Surgical exposure of the petrous internal carotid artery: practical application for skull base surgery

Fresh Cadaver Simulation Model with Continuous Extracorporeal Circulation as a Training Platform for Intracranial High-Flow Bypass: Technical Note and Rheologic Feasibility Evaluation

Introduction As endovascular techniques evolve toward replacing open surgery, several clinical scenarios still require surgical revascularization. Characterizing this era are decreasing surgical volumes and lack of realistic training models. In an effort to develop lifelike simulation models, we developed a platform for surgical training on high-flow bypass in a fresh cadaver model. Our technique incorporated an extracorporeal circulating system that resembled clinical conditions and confirmed anastomosis efficacy by clinical parameters.

Methods On three fresh cadaveric heads, the subtemporal approach exposed the petrous internal carotid artery (ICA) (C2) as the donor vessel for an interposition radial artery graft. Using a continuous extracorporeal circulation system, the bypass model was tested in three fresh heads and verified using clinical technologies.

Results Successful C2 ICA to M2 anastomosis was completed in all three fresh heads, confirmed with qualitative and quantitative Doppler, and indocyanine green angiography. Antegrade distribution through graft and revascularized territory was documented on postoperative computed tomography (CT) scan with radiopaque silicone injected through the ipsilateral carotid.

Conclusion This study confirmed the feasibility of a totally intracranial high-flow bypass in a fresh cadaver model that achieved hemodynamic features aligned with those of normal middle cerebral artery flow in the clinical setting.

Use of Neuroanatomic Knowledge and Neuronavigation System for a Safe Anterior Petrosectomy

Introduction: The petroclival region is among the most challenging anatomical areas to deal with in skull base surgery. Drilling of the anterior part of the petrous bone during the anterior transpetrosal approach involves the risk of injury of the cochlea, superior semicircular canal, internal carotid artery, and internal auditory canal. A thorough understanding of the microneurosurgical anatomy of this region is mandatory to execute the transpetrosal approaches, decreasing the risk of complications. The aim of this study is to describe the anatomical structures of the petroclival region, highlighting the importance of neuronavigation for safe performance of the anterior transpetrosal approach. Methods: Three adult cadaveric human heads were formalin-fixed and injected with colored silicone. They underwent an axial 1 mm slab CT scan, which was used for neuronavigation during the surgical approaches. The anterior petrosectomy was performed with the aid of neuronavigation during the drilling of the petrous bone. The surgical management of a patient harboring a petroclival meningioma, operated on using an anterior transpetrosal approach, was reported as an illustrative case. Results: The anterior petrosectomy was completed accurately with wide exposure of the surgical target without injuring the cochlea and other structures in all three cadaveric specimens. In the surgical case, no approach-related complications occurred, and a gross total resection of the tumor was achieved. Conclusions: Deep knowledge of the location and relationships of the vital elements located within the temporal bone, along with the use of neuronavigation, are the key aspects to perform the anterior transpetrosal approach safely, reducing the risk of complications.

Clinical utility and versatility of the petrous segment of the internal carotid artery in revascularization

Direct approaches to high cervical lesions, including tumors and aneurysms, carry significant risks. This renders alternative approaches desirable, with vascular disease amenable to exclusion and revascularization to the intracranial circulation, including the petrous or supraclinoid segments of the internal carotid artery (ICA). The cervicopetrous ICA bypass via saphenous venous grafting has proven an effective strategy for treating and excluding these lesions. In current practice, this is performed via an extradural subtemporal approach to access the petrous segment of the ICA and a cervical incision for access to the cervical ICA. The venous graft is alternately tunneled subcutaneously or in situ through the cervical ICA, with the latter eschewing external compression, kinking, and torsion, which increases risk of graft thrombosis with the former. Maxillary or middle meningeal arteries may also serve as donors to the petrous ICA. Moreover, the petrous ICA may be used as a donor in revascularization procedures, to the supraclinoid segment of the ICA and the middle cerebral artery, with petrous supraclinoid and petrous-MCA bypasses described. Clinical utility and operative approaches bypassing to or from the petrous ICA in revascularization procedures are reviewed and discussed.

Anatomic Characteristics of Intrapetrous Carotid Artery: A 3-Dimensional Segmentation Study on Head Computed Tomography Scan

BACKGROUND

The intrapetrous carotid artery (IPCA) is one of the most unexplored anatomic regions, and its 3-dimensional reconstruction in living subjects is still missing. This study aims to describe the IPCA on 3D models extracted from head computed tomography (CT) scans.

METHODS

The intrapetrous carotid artery was manually segmented on head CT scans of 100 healthy patients free from vascular and neurologic pathologies (50 men and 50 women; age range, 18-91 years). Angles of the posterior and anterior genu, diameter and length of the horizontal portion, and volume of the entire canal were calculated through 3D analysis software. Statistically significant differences according to sex and side were assessed through 2-way analysis of variance (P < 0.05). Correlation of each measurement with age was calculated as well.

RESULTS

On average, the angles of the posterior and anterior genu were 120.1° ± 10.4° and 118.0° ± 10.0° in men and 119.5° ± 9.2° and 117.6° ± 10.3° in women, respectively, without statistically significant differences according to sex or side (P > 0.05). The average length and diameter of the horizontal part were, respectively, 25.5 ± 2.9 and 5.8 ± 0.8 mm in men and 24.0 ± 2.3 and 5.3 ± 0.8 mm in women. The volume of the IPCA was 0.941 ± 0.215 cm³ in men and 0.752 ± 0.159 cm³ in women. The length and diameter of the horizontal portion and the volume of the IPCA showed statistically significant differences according to sex (P < 0.05). No correlation with age was found.

CONCLUSIONS

This study provides data concerning not only linear and angular measurements, but also volumes of the IPCA, which are useful in planning surgical interventions of the cranial base.

Anatomic Assessment of Petrous Internal Carotid Artery, Facial Nerve, and Cochlea Through the Anterior Transpetrosal Approach

The aim of this study was to measure the related parameters of the cochlea, so as to allow preoperative assessment of the anatomic relationship of the petrous internal carotid artery (ICA), the facial nerve (FN), and the cochlea during skull base surgery. Seven parameters of these 3 structures were examined in the computed tomographic scan of 120 patients. The shortest distance from the cupula cochleae to the petrous ICA and the FN is as follows: 19.39 (1.01) mm to the stylomastoid foramen (D2), 10.27 (0.80) mm to the midpoint of the genu of FN canal (D3), 13.66 (0.88) mm to the exocranial opening of the carotid canal (D4), and 5.64 (1.03) mm to the midpoint of carotid knee (D5). The shortest distance between the mastoid segment of FN canal and the vertical segment of the petrous ICA (D6) was 13.33 (1.25) mm. The angle between D2 and D3 was measured at 45.66 (3.31)°, and the angle between D4 and D5 was measured at 41.08 (2.64)°. Clinically, it is relatively safe to work within the distances and angles measured in this research, and these results may give surgeons a practical and specific view of these 3 structures in the skull base approaches such as anterior transpetrosal approach to achieve the best possible surgical outcome and maximize safety.

The impact of the cochlear-carotid interval on tinnitus perception

PURPOSE

We hypothesized that the cochlear-carotid interval (CCI), which is defined as the smallest distance along the petrous segment of the internal carotid artery and basal turn of cochlea, may be associated with direct stimulation of hair cells, thereby affecting tinnitus perception. The aim of this study was to investigate the relationships between the CCI, tinnitus perception, and accompanying hearing loss in patients with tinnitus.

METHODS

The CCI on both sides was measured independently by two observers from the temporal 3D b-FFE MR images of 25 patients with tinnitus and 20 age/gender matched control subjects. The relationships between CCI, tinnitus visual analog scale (VAS), and tinnitus handicap inventory (THI) were investigated.

RESULTS

CCI ranged 0.2-5.6 mm (1.9 ± 1.5) on the right and 0.1-5.4 mm (2.2 ± 1.6) on the left side in the patient group and 0.5-5.4 (1.9 ± 1.4) mm on the right and 0.3-6.7 (2.3 ± 1.7) on the left side in the control group. The differences between the two groups were not statistically significant (p > 0.05). CCI showed a strong negative correlation with THI and VAS scores on both sides. Correlation of audiologic findings with CCI revealed a significant negative correlation with pure tone average of the ipsilateral ear most affectedly at high frequencies.

CONCLUSION

The strong negative correlation of CCI with tinnitus-related distress and accompanying sensorineural hearing loss predominantly at high frequencies suggests that further studies on patients with tinnitus that focus on this small area may help to improve the knowledge of tinnitus pathophysiology.

Maximizing the Petroclival Region Exposure Via a Suboccipital Retrosigmoid Approach: Where Is the Intrapetrous Internal Carotid Artery?

BACKGROUND

Recent reports have validated the use of retrosigmoid approach extensions to deal with petroclival lesions.

OBJECTIVE

To describe the topographic retrosigmoid anatomy of the intrapetrous internal carotid artery (IICA), providing guidelines for maximizing the petroclival region exposure via this route.

METHODS

The IICA was exposed bilaterally in 6 specimens via a retrosigmoid approach in the semisitting position. Its topographic relationship with pertinent posterolateral cranial base landmarks was quantified with neuronavigation.

RESULTS

Safe exposure of the IICA and the surrounding inframeatal/petroclival regions was accomplished in all specimens. On average, the IICA genu was 15.08 mm anterolateral to the XI nerve in the jugular foramen, 16.18 mm anteroinferolateral to the endolymphatic sac, and 10.63 mm anteroinferolateral to the internal acoustic meatus. On average, the IICA horizontal segment was 9.92 mm inferolateral to the Meckel cave, and its midpoint was 19.96 mm anterolateral to the XI nerve in the jugular foramen. The mean distance from the IICA genu to the cochlea was 1.96 mm. The genu and the midpoint of the horizontal segment of the IICA were exposed at a depth of approximately 14.50 mm from the posterior pyramidal wall with the use of different drilling angles (49.74° vs 39.54°, respectively).

CONCLUSION

Knowledge of the IICA general relationship with these landmarks (combined with a careful assessment of the preoperative imaging and with the use of intraoperative navigation and micro-Doppler) may help to enhance the inframeatal/petroclival region exposure via a retrosigmoid route, maximizing safe inframeatal and suprameatal petrous bone removal while minimizing neurovascular complications.

Cochlear line: a novel landmark for hearing preservation using the anterior petrosal approach

OBJECT

The goal of this study was to develop a practical landmark for the safe and easy identification of the cochlea when performing anterior petrosectomy based on cadaver dissection results.

METHODS

The cochlear line was defined as the line drawn from the crossing point between the greater superficial petrosal nerve (GSPN) and the petrous internal carotid artery to the line drawn over the apex of the superior circumference of the dura of the internal auditory canal at a right angle. The validity of the cochlear line marking the anteromedial perimeter of the cochlea at the angle of the GSPN and the internal acoustic canal as a practical landmark were evaluated using 5 cadaver heads.

RESULTS

The mean distance (± SD) measured from the cochlear line to the margin of the cochlear cavity was 2.25 ± 0.51 mm (range 1.50-3.00 mm).

CONCLUSIONS

Anterior petrosectomy can be performed more efficiently by using the cochlear line as a key landmark to preserve the cochlea.

Impingement of the carotid canal on the basal turn of the cochlea as pertaining to cochlear implantation

HYPOTHESIS

To evaluate the relation of the basal turn of the cochlea with the carotid canal as pertaining to cochlear implantation.

BACKGROUND

Cochlear implantation is an established mode of treatment for patients with bilateral profound sensorineural hearing loss. An intricate knowledge of both the typical and atypical topography of the cochlea with the carotid canal is essential for safely conducting cochlear implantation.

DESIGN

Fifty-eight cadaveric temporal bones were microdissected to expose the medial wall of the middle ear. To open the basal turn of the cochlea, the promontory was drilled. The carotid canal was unroofed to reveal the internal carotid artery. The minimum distance between the basal turn of the cochlea and the vertical part of the carotid canal was measured.

RESULTS

The minimum distance between the basal turn of the cochlea and the carotid canal ranged from 0 to 3.9 mm (mean ± SD, 1.3 ± 0.8 mm). The carotid canal was abutting the basal turn of the cochlea in three cases, and impingement of the carotid canal on the anterior cochlear wall was found in five (8.6%) cases.

CONCLUSION

Preoperative knowledge of findings like impingement (8.6%) and abutment (5.2%) of the carotid canal on the basal turn of the cochlea is of immense importance in cochlear implantation, which may otherwise lead to disastrous consequences during surgery.

Microsurgical localization of the cochlea in the extended middle fossa approach

Objective In the extended middle fossa approach, a portion of the petrous bone known as Kawase's rhomboid can be drilled to expose the posterior fossa through a middle fossa corridor. During this bony resection, the cochlea is placed at risk. The objective of this study was to objectively detail the position of the cochlea in relation to reliable surgical landmarks. Methods Eleven cadaveric specimens were dissected-including six cadaveric heads and five dry temporal bones by means of an anterior petrosectomy with skeletonization of the cochlea. Three anatomic measurements describing the location of the cochlea in relation to the extrapolated intersection of the greater superficial petrosal nerve (GSPN) and facial nerve were recorded. These measurements were then correlated with thin-cut temporal bone computed tomography scans from 25 patients with morphologically normal inner ears. Results In the cadaveric specimens, the anterior border of the membranous basal turn of the cochlea was located an average of 7.56 mm (6.4 to 8.9 mm) anterior to the extrapolated junction of the GSPN and facial nerve, as measured along the course of the GSPN. The medial border of the membranous cochlea (medial margin of basal turn) was located an average of 8.2 mm (6.9 to 8.9 mm) medial to the extrapolated junction of the GSPN and facial nerve, as measured along the course of the facial nerve. The average maximum distance from the extrapolated junction of the GSPN and facial nerve to the membranous cochlea was 9.3 mm (8.2 to 10.3 mm). These anatomic measurements correlated well with radiologic measurements of the same parameters. Conclusion When drilling Kawase's rhomboid, it is useful to locate the extrapolated junction of the GSPN and the facial nerve. Drilling of the anteromedial petrous bone outside of a radius of 12.5 mm from the extrapolated junction of GSPN and facial nerve appears to be associated with a low degree of risk to the cochlear apparatus.

The importance of carotid-cochlear interval in the etiology of hearing loss

Carotid-cochlear interval (CCI) is the minimal distance between petrous segment of internal carotid artery (ICA) and basal turn of cochlea. Pulsations of the ICA might create fluid pressure changes and direct stimulation of hair cells on the basilar membrane of basal turn of cochlea which is responsible for mid-tone frequencies. The purpose of this study was to investigate whether CCI has a role in the etiology of mid-tone hearing loss and to obtain reference measurements of CCI on MRI. A total of 117 subjects were consecutively enrolled into this retrospective study during a 4 month period. All examinations were performed on a 1.5 T MRI system. The images were transferred to the workstation and reformatted. The CCI was measured on reformatted 3D FIESTA images. The audiologic findings were correlated. We reviewed the temporal MRI studies of 90 consecutive patients [M/F: 48/42, Mean age 45.6 ± 16.6 (10-78)]. As a total 180 sides were evaluated. The CCI ranged from 0 to 9 mm. The CCI didn't exhibit a significant association with subject age or gender. There were no significant differences between readers or sides. There were statistically significant correlation between CCI and level of frequency and degree of hearing loss (p = 0.004 and p = 0.002). The knowledge of CCI is essential prior to otosurgical procedures. There was linear correlation among CCI and level of frequency and degree of hearing loss. CCI of the group including all types of middle frequency hearing loss was longer compared to the normal group.

Petrous carotid exposure with eustachian tube preservation: a morphometric elucidation

Inadvertent injury to eustachian tube leading to cerebrospinal fluid rhinorrhea is a known complication associated with drilling of Glasscock's triangle to expose the horizontal petrous internal carotid artery (ICA) for management of difficult tumors (especially malignant) or aneurysms at the cranial base. Contrary to the usual approach, we hypothesize that a "medial-to-lateral" approach to Glasscock's triangle drilling will minimize eustachian tube injury. Four formalin-fixed human cadaveric heads were dissected, and underwent appropriate morphometric analysis; yielding a total of eight datasets. The diameter of the horizontal petrous ICA exposed was 4.7 ± 0.9 mm (range, 3.8 to 5.6 mm).The mean distance from the medial carotid wall midpoint to the medial-most point on the eustachian tube was 6.35 ± 0.58 mm (range, 5.4 to 7.1 mm), yielding a "safety zone" for eustachian tube, ranging 0.2 to 1.9 mm lateral to the lateral carotid wall. With the medial-to-lateral approach, the eustachian tube remained preserved in all the specimens. The results of our study provide a practical, consistent, and safe method of maximizing horizontal petrous carotid artery exposure while minimizing the eustachian tube injury.

Carotid artery-cochlear dehiscence: a review

This case report describes carotid-cochlear dehiscence, a rare and possibly fatal condition if missed or ignored on initial work-up of several otologic procedures. Thinning of the bony plate separating the carotid canal from other anatomic structures can occur anywhere along the course of the canal, including the carotid-cochlear bony plate. This condition should be recognized by all otolaryngologists in that it can mimic other otologic pathologies. The aim of this report was to call attention to this condition and its associated mimicking symptoms and inform on its proper management. The idea for this review was formed from the case of a patient who presented with pulsatile tinnitus and was found to have carotid-cochlear dehiscence. Carotid-cochlear dehiscence is a rare anatomic variation of which the neurotologic surgeon should be aware. This condition can mimic common otolaryngologic pathologies that regularly present themselves in clinical settings. We present what we believe to be the fourth reported case of carotid-cochlear dehiscence in the literature. The patient presented having only the complaint of pulsatile tinnitus and was later diagnosed with this rare condition. We advocate a thorough preoperative work-up, including high-resolution computed tomography and careful operative planning in a case-specific manner. This is especially important when common pathologies do not become apparent after careful investigation.

Temporal bone dissection for neurosurgery residents: identifying the essential concepts and fundamental techniques for success

BACKGROUND

Many contemporary neurosurgery residents, cordoned by work hour restrictions and drawn to newer technologies such as endovascular therapy, lack the proper direction necessary to learn the essentials of temporal bone dissection. A thorough knowledge of temporal bone anatomy combined with guidance regarding proper surgical technique makes temporal bone dissection an efficacious and fundamental learning activity. There is currently no concise guide for neurosurgical training programs to use in teaching the essentials of this dissection.

METHODS

Over several years, the authors worked with neurosurgery residents to determine the key concepts necessary to gain a fundamental working knowledge of temporal bone dissection.

RESULTS

We have identified 5 essential surgical principles and developed a step-by-step dissection technique useful for neurosurgery residents.

CONCLUSIONS

Using this template, neurosurgery residents can make the most of their time in the skull base laboratory, becoming familiar with relevant temporal bone anatomy in situ and becoming facile with the surgical techniques necessary for its safe dissection.

An anatomic study of the horizontal petrous internal carotid artery: Sex and age differences

OBJECTIVE

This study aimed to determine the length and diameter of the horizontal portion of the petrous carotid artery (HPCA) and to evaluate sex and age differences in these variables.

METHODS

We examined standard axial sinus computed tomographic images in 345 patients (690 sides), measuring length and diameter of the HPCA and the angle between right and left HPCA using computer software.

RESULTS

The HPCA averaged 26.7 mm in length and 5.7 mm in diameter. The angle between the right and left HPCA averaged 101.5 degrees . HPCA length averaged 27.1mm in men and 25.8mm in women; HPCA diameter averaged 5.9 mm in men and 5.3 mm in women. The HPCA of men was approximately 0.8 mm wider and the angle between right and left HPCA was on average 8.7 degrees more obtuse in the 60+ years group than in the <or=19 years group. The HPCA of men was approximately 1.0mm shorter in the 60 years+ group than in both the 20-39 years group and the 40-59 years group.

CONCLUSIONS

Length, diameter and angle of the HPCA exhibited significant sex differences. Aging affected the HPCA in men. This information may be very important not only for surgery of the petrous region or middle fossa but also for anthropological investigation.

Three-dimensional computed tomographic analysis of the relationship between the arcuate eminence and the superior semicircular canal

OBJECTIVE

The location of the superior semicircular canal (SSC) is often determined intraoperatively based on its topographic association with the arcuate eminence (AE). This determination is not always possible because of the potential variability in the relationship between these two structures. The goal of this study was to describe the three-dimensional (3-D) relationship between the AE and SSC using 3-D computed tomography (CT) and to evaluate the utility of 3-D CT for preoperative planning for surgical approaches to the middle cranial fossa.

METHODS

We studied 11 patients (22 sides) radiographically using 0.8- to 1-mm thick reconstructed CT images. A standard set of structural relationships was measured between the AE, SSC, and other regional landmarks.

RESULTS

3-D CT clearly demonstrated the relationships between traditional landmarks along the petrous ridge and middle cranial fossa. The relationship between the arcuate eminence and SSC was found to be highly variable. The average distance between the tips of the two structures was found to be 5.7 mm (range, 2.7-10.4 mm).

CONCLUSIONS

There is significant variability in the relationship between the AE and the SSC. The AE is not a consistent or reliable landmark for identifying the precise position of the SSC. Detailed preoperative information regarding the relationship between the AE, SSC, and other bony landmarks can be easily and quickly assessed using 3-D CT.

Microscopic anatomy of the carotid canal and its relations with cochlea and middle ear

The knowledge of the relations between the noble and vital structures of temporal bone is still a great challenge for the otologic surgeon. The microscopic anatomic studies of the temporal bone are one of the greatest help to prevent lesions during surgical intervention. Aim: To study the anatomic correlations between the carotid canal and the cochlea, and the occurrence of dehiscence of the carotid canal in the middle ear tympanic cavity. Material and Methods: Microscopic study of 122 human temporal bones. RESULTS: The average distance between the carotid canal and the cochlea were: the shortest distance, 1.05mm; basal turn, 2.04mm; middle turn, 2.32mm; and apical turn, 5.70mm. The occurrence of dehiscence of the carotid canal inside the tympanic cavity was 35.2%. Conclusion: The small distances between the cochlea and carotid canal, and the high incidence of dehiscence in the tympanic cavity remind us that anatomical knowledge of the temporal bone is required for the best qualification of otologists.

Infratemporal Fossa Approach to the Hypoglossal Canal: Practical Landmarks for Elusive Anatomy

OBJECTIVE

At the conclusion of the article the readers should be able to safely and reliably find the hypoglossal canal using the infratemporal fossa approach.

HYPOTHESIS

Very little has been written on the regional anatomy of the hypoglossal canal as seen through a transtemporal approach. This project attempts to further define the anatomy of the hypoglossal canal and provide the surgeon with guidelines for reaching it. Our hypothesis is that the hypoglossal canal can be safely and consistently reached by way of the temporal bone with preservation of hearing and cranial nerves (CN) IX to XI.

STUDY DESIGN

Prospective anatomic study.

METHODS

The study was performed using cadaver temporal bones. Infratemporal fossa Fisch type-A dissections were performed. The hypoglossal canal was then completely exposed. The distance from the canal to the jugular bulb, carotid artery, round window, lateral canal, and roots of CN IX to XI were recorded.

RESULTS

Fifteen temporal bones were dissected and measured. The position of the hypoglossal canal is consistently located anterior, inferior, and medial to the jugular bulb. The distance from midcanal to the jugular bulb and the roots of CN IX to XI at the posterior fossa dura was 5.3 mm +/- 0.82 and 7.1 mm +/- 2.49, respectively. The distance from the carotid artery where it meets the jugular vein to the midcanal was 15.3 mm +/- 2.09. The distance from the round window to the canal was 21.7 mm +/- 3.17.

CONCLUSIONS

The hypoglossal canal can be consistently reached using the infratemporal fossa approach. Hearing and CN IX to XI can be preserved. The distance from the jugular bulb and roots of CN IX to XI can be used as guideposts. If a tumor is involving the bulb, then the carotid artery and the round window are the next most reliable indicators of position.

Temporomandibular Joint-preserving Preauricular Subtemporal-Infratemporal Fossa Approach: Surgical Technique and Clinical Application

OBJECTIVE:

The preauricular subtemporal-infratemporal (PSI) approach is commonly used to resect clival tumors and other lesions anterior to the brainstem. One of the surgical steps in this approach is a condylar osteotomy or a condylectomy, which often leads to temporomandibular joint dysfunction. We describe a modification of the PSI approach that preserves the temporomandibular joint without sacrificing the ability to mobilize the petrous internal carotid artery or gain surgical access to the clivus and anterior brainstem.

METHODS:

Anatomic studies in cadaveric specimens were performed, and the extent of exposure of critical skull base and intradural structures was documented with postdissection fine-cut computed tomographic scans. This modification of the PSI approach was subsequently used in three consecutive patients with a clival chondrosarcoma, and the completeness of tumor resection was documented with postoperative magnetic resonance imaging and computed tomographic scans.

RESULTS:

This approach allowed complete mobilization of the petrous internal carotid artery and surgical access to the mid-lower clivus, jugular tubercle, hypoglossal canal, occipital condyle, anterior brainstem, and the origin of the trigeminal through hypoglossal nerves. It also proved to be safe and feasible in the three patients who underwent surgical resection of a clival chondrosarcoma, allowing a complete tumor removal.

CONCLUSION:

This variation of the PSI approach is practical, has no additional morbidity, and provides complete access to critical cranial base regions and tumor margins. It can certainly be used as an alternative to the standard PSI approach when dealing with clival tumors and other lesions anterior to the brainstem.

Three-dimensional computed tomographic cranial base measurements for improvement of surgical approaches to the petrous carotid artery and apex regions

OBJECTIVE

The bony and vascular anatomic features in the region of the petrous apex can vary significantly. These variations affect the operative view obtained via extended subtemporal or anterior transpetrosal approaches to cranial base lesions for individual patients. The goal of this study was to evaluate three-dimensional computed tomography as a means of obtaining detailed preoperative anatomic information regarding bony and vascular landmarks and spatial relationships in the region of the petrous carotid artery and petrous apex.

METHODS

We radiographically studied 15 patients (30 sides), using 0.8- to 1-mm-thick, reconstructed, computed tomographic images. Special attention was given to the course of the petrous carotid artery.

RESULTS

The petrous carotid artery was located lateral to the trigeminal impression. The size of the petrous apex medial to the horizontal petrous carotid artery was observed to be variable. The width of bone from the trigeminal impression to the wall of the internal auditory canal averaged 9.6 mm (range, 5.2-16.1 mm). A variable amount of bone overlying the internal auditory canal (4.5 mm) was also present. Multiple other relationships among key landmarks were quantified.

CONCLUSION

There is significant variability in the anatomic features of the petrous apex among patients. For each patient, detailed preoperative information regarding the amount of bone to be removed during a cranial base procedure can be obtained using three-dimensional computed tomography. This information may be critical for determination of the amount of extra exposure that can be achieved via an anterior petrosectomy for each patient.