Li8. Apart from the lethal and other neurological complications, post-meningitic labyrinthitis ossificans may develop, potentially resulting in total hearing loss particularly in the patient with single-sided deafnessReference Trakimas, Knoll, Castillo-Bustamante, Kozin and Remenschneider9. In such cases, delayed diagnosis and treatment may also preclude the possibility of cochlear implantation. Given these serious consequences, it is crucial to thoroughly investigate the underlying cause of meningitis in these patients.
In IEM, particularly in cases of IP-I and CH-II, a cyst may occur at the stapes footplate due to endosteal developmental abnormalities.Reference Sennaroglu10, Reference Sennaroglu, Boya and Redleaf11 In some cases, even in the absence of a fistula, an endosteal developmental anomaly may be present in a portion of the vestibule, such as the lateral semicircular canal. These abnormalities may appear completely normal on macroscopic examination but can be detected histologically. In certain patients, the modiolar base may remain intact, preventing CSF pressure from being transmitted to the inner ear. Therefore, the pathogenesis is not necessarily related to increased CSF pressure. Importantly, in IP-Ipatients, even in the absence of a visible fistula, structural weakness may still be present in other regions of the otic capsule, predisposing to recurrent meningitis. Such patients often pose significant diagnostic challenges.
In our clinic, cochlear implantation was performed in 414 patients with an IEM. Among these patients, those with IP-I anomaly constituted the majority (60 patients; 14.5 per cent). The rate of intra-operative gusher following cochleostomy in patients with IP-I anomaly was found to be 51.6 per cent (31 cases). Eftekharian et al reported a gusher rate of 86.4 per cent in patients in 18 IP-I cases.Reference Eftekharian, Eftekharian, Mokari and Fazel12 In cases where intra-operative gusher occurred and subsequent meningitis developed during follow-up, the initial suspicion is often of a CSF leak from the side of the implant. Since the tympanic membrane remains intact in these patients, the CSF leak typically presents as rhinorrhea. Therefore, the side of nasal discharge should be the first question asked during evaluation. Another diagnostic clue when determining the side of CSF leakage is the appearance of the tympanic membrane; a dull and bulging membrane may indicate the affected side.
In all of our patients, pre-operative CT scans demonstrated normal aeration in the middle ear and mastoid on the cochlear implant side, while the contralateral side showed complete opacification of the normally air-filled spaces. Retrospective review of previous MRI scans confirmed the diagnosis by identifying a stapes footplate cyst (Figure 2).
Magnetic resonance imaging of the patients stapes footplate cyst, respectively (white arrows indicates stapes footplate cyst location).
On retrospective review of the patient’s pre-implant imaging, a cystic lesion at the level of the oval window was identified on MRI. However, temporal bone CT did not demonstrate middle ear opacification suggestive of pre-existing CSF leakage (Table 1).
Once the patient’s clinical condition stabilized following meningitis, surgical intervention was planned. In all three of our cases, we operated using an endaural approach with microscope. However, with advancements in endoscopic systems and increased familiarity with temporal bone anatomy, endoscopic approaches have become viable alternatives.Reference Mittal, Chappity, Grover, Gupta, Pradhan and Parida13, Reference Kou, Zhu, JW, Mitchell and Isaacson14 Some reports advocate for a direct subtotal petrosectomy approach in such patients.Reference Morelli, Damam, Yilala, Fancello, Ferraro and Caruso15 In our first case, the fistula was closed twice; however, due to persistent leakage, a subtotal petrosectomy was ultimately required. In this patient, stapes was removed during the first operation. We believe keeping the stapes intact is very important to avoid recurrence of CSF leak. To date, 32 patients in our clinic have undergone surgery for stapes footplate cysts. With growing experience, the need for subtotal petrosectomy has significantly diminished.
Two surgical principles are critical in the management of these cases.Reference Sennaroglu and Bajin4 First, the stapes and incus should not be removed merely to improve visualization, as these ossicles provide structural support for the fascia graft and help prevent its displacement. Second, if the fistula at the footplate is very small, it should be carefully enlarged using a 0.5-mm drill in a controlled manner. This is because placing a fascia graft into a very small defect can lead to excessive manipulation with fracture of the footplate (Fig. 3).
In Case 3, the stapes footplate fistula location and after closure with tttttemporal fascia, respectively (black arrow indicates fistula location).
In conclusion, in patients with inner ear malformations presenting with recurrent meningitis, the possibility of a stapes footplate cyst should always be considered as an underlying aetiology. Even in cases where a prior history of intra-operative gusher during cochlear implantation exists, the contralateral ear must be thoroughly evaluated. A meticulous radiological and clinical assessment of both ears is essential to avoid delayed diagnosis and to ensure appropriate surgical management.
• In incomplete partition type I (IP-I) malformations, cerebrospinal fluid (CSF) leaks may arise from subtle endosteal defects or stapes footplate cysts that are not evident on initial imaging
• These occult lesions frequently involve the contralateral ear and can lead to delayed diagnosis and recurrent meningitis
• The presence of an intra-operative gusher during cochlear implantation does not necessarily indicate a persistent leak at the implant site
• Laterality of rhinorrhea and careful review of follow-up magnetic resonance imaging (MRI) may provide diagnostic clues, occasionally revealing stapes footplate cysts
• Surgical closure of contralateral stapes footplate fistulas using an ossicle-preserving, plug-like fascia technique is effective in preventing recurrence
• Subtotal petrosectomy should be reserved for refractory cases, as preservation of ossicular support may reduce graft displacement and failure
Acknowledgements
This study received no funding. There is no disclosure of funding.
