Posterior Transpetrosal Approach: Less is More

Anatomical Study of the Supratentorial Extension for the Retrolabyrinthine Presigmoid Approaches

BACKGROUND

Supratentorial craniotomy represents the upper part of the combined trans-tentorial or the supra-infratentorial presigmoid approach. In this study, we provide qualitative and quantitative analyses for the supratentorial extension of the presigmoid retrolabyrinthine suprameatal approach (PRSA).

METHODS

The infratentorial PRSA followed by the supratentorial extension craniotomy with dividing and removal of the tentorial strip were performed on both sides of 5 injected human cadaver heads (n = 10 sides). Quantitative analysis was performed for the surface area gained (surgical accessibility) by adding the supratentorial craniotomy. Qualitative analysis was performed for the parts of the brainstem, cranial nerves, and vascular structures that became accessible by adding the supratentorial craniotomy. The anatomical obstacles encountered in the added operative corridor were analyzed.

RESULTS

The supratentorial extension of PRSA provides an increase in surgical accessibility of 102.65% as compared to the PRSA standalone. The mean surface area of the exposed brainstem is 197.98 (standard deviation: 76.222) and 401.209 (standard deviation: 123.96) for the infratentorial and the combined supra-infratentorial presigmoid approach, respectively. Exposure for parts of III, IV, and V cranial nerves is added after the extension, and the surface area of the outer craniotomy defect has increased by 60.32%. Parts of the basilar, anterior inferior cerebellar, and superior cerebellar arteries are accessible after the supratentorial extension.

CONCLUSIONS

The supratentorial extension of PRSA allows access to the supra-trigeminal area of the pons and the lower part of the midbrain. Considering this surgical accessibility and exposure significantly assists in planning such complex approaches while targeting central skull base lesions.

Key role of microsurgical dissections on cadaveric specimens in neurosurgical training: Setting up a new research anatomical laboratory and defining neuroanatomical milestones

Introduction

Neurosurgery is one of the most complex surgical disciplines where psychomotor skills and deep anatomical and neurological knowledge find their maximum expression. A long period of preparation is necessary to acquire a solid theoretical background and technical skills, improve manual dexterity and visuospatial ability, and try and refine surgical techniques. Moreover, both studying and surgical practice are necessary to deeply understand neuroanatomy, the relationships between structures, and the three-dimensional (3D) orientation that is the core of neurosurgeons' preparation. For all these reasons, a microsurgical neuroanatomy laboratory with human cadaveric specimens results in a unique and irreplaceable training tool that allows the reproduction of patients' positions, 3D anatomy, tissues' consistencies, and step-by-step surgical procedures almost identical to the real ones.

Methods

We describe our experience in setting up a new microsurgical neuroanatomy lab (IRCCS Neuromed, Pozzilli, Italy), focusing on the development of training activity programs and microsurgical milestones useful to train the next generation of surgeons. All the required materials and instruments were listed.

Results

Six competency levels were designed according to the year of residency, with training exercises and procedures defined for each competency level: (1) soft tissue dissections, bone drilling, and microsurgical suturing; (2) basic craniotomies and neurovascular anatomy; (3) white matter dissection; (4) skull base transcranial approaches; (5) endoscopic approaches; and (6) microanastomosis. A checklist with the milestones was provided.

Discussion

Microsurgical dissection of human cadaveric specimens is the optimal way to learn and train on neuroanatomy and neurosurgical procedures before performing them safely in the operating room. We provided a “neurosurgery booklet” with progressive milestones for neurosurgical residents. This step-by-step program may improve the quality of training and guarantee equal skill acquisition across countries. We believe that more efforts should be made to create new microsurgical laboratories, popularize the importance of body donation, and establish a network between universities and laboratories to introduce a compulsory operative training program.

The historical perspective in approaches to the spheno-petro-clival meningiomas

The current literature regarding surgical treatment for tumors in the sphenopetroclival (SPC) region is merely scarce. Through a comprehensive literature review, we investigated the indications, outcomes, and complications of different surgical approaches to the SPC meningiomas. Given its complicated relationship between these slow-progression tumors and some critical neurovascular structures in the SPC region, surgical treatment of these tumors faces the challenge of achieving a maximal grade of resection, while preserving patient functionality. The development of new surgical techniques and approaches in recent years have permitted the advancement in the treatment of these tumors, with acceptable rates of morbidity and mortality. The choice of a surgical approach as a treatment for the lesion depends mainly on the type of tumor extension, surgeon's preferences, and the displacement of neurovascular structures. Rather than focusing on one single strategy of treatment, the skull-base surgeon should tailor the approach based on the origin and features of the lesion; as well as the peculiarities of the surgical anatomy. This strategy aims to decrease morbidity and to optimize tumor resection and patient quality of life.

Comparative Analysis of Transpetrosal Approaches to the Internal Acoustic Meatus Using Three-Dimensional Radio-Anatomical Models

Background The transcrusal approach that involves partial removal of the labyrinth was recently described to approach lesions of the cerebellopontine angle. It carries the benefit of hearing preservation and was suggested to have equivalent exposure of the petroclival surface compared with the transcochlear/transotic approaches. The current study was designed to assess if the transcrusal approach could achieve as good access to the internal auditory meatus (IAM) as the more destructive translabyrinthine exposure. Methods Fifty disease-free high-resolution computed tomography scans of the temporal bone were reviewed. Surgical freedom, angle of attack, and angle of trajectory to the internal acoustic canal were measured in three-dimensional models. Results Surgical freedom and angles of attack showed steady increments with the progression of petrous bone resection from the retrolabyrinthine-transcrusal-translabyrinthine approaches. The angle of access to the IAM axis was dramatically reduced in the translabyrinthine approach compared with the transcrusal and retrolabyrinthine approaches (37.51 ± 5.7, 24.56 ± 4.6, and 3.17 ± 2.85 degrees, respectively; n = 50; average plus or minus standard deviation, p < 0.001). Conclusion Using this novel radio-anatomical system, we demonstrate the advantage of the translabyrinthine approach to the axis of the internal auditory canal. The transcrusal approach lags behind the translabyrinthine corridor and should be considered alongside the subtemporal and retrosigmoid approaches designed to spare hearing.

Predicting the presigmoid retrolabyrinthine space using a sigmoid sinus tomography classification: A cadaveric study

BACKGROUND

The presigmoid retrolabyrinthine space is characterized by a widely variable size. The main structure involved in this large variability is the sigmoid sinus. Few studies have attempted to establish a reliable classification of sigmoid sinus to predict the presigmoid retrolabyrinthine space. We used tomographic mapping of human cadaver temporal bones to classify the position of sigmoid sinus and performed a cadaveric study to assess the validity of a novel classification in predicting the presigmoid retrolabyrinthine space.

METHODS

Ten human cadaver temporal bones were randomly selected and subjected to fine-cut computed tomography scanning to classify the position of sigmoid sinus using a reference line. The specimens were classified into medial and lateral groups and each specimen was then subjected to mastoidectomy. The groups were compared using quantitative and qualitative analysis.

RESULTS

The medial group showed a larger distance between the sigmoid sinus and the external auditory canal and a shallower lateral semicircular canal. In the lateral group, the mastoidectomy was more demanding, and the Trautmann's triangle was typically narrower and often "hidden" medially to the sigmoid sinus.

CONCLUSIONS

The tomographic classification proposed in this study predicts, in a cadaveric model, the presigmoid retrolabyrinthine space. It may help the surgeon select the best approach to reach the petroclival region and lead to safer neurological and otological surgeries.

Transcrusal approach to the retrochiasmatic region with special reference to temporal lobe retraction: an anatomical study

BACKGROUND

The retrochiasmatic region is one of the most challenging areas to surgically expose. The authors evaluated the transcrusal approach, which involves removal of the superior and posterior semicircular canal from the ampulla to the common crus, to expose the retrochiasmatic region and compared it with the retrolabyrinthine approach, both of which are a variation of the posterior petrosal approach with hearing preservation, with a special emphasis on the influence of temporal lobe retraction.

METHODS

Six sides of silicone-injected cadaveric heads were dissected using two approaches: the transcrusal approach and the retrolabyrinthine approach. For each craniotomy, 3 exposure parameters in the retrochiasmatic region were measured: (1) horizontal distance, (2) vertical distance, and (3) triangular area of exposure, at three different levels of temporal lobe retractions: 0, 5, and 10 mm of retraction from the level of the tentorial incisura.

RESULTS

Without temporal lobe retraction, only the transcrusal and not the retrolabyrinthine approach provided a direct exposure of the retrochiasmatic region, especially in the horizontal distance (p < 0.001). At all levels of temporal lobe retraction, the transcrusal approach provided greater exposure in the horizontal and vertical distances and in the area of exposure. Nonetheless, in the horizontal distance, the difference between the transcrusal and retrolabyrinthine approaches decreased along with increased temporal lobe retraction, and almost no difference was obtained at 10 mm of retraction.

CONCLUSIONS

Posterior petrosal approaches can provide an excellent exposure of the retrochiasmatic region. Of these two approaches, namely, transcrusal and retrolabyrinthine with hearing preservation, the transcrusal approach offers greater exposure than the retrolabyrinthine approach. The beneficial effect of partial labyrinthectomy of the transcrusal approach to the retrochiasmatic region is accentuated in the exposure of the horizontal distance with less temporal lobe retraction.

The transcrusal approach: a 10-year experience at one Canadian center

OBJECTIVE

This study reviewed the experience and outcomes of 1 surgical team (L.S.P., S.P.L.) using the transcrusal approach.

METHODS

Ten-year retrospective review of 17 consecutive patients requiring transcrusal exposure of the petrous apex and upper brainstem was performed. The main outcome measures included hearing and facial nerve preservation as measured by standard audiography and postoperative assessment using the House-Brackmann scale.

RESULTS

Operative indications included meningioma (5 patients), epidermoid/dermoid cyst (3 patients), trigeminal schwannoma (3 patients), giant or large upper basilar artery aneurysm (3 patients), pontine cavernoma (1 patient), chondrosarcoma (1 patient), and clival melanocytoma (1 patient). Average tumor size was 3.6 cm. Complete resection was achieved in 50% of patients with petroclival tumors. Follow-up data were obtained for 14 patients at 20 +/- 4 months. Serviceable hearing was preserved in 58%. Sixty-four percent of patients demonstrated House-Brackmann stage I facial nerve function. Two patients died perioperatively (brainstem infarction). Two patients became hemiparetic, with 1 improving substantially. CSF leaks developed in 3 patients. Forty-seven percent of patients demonstrated cranial nerve V deficits. Forty-one percent of patients demonstrated deficits of cranial nerve III, IV, or VI. Vertigo, vestibular disturbance, hydrocephalus, temporal lobe contusion, or hematoma did not develop in any patients.

CONCLUSION

The transcrusal approach provides adequate exposure for most petroclival lesions and giant aneurysms of the upper basilar artery while offering the possibility of hearing preservation. Like all approaches to large tumors and aneurysms in this region, there is a significant risk of morbidity and mortality. However, this approach is an excellent alternative to other techniques that necessitate deliberate sacrifice of ipsilateral hearing.