Evaluation of subarcuate canal on CT images in the perspective of clinical basis

OBJECTIVES

The aim of our study to contribute to the field of morphometrics by including measurements of the SAC and SAF and their distances from surrounding structures, particularly for surgeons involved in retrosigmoid approach for internal acoustic meatus tumor surgery and cerebellopontine angle surgery. Although there is limited information in the literature regarding the role of the subarcuate fossa (SAF) and subarcuate canal (SAC), it has been suggested that the SAC may be a potential pathway for infection from the middle ear to the posterior cranial fossa, and cerebellar abscesses may have this origin.

METHODS

For the images of our study, computerized tomography images of 118 individuals (59 females and 59 males) between the ages of 18-65 who applied to Bayındır Health Group.

RESULTS

The width of the cranial opening of the subarcuate canal was determined as 44 ± 0.54 mm, width of the labyrinth opening of the subarcuate canal was determined as 60 ± 0.42 mm, Length of the subarcuate canal was determined as 8.79 ± 2.31 mm, width of the subarcuate canal was determined as 5.54 ± 1.75 mm, and depth of subarcuate fossa was determined as 1.67 ± 0.69 mm. The distance of the cranial opening of the subarcuate canal to the superior semicircular canal (SSC-SAC/C) was measured as 5.33 ± 1.81 mm, The distance of the labyrinth opening of the subarcuate canal to the superior semicircular canal (SSC-SAC/L) was measured as 3.90 ± .98 mm, length of the petrous part of the temporal bone medial to the anterior semicircular canal measured from the apex to the SSCD (PLM) was measured as 33.56 ± 0.42 mm. No statistically significant differences were found between the right and left sides.

CONCLUSIONS

The morphometric measurements obtained in this study can provide useful information for neurosurgeons, neurotologist and otolaryngologists involved in retrosigmoid approach for internal acoustic meatus tumor surgery and cerebellopontine angle surgery, and for patients undergoing cochlear implant planning with a retrofacial approach.

Detailed Radiomorphometric Analysis of the Surgical Corridor for the Suprageniculate Approach

BACKGROUND

The suprageniculate fossa (SGF) is located between the geniculate ganglion, the middle cranial fossa (MCF) and the anterior semicircular canal (ASCC). An endoscopic transcanal approach has been recently proposed to treat the different lesions in this area. The aim of the study is to describe the anatomical pathway of this approach by measuring the dimensions of its boundaries while checking their correlation with the pneumatization of the SGF area.

METHODS

This is a retrospective anatomical analysis of Cone Beam CT scans of 80 patients, for a total of 160 temporal bones analyzed. Two checkpoints were measured for the SGF route, as an internal and an external window. These are triangles between the MCF dura, the geniculate ganglion and the ASCC on parasagittal and axial planes. The pneumatization of the SGF was also assessed, classified and correlated with the measured dimensions.

RESULTS

The depth of the SGF was 7.5 ± 1.8 mm. The width of the external window was 7.5 ± 1.9, 5.6 ± 2.4 and 1.6 ± 1.6 mm for the posterior, middle and anterior points of measurement, respectively. The height of the internal window was 7.6 ± 1.2, 4.5 ± 1.5 and 1.7 ± 1.7 mm for the posterior, middle and anterior points of measurement, respectively. Type A pneumatization was found in 87 cases, type B in 34 and type C in 39. The degree of pneumatization directly correlated to the depth and height of the fossa.

CONCLUSIONS

The suprageniculate approach route is defined by the internal and external windows which should be evaluated during a pre-surgery imaging assessment. The detailed anatomy of the approach and the novel classification of the pneumatization of the SGF are here described which may be useful to plan a safer procedure with minimal complications.

Comparative Anatomic Analysis of Neuronavigated Transmastoid-Infralabyrinthine Approaches for Jugular Fossa Pathologies: Short Anterior Rerouting Versus Nonrerouting and Tailored Nonrerouting Techniques

BACKGROUND AND OBJECTIVES

Access to the jugular fossa pathologies (JFPs) via the transmastoid infralabyrinthine approach (TI-A) using the nonrerouting technique (removing the bone anterior and posterior to the facial nerve while leaving the nerve protected within the fallopian canal) or with the short-rerouting technique (rerouting the mastoid segment of the facial nerve anteriorly) has been described in previous studies. The objective of this study is to compare the access to Fisch class C lesions (JFPs extending or destroying the infralabyrinthine and apical compartment of the temporal bone with or without involving the carotid canal) between the nonrerouting and the short-rerouting techniques. Also, some tailored steps to the nonrerouting technique (NR-T) were outlined to enhance access to the jugular fossa (JF) as an alternative to the short-rerouting technique.

METHODS

Neuronavigated TI-A was performed using the nonrerouting, tailored nonrerouting, and short-rerouting techniques on both sides of 10 human head specimens. Exposed area, horizontal distance, surgical freedom, and horizontal angle were calculated using vector coordinates for nonrerouting and short-rerouting techniques.

RESULTS

The short-rerouting technique had significantly higher values than the NR-T ( P < .01) for the exposed area (169.1 ± SD 11.5 mm 2 vs 151.0 ± SD 12.4 mm 2 ), horizontal distance (15.9 ± SD 0.6 mm vs 10.6 ± SD 0.5 mm 2 ), surgical freedom (19 650.2 ± SD 722.5 mm 2 vs 17 233.8 ± SD 631.7 mm 2 ), and horizontal angle (75.2 ± SD 5.1° vs 61.7 ± SD 4.6°). However, adding some tailored steps to the NR-T permitted comparable access to the JF.

CONCLUSION

Neuronavigated TI-A with the short-rerouting technique permits wider access to the JF compared with the NR-T. However, the tailored NR-T provides comparable access to the JF and may be a better option for class C1 and selected class C2 and C3 JFPs.

Assessing the feasibility of the transmastoid infralabyrinthine approach without decompression of the jugular bulb to the extradural part of the petrous apex and petroclival junction prior to surgery

BACKGROUND AND OBJECTIVE

This study aims to define specific measurements on cranial high-resolution computed tomography (HRCT) images prior to surgery to prove the feasibility of the navigated transmastoid infralabyrinthine approach (TI-A) without rerouting of the facial nerve (FN) and decompression of the jugular bulb (JB) in accessing the extradural-intrapetrous part of petrous bone lesions located at the petrous apex and petroclival junction.

MATERIALS AND METHODS

Vertical and horizontal distances of the infralabyrinthine space were measured on cranial HRCT images prior to dissection. Subsequently, the area of access was measured on dissected human cadaveric specimens. Infralabyrinthine access to the extradural part of the petrous apex and petroclival junction was evaluated on dissected specimens by two independent raters. Finally, the vertical and horizontal distances were correlated with the area of access.

RESULTS

Fourteen human cadaveric specimens were dissected bilaterally. In 54% of cases, the two independent raters determined appropriate access to the petrous apex and petroclival junction. A highly significant positive correlation (r = 0.99) was observed between the areas of access and the vertical distances. Vertical distances above 5.2 mm were considered to permit suitable infralabyrinthine access to the extradural area of the petrous apex and petroclival junction.

CONCLUSIONS

Prior to surgery, vertical infralabyrinthine distances on HRCT images above 5.2 mm provide suitable infralabyrinthine access to lesions located extradurally at the petrous apex and petroclival junction via the TI-A without rerouting of the FN and without decompression of the JB.

Novel Multiportal Approach to the Internal Auditory Canal for Hearing-Preserving Surgery: Feasibility Assessment in Dissections

OBJECTIVE

State-of-the-art, minimally invasive endoscopic transcanal surgery of the internal auditory canal (IAC) sacrifices the cochlea with complete hearing loss. With a combination of the transcanal infracochlear and transmastoid retrolabyrinthine approaches, we aim to preserve hearing and enable minimally invasive surgical treatment of vestibular schwannoma. In this study, we investigate the anatomical indications and the feasibility of both approaches in dissections, in human whole head specimens.

METHODS

We operated whole head anatomical specimens with a four-handed technique, using the retrolabyrinthine approach as the main surgical corridor and the infracochlear approach for endoscopic visualization. We tested 4 different powered surgical systems. We collected intraoperative data on the size of the access windows, the surgical freedom, and the exposed area of the IAC. Finally, we evaluated the outcome in postoperative computed tomography scans.

RESULTS

Six out of 14 sides were anatomically suitable and qualified for the surgery based on preoperative computed tomography. In all attempted sides, the IAC could be reached and opened, leaving the ossicular chain and the labyrinth intact. 51%-75% of the length and 22%-40% of the circumference of the IAC could be exposed. All tested instruments were beneficial at different stages of the surgery. The four-handed technique enabled good maneuverability of the instruments.

CONCLUSIONS

The combined multiportal approach to the IAC is feasible with a good surgical exposure and full anatomical preservation of hearing. State-of-the-art surgical instruments in specimens with suitable anatomy are sufficient to perform this approach.

Hearing-Preserving Approaches to the Internal Auditory Canal: Feasibility Assessment from the Perspective of an Endoscope

OBJECTIVE

Minimally invasive transcanal transpromontorial endoscopic approaches to the internal auditory canal sacrifice the cochlea. Two hearing-preserving approaches, the exclusively endoscopic transcanal infracochlear approach and the endoscope-assisted transmastoid retrolabyrinthine approach, have been controversially discussed in the literature. In this study, we examine the feasibility of these 2 approaches by means of three-dimensional surface models, a population-based analysis of the available surgical space, and dissections in human whole-head specimens.

METHODS

We reconstructed three-dimensional surface models based on clinical high-resolution computed tomography scans of 53 adult temporal bones. For both approaches, we measured the maximal extensions and the area of the surgical access windows located between landmarks on the surrounding anatomic structures. We then identified the limiting extensions and derived the cumulative distribution to describe the available surgical space. Dissections were performed to validate the corridors and landmark selection.

RESULTS

The limiting extension for the infrachochlear approach is 7.0 ± 2.7 mm from the round window to the dome of the jugular bulb. The limiting extension for the retrolabyrinthine approach is 6.4 ± 1.5 mm from the dura of the posterior fossa to the facial nerve. The cumulative distribution shows that 80% of the cohort have access window extensions ≥3 mm for both approaches.

CONCLUSIONS

This study shows that in a high percentage of the measured cohort, the access windows are sufficiently large for endoscopic approaches to the internal auditory canal. With appropriate instrumentation, these hearing-preserving minimally invasive approaches may evolve into alternatives to surgical treatment.

Temporal Bone Pneumatization: Relationship With Sex and Variants of the Ethmoid and Sphenoid Bone

ABSTRACT

Pneumatization variants of the temporal bone have a crucial importance in several surgical interventions. However, very few data are known about possible correlation with other pneumatization variants.Pneumatization of glenoid fossa, petrous apex, and infralabyrinthine portion of temporal bone was assessed in 200 computed tomography scans, equally divided between males and females (18-92 years). Pneumatization variants of the ethmoid (concha bullosa, agger nasi, pneumatized crista galli) and the sphenoid sinuses (pneumatized pterygoid processes, anterior clinoid processes, dorsum sellae, volume) were recorded as well.Differences in prevalence of each pneumatization type according to sex and side, among different portions of the temporal bone, and between temporal bone and the pneumatized variants of the ethmoid bone and sphenoid sinuses, were assessed through chi-square test (P < 0.05). Differences in sphenoid volume among different pneumatization degrees of the temporal bone were assessed through 1-way analysis of covariance test (P < 0.05).Pneumatization of the petrous apex and the infralabyrinthine portion was significantly more frequent in males than in females, whereas pneumatization of the glenoid fossa was more often observed on the right side (P < 0.05). Variants of the temporal bone are all related one with each other in males, whereas in females only the relationship between pneumatized petrous apex and infralabyrinthine portion was found. Moreover, in females the pneumatized petrous apex was related with pneumatized anterior clinoid process, and the pneumatized infralabyrinthine portion was related with the sphenoid sinus volume.Results may be useful for predicting these important variants in planning surgical interventions of the cranial base.

Extended Retro/Infralabyrinthine Approach to Cerebellopontine Angle and Internal Auditory Canal, a Radio-Anatomic Study

INTRODUCTION

There is a considerable controversy about approaches that preserve hearing in acoustic neuroma surgery. Transtemporal approaches have the advantage of extradural drilling and minimal cerebellar retraction. We aimed to measure the limits and exposure of extended infra/retrolabyrinthine approach using temporal bone dissection and temporal high resolution computed tomography (HRCT).

MATERIALS AND METHODS

Hundred temporal bone sides (unpaired) underwent HRCT. The images were used to estimate the limits and exposure of infra/retrolabyrinthine approach. Also, 10 temporal bone sides underwent the same imaging protocol then were dissected to measure actual exposure and limits of dissection. These measures were compared with those retrieved by HRCT to find if they are appropriate to be applied in general population.

RESULTS

Mean posterior fossa angle of vision (24.5 degrees), retrolabyrinthine (internal auditory canal) IAC (58.6%), and infralabyrinthine IAC exposures (73.2%) were documented based on data retrieved from CT scan. After temporal bone dissection, posterior fossa (p = 0.139) and infralabyrinthine exposures (p = 0.674) were not statistically different comparing with measures retrieved from CT scan; however, retrolabyrinthine exposure was overestimated (p = 0.012).

CONCLUSION

We found that at least 20% more of IAC length can be exposed by extension of retrolabyrinthine to infralabyrinthine dissection. Infralabyrinthine exposure can be estimated preoperatively using temporal bone CT but the same is not true for retrolabyrinthine exposure.

Petrous Apex Cholesterol Granulomas: Outcomes, Complications, and Hearing Results From Surgical and Wait-and-Scan Management

OBJECTIVE

1. To analyze the surgical outcomes in the management of petrous apex cholesterol granulomas (PACG) with a brief literature review.2. To evaluate the importance of wait-and-scan management option.

STUDY DESIGN

Retrospective review.

SETTING

Quaternary referral center for otology and skull base surgery.

SUBJECTS AND METHODS

Charts of 55 patients with at least 12 months of follow-up were analyzed for demographic, clinical, audiometric, and radiological features. Patients were divided into surgical group (SG) (n = 31) and wait-and-scan (n = 24) (WS) group. Surgical approach was chosen as per hearing status and PACG extension and relation to nearby neurovascular structures and included either drainage by transmastoid-infralabyrinthine approach (TM-IL)/transcanal-infracochlear approach (TC-IC) or resection by infratemporal fossa type B approach (ITF-B). The combination of ITF-B with trans-otic (TO) approach or TO approach solely was used in unserviceable hearing cases. Postoperative outcomes and complications were evaluated in SG.

RESULTS

Postoperative symptom relief was observed in 24 patients (77.4%). Diplopia and paresthesia recovered in each case and improvement in headache, dizziness, tinnitus, and hearing loss was observed in 87.1% cases. Serviceable hearing was preserved in 24 of 26 cases. Postoperative complication rate was 32.2% including incidences of profound hearing loss, facial nerve paresis, carotid artery injury and intraoperative CSF leaks. Revision surgery was required in 3 (9.6%) cases, after TM-IL approach.

CONCLUSION

Surgical drainage is preferable to more aggressive resection procedures, with the latter reserved for recurrent lesions or lesions with severe hearing loss/involvement of critical neurovascular structures. ITF-B approach provides adequate cyst and neurovascular control for resection, while avoiding brain retraction. An initial wait-and-scan approach can be used in most patients where symptoms and imaging justify so.

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.

Surgical Anatomy of the Human Round Window Region: Implication for Cochlear Endoscopy Through the External Auditory Canal

OBJECTIVE

To enable development of an endoscope for cellular-level optical imaging of the inner ear.

STUDY DESIGN

A prospective study of 50 cadaveric human temporal bones to define detailed surgical anatomy of the round window (RW) region and the range of angles necessary to reach the RW membrane perpendicularly via the external ear canal.

MAIN OUTCOME MEASURE

The transcanal angle to the RW membrane was surgically measured in 3D intact specimens, and correlated with the angle calculated from temporal bone computed tomography (CT) scans of the same specimens obtained before and after measurements in situ.

RESULTS

Surgically measured transcanal angles to the RW membrane correlated well with the radiographically measured angles. The angles ranged from 110 to 127 degrees, with the median of 115 degrees and the middle 50% ranging from 109 to 119 degrees. Four temporal bones were excluded because of pathology. The opening of the RW niche was located posteriorly in six bones (13%), inferiorly in 18 bones (39%), and postero-inferiorly in 22 bones (48%). The angles were not statistically different among the three orientations of the RW niche.

CONCLUSIONS

By correlating measurement from cadaveric human temporal bones and their CT scans, we defined key parameters necessary for designing an endoscope for intracochlear imaging using a minimally invasive approach through the external auditory canal. The excellent correlation between the measurement on the CT scan and the actual shape of the probe that was able to reach the RW through the ear canal enables selection of the probe using the CT data.

Decompression of the Jugular Bulb for Enhanced Infralabyrinthine Access to the Petroclival Region: A Quantitative Analysis

Objectives To describe an enhanced infralabyrinthine approach to petroclival lesions with jugular bulb decompression, and to quantify surgical access using a flat-panel computed tomography image protocol. Design Retrospective case series and paired comparison of pre- versus post-dissection anatomy. Setting Tertiary academic medical center. Participants Four patients presenting with petroclival lesions. Six fresh cadaveric specimens were used for temporal bone dissection. Main Outcome Measures Axial and coronal dimensions, and access angles of the infralabyrinthine surgical corridor. Results Decompression of the jugular bulb increased the craniocaudal width of the infralabyrinthine corridor from 0.9 to 7.9 mm to 6.5 to 11.6 mm. The mean increase of 4 mm was statistically significant (t = 3.7; p < .05). There was also a significant widening of the infralabyrinthine window along the axial dimension by 0.9 to 4.5 mm or a mean of 2 mm (t = 3.7; p < .05). Angles of access to the petroclival region were wider following jugular bulb decompression, particularly in the coronal plane (mean difference 7.9 degrees; t = 5.0; p < .005) but less so in the axial plane (mean difference 4.7 degrees; t = 2.5; p = .05). Conclusions Jugular bulb decompression enhances infralabyrinthine access to petroclival lesions, permitting the removal of tissue for diagnoses or partial resection, without significant additional morbidity.