Radiographic anatomy of the infracochlear approach to the petrous apex for computer-assisted surgery

Morphometric Analysis of the Retrolabyrinthine Approach to the Posterior Fossa

INTRODUCTION

The retrolabyrinthine approach provides shorter working distance and less cerebellar retraction compared with the retrosigmoid approach to the internal acoustic canal (IAC) and cerebellopontine angle cistern. However, exposure of the ventral surface of the brainstem and petroclival region may be restricted. Trautmann's triangle (TT), an area intimately related to this region, demonstrates significant anatomical variability, which may adversely affect the ease of the approach. The aim of this study is to evaluate anatomic parameters of the posterior fossa that may anticipate a challenging situation in approaching the IAC and the petroclival region through the retrolabyrinthine approach.

METHODS

It was performed a radioanatomic analysis of 75 cerebral angiotomography exams to identify parameters that could potentially reduce areas of surgical exposure.

RESULTS

Large variations were observed in the area of exposure of the TT (553%) and the height of the jugular bulb (234%). Shorter distances from the sigmoid sinus to the posterior semicircular canal and high-riding jugular bulb were associated with smaller areas of exposure. Dominant and laterally positioned sigmoid sinuses and less pneumatized mastoids were associated with potentially unfavorable conditions, including a narrower angle of attack to the IAC. Increased petrous slopes and petroclival angles were associated with smaller petroclival areas and shallower clival depths.

CONCLUSIONS

This study of the posterior fossa reveals remarkable anatomic variation in the region. These findings should be taken into consideration during the preoperative planning of retrolabyrinthine approaches in order to offer safer and more effective surgical procedures.

[The infracochlear approach for diagnostic petrous apicotomy]

Diagnostic and therapeutic approaches to the petrous apex involve sub-/transtemporal, retrosigmoidal, infratemporal and-lesser invasive-e. g. infracochlear, infralabyrinthine or under favourable anatomic conditions, transsphenoidal surgical pathways. For diagnostic purposes, minimally invasive approaches should be preferred due to their lesser morbidity. This article illustrates the infracochlear approach to the petrous apex in the case of a diagnostic indication in a patient with an incidental, asymptomatic tumorous lesion of the right petrous apex with bony erosion. After the bone of the floor of the ear canal and the hypotympanum was removed, the carotid artery and the jugular bulb were identified using a diamond burr. The route to the petrous apex is triangled by the cochlea superiorly, the jugular bulb posteriorly, and the carotid artery anteriorly. After opening the petrous apex lesion, biopsies were taken. The defect in the floor of the ear canal and the hypotympanum was reconstructed with cartilage and temporalis fascia. The patient recovered quickly from surgery without vertigo or hearing loss. Histological evaluation showed a chondrosarcoma. The patient opted for primary radiation therapy (C12, 63 Gy). The infracochlear approach is minimally invasive and can offer access to the petrous apex with minimal morbidity. The pathway, however, is narrow and deep and bounded by the jugular bulb and the carotid artery. The available space can be estimated from preoperative CT scans and, if possible, with 3D reconstructions. Navigation can additionally enhance safety.

A morphometric study of the structures bordering the infra-cochlear corridor - Relevant for endoscopic/microscopic ear surgery

Application of surgical endoscope, used alone or in combination with the surgical microscope, for the operative management of ear and temporal bone conditions may allow improved access and clearance of disease. Preservation of normal structures may also be improved.

As the use of this tool is increasing, the need for better understanding of the anatomy of the ear is becoming evident. This is particularly so for endoscopic surgery aiming at removal of lesions involving the infra-cochlear corridor and/or petrous apex.

Human temporal bone-derived labyrinth casts (molds), originally made for endolymphatic duct and sac analysis which genuinely represent the membranous labyrinth and its adjacent soft tissues, were morphometrically analyzed in terms of the anatomic relations between structures in and around the infra-cochlear corridor. The distance between the petrous carotid artery (PCA) and the basal turn of the cochlea, the distance between PCA and infra-cochlear vein (ICV)/cochlear aqueduct (CA), and the distance between the lower surface of basal cochlear turn and the point where the carotid artery and jugular vein (JV) meet close to the jugular foramen, were measured to be around 1.3 mm, 6 mm and 8 mm respectively, thus constituting an approximate 6 × 8 mm² infra-cochlear corridor. This analysis and further study with larger samples might be helpful for operation via this corridor led to the petrous apex where cholesterol granuloma, cholesteatoma and other lesions are not uncommon.

Endoscopic Infracochlear Approach for Drainage of Petrous Apex Cholesterol Granulomas: A Case Series

OBJECTIVE

To describe the feasibility and technical nuances of a transcanal endoscopic infracochlear approach for drainage of petrous apex cholesterol granulomas.

STUDY DESIGN

Retrospective case review.

SETTING

Tertiary care university hospital.

PATIENTS

A 32-year-old man with bilateral petrous apex cholesterol granulomas and a 54-year-old man with a left-sided petrous apex granuloma each with symptoms necessitating surgical intervention.

INTERVENTIONS

Transcanal endoscopic infracochlear approach for drainage of the cholesterol granulomas.

MAIN OUTCOME MEASURES

Operation efficacy, corridor size, and perioperative morbidity.

RESULTS

All three cholesterol granulomas were successful drained without violating the cochlea, jugular bulb, or carotid artery. The dimensions of the infracochlear surgical corridor measured 5 mm × 6 mm, 3.5 mm × 3.5 mm, and 6 mm × 4 mm, respectively. All corridors facilitated visualization within the cyst and allowed lyses of adhesions for additional cyst content eradication. All patients had resolution of their acute symptoms. Two of the three subjects had serviceable hearing before and after their procedures. One patient required revision surgery 2-months after their initial procedure secondary to recurrent symptoms from acute hemorrhage within the cyst cavity. The infracochlear tract in this patient was noted to be patent.

CONCLUSIONS

A transcanal endoscopic infracochlear approach is feasible for the management of cholesterol granuloma. The surgical access was wide enough to introduce the endoscope into the petrous apex cavity in each case. Further studies are needed to compare the efficacy and perioperative morbidity versus the traditional postauricular transtemporal approaches.

Quantitative imaging analysis of transcanal endoscopic Infracochlear approach to the internal auditory canal

PURPOSE

A transcanal endoscopic infracochlear surgical approach to the internal auditory canal (IAC) in a human temporal bone model has previously been described. However, the proportion of patients with favorable anatomy for this novel surgical technique remains unknown. Herein, we perform a quantitative analysis of the transcanal endoscopic infracochlear corridor to the IAC based on computed tomography.

MATERIALS AND METHODS

High resolution computed tomography scans of adult temporal bones were measured to determine the accessibility of the IAC when using an endoscopic transcanal, cochlear-sparing surgical corridor.

RESULTS

This approach to the IAC was feasible in 92% (35 of 38) specimens based on a minimum distance of 3mm between the basilar turn of the cochlear and the great vessels (jugular bulb and carotid artery).

CONCLUSIONS

Infracochlear access to the IAC is feasible in the majority of adult temporal bones and has implications for future hearing preservation drug delivery approaches to the IAC.

Radiographic Assessment of the presigmoid retrolabyrinthine approach

Background:

Lesions of the petroclival fissure are difficult to access surgically. Both retrosigmoid and presigmoid retrolabyrinthine approaches have been described to successfully treat these complex tumors. The retrosigmoid approach offers quick and familiar access, whereas the presigmoid retrolabyrinthine approach reduces the operative distance and the need for cerebellar retraction. The presigmoid retrolabyrinthine approach, however, is constrained by anatomical limits that can be subject to patient variation. We sought to characterize the surgically relevant variation to guide preoperative assessment.

Methods:

One hundred and seventy-seven high-resolution computed tomography scans of the head (without preexisting pathology) were reviewed. Three hundred and fifty-four temporal bone scans were analyzed for level of aeration, size of Trautmann's triangle dura, and petrous slope. Petrous slope is the angle between the anterior sigmoid sinus and the petroclival fissure at the level of the internal acoustic canal.

Results:

Trautmann's triangle area had a mean of 185.15 mm² (range 71.4–426.7 mm²). Petrous slope had a mean value of 149° (range 106–178°). Increasing aeration was found to be correlated with decreasing petrous slope and decreasing Trautmann's triangle area.

Conclusion:

The presigmoid retrolabyrinthine approach is uniquely confined. Variations in temporal bone anatomy can have dramatic impacts on the operative time, risk profile, and final exposure. Preoperative assessment is critical in guiding the surgeon on the appropriateness of approach. Preoperative measurement of Trautmann's triangle, petrous slope, and aeration can help to reduce surgical morbidity.

Usefulness of image guidance in the surgical treatment of petrous apex cholesterol granuloma

The petrous apex is a pyramid-shaped structure, located medial to the inner ear and the intrapetrous segment of the internal carotid artery. Lesions of the petrous apex can be surgically treated through different surgical routes. Because of the important neurovascular structures located inside the temporal bone, anatomical 3D knowledge is paramount. For this reason, image-guided surgery could represent a useful tool. We report the case of a young woman who came to our observation for a trigeminal neuralgia due to a petrous apex cholesterol granuloma. The lesion was treated through the placement of a drainage tube via an infracochlear approach, with the aid of neuronavigation and intraoperative MRI. Preoperative CT scan images and intraoperative MRI images were fused for surgical planning. The accuracy of the neuronavigation system has proved to be good, and the safety of the procedure was enhanced. Therefore, neuronavigation and intraoperative MRI, though not available in all neurootological centres, should be considered useful tools in these challenging procedures.

A Systematic Review of Simulators in Otolaryngology

Objective

To conduct a systematic review of published articles that describe simulators that could be used in otolaryngology for education, skill acquisition, and/or skill improvement.

Data Sources

Ovid and Embase databases searched July 14, 2011.

Review Methods

Three hundred fifty-three abstracts were independently reviewed by both authors, then 154 eligible articles were reviewed by both authors, and 95 articles were categorized by organ system (eg, otologic); type of simulator (eg, physical, virtual); whether the simulator was a prototype, could be purchased, or was constructed; validation; and level of learning assessment. Discrepancies were resolved by re-review and discussion.

Results

In addition to 11 overview articles, 28 articles described 16 otology simulators, most of which are virtual and prototypes. Ninteen articles described 10 sinus/rhinology simulators; most are virtual surgery simulators and prototypes. Eight articles described 8 oral cavity simulators, and 8 articles described neck simulators. Seventeen articles described 13 bronchoscopy simulators; several are full-body high-technology manikins adapted from other purposes. Five articles described eclectic simulators, including some for learning nontechnical and teamwork skills. Half of the simulators have been validated. Learning levels were often not assessed or assessment was limited to the learners’ perceptions.

Conclusion

A wide variety of simulators are available or under development. Lack of unified validation concepts and limited descriptions restricted our ability to assess model characteristics, availability, and validation. Simulators are emerging as powerful tools to facilitate learning; this review may provide a platform for discussion and refinement of the information reported and analyzed in evaluating simulators.

Anatomic comparison of nasal versus lateral surgical access to the petrous apex

To compare anatomic access to the petrous apex via the nasal and lateral approaches. Hundred consecutive fine-cut CT temporal bones at the Royal Melbourne Hospital from July 27, 2007 to October 30, 2010 were reviewed. Easy lateral access allowed use of a 4 mm burr past vital structures. Easy nasal access was defined as sphenoid pneumatization to/beyond the posterior sella and laterally beyond the maxillary/vidian nerves. Three patients with petrous apex pathology were also reviewed. Easy lateral and nasal access occurred in 74 (37%) and 79 (39.5%) sides, respectively. Easy nasal and lateral access were not strongly correlated (r = 0.10, P = 0.15). A well-pneumatized mastoid (62.5%) was strongly correlated with a large sphenoid (63%, P < 0.001). Pneumatization of the mastoid corresponds to sphenoid sinus size. However, surgical access to the petrous apex is more determined by proximity of vital structures. Easy surgical access via the nasal or lateral approaches was not strongly correlated. Petrous apex lesions requiring surgery should be considered for both approaches.

Training and simulation in otolaryngology

This article focuses on key issues surrounding the needs and application of simulation technologies for technical skills training in otolaryngology. The discussion includes an overview of key topics in training and learning, the application of these issues in simulation environments, and the subsequent applications of these simulation environments to otolaryngology. Examples of past applications are presented, with discussion of how the interplay of cultural changes in surgical training in general along with the rapid advancements in technology have shaped and influenced their adoption and adaptation. The authors conclude with emerging trends and potential influences advanced simulation and training will have on technical skills training in otolaryngology.