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An extended middle fossa approach combined with a suboccipital craniectomy to the base of the skull in the posterior fossa
Surg Neural 1987;28:245-52
An Extended Suboccipital Posterior
Middle Fossa Approach Craniectomy
245
Combined with a
to the Base of the Skull in the
Fossa
Saburo Sakaki, M.D., Sadanori Takeda, M.D., Hitoshi Fujita, M.D., and Shinsuke Ohta, M.D. Department
of Neurological
Surgery, Ehime University
School of Medicine, Ehime, Japan
Sakaki S, Takeda S, Fujita H, Ohta S. An extended middle fossa approach combined with a suboccipital craniectomy to the base of the skull in the posterior fossa. Surg Neural 1987;28:245-52. A new approach to the base of the skull in the posterior fossa is described. This approach involves removing the petrous bone without any injury to the labyrinth, and dividing the superior petrosal sinus and tentorium cerebelli. A combined suboccipital craniectomy is used for excision of the portion of tumors that extended inferiorly. Total or subtotal removal of tumors was performed in 11 patients and partial removal in 3 patients, without any operative mortality. The facial nerve was preserved in all patients and hearing was retained in 9 of 12 patients. This approach is useful for large tumors located around the clivus. KEY WORDS: Extended middle fossa approach; Suboccipital approach; Base of the skull; Posterior fossa tumor; Facial and cochlear functions
Among the various extra-axial tumors in the posterior fossa, those arising from the petrous apex or &us, or tumors extending anteriorly to the brainstem have presented difficult surgical problems. The conventional suboccipital approach has failed to achieve adequate access for removal of these tumors because of the interposition of the cerebellum and brainstem [4,7,10,19,21]. Up to now, several extended or combined lateral approaches have been used for better exposure of this region [1,2,5-13,15-18,201. The rationale behind these surgical procedures is the concept that all the anatomic structures in this region can be adequately identified in the surgical field by the shortest route, although every approach has been modified differently by different sur-
Adu’re~s reprint requests to: Saburo Sakaki, M.D., Department of Neurological Surgery, Ehime University Medical School, Onsen-Gun, Shigenobu-Cho, Ehime 791-02, Japan. Received
February
5, 1987; accepted
April
0 1987 by Elsevier Science Publishing Co., Inc.
16, 1987.
geons according to their familiarity with the anatomy of the temporal bone. We have developed an extended middle fossa approach combined with a suboccipital craniectomy for the removal of large extra-axial tumors located at the base of the skull in the area of the posterior fossa. This article describes the surgical technique and its results in 14 patients treated by this method.
Clinical Material Fourteen patients were selected as candidates for an extended middle fossa approach combined with a suboccipital craniectomy on the basis of the location, size, extension, and suspected pathology of the tumors. The 14 patients were chosen from 60 patients who were admitted to the Ehime University Hospital from April 1978 to November 1986, all of whom had extra-axial tumors in the posterior fossa (Table 1). Upon admission, all patients were evaluated by means of neurologic and neuroradiologic examinations including computed tomography (CT).
Operative Technique The patient is placed in the supine or park bench position with the head turned 90” toward the side contralateral to the tumors, and fixed by three-point fixation so that the squamous portion of the temporal bone lies horizontally. As a rule, a catheter is inserted into the lateral ventricle through a frontal burr hole, to decompress the ventricle during retraction of the temporal lobe and to cope with postoperative brain swelling. The skin incision is made from a point overlying the zygomatic arch and encircles the external ear, with the posterior limb ending approximately at a point a few centimeters medial and below the tip of the mastoid process as shown in Figure 1. The scalp flap is turned down, and the mastoid process and upper margin of the external auditory canal are exposed. A free temporal bone flap is 0090-3019/87/$3.50
246
Sakaki et al
Surg Neural 1987;28:245-52
1. Operative Approaches in 60 Patients with Extra-axial Tumors in the Posterior Fossa
Table
Unilateral suboccipital craniectomy (a)
Extended middle fossa approach combined with suboccipital craniectomy (n)
Acoustic neurinoma” Trigeminal neurinoma Meningioma Epidermoid cyst Chordoma Craniopharyngioma
35 8 4 -
1 2 7 2 1 1
Total
47
14
“One patient with acoustic neurinoma
was operated
on by both approaches
at an interval.
made near the floor of the middle cranial fossa, followed by a unilateral suboccipital craniectomy across the transverse-sigmoid sinus junction. The dura mater is separated from the anterior surface of the pyramid to the level of the sulcus of the superior petrosal sinus from above, and the hiatus of the facial canal from the front. The mastoid bone is drilled away with steel burrs from the mastoid cells posteriorly to the level of the compact plate of the sigmoid sinus, and the lateral part of the petrous bone is removed medially near the level of the arcuate eminence, with the inner ear, particularly the semicircular canals, being completely intact in order to preserve the postoperative potential for inner ear functions. Practically, it is wise to limit the removal of the lateral part of the petrous pyramid to within 1 cm from its base. Next, the bone overlying the sigmoid sinus is completely removed with diamond burrs, while the superior petrosal sinus is gently separated from its sulcus, from the orifice of the superior petrosal sinus to the sigmoid sinus toward the petrous apex. The dura mater over the temporal lobe is opened vertically over the anterior portion taking care to avoid the veins coming from the temporal lobe, and the dural incision is made inferiorly across the floor of the middle fossa to the superior petrosal sinus. The dura mater over the posterior fossa is opened vertically down to the jugular bulb in front of the sigmoid sinus, after which the superior petrosal sinus is divided between hemostatic clips. The tentorium cerebelli is incised to the incisura parallel to the superior petrosal sinus with upward retraction of the temporal lobe, and the tentorial flap is laid back to expose a surgical field. Finally, additional dural openings at right angles to the previous incisions are made, and the suboccipital dura is incised in a radiating fashion when required. All these separated dura mater are supported by suture threads (Figure 2). A selfretaining retractor is used to retract the temporal lobe upwards and a second retractor holds the cerebellar
hemisphere posteriorly, while cerebrospinal fluid (CSF) is drained through the ventricular catheter. When these procedures have been adequately carried out, the tumor will be visualized in the center, and the superior, anterior, and lateral aspects of the cerebellopontine angle will come into view. Occasionally, it is possible to better visualize the anterior aspect of the brainstem by further removal of the petrous bone along the sulcus of the superior petrosal sinus in the direction of the petrous apex. We then proceed to remove the tumor by gutting the central core with a CUSA or CO* laser. After enucleation of the tumor, the capsule is dissected from the surrounding structures while we identify all the anatomic structures; in the case of a petrosal meningioma, for example, we can identify the area from the fourth and fifth cranial nerves superiorly, from the cerebellar hemisphere and brainstem posteromedially, from the seventh and eighth cranial nerves ventrolaterally, and from the ninth and tenth cranial nerves inferiorly (Figure 3). When the tumors extend inferiorly below the jugular bulb (dissection of tumors from the vagus group is considered to be difficult from above), the suboccipital approach is preferable to the middle fossa approach for removal of the inferior portion of the tumors (Figure 4). After complete hemostasis, the dura mater is sutured, leaving the tentorium cerebelli open, and pieces of fat or muscle are placed on the surface of the drilled portion
Figure 1. Scalp incision and extent of bone remwalfor the extended middle foua approach combined with suboccipital craniectomy.
Combined
Approach to Base of the Skull
Surg Neurol 1987;28:245-52
sup. petrosal
247
sinus
Figure 2. The opening of the dura mater is shown. The superior petrosal sinus and tentorium cerebeh’i are divided in front of the sigmoid sinus.
post. fossa
of the mastoid and petrous bone to prevent postoperative liquorrhea. The removed temporal bone is replaced, and cranioplasty is performed with a resin plate when the bone defect is large enough in the region of the craniectomy.
Results As shown in Table 2, 14 patients with large extra-axial tumors in the posterior fossa were operated on by means of the extended middle fossa approach combined with suboccipital craniectomy using the operating microscope. All tumors were located at the base of the skull in the posterior fossa and extended anteriorly to the brainstem or cephalad to the middle fossa. Pre- and postoperative CT scans of representative patients are shown in Figure 5. There were 3 males and 11 females, with ages ranging from 12 to 68 years (mean age 4 1 years). All meningiomas were 3 cm or larger in the greatest diameter, including two clivus meningiomas, two tentorial meningiomas arising from the tentorial notch and extending almost to the posterior fossa and partly to the middle fossa, two huge petrosal meningiomas arising from the posterior surface of the petrous bone medial to the porus acusticus internus which extended partly to the middle fossa, and a parasellar meningioma extending almost to the posterior fossa. Two trigeminal neurinomas were large cystic tumors of the root type developing anteriorly to the brainstem. There was one acoustic neurinoma, which had been previously operated on through a suboccipital craniectomy with
dura
incomplete removal, and which had recurred in the region anterior to the brainstem. Of two epidermoid cysts, a huge one extended from the right cerebellopontine angle medially, anterior to the brainstem, and into the contralateral left cerebellopontine angle, and the other one was located in the left cerebellopontine angle and extended from the middle fossa to the foramen magnum. There was one craniopharyngioma which had a large extension to the posterior fossa. As shown in Table 3, total or subtotal removal was performed in 11 of 14 patients (79%). In the patients with meningioma, gross total removal was carried out in 3 patients, and subtotal removal in 3 patients; subtotal removals were due to an invasion of the tumor to the tentorium (case l), the difficulty in dissecting the tumor from the brainstem (case 2), and the fact that a small piece of the tumor was left on the exit zone of the facial nerve (case 3). In the patient with the parasellar tumor, the part of the tumor that enveloped the internal carotid artery was left in place. In the patients with trigeminal neurinomas, one was totally removed and the other subtotally because an invasive part of the tumor was left on the entry zone of the trigeminal nerve (case 8). One epidermoid cyst had developed so extensively among the cranial nerves and blood vessels that total removal of the tumor was abandoned (case 11). In the two patients with craniopharyngioma (1) and chordoma (l), partial removal of the tumors was planned prior to surgery for the relief of symptoms. The operative results are classified into four groups: excellent, when patients return to their previous social activity with or without
248
Surg Neural 1987;28:245-52
Sakaki et al
,
IVth nerve , sup. petrosal
sinus
br‘ain stem
tentor ium post. fossa dura \
psigmoid
sinus
Figure 3. The temporal lobe is retracted superiorly and the cerebeLar hemisphere posteriorly, by self-retaining retractors. The superior, anterior, and lateral aspects of the cerebellopontineangle are displayed through the extended middle fossa approach; the tumor is visualized in the center, with the fourth craniaI nerve running on the surface of the tumor.
Figure 4. The inferior aspect of the tumor is visualized through the suboccipital approach.
temporal
lobe I
sigmoid
sinus
ten tor ium,
\ \
urn
IXth, xcipital
dura
Combined
Approach
to Base of the Skull
Surg Neurol 1987;28:245-52
249
2. Extended Middle Fossa Approach: Summary of Patients
Table
Pathology Case no.
Age/sex
and location of tumor
Initial symptoms
1
47lF
Tentorial meningioma
Gait disturbance
2
35iF
Clivus meningioma
Gait and speech disturbances
3
12/F
Gait disturbance; left hearing loss
4 5
&IF 54iF
6
43/M
Petrous apex meningioma; middle fossa extension Tentorial meningioma Parasellar meningioma; posterior fossa extension Clivus meningioma
7 8
47/F 54/F
Petrous apex meningioma Trigeminal neurinoma
Right facial numbness Headache; vomiting
9
53/M
Trigeminal neurinoma
Left facial numbness
10 11
39/F 34/M
Acoustic neurinoma Epidermoid cyst
12 13
4 l/F 2 l/F
Epidermoid cyst Craniopharyngioma
Gait disturbance Right trigeminal neuralgia Left trigeminal neuralgia Headache; visual loss
14
21/F
Chordoma
Dysphagia; diplopia
Headache; diplopia Left visual loss; gait disturbance Left-sided weakness; left hemifacial spasm
Neurological findings on admission”
Left V hypesthesia; nystagmus; ataxic gait Papilledema; nystagmus; dysphagia; right hemiparesis; ataxic gait Nystagmus; diminished hearing; ataxic gait
Size of tumor on CT scans (cm)
3.6 x 2.8 x 3.0 4.2 x 3.6 x 5.0
4.8 x 4.3 x 6.0
Left abducens paresis Left papilla atrophy; left III palsy; right hemiparesis Left hemifacial spasm; diminished hearing; ataxic gait Right V hypesthesia Papilledema; left V, IX, X, XII involvements Left V, IX, X involvements Left VII palsy; ataxic gait Right V hypesthesia
2.4 x 2.1 x 3.0
Left V hypesthesia Impairment of visual acuity Left V, VI, XII; right
I.2 x 1.0 x 3.0 2.9 x 2.4 x 1.5
6.0 x 3.6 x 5.0
4.2 x 3.9 x 5.0
3.8 x 2.8 x 3.0 4.3 x 4.3 x 6.0 2.6 x 1.9 x 4.0 2.2 x 2.2 x 2.0 3.3 x 4.0 x 3.0
3.6 x 6.0 x 3.0
VII, VIII, IX, x, XI involvements “Roman numerals indicate cranial nerves
neurological deficits; good, when patients are able to take care of themselves; poor, when patients are unable to take care of themselves; and dead. In the present series, 9 patients (64%) were rated as excellent, 4 (29%) good, and 1 poor at follow-up examination ranging from 4 months to 7 years (average of 2 years and 4 months) after the surgery. In only one patient (case 6) the neurological state became worse with left sixth nerve palsy after the operation; however, this was improving at follow-up examination 9 months after the operation. Two patients with meningiomas (cases 1 and 3) and one patient with a neurinoma (case 8) were operated on with this combined approach in two stages at intervals of 2 months, 1 year, and 7 months, respectively, and finally, these tumors were subtotally removed. The facial nerve function returned in all patients who had had normal function prior to the operation; this was assessed as complete recovery in all of them at follow-up examinations. Hearing was preserved postoperatively in 9 of minor
12 patients tion.
Three
erative free
(7 5%) who had had good patients
period,
but
on anticonvulsant
had since
seizures then
therapy
preoperative
func-
in the
early
postop-
have
been
seiture-
they during
the follow-up
pe-
riod. In these patients, postoperative CT scans showed a low-density area in the temporal lobe, which suggested brain contusion due to retraction during the operations. There were two patients with postoperative CSF leakage presenting as rhinorrhea, in whom the leaks through the mastoid air cells were operatively closed with bone wax and muscle.
Discussion It is an extremely difficult surgical problem to approach the large tumors arising from the clivus or petrous bone medial to the porus acusticus, or the tumors located in the region anterior to the brainstem, because of the position of the lesions anterior to the brainstem and the lesions in direct contact with the major blood vessels and cranial nerves. Attempts have been made for better approaches to the tumors in this region. Hitselberger and House [S] described a combined suboccipital-petrosal approach to large tumors in the cerebellopontine angle: in this report the authors extended their previously developed translabyrinthine approach posteriorly beyond the sigmoid sinus into the suboccipital
250
Surg Neural 1987;28:245-52
Figure 5. Pre- and postoperative CT scans of the representative patients. IL& Case 3; petrous apex meningioma with middle fossa extension, second pre- (a) and postoperative (b). (wr) Case 6; chvus meningioma, pre(c) and postoperative (d). (w) Case 7; petrous apex meningioma, pre(e) and postoperative (0.
region and achieved a wider exposure of the cerebellopontine angle than had been possible using the translabyrinthine or unilateral suboccipital approach alone, by mobilizing the sigmoid sinus anteriorly, posteriorly, or both, or even dividing it [9]. This approach has the distinct advantage for tumors extending below the jugular bulb. Later on, these authors reported { 10,l l] a transcochlear approach for the removal of tumors arising from the petrous bone medial to the porus acusticus or the clivus. The transcochlear approach is accomplished by a forward extension of the translabyrinthine opening of the petrous bone into the cerebellopontine angle, so that the advantage of direct access not only to the tumors
Sakaki et al
in this region but also to the blood supply of the tumors is gained, although removal of the petrous temporal bone and rerouting the facial nerve require an excellent neurotological technique. Morrison and King [ 12,157 described a translabyrinthine-transtentorial approach, in which the exposure of the cerebellopontine angle was greatly extended upwards through the middle fossa after drilling out the petrous temporal bone and dividing the superior petrosal sinus and tentorium cerebelli. They used their approach for various lesions in the cerebellopontine angle other than acoustic neurinomas, with successful operative results. However, they reported also that their approach could not provide an adequate exposure to tumors extending inferiorly toward the foramen magnum [15]. Bochenek and Kukwa [l] also developed an extended approach through the middle fossa, which was nearly the same as that of Morrison and King, but with incomplete labyrinthectomy. They drilled out the lateral part of the petrous bone up to the level of
Combined
Approach to Base of the Skull
251
Surg Neural 1987;28:245-52
Table
3. Subtotal or Total Removal Approach: Summary of Patients Operative
Case IlO.
Operation
result
and follow-up period
1
Subtotal
removal
Excellent,
2
Subtotal
removal
3
Subtotal
removal
Excellent, 2 yr and 6 mo Excellent,
4
Gross
5
Partial
removal
6
Gross
total removal
Acoustic
Facial nerve function
nerve function
(tumor side)
(tumor side)
Preoperative
Postoperative
Preoperative
Postoperative
Normal
Normal
Normal
Normal
Normal
Normal
Normal
Normal
Normal
Normal
Diminished
Normal
Normal
Normal
3v
total removal
2 yr Excellent, 1 yr and 4 mo Poor, 11 mo Good,
Complication”
Left V slight hypesthesia; Seizures
seizure
Deafness
-
Normal
Normal
-
Normal
Normal
Normal
Left III palsy
Normal
Paresis
Diminished
Deafness
Left abducens
Normal
Normal
Normal
Normal
Normal
Normal
Normal
Deafness
Liquorrhea (operative repair) Left V hypesthesia
Normal
Normal
Normal
Normal
Left V anesthesia
Palsy
Palsy
Deafness
Deafness
-
Normal
Normal
Normal
Normal
-
Normal
Normal
Normal
Normal
Normal
Normal
Normal
Normal
Palsy
Palsy
Deafness
Deafness
hearing
hearing
palsy
9 mo 7
Gross
8
Subtotal
total removal removal
9
Total removal
10
Total removal
11
Subtotal
12
Total removal
13
Partial
removal
14
Partial
removal
removal
Excellent, 4 mo Excellent, 7 yr Good, 1 yr and 5 mo Good, 1 yr Excellent, 4 yr and 7 mo Excellent, 1 yr and 10 mo Excellent, 4 yr Good, but died 2 yr after
Liquorrhea repair)
(operative -
Seizures
“Roman numerals indicate cranial nerves
the compact plate of the sigmoid sinus posteriorly and to the lumen of the lateral semicircular canal medially, and incised the tentorium cerebelli without dividing the superior petrosal sinus. They stated that a wider visualization of the cerebellopontine angle could be obtained by their approach rather than by the route through the labyrinth. Hakuba [7] proposed a transpetrosal-transtentorial approach, which was also a modification of Morrisons’s and King’s approach but with incomplete labyrinthectomy and combined suboccipital craniectomy. Thus, the extended middle fossa approach combined with labyrinthectomy can provide an appropriate exposure for tumors located in the region from the cerebellopontine angle to the anterior aspect of the brainstem, especially for those extending to the middle fossa. However, it does not provide good access to the tumors with an inferior extension toward the foramen magnum, and a complete or incomplete labyrinthectomy sacrifices the cochlear and vestibular functions to achieve a wide exposure of the cerebellopontine angle by the shortest route. Our approach described here has been developed on
the basis of the following concepts: it gives a better exposure in the surgical field of the cerebellopontine angle and of the region anterior to the brainstem; it can be extended toward the middle fossa and below the jugular bulb up to the foramen magnum at any given moment; it provides visualization of all anatomic structures in this region from different angles and provides a nearer route to the blood supply of the tumors; it permits the possible restoration or retention of auditory function in patients with good hearing preoperatively; and it has the advantages of both the middle fossa transtentorial approaches and the suboccipital ones. For these purposes, the lateral part of the petrous bone can be partially removed within 1 cm of its base, enough to uncover the sigmoid sinus and superior petrosal sinus, but the labyrinth will not be injured at all [lb]. Upon dividing the superior petrosal sinus and tentorium cerebelli, an excellent exposure of th, cerebellopontine angle can be obtained. To achieve a wider exposure in the region anterior to the brainstem, further removal of the petrous bone can be carried out along the petrous ridge in the direction of its apex; care must be taken
252
Surg Neurol 1987;28:245-52
not to injure the facial nerve or the cochlea. A combined suboccipital craniectomy was used for the excision of the portion of the tumors that extended inferiorly. This approach was used only in exceptional situations when the patients had large tumors extending toward the anterior aspect of the brainstem, and especially, when they had good hearing preoperatively. In the present series, a good surgical field was gained for removal of the tumors through the middle fossa in only 8 patients. In the rest of the patients, however, the lower portion of the tumors was not visualized well enough from above because the tumors extended below the jugular bulb, so the suboccipital dura was incised and the tumors were successfully excised through the suboccipital approach. It is often necessary to take both approaches in sequence intraoperatively. The surgical results for meningiomas in the posterior fossa depend mainly on the site of dural attachment and the direction of the extension of the tumor [14]. In a series of 28 patients operated on for petrosal meningioma, according to Olivecrona, there were 12 fatalities (43%) in whom nearly all of the tumors arose from the posterior surface of the petrous bone medial to the porus and Schneck [3], in reviewacusticus {l 11. Cherington ing the patients with clivus meningioma enumerated in the literature and including their own cases, reported that among 29 patients, there were 16 who died within 2 weeks of surgery, 4 within 7 months, and 1 who succumbed 12 months after biopsy, and that the l-year survival rate after diagnosis was 25% or less. In the present series, we performed total or subtotal removals in 6 patients with large meningiomas, 2 patients with trigeminal neurinomas, 2 patients with epidermoid cysts, and 1 patient with an acoustic neurinoma, and partial removal was performed in 1 patient with a meningioma, 1 with a craniopharyngioma, and 1 with a chordoma, for relief of symptoms. The main reason why we abandoned total or gross total removal in the cases who had subtotal removals was not due to an inadequate operative exposure but because of difficulty in dissecting the tumors from the surrounding neural or vascular structures, or because of the invasion of the tumors into the dura mater. As a result, there was no mortality and a very low percentage of morbidity. The facial nerve function returned in all patients who had had good preoperative facial function, and hearing was preserved postoperatively in 75% of the patients with good preoperative hearing. These results in our series are good compared with those of other series in which the various extended middle fossa or translabyrinthine approaches were used C10,13,15,18,20). On the basis of these results, we recommend the extended middle fossa approach without labyrinthectomy, but combined with suboccipital craniectomy as
Sakaki et al
the appropriate surgical procedure for large extra-axial tumors located around the clivus, particularly in the patients with good preoperative hearing [ 181. We believe that this approach may be useful for basilar trunk aneurysms in the future.
References 1. Bochenek Z, Kukwa A. An extended approach through the middle cranial fossa to the internal auditory meatus and the cerebellopontine angle. Acta Otolaryngol 1975;80:410-4. Bucy PC. Exposure of the posterior rosurg 1966;24:820-32. Cherington M, Schneck 1966;16:86-92.
SA. Clivus
or cerebellar
fossa. J Neu-
meningiomas.
Neurology
DiTullio MV, Malkasian D, Rand RW. A critical comparison of neurosurgical and otolaryngological approaches to acoustic neuromas. J Neurosurg 1978;48:1-12. 5. Glasscock ME III, Hays JW. The translabyrinthine acoustic and other cerebellopontine angle tumors. 1973;82:415-27.
removal of Ann Otol
6. Glasscock ME III, Hays JW, Jackson CG, Steenerson RL. A onestage combined approach for the management of large cerebellopontine angle tumors. Laryngoscope 1978;88:1563-76. angle tumors with 7. Hakuba A. Total removal of cerebellopontine a combined transpetrosal-transtentorial approach. No Shinkei Geka 1978;6:347-54 (Jpn). 8. Hitselberger ebellopontine Otolaryngol
WE, House WF. A combined angle. A suboccipital-petrosal 1966;84:267-85.
approach to the cerapproach. Arch
bone removal 9. House WF. Evolution of transtemporal tumors. Arch Otolaryngol 1964;80:731-41.
af acoustic
WE. Surgery of the skull 10. House WF, De La Cruz A, Hitselberger base. Transcochlear approach to the petrous apex and clivus. Arch Otolaryngol 1978;86:770-9. 11. House WF, Hitselberger WE. The transcochlear skull base. Arch Otolaryngol 1976;102:334-42.
approach
to the
12. King ‘IT, Morrison AW. Translabyrinthine and transtentorial removal of acoustic nerve tumors. Results in 150 cases. J Neurosurg 1980;52:210-6. 13. Maddox goscope
HE III. The lateral approach 1977;87:1572-8.
14. Markham JW, Fager CA, Horrax the posterior fossa. Arch Neural
to acoustic
G, Poppen Psychiatry
tumors.
Laryn-
JL. Meningiomas 1955;74:163-70.
of
AW, King IT. Experiences with a translabyrin15. Morrison thine-transtentorial approach to the cerebellopontine angle. Technical note. J Neurosurg 1973;38:382-90. 16. Ogata M. An anatomical and technical No Shinkei Geka 1983;11:463-7 1. 17. Ojemann RG, Montgomery gical treatment of acoustic 895-9.
note for surgery
of clivus.
WW, Weiss AD. Evaluation and surneuroma. N Engl J Med 1972;287:
transtentorial approach 18. Rosomoff HL. The subtemporal cerebellopontine angle. Laryngoscope 197 1;81: 1448-54. 19. Sheptak PE, Jannetta PJ. The two-stage excision neurinomas. J Neurosurg 1979;51:37-41.
to the
of huge acoustic
in patients 20. Tator CH, Nedzelski JM. Facial nerve preservation with large acoustic neuromas treated by a combined middle fossa transtentorial translabyrinthine approach. J Neurosurg 1982;57: 1-7. 21. Yasargil MG, Fox JL. The microsurgical neurinomas. Surg Neurol 1974;2:393-8.
approach
to acoustic
An Extended Suboccipital Posterior
Middle Fossa Approach Craniectomy
245
Combined with a
to the Base of the Skull in the
Fossa
Saburo Sakaki, M.D., Sadanori Takeda, M.D., Hitoshi Fujita, M.D., and Shinsuke Ohta, M.D. Department
of Neurological
Surgery, Ehime University
School of Medicine, Ehime, Japan
Sakaki S, Takeda S, Fujita H, Ohta S. An extended middle fossa approach combined with a suboccipital craniectomy to the base of the skull in the posterior fossa. Surg Neural 1987;28:245-52. A new approach to the base of the skull in the posterior fossa is described. This approach involves removing the petrous bone without any injury to the labyrinth, and dividing the superior petrosal sinus and tentorium cerebelli. A combined suboccipital craniectomy is used for excision of the portion of tumors that extended inferiorly. Total or subtotal removal of tumors was performed in 11 patients and partial removal in 3 patients, without any operative mortality. The facial nerve was preserved in all patients and hearing was retained in 9 of 12 patients. This approach is useful for large tumors located around the clivus. KEY WORDS: Extended middle fossa approach; Suboccipital approach; Base of the skull; Posterior fossa tumor; Facial and cochlear functions
Among the various extra-axial tumors in the posterior fossa, those arising from the petrous apex or &us, or tumors extending anteriorly to the brainstem have presented difficult surgical problems. The conventional suboccipital approach has failed to achieve adequate access for removal of these tumors because of the interposition of the cerebellum and brainstem [4,7,10,19,21]. Up to now, several extended or combined lateral approaches have been used for better exposure of this region [1,2,5-13,15-18,201. The rationale behind these surgical procedures is the concept that all the anatomic structures in this region can be adequately identified in the surgical field by the shortest route, although every approach has been modified differently by different sur-
Adu’re~s reprint requests to: Saburo Sakaki, M.D., Department of Neurological Surgery, Ehime University Medical School, Onsen-Gun, Shigenobu-Cho, Ehime 791-02, Japan. Received
February
5, 1987; accepted
April
0 1987 by Elsevier Science Publishing Co., Inc.
16, 1987.
geons according to their familiarity with the anatomy of the temporal bone. We have developed an extended middle fossa approach combined with a suboccipital craniectomy for the removal of large extra-axial tumors located at the base of the skull in the area of the posterior fossa. This article describes the surgical technique and its results in 14 patients treated by this method.
Clinical Material Fourteen patients were selected as candidates for an extended middle fossa approach combined with a suboccipital craniectomy on the basis of the location, size, extension, and suspected pathology of the tumors. The 14 patients were chosen from 60 patients who were admitted to the Ehime University Hospital from April 1978 to November 1986, all of whom had extra-axial tumors in the posterior fossa (Table 1). Upon admission, all patients were evaluated by means of neurologic and neuroradiologic examinations including computed tomography (CT).
Operative Technique The patient is placed in the supine or park bench position with the head turned 90” toward the side contralateral to the tumors, and fixed by three-point fixation so that the squamous portion of the temporal bone lies horizontally. As a rule, a catheter is inserted into the lateral ventricle through a frontal burr hole, to decompress the ventricle during retraction of the temporal lobe and to cope with postoperative brain swelling. The skin incision is made from a point overlying the zygomatic arch and encircles the external ear, with the posterior limb ending approximately at a point a few centimeters medial and below the tip of the mastoid process as shown in Figure 1. The scalp flap is turned down, and the mastoid process and upper margin of the external auditory canal are exposed. A free temporal bone flap is 0090-3019/87/$3.50
246
Sakaki et al
Surg Neural 1987;28:245-52
1. Operative Approaches in 60 Patients with Extra-axial Tumors in the Posterior Fossa
Table
Unilateral suboccipital craniectomy (a)
Extended middle fossa approach combined with suboccipital craniectomy (n)
Acoustic neurinoma” Trigeminal neurinoma Meningioma Epidermoid cyst Chordoma Craniopharyngioma
35 8 4 -
1 2 7 2 1 1
Total
47
14
“One patient with acoustic neurinoma
was operated
on by both approaches
at an interval.
made near the floor of the middle cranial fossa, followed by a unilateral suboccipital craniectomy across the transverse-sigmoid sinus junction. The dura mater is separated from the anterior surface of the pyramid to the level of the sulcus of the superior petrosal sinus from above, and the hiatus of the facial canal from the front. The mastoid bone is drilled away with steel burrs from the mastoid cells posteriorly to the level of the compact plate of the sigmoid sinus, and the lateral part of the petrous bone is removed medially near the level of the arcuate eminence, with the inner ear, particularly the semicircular canals, being completely intact in order to preserve the postoperative potential for inner ear functions. Practically, it is wise to limit the removal of the lateral part of the petrous pyramid to within 1 cm from its base. Next, the bone overlying the sigmoid sinus is completely removed with diamond burrs, while the superior petrosal sinus is gently separated from its sulcus, from the orifice of the superior petrosal sinus to the sigmoid sinus toward the petrous apex. The dura mater over the temporal lobe is opened vertically over the anterior portion taking care to avoid the veins coming from the temporal lobe, and the dural incision is made inferiorly across the floor of the middle fossa to the superior petrosal sinus. The dura mater over the posterior fossa is opened vertically down to the jugular bulb in front of the sigmoid sinus, after which the superior petrosal sinus is divided between hemostatic clips. The tentorium cerebelli is incised to the incisura parallel to the superior petrosal sinus with upward retraction of the temporal lobe, and the tentorial flap is laid back to expose a surgical field. Finally, additional dural openings at right angles to the previous incisions are made, and the suboccipital dura is incised in a radiating fashion when required. All these separated dura mater are supported by suture threads (Figure 2). A selfretaining retractor is used to retract the temporal lobe upwards and a second retractor holds the cerebellar
hemisphere posteriorly, while cerebrospinal fluid (CSF) is drained through the ventricular catheter. When these procedures have been adequately carried out, the tumor will be visualized in the center, and the superior, anterior, and lateral aspects of the cerebellopontine angle will come into view. Occasionally, it is possible to better visualize the anterior aspect of the brainstem by further removal of the petrous bone along the sulcus of the superior petrosal sinus in the direction of the petrous apex. We then proceed to remove the tumor by gutting the central core with a CUSA or CO* laser. After enucleation of the tumor, the capsule is dissected from the surrounding structures while we identify all the anatomic structures; in the case of a petrosal meningioma, for example, we can identify the area from the fourth and fifth cranial nerves superiorly, from the cerebellar hemisphere and brainstem posteromedially, from the seventh and eighth cranial nerves ventrolaterally, and from the ninth and tenth cranial nerves inferiorly (Figure 3). When the tumors extend inferiorly below the jugular bulb (dissection of tumors from the vagus group is considered to be difficult from above), the suboccipital approach is preferable to the middle fossa approach for removal of the inferior portion of the tumors (Figure 4). After complete hemostasis, the dura mater is sutured, leaving the tentorium cerebelli open, and pieces of fat or muscle are placed on the surface of the drilled portion
Figure 1. Scalp incision and extent of bone remwalfor the extended middle foua approach combined with suboccipital craniectomy.
Combined
Approach to Base of the Skull
Surg Neurol 1987;28:245-52
sup. petrosal
247
sinus
Figure 2. The opening of the dura mater is shown. The superior petrosal sinus and tentorium cerebeh’i are divided in front of the sigmoid sinus.
post. fossa
of the mastoid and petrous bone to prevent postoperative liquorrhea. The removed temporal bone is replaced, and cranioplasty is performed with a resin plate when the bone defect is large enough in the region of the craniectomy.
Results As shown in Table 2, 14 patients with large extra-axial tumors in the posterior fossa were operated on by means of the extended middle fossa approach combined with suboccipital craniectomy using the operating microscope. All tumors were located at the base of the skull in the posterior fossa and extended anteriorly to the brainstem or cephalad to the middle fossa. Pre- and postoperative CT scans of representative patients are shown in Figure 5. There were 3 males and 11 females, with ages ranging from 12 to 68 years (mean age 4 1 years). All meningiomas were 3 cm or larger in the greatest diameter, including two clivus meningiomas, two tentorial meningiomas arising from the tentorial notch and extending almost to the posterior fossa and partly to the middle fossa, two huge petrosal meningiomas arising from the posterior surface of the petrous bone medial to the porus acusticus internus which extended partly to the middle fossa, and a parasellar meningioma extending almost to the posterior fossa. Two trigeminal neurinomas were large cystic tumors of the root type developing anteriorly to the brainstem. There was one acoustic neurinoma, which had been previously operated on through a suboccipital craniectomy with
dura
incomplete removal, and which had recurred in the region anterior to the brainstem. Of two epidermoid cysts, a huge one extended from the right cerebellopontine angle medially, anterior to the brainstem, and into the contralateral left cerebellopontine angle, and the other one was located in the left cerebellopontine angle and extended from the middle fossa to the foramen magnum. There was one craniopharyngioma which had a large extension to the posterior fossa. As shown in Table 3, total or subtotal removal was performed in 11 of 14 patients (79%). In the patients with meningioma, gross total removal was carried out in 3 patients, and subtotal removal in 3 patients; subtotal removals were due to an invasion of the tumor to the tentorium (case l), the difficulty in dissecting the tumor from the brainstem (case 2), and the fact that a small piece of the tumor was left on the exit zone of the facial nerve (case 3). In the patient with the parasellar tumor, the part of the tumor that enveloped the internal carotid artery was left in place. In the patients with trigeminal neurinomas, one was totally removed and the other subtotally because an invasive part of the tumor was left on the entry zone of the trigeminal nerve (case 8). One epidermoid cyst had developed so extensively among the cranial nerves and blood vessels that total removal of the tumor was abandoned (case 11). In the two patients with craniopharyngioma (1) and chordoma (l), partial removal of the tumors was planned prior to surgery for the relief of symptoms. The operative results are classified into four groups: excellent, when patients return to their previous social activity with or without
248
Surg Neural 1987;28:245-52
Sakaki et al
,
IVth nerve , sup. petrosal
sinus
br‘ain stem
tentor ium post. fossa dura \
psigmoid
sinus
Figure 3. The temporal lobe is retracted superiorly and the cerebeLar hemisphere posteriorly, by self-retaining retractors. The superior, anterior, and lateral aspects of the cerebellopontineangle are displayed through the extended middle fossa approach; the tumor is visualized in the center, with the fourth craniaI nerve running on the surface of the tumor.
Figure 4. The inferior aspect of the tumor is visualized through the suboccipital approach.
temporal
lobe I
sigmoid
sinus
ten tor ium,
\ \
urn
IXth, xcipital
dura
Combined
Approach
to Base of the Skull
Surg Neurol 1987;28:245-52
249
2. Extended Middle Fossa Approach: Summary of Patients
Table
Pathology Case no.
Age/sex
and location of tumor
Initial symptoms
1
47lF
Tentorial meningioma
Gait disturbance
2
35iF
Clivus meningioma
Gait and speech disturbances
3
12/F
Gait disturbance; left hearing loss
4 5
&IF 54iF
6
43/M
Petrous apex meningioma; middle fossa extension Tentorial meningioma Parasellar meningioma; posterior fossa extension Clivus meningioma
7 8
47/F 54/F
Petrous apex meningioma Trigeminal neurinoma
Right facial numbness Headache; vomiting
9
53/M
Trigeminal neurinoma
Left facial numbness
10 11
39/F 34/M
Acoustic neurinoma Epidermoid cyst
12 13
4 l/F 2 l/F
Epidermoid cyst Craniopharyngioma
Gait disturbance Right trigeminal neuralgia Left trigeminal neuralgia Headache; visual loss
14
21/F
Chordoma
Dysphagia; diplopia
Headache; diplopia Left visual loss; gait disturbance Left-sided weakness; left hemifacial spasm
Neurological findings on admission”
Left V hypesthesia; nystagmus; ataxic gait Papilledema; nystagmus; dysphagia; right hemiparesis; ataxic gait Nystagmus; diminished hearing; ataxic gait
Size of tumor on CT scans (cm)
3.6 x 2.8 x 3.0 4.2 x 3.6 x 5.0
4.8 x 4.3 x 6.0
Left abducens paresis Left papilla atrophy; left III palsy; right hemiparesis Left hemifacial spasm; diminished hearing; ataxic gait Right V hypesthesia Papilledema; left V, IX, X, XII involvements Left V, IX, X involvements Left VII palsy; ataxic gait Right V hypesthesia
2.4 x 2.1 x 3.0
Left V hypesthesia Impairment of visual acuity Left V, VI, XII; right
I.2 x 1.0 x 3.0 2.9 x 2.4 x 1.5
6.0 x 3.6 x 5.0
4.2 x 3.9 x 5.0
3.8 x 2.8 x 3.0 4.3 x 4.3 x 6.0 2.6 x 1.9 x 4.0 2.2 x 2.2 x 2.0 3.3 x 4.0 x 3.0
3.6 x 6.0 x 3.0
VII, VIII, IX, x, XI involvements “Roman numerals indicate cranial nerves
neurological deficits; good, when patients are able to take care of themselves; poor, when patients are unable to take care of themselves; and dead. In the present series, 9 patients (64%) were rated as excellent, 4 (29%) good, and 1 poor at follow-up examination ranging from 4 months to 7 years (average of 2 years and 4 months) after the surgery. In only one patient (case 6) the neurological state became worse with left sixth nerve palsy after the operation; however, this was improving at follow-up examination 9 months after the operation. Two patients with meningiomas (cases 1 and 3) and one patient with a neurinoma (case 8) were operated on with this combined approach in two stages at intervals of 2 months, 1 year, and 7 months, respectively, and finally, these tumors were subtotally removed. The facial nerve function returned in all patients who had had normal function prior to the operation; this was assessed as complete recovery in all of them at follow-up examinations. Hearing was preserved postoperatively in 9 of minor
12 patients tion.
Three
erative free
(7 5%) who had had good patients
period,
but
on anticonvulsant
had since
seizures then
therapy
preoperative
func-
in the
early
postop-
have
been
seiture-
they during
the follow-up
pe-
riod. In these patients, postoperative CT scans showed a low-density area in the temporal lobe, which suggested brain contusion due to retraction during the operations. There were two patients with postoperative CSF leakage presenting as rhinorrhea, in whom the leaks through the mastoid air cells were operatively closed with bone wax and muscle.
Discussion It is an extremely difficult surgical problem to approach the large tumors arising from the clivus or petrous bone medial to the porus acusticus, or the tumors located in the region anterior to the brainstem, because of the position of the lesions anterior to the brainstem and the lesions in direct contact with the major blood vessels and cranial nerves. Attempts have been made for better approaches to the tumors in this region. Hitselberger and House [S] described a combined suboccipital-petrosal approach to large tumors in the cerebellopontine angle: in this report the authors extended their previously developed translabyrinthine approach posteriorly beyond the sigmoid sinus into the suboccipital
250
Surg Neural 1987;28:245-52
Figure 5. Pre- and postoperative CT scans of the representative patients. IL& Case 3; petrous apex meningioma with middle fossa extension, second pre- (a) and postoperative (b). (wr) Case 6; chvus meningioma, pre(c) and postoperative (d). (w) Case 7; petrous apex meningioma, pre(e) and postoperative (0.
region and achieved a wider exposure of the cerebellopontine angle than had been possible using the translabyrinthine or unilateral suboccipital approach alone, by mobilizing the sigmoid sinus anteriorly, posteriorly, or both, or even dividing it [9]. This approach has the distinct advantage for tumors extending below the jugular bulb. Later on, these authors reported { 10,l l] a transcochlear approach for the removal of tumors arising from the petrous bone medial to the porus acusticus or the clivus. The transcochlear approach is accomplished by a forward extension of the translabyrinthine opening of the petrous bone into the cerebellopontine angle, so that the advantage of direct access not only to the tumors
Sakaki et al
in this region but also to the blood supply of the tumors is gained, although removal of the petrous temporal bone and rerouting the facial nerve require an excellent neurotological technique. Morrison and King [ 12,157 described a translabyrinthine-transtentorial approach, in which the exposure of the cerebellopontine angle was greatly extended upwards through the middle fossa after drilling out the petrous temporal bone and dividing the superior petrosal sinus and tentorium cerebelli. They used their approach for various lesions in the cerebellopontine angle other than acoustic neurinomas, with successful operative results. However, they reported also that their approach could not provide an adequate exposure to tumors extending inferiorly toward the foramen magnum [15]. Bochenek and Kukwa [l] also developed an extended approach through the middle fossa, which was nearly the same as that of Morrison and King, but with incomplete labyrinthectomy. They drilled out the lateral part of the petrous bone up to the level of
Combined
Approach to Base of the Skull
251
Surg Neural 1987;28:245-52
Table
3. Subtotal or Total Removal Approach: Summary of Patients Operative
Case IlO.
Operation
result
and follow-up period
1
Subtotal
removal
Excellent,
2
Subtotal
removal
3
Subtotal
removal
Excellent, 2 yr and 6 mo Excellent,
4
Gross
5
Partial
removal
6
Gross
total removal
Acoustic
Facial nerve function
nerve function
(tumor side)
(tumor side)
Preoperative
Postoperative
Preoperative
Postoperative
Normal
Normal
Normal
Normal
Normal
Normal
Normal
Normal
Normal
Normal
Diminished
Normal
Normal
Normal
3v
total removal
2 yr Excellent, 1 yr and 4 mo Poor, 11 mo Good,
Complication”
Left V slight hypesthesia; Seizures
seizure
Deafness
-
Normal
Normal
-
Normal
Normal
Normal
Left III palsy
Normal
Paresis
Diminished
Deafness
Left abducens
Normal
Normal
Normal
Normal
Normal
Normal
Normal
Deafness
Liquorrhea (operative repair) Left V hypesthesia
Normal
Normal
Normal
Normal
Left V anesthesia
Palsy
Palsy
Deafness
Deafness
-
Normal
Normal
Normal
Normal
-
Normal
Normal
Normal
Normal
Normal
Normal
Normal
Normal
Palsy
Palsy
Deafness
Deafness
hearing
hearing
palsy
9 mo 7
Gross
8
Subtotal
total removal removal
9
Total removal
10
Total removal
11
Subtotal
12
Total removal
13
Partial
removal
14
Partial
removal
removal
Excellent, 4 mo Excellent, 7 yr Good, 1 yr and 5 mo Good, 1 yr Excellent, 4 yr and 7 mo Excellent, 1 yr and 10 mo Excellent, 4 yr Good, but died 2 yr after
Liquorrhea repair)
(operative -
Seizures
“Roman numerals indicate cranial nerves
the compact plate of the sigmoid sinus posteriorly and to the lumen of the lateral semicircular canal medially, and incised the tentorium cerebelli without dividing the superior petrosal sinus. They stated that a wider visualization of the cerebellopontine angle could be obtained by their approach rather than by the route through the labyrinth. Hakuba [7] proposed a transpetrosal-transtentorial approach, which was also a modification of Morrisons’s and King’s approach but with incomplete labyrinthectomy and combined suboccipital craniectomy. Thus, the extended middle fossa approach combined with labyrinthectomy can provide an appropriate exposure for tumors located in the region from the cerebellopontine angle to the anterior aspect of the brainstem, especially for those extending to the middle fossa. However, it does not provide good access to the tumors with an inferior extension toward the foramen magnum, and a complete or incomplete labyrinthectomy sacrifices the cochlear and vestibular functions to achieve a wide exposure of the cerebellopontine angle by the shortest route. Our approach described here has been developed on
the basis of the following concepts: it gives a better exposure in the surgical field of the cerebellopontine angle and of the region anterior to the brainstem; it can be extended toward the middle fossa and below the jugular bulb up to the foramen magnum at any given moment; it provides visualization of all anatomic structures in this region from different angles and provides a nearer route to the blood supply of the tumors; it permits the possible restoration or retention of auditory function in patients with good hearing preoperatively; and it has the advantages of both the middle fossa transtentorial approaches and the suboccipital ones. For these purposes, the lateral part of the petrous bone can be partially removed within 1 cm of its base, enough to uncover the sigmoid sinus and superior petrosal sinus, but the labyrinth will not be injured at all [lb]. Upon dividing the superior petrosal sinus and tentorium cerebelli, an excellent exposure of th, cerebellopontine angle can be obtained. To achieve a wider exposure in the region anterior to the brainstem, further removal of the petrous bone can be carried out along the petrous ridge in the direction of its apex; care must be taken
252
Surg Neurol 1987;28:245-52
not to injure the facial nerve or the cochlea. A combined suboccipital craniectomy was used for the excision of the portion of the tumors that extended inferiorly. This approach was used only in exceptional situations when the patients had large tumors extending toward the anterior aspect of the brainstem, and especially, when they had good hearing preoperatively. In the present series, a good surgical field was gained for removal of the tumors through the middle fossa in only 8 patients. In the rest of the patients, however, the lower portion of the tumors was not visualized well enough from above because the tumors extended below the jugular bulb, so the suboccipital dura was incised and the tumors were successfully excised through the suboccipital approach. It is often necessary to take both approaches in sequence intraoperatively. The surgical results for meningiomas in the posterior fossa depend mainly on the site of dural attachment and the direction of the extension of the tumor [14]. In a series of 28 patients operated on for petrosal meningioma, according to Olivecrona, there were 12 fatalities (43%) in whom nearly all of the tumors arose from the posterior surface of the petrous bone medial to the porus and Schneck [3], in reviewacusticus {l 11. Cherington ing the patients with clivus meningioma enumerated in the literature and including their own cases, reported that among 29 patients, there were 16 who died within 2 weeks of surgery, 4 within 7 months, and 1 who succumbed 12 months after biopsy, and that the l-year survival rate after diagnosis was 25% or less. In the present series, we performed total or subtotal removals in 6 patients with large meningiomas, 2 patients with trigeminal neurinomas, 2 patients with epidermoid cysts, and 1 patient with an acoustic neurinoma, and partial removal was performed in 1 patient with a meningioma, 1 with a craniopharyngioma, and 1 with a chordoma, for relief of symptoms. The main reason why we abandoned total or gross total removal in the cases who had subtotal removals was not due to an inadequate operative exposure but because of difficulty in dissecting the tumors from the surrounding neural or vascular structures, or because of the invasion of the tumors into the dura mater. As a result, there was no mortality and a very low percentage of morbidity. The facial nerve function returned in all patients who had had good preoperative facial function, and hearing was preserved postoperatively in 75% of the patients with good preoperative hearing. These results in our series are good compared with those of other series in which the various extended middle fossa or translabyrinthine approaches were used C10,13,15,18,20). On the basis of these results, we recommend the extended middle fossa approach without labyrinthectomy, but combined with suboccipital craniectomy as
Sakaki et al
the appropriate surgical procedure for large extra-axial tumors located around the clivus, particularly in the patients with good preoperative hearing [ 181. We believe that this approach may be useful for basilar trunk aneurysms in the future.
References 1. Bochenek Z, Kukwa A. An extended approach through the middle cranial fossa to the internal auditory meatus and the cerebellopontine angle. Acta Otolaryngol 1975;80:410-4. Bucy PC. Exposure of the posterior rosurg 1966;24:820-32. Cherington M, Schneck 1966;16:86-92.
SA. Clivus
or cerebellar
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removal of Ann Otol
6. Glasscock ME III, Hays JW, Jackson CG, Steenerson RL. A onestage combined approach for the management of large cerebellopontine angle tumors. Laryngoscope 1978;88:1563-76. angle tumors with 7. Hakuba A. Total removal of cerebellopontine a combined transpetrosal-transtentorial approach. No Shinkei Geka 1978;6:347-54 (Jpn). 8. Hitselberger ebellopontine Otolaryngol
WE, House WF. A combined angle. A suboccipital-petrosal 1966;84:267-85.
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af acoustic
WE. Surgery of the skull 10. House WF, De La Cruz A, Hitselberger base. Transcochlear approach to the petrous apex and clivus. Arch Otolaryngol 1978;86:770-9. 11. House WF, Hitselberger WE. The transcochlear skull base. Arch Otolaryngol 1976;102:334-42.
approach
to the
12. King ‘IT, Morrison AW. Translabyrinthine and transtentorial removal of acoustic nerve tumors. Results in 150 cases. J Neurosurg 1980;52:210-6. 13. Maddox goscope
HE III. The lateral approach 1977;87:1572-8.
14. Markham JW, Fager CA, Horrax the posterior fossa. Arch Neural
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G, Poppen Psychiatry
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JL. Meningiomas 1955;74:163-70.
of
AW, King IT. Experiences with a translabyrin15. Morrison thine-transtentorial approach to the cerebellopontine angle. Technical note. J Neurosurg 1973;38:382-90. 16. Ogata M. An anatomical and technical No Shinkei Geka 1983;11:463-7 1. 17. Ojemann RG, Montgomery gical treatment of acoustic 895-9.
note for surgery
of clivus.
WW, Weiss AD. Evaluation and surneuroma. N Engl J Med 1972;287:
transtentorial approach 18. Rosomoff HL. The subtemporal cerebellopontine angle. Laryngoscope 197 1;81: 1448-54. 19. Sheptak PE, Jannetta PJ. The two-stage excision neurinomas. J Neurosurg 1979;51:37-41.
to the
of huge acoustic
in patients 20. Tator CH, Nedzelski JM. Facial nerve preservation with large acoustic neuromas treated by a combined middle fossa transtentorial translabyrinthine approach. J Neurosurg 1982;57: 1-7. 21. Yasargil MG, Fox JL. The microsurgical neurinomas. Surg Neurol 1974;2:393-8.
approach
to acoustic