Computed tomography evaluation of air cells in the petrous bone--relationship with postoperative cerebrospinal fluid rhinorrhea

An algorithm for the surgical approach to spontaneous temporal bone CSF leak

OBJECTIVE

To suggest a comprehensive algorithm for the surgical approach for correcting of sources of temporal bone CSF leaks.

METHODS

A case series for patients operated in a single academic tertiary referral center between 2011 and 4.2022. Included in the study were 46 patients, 5 of whom had a bilateral problem, resulting in 51 pathologic temporal bones. The presentation was an active CSF leak (38 patients) or bacterial otogenic meningitis (8 patients). Follow up ranged from 8 months to 5 years.

RESULTS

Of the 42 ears operated via the default middle fossa approach, 37 were successful (88 %) in controlling CSF leak. None had intracranial complications or sensorineural hearing loss. Location, number and size of the defects, hearing status, associated superior semicircular canal dehiscence, additional intra-temporal or intra-cranial pathologies may indicate a transmastoid approach. Of the six ears that had a canal wall up mastoidectomy as a primary procedure, one required revision due to ongoing CSF leak. Five revision cases and three primary cases were effectively sealed with a subtotal petrosectomy and obliteration. One was lost to follow-up. Hearing was reconstructed with bone-anchored hearing implants in 6 out of these 8 ears.

CONCLUSIONS

The middle fossa approach could be used as a default approach for sealing TD. There are a number of indications for transmastoid approaches in both primary and revision cases. Obliteration of the ear was used in all revision cases. The suggested algorithm can help in planning surgery for temporal bone CSF leaks or a history of otogenic meningitis.

An inter-observer assessment of mastoid pneumatization and degree classification using sigmoid sinus: comparing two levels of temporal bone computed tomograms

BACKGROUND

The degree of mastoid pneumatization of the temporal bone (TB) has been implicated in the pathogenesis of TB diseases and surgical implications, and planning of a few otologic surgeries. However, there is lack of consensus in the classification of the degree of pneumatization. This study aimed to suggest a simple, quick, and less-burden classification system for assessing and rating the degree of pneumatization by comparing two levels of TB computed tomographs (CTs) using the SS as a reference in an inter-observer assessment among otologists.

METHODS

This was a randomized pilot survey among otologists. A questionnaire consisting of different axial CTs of TB taken at two levels: the level of malleoincudal junction (MIJ) and the level of lateral semicircular canal (LSCC), with different pneumatization patterns, was used to assess participants' impressions of the degree of pneumatization. The terms "hypo-," "moderate," "good," and "hyper-" pneumatization were listed as options to rate their impressions on the degree of mastoid pneumatization of the TB images using the SS as a reference structure. Likert scale was used to assess their level of agreement or disagreement with using SS as a reference in evaluating mastoid pneumatization.

RESULTS

Participants who correctly rated images taken at the level of LSCC according to their respective degree of pneumatization were significantly higher (p < 0.05) regardless of their year of experience compared to those that correctly rated corresponding images taken at the level of MIJ. A 76% positivity in their level of agreement with the use of sigmoid sinus in evaluating mastoid pneumatization was observed on the Likert-scale chart.

CONCLUSION

Findings from this study suggest that evaluating air cells around the SS at the level of LSCC on CTs could be easier in assessing and classifying the degree of mastoid pneumatization.

Differences in mastoid pneumatization between Asians and Caucasians

BACKGROUND

Anatomical differences of the mastoid pneumatization in Asian and Caucasian patients must be considered when performing the retrosigmoid craniotomy since it may have implications to avoid specific complications such as cerebrospinal fluid infections or fistula.

METHODS

We selected cranial CT scans of 120 Asian and 120 Caucasian patients, who were treated at the Mitsui Memorial Hospital (Japan) and at the Heidelberg University Hospital (Germany). Mastoid pneumatization was classified according to the relationship of the mastoid air cells (MAC) to the sigmoid sinus (Type I - III). The risk of mastoid air cell opening through craniotomy increases from Type I to III. Comparative analyses between gender and ethnicities were performed using the Chi² Test and the independent T-Test and considered significant if p < 0.05.

RESULT

In Caucasians, Type III pneumatization was significantly overrepresented compared to Type II or I, compared to the Asian cohort (Type III:II:I in Caucasians = 60 %:26 %:14 %; in Asians = 28 %:43 %:29 %). Importantly, we found significant differences in pneumatization types between Caucasians and Asians in both gender subgroups (m: Type III 60 % vs 35 %; Type II 30 % vs 36.7 %; Type I 10 % vs 28.3 %, p = 0.008; f: Type III 60 % vs 23.3 %, Type II 21.7 % vs 48.3 %, Type III 18.3 % vs 28.3 %, p < 0.001; Chi² Test).

CONCLUSION

Caucasian patients are more prone to the opening of the mastoid air cells than Asian patients when performing a retrosigmoid craniotomy due to differences in the degree of mastoid pneumatization. This may help to avoid complications such as postoperative infections or cerebrospinal-fluid fistula.

Lariboisiere Hospital pre-operative surgical checklist to improve safety during transpetrosal approaches

BACKGROUND

Transpetrosal approaches are technically complex and require a complete understanding of surgical and radiological anatomy. A careful evaluation of pre-operative magnetic resonance imaging and computed tomography scan is mandatory, because anatomical or pathological variations are common and may increase the risk of complications related with the approach.

METHODS

Pre-operative characteristics of venous and petrous bone anatomy were analysed and correlated with intraoperative findings, using injected magnetic resonance imaging and thin-slices computed tomography scan. These data regularly checked before each transpetrosal approach were progressively included in the presented checklist.

RESULTS

Transpetrosal approaches have been used in 101 patients. Items included in the checklist were petrous bone pneumatization, angle between petrous apex and clivus, dehiscence of petrous carotid artery, dehiscence of geniculate ganglion, distance between superior semicircular canal and middle fossa floor, distance between cochlea and middle fossa floor, sigmoid sinus dominance, transverse sigmoid sinus junction depth to the outer cortical bone, jugular bulb height (high or low), location of the vein of Labbé, characteristics of superior petrosal vein complex.

CONCLUSION

The presented checklist provides a systematic scheme of consultation of characteristic of venous and petrous bone anatomy for transpetrosal approaches. In our experience, the use of this checklist reduces the risk of complications related with approach, by minimizing the neglect of crucial information.

How to Precisely Open the Internal Auditory Canal for Resection of Vestibular Schwannoma via the Retrosigmoid Approach

Objective

The aim of this study was to investigate how to precisely expose the intrameatal portion of vestibular schwannomas (VSs) without damaging the labyrinth.

Methods

This was a retrospective study of patients who had undergone retrosigmoid resection of a VS in our institution from April 2018 to December 2021. The patients were divided into microsurgery (MS) and navigation endoscopic-assisted (combined surgery, CS) groups and the effects of image guidance and endoscopy evaluated. The tumors in the CS group were then divided into medial and lateral types by fusion imaging and the differences between the two types analyzed.

Results

Data of 84 patients were analyzed. Residual tumor was detected by postoperative MRI at the fundus of the internal auditory canal in 5 of the 31 patients in the MS group and 1 of the 53 in the CS group. The labyrinth was damaged in four patients in the MS group but was not damaged in any of the CS group patients. The CS group included 29 lateral type and 24 medial type schwannomas. Endoscopic-assisted resection of residual tumor in the IAC was performed significantly more often on medial than on lateral tumors.

Conclusion

Navigation and endoscopy are useful in assisting the exposure of the intrameatal portion of VSs. Preoperative MRI/CT fusion imaging is helpful in preoperative evaluation and surgical planning in patients undergoing VS surgery. Tumors of the medial type require endoscopic assistance for resection.

An aberrant venous channel mimicking the perilabyrinthine cells in the petrous bone of a patient with vestibular schwannoma: illustrative case

BACKGROUND

Anatomical variations, such as high jugular bulbs and air cell development in the petrosal bone, should be evaluated before surgery. Most bone defects in the internal auditory canal (IAC) posterior wall are observed in the perilabyrinthine cells. An aberrant vascular structure passing through the petrous bone is rare.

OBSERVATIONS

A 48-year-old man presented with a right ear hearing disturbance. Magnetic resonance imaging revealed a 23-mm contrast-enhancing mass in the right cerebellopontine angle extending into the IAC, consistent with a right vestibular schwannoma. Preoperative bone window computed tomographic scans showed bone defects in the IAC posterior wall, which ran farther posteroinferiorly in the petrous bone, reaching the medial part of the jugular bulb. The tumor was accessed via a lateral suboccipital approach. There was no other major vein in the cerebellomedullary cistern, except for the vein running from the brain stem to the IAC posterior wall. To avoid complications due to venous congestion, the authors did not drill out the IAC posterior wall or remove the tumor in the IAC.

LESSONS

Several aberrant veins in the petrous bone are primitive head sinus remnants. Although rare, their surgical implication is critical in patients with vestibular schwannomas.

Prevention of cerebrospinal fluid leak after vestibular schwannoma surgery: a case-series focus on mastoid air cells' partition

BACKGROUND

Petrous bone pneumatization may be related to cerebrospinal fluid (CSF) leak secondary to vestibular schwannoma surgery.

OBJECTIVE

To assess the association between petrous bone pneumatization and CSF leak in vestibular schwannoma surgery.

METHODS

A retrospective study included 222 consecutive vestibular schwannoma patients treated via a retrosigmoid or translabyrinthine approach in a 17-year period in one University Hospital. Association of CSF leak and petrous bone pneumatization, as seen on CT scans, was assessed on ANOVA and Student's t or Chi-squared test in case of non-parametric distribution.

RESULTS

One hundred and 75 resections were performed on a retrosigmoid approach and 47 on a translabyrinthine approach. Mean age was 53.6 ± 12.9 years. Mean follow-up was 5 years 6 months. Twenty-six patients (11.7%) showed CSF leak and 8 (3.6%) meningitis. Approach (p = 0.800), gender (p = 0.904), age (p = 0.234), body-mass index (p = 0.462), tumor stage (p = 0.681) and history of schwannoma surgery (p = 0.192) did not increase the risk of CSF leak. This risk was unrelated to mastoid pneumatization (p = 0.266). There was a highly significant correlation between internal acousticus meatus (IAM) posterior wall pneumatization and CSF leak after retrosigmoid surgery (p = 0.008). Eustachian tube packing in the translabyrinthine approach did not decrease risk of CSF leak (p = 0.571).

CONCLUSION

Degree of petrous bone pneumatization was not significantly related to risk of CSF leak, but pneumatization of the posterior IAM wall increased this risk in retrosigmoid surgery. Eustachian tube packing in the translabyrinthine approach is not sufficient to prevent postoperative CSF leak. Both approaches had similar rates of CSF leaks, around 12%.

Quantitative three-dimensional computed tomography analysis of sinus tympani volume in temporal bones with petrous apex pneumatization

OBJECTIVE

To investigate the association between sinus tympani volume and petrous apex pneumatization in this retrospective-archival temporal bone computed tomography study.

METHODS

We included 46 temporal bones with pneumatized petrous apex from 26 patients and 52 temporal bones without petrous apex pneumatization from 26 other patients. Using OsiriX software for MacOS (version 3.8.1, Pixmeo), we measured the volumes from three-dimensional sinus tympani models and compared the sinus tympani volumes and depths between the temporal bones with and without pneumatized petrous apex.

RESULTS

Among 150 patients totally reviewed, 26 (17.3%) had petrous apex pneumatization. The median sinus tympani volume was 16.05 (5.6-59.7) mm³ in temporal bones with pneumatized petrous apex and 8.7 (1.76-59.7) mm³in temporal bones without. The sinus tympani volume was significantly greater in temporal bones with pneumatized petrous apex compared to those without (p < 0.001). Additionally, temporal bones with pneumatized petrous apex had a significantly deeper sinus tympani [median depth = 2.17 (0-3.04) mm] compared to the temporal bones without [median depth = 1.69 (0-3.73) mm] (p = 0.045). We found that petrous apex pneumatization was associated with deeper and larger sinus tympani.

CONCLUSION

Patients with pneumatized petrous apex had a greater sinus tympani volume associated with the increased risk of residual cholesteatoma.

Surgery of the lateral skull base: a 50-year endeavour

Disregarding the widely used division of skull base into anterior and lateral, since the skull base should be conceived as a single anatomic structure, it was to our convenience to group all those approaches that run from the antero-lateral, pure lateral and postero-lateral side of the skull base as “Surgery of the lateral skull base”. “50 years of endeavour” points to the great effort which has been made over the last decades, when more and more difficult surgeries were performed by reducing morbidity. The principle of lateral skull base surgery, “remove skull base bone to approach the base itself and the adjacent sites of the endo-esocranium”, was then combined with function preservation and with tailoring surgery to the pathology. The concept that histology dictates the extent of resection, balancing the intrinsic morbidity of each approach was the object of the first section of the present report. The main surgical approaches were described in the second section and were conceived not as a step-by-step description of technique, but as the highlighthening of the surgical principles. The third section was centered on open issues related to the tumor and its treatment. The topic of vestibular schwannoma was investigated with the current debate on observation, hearing preservation surgery, hearing rehabilitation, radiotherapy and the recent efforts to detect biological markers able to predict tumor growth. Jugular foramen paragangliomas were treated in the frame of radical or partial surgery, radiotherapy, partial “tailored” surgery and observation. Surgery on meningioma was debated from the point of view of the neurosurgeon and of the otologist. Endolymphatic sac tumors and malignant tumors of the external auditory canal were also treated, as well as chordomas, chondrosarcomas and petrous bone cholesteatomas. Finally, the fourth section focused on free-choice topics which were assigned to aknowledged experts. The aim of this work was attempting to report the state of the art of the lateral skull base surgery after 50 years of hard work and, above all, to raise questions on those issues which still need an answer, as to allow progress in knowledge through sharing of various experiences. At the end of the reading, if more doubts remain rather than certainties, the aim of this work will probably be achieved.

Meningitis for Streptococcus salivarius Secondary to Paradoxical Cerebrospinal Fluid Rhinorrhea as a Complication of Retrosigmoid Approach

Rhinorrhea secondary to a retrosigmoid approach is rare, but when it manifests, it is due to a paradoxical cerebrospinal fluid (CSF) leak, as a result of the communication between the mastoid cells, middle ear, and eustachian tube, which finally ends on the release of CSF through the nasopharynx. Abnormal communications increases the risk of infections, not only at the surgical site but also through an ascending path. Magnetic resonance cisternography (MRC) with intrathecal gadolinium injection through a lumbar puncture not only allows an adequate diagnosis but also helps to establish management plans. Here, we present an eighty-three-year-old female patient, with a history of trigeminal neuralgia, who underwent retrosigmoid approach to perform trigeminal microvascular decompression. After intervention, the patient consulted for rhinorrhea, fever, and headache. Lumbar puncture was performed, resulting on the isolation of Streptococcus salivarius in CSF. Nuclear MRC with intrathecal gadolinium injection was performed, identifying a paradoxical CSF leak. Failure in medical management with conservative treatment ends in surgical reexploration, identifying a bone defect in mastoid cells, which was corrected.

Analysis of various tracts of mastoid air cells related to CSF leak after the anterior transpetrosal approach

OBJECTIVE

The anterior transpetrosal approach (ATPA) was established in 1984 and has been particularly effective for petroclival tumors. Although some complications associated with this approach, such as venous hemorrhage in the temporal lobe and nervous disturbances, have been resolved over the years, the incidence rate of CSF leaks has not greatly improved. In this study, some varieties of air cell tracts that are strongly related to CSF leaks are demonstrated. In addition, other pre- and postoperative risk factors for CSF leakage after ATPA are discussed.

METHODS

Preoperative and postoperative target imaging of the temporal bone was performed in a total of 117 patients who underwent ATPA, and various surgery-related parameters were analyzed.

RESULTS

The existence of air cells at the petrous apex, as well as fluid collection in the mastoid antrum detected by a postoperative CT scan, were possible risk factors for CSF leakage. Tracts that directly connected to the antrum from the squamous part of the temporal bone and petrous apex, rather than through numerous air cells, were significantly related to CSF leak and were defined as “direct tract.” All patients with a refractory CSF leak possessed “unusual tracts” that connected to the attic, tympanic cavity, or eustachian tube, rather than through the mastoid antrum.

CONCLUSIONS

Preoperative assessment of petrous pneumatization types is necessary to prevent CSF leaks. Direct and unusual tracts are particularly strong risk factors for CSF leaks.

Understanding Anatomy of the Petrous Pyramid-A New Compartmental Approach

BACKGROUND

Learning surgical anatomy of the petrous pyramid can be a challenge, especially in the beginning of the training process. Providing an easier, holistic approach can be of help to everyone with interest in learning and teaching skull base anatomy. We present the complex organization of petrous pyramid anatomy using a new compartmental approach that is simple to understand and remember.

METHODS

The surfaces of the petrous pyramid of two temporal bones were examined; and the contents of the petrous pyramid of 8 temporal bones were exposed through progressive drilling of the superior surface.

RESULTS

The petrous pyramid is made up of a bony container, and its contents were grouped into 4 compartments (mucosal, cutaneous, neural, and vascular). Two reference lines were identified (mucosal and external-internal auditory canal lines) intersecting at the level of the middle ear. The localization of contents relative to these reference lines was then described, and 2 methods of segmentation (the X method and the V method) were then proposed. This description was then used to describe middle ear relationships, facial nerve anatomy, and air cell distribution.

CONCLUSIONS

This new compartmental approach allows a comprehensive understanding of the distribution of petrous pyramid contents. Dividing it into anatomic compartments, and then navigating this mental map along specific reference points, lines, spaces, and segments, could create a useful tool to teach or learn its complex tridimensional anatomy.

Petrous Apex Pneumatization: Influence on Postoperative Cerebellopontine Angle Tumor Cerebrospinal Fluid Fistula

OBJECTIVE

Multiple investigators have sought to identify risk factors for cerebrospinal fluid (CSF) leak following cerebellopontine angle (CPA) tumor resection. We evaluated whether pneumatization of the petrous apex (PA) is a risk factor for CSF fistula.

METHOD

We conducted a retrospective chart review at 2 major tertiary academic institutions undergoing CPA tumor resection and analyzed their respective head or temporal computed tomography (CT) scans if available.

RESULTS

A total of 91 cases were identified; 51 (64%) demonstrated PA pneumatization, and a total of 17 CSF leaks were identified. We discovered higher rates of CSF leak (25.0% vs 13.7%; P = .273) and CSF rhinorrhea (15.0% vs 5.9%; P = .174) in patients with PA pneumatization compared to those without PA pneumatization.

CONCLUSIONS

Isolated PA pneumatization may be a risk factor and communication pathway for CSF fistula. Further studies will need to be broadened across multiple institutions to draw any additional and stronger conclusions.

Classification of Temporal Bone Pneumatization on High-Resolution Computed Tomography: Prevalence Patterns and Implications

Objective The degree of pneumatization of the temporal bone has implications in the pathophysiology and surgical considerations of many temporal bone disorders. This study aims to identify common pneumatization patterns in the petrous apex, mastoid, and infralabyrinthine compartments of the temporal bone. Variables associated with temporal bone pneumatization were also identified. Study Design Case series with chart review. Setting Single tertiary hospital. Subjects and Methods In total, 299 high-resolution computed tomography scans of the temporal bone performed on patients between 2013 and 2016 were reviewed. Only normal temporal bone scans in patients aged 13 years and older were included. Previously published grading systems were used to classify pneumatization patterns in the petrous apex, mastoid, and infralabyrinthine region. Results The most common pneumatization pattern in the petrous apex was group 2 (less than half of the petrous apex medial to the labyrinth is pneumatized), that in the mastoid was group 4 (hyperpneumatization), and that in the infralabyrinthine region was type B (limited pneumatization), at 54.8%, 55.4%, and 76.0% of patients, respectively. Patients with increased pneumatization of 1 temporal bone compartment tended to have increased pneumatization of the same compartment on the contralateral side and the other compartments on the ipsilateral side ( P < .05). Younger age ( P < .001) and male sex ( P = .001) were associated with increased pneumatization in the petrous apex and infralabyrinthine compartments. Conclusion The degree of temporal bone pneumatization varies among the different compartments. Age and sex have a significant association with the degree of pneumatization of the petrous apex and infralabyrinthine compartment.

Pneumatization Patterns of the Petrous Apex and Lateral Sphenoid Recess

Introduction  The petrous apex poses a challenge for surgical intervention due to poor access. As intraoperative image guidance and surgical instrumentation improve, newer endoscopic approaches are increasingly favored. This study aims to provide normative data on the anatomy of the lateral sphenoid sinus recess and petrous apex. These normative data could assist in determining the efficacy of a transnasal transsphenoidal approach to lesions of the anteroinferior petrous apex. Methods  This is a retrospective study investigating normative data on all maxillofacial computed tomography (CT) scans performed at a level I trauma center over a 6-month period. All appropriate images had the pneumatization pattern of the petrous apex and lateral recess of the sphenoid sinus reviewed by a single otologist and graded bilaterally. These were then analyzed in SPSS; Pearson correlation analyses and χ ² test were used. Results  A total of 481 patients were identified, yielding a total of 962 temporal bones and sphenoid sinuses for analysis. Eighty-eight percent of sides analyzed had a nonpneumatized lateral recess. The petrous apex was nonpneumatized in 54% of sides analyzed. There was a correlation noted between the degree of pneumatization of the petrous apex and pneumatization of the lateral recess of the sphenoid. Conclusion  This study is the first to provide normative data comparing pneumatization of the petrous apex and sphenoid sinus. These data may support future work evaluating the utility of an endonasal approach to the petrous apex.

Clinically relevant human temporal bone measurements using novel high-resolution cone-beam CT

OBJECTIVE

To test the feasibility of measuring fine temporal bone structures using a newly established cone-beam computed tomography (CBCT) system.

MATERIALS AND METHODS

Six formalin-fixed human cadaver temporal bones were imaged using a high-resolution CBCT system that has 900 frames and copper + aluminum filtration. Fine temporal bone structures, including those of the facial nerve canal and vestibular structures, were identified and measured.

RESULTS

The fine structures of the middle ear, including the tympanic membrane, tendon of the tensor tympani, cochleariform process of the semicanal of the tensor tympani, pyramidal eminence, footplate of the stapes, full path of the facial nerve within the temporal bone, supralabyrinthine space, semicircular canals, pathway of the subarcuate canal, and full path of the vestibular aqueduct, were clearly demonstrated. The vestibular aqueduct has a midpoint width of 0.4 ± 0.0 mm and opercular width of 0.5 ± 0.1 mm (mean ± SD). The length of the internal acoustic meatus was 10.6 ± 1.2 mm (mean ± SD), and the diameter of the internal acoustic meatus was 3.7 ± 0.3 mm (mean ± SD).

CONCLUSION

This novel high-resolution CBCT system has potentially broad applications in the diagnosis of inner ear disease and in monitoring associated pathological changes, surgical planning, navigation for the ear surgery, and temporal bone training.

Anatomical Factors Influencing Pneumatization of the Petrous Apex

Objectives

Aim of the present study was to define the relationship between petrous apex pneumatization and the nearby major anatomical landmarks using temporal bone computed tomography (CT) images.

Methods

This retrospective, Institutional Review Board-approved study analyzed CT images of 84 patients that showed normal findings bilaterally. Pneumatization of the petrous apex was classified using two methods. Eight parameters were as follows: angle between the posterior cranial fossa and internal auditory canal, Morimitsu classification of anterior epitympanic space, distance between the carotid canal and jugular bulb, distance between the cochlear modiolus and carotid canal, distance between the tympanic segment and jugular bulb, high jugular bulb, distance between the vertical segment and jugular bulb, and distance between the lateral semicircular canals and middle cranial fossa.

Results

There was a significant difference in Morimitsu classification of the anterior epitympanic space between the two classification methods. Poorly pneumatic upper petrous apices were distributed uniformly in three types of Morimitsu classification, but more pneumatic upper petrous apices were found more often in anterior type. Lower petrous apex was well pneumatized regardless of the types of anterior epitympanic space, but the largest amount of pneumatization was found more frequently in the anterior type of anterior epitympanic space.

Conclusion

This study showed that there was no reliable anatomic marker to estimate petrous apex pneumatization and suggests that the pneumatization of the petrous apex may be an independent process from other part of the temporal bone, and may not be influenced by the nearby major anatomical structures in the temporal bone. In this study, the anterior type of anterior epitympanic space was found to be closely related to more well-pneumatized petrous apices, which implies that the anterior saccule of the saccus medius may be the main factor influencing pneumatization of the petrous apex.

Diffusion tensor tractography of normal facial and vestibulocochlear nerves

PURPOSE

Diffusion tensor tractography (DTT) is not adequately reliable for prediction of facial and vestibulocochlear (VII-VIII) nerve locations, especially relative to a vestibular schwannoma (VS). Furthermore, it is often not possible to visualize normal VII-VIII nerves by DTT (visualization rates were 12.5-63.6%). Therefore, DTT post-processing was optimized for normal VII-VIII nerve visualization with and without manual noise elimination.

METHODS

DTT examinations of ten patients were evaluated to assess the improvement in performance by modifying seed region of interest (ROI) and fractional anisotropy (FA) threshold. Seed ROI was placed at the porus of the internal auditory meatus, and FA threshold values were either fixed or variable for each patient. DTT visualization of cranial nerves VII-VIII was evaluated and the noise effect was measured.

RESULTS

Cranial nerves VII-VIII were visualized in 90% of patients without using manual noise elimination by modifying the seed ROI and FA threshold. The visualization rate with FA threshold of the upper limit in each patient (100%) was significantly higher than that with FA threshold of 0.1 (75%) (p = 0.02). The incidence rate of noise with FA threshold of the upper limit (10%) was not significantly different than the FA threshold of 0.1 (20%) (p = 0.66).

CONCLUSION

Seed ROI modification and FA thresholding can improve the visualization of cranial nerve VII-VIII locations in DTT. This technique is promising for its potential to determine the relationship of cranial nerves VII-VIII to VS.

The pneumatization patterns of the roof of the parapharyngeal space in CBCT

INTRODUCTION

The rhinopharynx and the parapharyngeal space (PPS) are complex anatomical territories located beneath the skull base. Thorough knowledge of the complex anatomy of the PPS is essential in treatment of pathologies such as parapharyngeal abscesses. The roof of the PPS is overlooked in anatomy. It was hypothesized that the pneumatization pattern of the PPS roof is individually variable, as determined by the variable pneumatization patterns of the sphenoid and temporal bones. The study was aimed at assessing the anatomy of the PPS roof in CBCT.

METHODS

The present study was performed retrospectively on a group of 35 subjects (37.1% males) evaluated by CBCT for various dental procedures.

RESULTS

The mean age of the group was 37.9 (SD: 14.2, range: 18 to 61). The major bony landmarks of the PPS roof were: the petrous apex with the carotid canal, the jugular foramen, the foramen lacerum, the sphenopetrosal fissure or suture, and the root of the pterygoid process. Variable patterns of pneumatization were determined by the petrous apex air cells and the pterygoalar recess of the sphenoidal sinus. As related to the individually pattern of pneumatization, the following types of the PPS roof were defined: (i) type 1 - not pneumatized PPS roof; (ii) type 2 - sphenoidal but not petrosal pneumatization of the PPS roof; (iii) type 3 - petrosal but not sphenoidal pneumatization of the PPS roof; (iv) type 4 - sphenoidal and petrosal pneumatizations of the PPS roof.

DISCUSSION

Although on the left side the degree of pneumatization was higher than on the right side, no statistical differences were recorded (p > 0.05). The pattern of pneumatizations in the PPS roof should be assessed when PPS involvement in otitis or sinusitis is considered.

Petrous bone pneumatization is a risk factor for cerebrospinal fluid fistula following vestibular schwannoma surgery

BACKGROUND

For the prevention of postoperative CSF fistula a better understanding of origins and risk factors is necessary.

OBJECTIVE

To identify the petrous bone air cell volume as a risk factor for developing CSF fistula, we performed a retrospective analysis.

METHODS

From 2000 to 2007 519 patients had a retrosigmoidal surgical removal of a vestibular schwannoma. The 22 who had a postoperative CSF fistula were chosen for evaluation in addition to 78 patients who were randomly selected in 4 equally sized cohorts: male/female with small/large tumors. Preoperative CT scans were analyzed regarding petrous bone air cell volume, area of visible pneumatization at the level of the internal auditory canal (IAC), tumor grade, and sex.

RESULTS

: Women developed nearly half as many CSF fistulas (2.7%) as men (5.2%). The mean volume of the petrous bone air cells was 10.97 mL (SD, 4.9; range, 1.38-27.25). It was significantly lower for women (mean, 9.23 mL; SD, 3.8) than for men (mean, 12.5 mL; SD, 5.28; P = .0008). The mean air cell volume of CSF-fistula patients was 13.72 mL (SD, 5.22). The difference concerning the air cell volume between patients who developed CSF fistulas and patients from the control group was significant (P = .0042). There was a significant positive correlation between the air cell volume and the area of pneumatization in one CT slide at the level of the IAC.

CONCLUSION

The higher incidence of CSF fistulas in men compared with women can be explained by means of differently pneumatized petrous bones. A high amount of petrous bone pneumatization has to be considered as a risk factor for the development of postoperative CSF fistula after vestibular schwannoma surgery.

How obliteration of petrosal air cells by vestibular schwannoma influences the risk of postoperative CSF fistula

INTRODUCTION

For postoperative CSF-fistula prevention a better understanding of its origins and risk factors is necessary. To identify the role of the tumor growth for the risk to develop CSF-fistula we performed a retrospective analysis.

METHODS

519 patients between the years 2000 and 2007 had a retrosigmoidal surgical removal of vestibular schwannoma in a standardized procedure. 22 CSF-fistula-patients were chosen for evaluation. 78 patients were randomly selected as control group in four equally sized cohorts: male/female with small/large tumors. Preoperative CT-scans were analyzed regarding IAC-length, diameter of the IAC porus (IAP), tumor size and pneumatization of the posterior wall (PW) of the IAC.

RESULTS

The mean length of the IAC was 1.2 cm, SD 0.17. There was a significant difference between the diameter of the IAP in cases of small tumors and those of large tumors. Patients with small tumors also showed a larger fraction with visible pneumatization of the PW (34.88%) in the CT-scan than patients with large tumors (24.07%). There is a positive correlation between tumor grade and diameter of the IAP. At the same time there is an inverse correlation between tumor grade and pneumatization of the PW.

CONCLUSIONS

Widening of the IAC by tumor growth may leads to obliteration of air cells in the PW and therefore can be protective concerning CSF-fistula. At the same time patients with small tumors and a visible pneumatization in the PW must be expected to have a higher risk of CSF-fistula.

Cerebrospinal fluid dynamics in skull base surgery

PURPOSE OF REVIEW

This review examines disturbances of cerebrospinal fluid (CSF) dynamics after skull base surgical and endoscopic approaches. Despite the continuing advancements and the effectiveness of skull base surgery, the incidence of postoperative rhinorrhea remains problematic. This adverse event carries a significant potential for major neurologic insult related to infection of the central nervous system.

RECENT FINDINGS

The contemporary literature provides excellent reports that summarize the management of this important clinical entity focusing on particular aspects of its diagnosis and treatment. Advances in various imaging technologies have enabled the accurate localization of CSF fistulas. However, their complexity requires physicians to have significant knowledge about the advantages and limitations of each test.

SUMMARY

Patients with CSF leaks are often referred to otolaryngologists to undergo transnasal endoscopic treatment. When CSF leaks are severe, recurrent, or not amenable to endoscopic treatment (previous posterior fossa or transpetrosal approach), the treatment choice is open repair through craniotomy.