Infratentorial Approach to Internal Acoustic Meatus

Surgical exposure of internal acoustic meatus via typical suboccipital retrosigmoid craniotomy is limited by inner ear structures that should remain intact if hearing preservation is attempted. Feasibility of supracerebellar-infratentorial approach to the meatus with more medial angle of exposure and with preservation of inner ear structures was studied on fresh cadavers and on computed tomography pictures of temporal bones. Anatomical relationships of internal acoustic meatus and adjacent structures show marked individual variability. When typical retrosigmoid craniotomy is used to expose meatal fundus, significant medial retraction of cerebellar hemisphere is required in 47% of the patients to avoid opening endolymphatic spaces. Internal acoustic foramen and meatus can be exposed via craniotomy situated under transverse sinus, with 10-15 mm downward retraction of cerebellum. Medial extent of craniotomy can be planned on preoperative imaging studies. Infratentorial supracerebellar exposure of internal acoustic meatus allows for more medial angle of surgical approach than standard retrosigmold craniotomy. It can be used when preoperative imaging studies show that anatomical relationships between internal acoustic meatus and inner ear structures would require excessive cerebellar retraction to visualize a whole tumor inside meatus.     

Infratentorial approach to internal acoustic meatus

Surgical exposure of internal acoustic meatus via typical suboccipital retrosigmoid craniotomy is limited by inner ear structures that should remain intact if hearing preservation is attempted. Feasibility of supracerebellar-infratentorial approach to the meatus with more medial angle of exposure and with preservation of inner ear structures was studied on fresh cadavers and on computed tomography pictures of temporal bones. Anatomical relationships of internal acoustic meatus and adjacent structures show marked individual variability. When typical retrosigmoid craniotomy is used to expose meatal fundus, significant medial retraction of cerebellar hemisphere is required in 47% of the patients to avoid opening endolymphatic spaces. Internal acoustic foramen and meatus can be exposed via craniotomy situated under transverse sinus, with 10-15 mm downward retraction of cerebellum. Medial extent of craniotomy can be planned on preoperative imaging studies. Infratentorial supracerebellar exposure of internal acoustic meatus allows for more medial angle of surgical approach than standard retrosigmold craniotomy. It can be used when preoperative imaging studies show that anatomical relationships between internal acoustic meatus and inner ear structures would require excessive cerebellar retraction to visualize a whole tumor inside meatus.     

A Combined Intradural Presigmoid-Transtransversarium-Transcondylar Approach to the Whole Clivus and Anterior Craniospinal Region: Anatomic Study

Surgical exposure of the clivus is difficult because of its proximity to vital neurovascular structures. The anatomic bases of a new surgical approach to this area are discussed. A supra-auricular skin incision is extended toward the posterior border of the sternocleidomastoid muscle. The vertebral artery is exposed from C2 to the occiput unroofing the foramen transversarium of C1. The bone removal consists of a posterior temporal craniotomy, a suboccipital craniectomy, including mastoidectomy with sigmoid sinus unroofing, removal of the lateral margin of the foramen magnum, of the medial third of the occipital condyle, and retrolabyrinthine petrous drilling. Posterior retraction of the vertebral artery facilitates occipital condyle drilling. Intradural exposure of the petroclival region is achieved by L-shaped cutting of the dura with the long branch placed infratentorially anterior to the sigmoid sinus. Intradural exposure of the craniospinal/upper cervical areas is achieved by cutting of the dura medial to the distal sigmoid sinus and by longitudinal cutting of the dura anterior to the vertebral artery. This approach allows multiple ports of entry to the clivus with full control of the vertebrobasilar system, and of the dural sinuses, and is anatomically suited for controlled removal of tumors located in these areas. This approach, or segments of it, has been used successfully in the treatment of large neoplasms of the craniovertebral junction.     

A combined intradural presigmoid-transtransversarium-transcondylar approach to the whole clivus and anterior craniospinal region: anatomic study

Surgical exposure of the clivus is difficult because of its proximity to vital neurovascular structures. The anatomic bases of a new surgical approach to this area are discussed. A supra-auricular skin incision is extended toward the posterior border of the sternocleidomastoid muscle. The vertebral artery is exposed from C2 to the occiput unroofing the foramen transversarium of C1. The bone removal consists of a posterior temporal craniotomy, a suboccipital craniectomy, including mastoidectomy with sigmoid sinus unroofing, removal of the lateral margin of the foramen magnum, of the medial third of the occipital condyle, and retrolabyrinthine petrous drilling. Posterior retraction of the vertebral artery facilitates occipital condyle drilling. Intradural exposure of the petroclival region is achieved by L-shaped cutting of the dura with the long branch placed infratentorially anterior to the sigmoid sinus. Intradural exposure of the craniospinal/upper cervical areas is achieved by cutting of the dura medial to the distal sigmoid sinus and by longitudinal cutting of the dura anterior to the vertebral artery. This approach allows multiple ports of entry to the clivus with full control of the vertebrobasilar system, and of the dural sinuses, and is anatomically suited for controlled removal of tumors located in these areas. This approach, or segments of it, has been used successfully in the treatment of large neoplasms of the craniovertebral junction.     

The combined supra-infratentorial pre-sigmoid sinus avenue to the petro-clival region. surgical technique and clinical applications

Summary Nine patients with tumours located at the petro-clival region were operated upon from June 1985 to June 1988 using a combined supra- and infratentorial approach anterior to the sigmoid sinus. Two patients had petroclival meningiomas. 4 foramen jugulare neurinomas and 3 glomus jugulare tumours. There was no mortality. Total tumour removal was accomplished in all the patients. All patients remained independent postoperatively. The surgical approach used involves a temporal craniotomy, a suboccipital craniectomy, an extensive mastoidectomy and petrous pyramid drilling without entering the bony labyrinth, the middle ear or the Fallopian canal. The dura is incised supratentorially over the posterior temporal lobe and infratentorially in front of the sigmoid sinus. The temporal lobe is retracted superiorly and the cerebellum and the sigmoid sinus medially. This approach makes use of a very short distance to the petroclival area, offers a multiangled exposure, preserves the dural sinuses, does not iatrogenically impair hearing and minimizes temporal lobe retraction. This exposure is particularly useful in large tumours.     

A surgical technique to expand the operative corridor for supracerebellar infratentorial approaches: technical note

Background

The supracerebellar infratentorial approach is a commonly used route in neurosurgery. It provides a narrow and deep corridor to the dorsal midbrain and pineal region. The authors describe a surgical technique to expand the operative corridor and the surgeon’s working angles during this approach.

Methods

Thirteen cases of patients who underwent resection of their lesions using this extended approach were reviewed. During their suboccipital craniotomy, additional bone over the transverse sinus (paramedian approach) and the confluence of the sinuses (midline approach) were removed. Two sutures (tentorial stay sutures) were anchored to the tentorium anterior to the transverse sinus and tension was applied. A video narrated by the senior author describes the details of technique.

Results

This additional bone removal and tentorial stay sutures led to gentle elevation of the tentorium and partial mobilization of the dural venous sinuses superiorly. This technique enhanced operative viewing through improved illumination and expanded working angles for microsurgical instruments while minimizing the need for fixed retractors and extensive cerebellar retraction. All patients underwent satisfactory removal of their lesions. No patient suffered from any related complication.

Conclusion

The use of stay sutures anchored on the tentorium is a simple and effective technique that expands the surgical corridor during supracerebellar infratentorial approaches.     

Lateral Suboccipital Retrosigmoid Approach with Tentorial Incision for Petroclival Meningiomas: Technical Note

Introduction The resection of petroclival meningiomas presents great neurosurgical challenges. Although multiple surgical approaches have been developed, the retrosigmoid route tends to be used to address tumors that are predominantly located in the posterior fossa. Our modification of the lateral suboccipital retrosigmoid approach with the placement of a tentorial incision yields good visualization of the supratentorial part of the tumor around the midbrain. Methods We treated four patients, one with primary and three with recurrent petroclival meningioma, by our modified approach. After lateral suboccipital craniotomy, the infratentorial part of the tumor was removed after detaching it from the tentorial surface. The cerebellar tentorium was then carefully incised from the supracerebellar angle, taking care not to damage the superior cerebellar artery and trochlear nerve. Results The operative field surrounding the midbrain was widened by this procedure, and safe dissection of the tumor from the brainstem and other neurovascular structures was performed with direct observation of the interface. Conclusions Our approach is a useful modification of the retrosigmoid approach to petroclival meningiomas. It facilitates the safe resection of the supratentorial part of the tumor in the ambient cistern behind the tentorium.     

Quantitative description of the far-lateral transcondylar transtubercular approach to the foramen magnum and clivus

OBJECT: The purpose of this study was to evaluate the far-lateral transcondylar transtubercular approach (complete FLA) based on quantitative measurements of the exposure of the foramen magnum and petroclival area obtained after each successive step of this approach. METHODS: The complete FLA was reproduced in eight specially prepared cadaveric heads (a total of 15 sides). The approach was divided into six steps: 1) C-1 hemilaminectomy and suboccipital craniectomy with unroofing of the sigmoid sinus (basic FLA); 2) partial resection of the occipital condyle (up to the hypoglossal canal); 3) removal of the jugular tuberculum; 4) mastoidectomy (limited to the labyrinth and the fallopian canal) and retraction of the sigmoid sinus; 5) resection of the lateral mass of C-1 with mobilization of the vertebral artery; and 6) resection of the remaining portion of the occipital condyle. After each successive step, a standard set of measurements was obtained using a frameless stereotactic device. The measurements were used to estimate two parameters: the size of the exposed petroclival area and the size of a spatial cone directed toward the anterior rim of the foramen magnum, which depicts the amount of surgical freedom available for manipulation of instruments. The initial basic FLA provided exposure of only 21 +/- 6% of the petroclival area that was exposed with the full, six-step maximally aggressive (complete) FLA. Likewise, only 18 +/- 9% of the final surgical freedom was obtained after the basic FLA was performed. Each subsequent step of the approach increased both petroclival exposure and surgical freedom. The most dramatic increase in petroclival exposure was noted after removal of the jugular tuberculum (71 +/- 12% of final exposure), whereas the least improvement in exposure occurred after the final step, which consisted of total condyle resection. CONCLUSIONS: The complete FLA provides wide and sufficient exposure of the foramen magnum and lower to middle clivus. The complete FLA consists of several steps, each of which contributes to increasing petroclival exposure and surgical freedom. However, the FLA may be limited to the less aggressive steps, while still achieving significant exposure and surgical freedom. The choice of complete or basic FLA thus depends on the underlying pathological condition and the degree of exposure required for effective surgical treatment.     

Operative neurosurgery: personal view and historical backgrounds (8) suboccipital craniotomy-sitting position-linear incision

Suboccipital craniotomy (SOC) can be classified into three types: midline, paramedian and lateral according to the site of linear incision. They are subdivided horizontally into cranial, intermediate and caudal, while the latter of the lateral SOC should be included into the paramedian caudal one (Fig. 1, 19). Sitting position for the craniotomy has several advantages over other positionings in spite of several known drawbacks especially air embolism: cleanliness of the operative field, good anatomical orientation, wider operative spaces obtained by gravitational downward displacement of the cerebellar hemisphere above all. Linear incision is considered to have no definite drawbacks as compared with other incisions such as the horse shoe or the hockey-stick incision and rather have advantages such as enabling effective access to the surgical target by the use of navigation, simpleness of craniotomy in the opening and the closure, and less pseudomeningocele complication. Although cranial and intermediate lateral SOCs are mainly for lesions in the upper and middle CP angle such as acoustic neurinomas or meningioma besides MVD for trigeminal neuralgia, these are applied also for cavernomas of the tectal and cerebellar peduncle, and meningiomas or chordomas of the upper and middle 1/3 of the petroclival region (Fig. 2-5). Importance of the SCTTA by cranial paramedian SOC for the management of lesions in the temporoposteromedial region including the tentorium and its incisura was emphasized and peduncular lesions at the lamina tecti and pons as well. Caudal paramedian SOC is appropriate for lesions in the lower CP angle along with MVD for hemifacial spasm and is furthermore applicable for foramen magnum meningiomas or lower clivus meningiomas by TVDRA (Fig. 6-13). Cranial midline SOC (paraculminar approach) is applicable for tumors of pineal regions and for lesions at the midbrain, thalamus, posterior part of the IIIrd ventricle. The TFUTA by lower midline SOC enables simple access to the IV ventricle and its floor for management of lesions at the tegmentum pontis such as cavernomas (Fig. 14-17). Statistics of a series of consecutive 1,573 surgical cases in the sitting position (1994-2003) are presented including detection rate of air embolism on the anesthetic charts (Fig. 18, Table). Air embolism was most frequent (21%) in the lateral SOC as compared with other SOCs (8.8% on the average). This happened during the extradural procedures in 80% and in 20% in the intradural procedures. Some important technical managements of bridging veins, venous plexus and cerebellar retraction are discussed in carrying out the SOCs.     

The middle fossa transpetrous approach for petroclival meningiomas

Seventeen patients with petroclival meningioma were operated on through a middle fossa transpetrous approach. This approach exposes the anterior cerebellopontine angle through a middle fossa craniotomy with removal of the petrous apex medial to the cochlea and petrous carotid artery. This approach may be enlarged by transection of the superior petrosal sinus and tentorium. The surgical technique and application of the middle fossa transpetrous approach for petroclival meningiomas is presented.     

The Middle Fossa Transpetrous Approach for Petroclival Meningiomas

Seventeen patients with petroclival meningioma were operated on through a middle fossa transpetrous approach. This approach exposes the anterior cerebellopontine angle through a middle fossa craniotomy with removal of the petrous apex medial to the cochlea and petrous carotid artery. This approach may be enlarged by transection of the superior petrosal sinus and tentorium. The surgical technique and application of the middle fossa transpetrous approach for petroclival meningiomas is presented.     

Guidelines for the Ligation of the Sigmoid or Transverse Sinus during Large Petroclival Meningioma Surgery

The authors present guidelines for the ligation of the transverse or sigmoid sinus during the surgical removal of petroclival meningiomas. The medical records and venograms of 14 patients with a petroclival meningioma requiring transverse or sigmoid sinus ligation treated in the Department of Neurosurgery, Seoul National University Hospital between 1986 and 1999 were reviewed. All patients successfully received a sinus trial clamping during the operation. The drainage pattern of the confluens of Herophili was classified into four types: Type A, confluens and equal on both transverse sinuses; Type B, confluens and nondominant transverse sinus on the tumor side; Type C, confluens and dominant transverse sinus on the tumor side; and Type D, unilateral transverse sinus only. Of the 14 cases, four were Type A, five were Type B, and two were Type C. There was no brain swelling after intraoperative test clamping of the sinus for more than 30 minutes. None of the cases developed postoperative complications related to the sinus ligation. Patients with Type A, B, or C drainage patterns were ideal candidates for sinus ligation, especially transverse sinus ligation, if the test clamping proved to be safe. The sinus was cut proximal to the superior petrosal sinus, distal to the vein of Labbé.     

Retrosigmoidal approach to the posterior cranial fossa. An anatomical study

Summary An anatomical study was performed in order to obtain help for orientation regarding the retrosigmoid approach and its osteoclastic craniotomy. The insertions of the sternocleidomastoid, the splenius capitis, the longissimus capitis and the obliquus capitis superior muscles were measured. The relationships of the insertions to different landmarks were also ascertained (FHP, suprameatal spine).In 37 specimens 6 burrholes with a standardized relationship to the Frankfurt Horizontal Plane (FHP) and the external auditory meatus, were performed. Due to the results of the relationship between burrholes and the sigmoid and transverse sinuses it is possible to give an optimal position for the initial burrhole of the osteoclastic craniotomy. A burrhole performed according to the result of this study has a relatively small risk concerning iatrogenic bleeding from the sigmoid and transverse sinuses caused by the burrhead of the drill.     

Transverse sinus stenoses in benign intracranial hypertension demonstrated on CT venography

Catheter studies show that patients with benign intracranial hypertension (BIH) frequently have high pressures in the intracranial venous sinuses proximal to stenotic lesions in the transverse sinuses. These lesions have now been demonstrated on MR venography. This study investigated whether they would be visible on CT. CT venography was performed on 10 patients with BIH and compared with 10 controls, matched for age and sex, undergoing CT angiography for subarachnoid haemorrhage. All controls were confirmed to have had ruptured intracranial aneurysms at craniotomy. Using a semi-automated technique to develop a profile of the cross-sectional areas along the lateral sinuses and to minimize observer bias, the narrowest point on each side was identified and summated in every subject. All patients with BIH exhibited a region of marked narrowing in both transverse sinuses, usually near the junction with the sigmoid sinus, rarely seen in our control group. Measured cross-sectional areas in these venous outflow tracts were substantially different between patients with BIH and controls (p<0.001). CT venography frequently demonstrates transverse sinus narrowing in BIH.     

Two-bone flap craniotomy for the transpetrosal–presigmoid approach to avoid a bony defect in the periauricular area after surgery on petroclival lesions: technical note

The authors describe a two-bone-flap craniotomy technique to avoid the bone defect caused by the transpetrosal–presigmoid approach. Briefly, this technique includes three steps. The first step is to elevate a temporoparietal bone flap located superiorly to the transverse and sigmoid sinuses. The second step is to dissect the transverse and sigmoid sinuses away from the bone by inserting a gelatin sponge. This maneuver provides hemostasis and protects the sinuses from injury. The third step is to cut a second bone flap including part of the temporal bone and the outer table of the mastoid bone with a high-speed drill system. After the operation, the two bone flaps are fixed in place with titanium osteosynthesis fixation material. This approach provides a simple, easy, and safe technique for the transpetrosal–presigmoid approach. The technique has been performed in 83 patients treated for petroclival neoplasms with excellent cosmetic results.     

Surface anatomy of the posterolateral cranium regarding the localization of the initial burr–hole for a retrosigmoid approach

Knowing the location of the venous sinuses is essential for the localization of the initial burr–hole for a retrosigmoid approach, in order to avoid inadvertent entry into the venous sinuses and limitation of the size of the bony opening. In this anatomic study, external landmarks of the posterolateral cranium have been studied, in order to reveal the relationship with the venous sinuses. Eighty-four dried adult human skulls were studied and study of both sides yielded 168 sides. Morphometric measurements of the posterolateral cranium have been performed and relations of the external landmarks with the venous sinuses have been studied. The anatomic position of the asterion was variable. The superior nuchal line was roughly parallel and below the lower margin of the sulcus of transverse sinus in all specimens. The sigmoid sinus, between the superior and inferior bends, seemed to descend along an axis defined by the junction of the squamosal–parietomastoid suture and the mastoid tip, in a slightly oblique fashion. In conclusion, a burr–hole placed just below the superior nuchal line and posterior to the axis defined by the mastoid tip and the squamosal-parietomastoid suture junction is appropriate for both avoiding inadvertent entry into the sinus and limiting the size of the craniotomy.     

Microsurgical anatomy of the tentorial sinuses

Variations of the tentorial sinus of cadaver cerebellar tentoria were examined under a surgical microscope. The tentorial sinuses were classified into four groups: Group I, in which the sinus received venous blood from the cerebral hemisphere; Group II, in which the sinus drains the cerebellum; Groups III, in which the sinus originates in the tentorium itself; and Group IV, in which the sinus originates from a vein bridging to the tentorial free edge. The tentorial sinuses of Groups I and II were frequently located in the posterior portion of the tentorium. The sinuses of Group I were short and most frequently present in the lateral portion of the tentorium. The tentorial sinuses of Group II, which were usually large and drained into the dural sinuses near the torcular, were separated into five subtypes according to the draining veins and direction of termination. The tentorial sinuses of Groups III and IV were located near the tentorial free edge or the straight sinus. The draining patterns of the tentorial sinuses and their draining veins (so-called "bridging veins") were present in most cases. Knowledge of this anatomy can benefit the neurosurgeon carrying out repair near or on the cerebellar tentorium.     

Quantification of the Advantages of the Extended Frontal Approach to Skull Base

This anatomic study evaluated the extent that a fronto-orbital osteotomy (FOO) added to a bilateral frontal craniotomy widened the exposure to the midline compartment of the anterior, middle, and posterior cranial fossae. The goal was to determine if osteotomy would significantly increase angles for two targets: the foramen magnum (FM) and anterior clinoid process (ACP). Stepwise dissections were performed on five cadaveric heads. A bilateral frontal craniotomy was made, followed by FOO. After the ethmoids were removed, the planum sphenoidale was drilled to enter the sphenoid sinus. Further drilling exposed the anterior clivus, which was drilled down to FM. Excellent exposure of the basilar artery, vertebral artery, and brain stem was achieved. With and without FOO, angles of exposure were measured for two targets: the ACP and FM. The angle of exposure after FOO increased markedly with an average gain of 76% for the ACP and of 80% for FM. Compared with a conventional bifrontal craniotomy, the addition of FOO increased the surgical exposure and minimized frontal lobe retraction for accessing lesions of the anterior, middle, and posterior cranial fossae.     

Far posterior subtemporal approach to the dorsolateral brainstem and tentorial ring: technique and clinical experience

OBJECTIVE: Surgical access to the posterolateral mesencephalon or tentorial ring can be problematic, depending on the angle of the tentorium and associated venous structures. A far posterior subtemporal approach was developed that uses the wide opening of the tentorium and the option of supratentorial retraction of the cerebellum to provide an excellent angle of approach to this region. Details of this technique and a series of eight patients with lesions treated by this approach are presented. METHODS: Seven cavernous malformations and one dural arteriovenous malformation were approached in eight patients. In this far posterior subtemporal approach, a horseshoe incision is centered slightly behind the ear, with the caudal extent of the craniotomy defined by the temporal fossa floor. The entry of the vein of Labbé into transverse sinus is identified intradurally. If the vein enters anteriorly in the exposure, it is mobilized. Retractors are then placed, and the tentorium is visualized and opened laterally, avoiding the trochlear nerve. A thin, tapered retractor can be used to retract the cerebellum posterolaterally away from the brainstem. RESULTS: This approach was used to treat eight patients, and their lesions were successfully resected. Seven patients experienced good outcomes, and one patient, who presented with Hunt-Hess Grade IV subarachnoid hemorrhage from a dural arteriovenous malformation, experienced a fair outcome. CONCLUSION: The far posterior subtemporal approach is effective for approaching carefully selected lesions of the posterolateral mesencephalon and tentorial ring.     

The effect of condylectomy on extreme lateral transcondylar approach to the anterior foramen magnum

Summary The dorsolateral, suboccipital, transcondylar technique was used in this cadaveric study. The angle and distance measurements in the corridors were taken intradurally both superior and inferior of the foramen magnum level. In the first stage of this study, the findings which were gained from the standard lateral suboccipital approach were compared with the findings after condyle and lateral atlantal mass removal. After condylectomy, the approach to anterior foramen magnum via both corridors was found to be shorter and the lateral angle of the exposure of the anterior foramen magnum was found to be wider. The considerable shortening of the distances to the anterior foramen magnum, especially in the superior corridor, emphasises the necessity of combining standard approaches with condylectomy. In addition, it was found that after condylectomy, considerable widening of both transverse and longitudinal planes in the inferior corridor allows the surgeon greater access to work on lesions. Furthermore, the freed space between the superior corridor and the inferior corridor, which was gained by condylectomy, shows that condylectomy provides a combined approach to the inferior and superior parts of the foramen magnum anteriorly.