Kawase Triangle Research Articles

Anatomical Comparison of Endoscopic and Microscopic Exposure of the Petroclinal Core Area Through the Extended Middle Skull Base Approach.

To compare the range of endoscopic and microscopic exposure of the petroclival core area through the middle skull base and to observe the corresponding anatomical structures. Ten intact adult cadaveric head specimens fixed with formaldehyde were craniotomized through an expanded middle skull base epidural approach on 20 sides. The distance from the greater superficial petrosal nerve to the petrous ridge was measured. When different degrees (1-3 degrees) of the Kawase triangle bone were removed, the exposed anatomical structure was observed, and the exposed core area of the rock slope was measured under an endoscope and microscope. The average distance from the greater superficial petrosal nerve to the petrous ridge was 14.26mm. During 1 to 2 degrees of bone removal, the petrous segment of the internal carotid artery (ICA) was not exposed, whereas during 3 degrees of bone removal, the petrous segment of the ICA was exposed. At 1 degree of bone removal, 400.62 ± 15.73mm2 of the area was exposed by endoscopy and 170.87 ± 8.93mm2 by microscopy, and the abducens nerve was not exposed. However, there was a significant difference between the two areas (P < 0.001). During 2 degrees of bone removal, 689.30 ± 32.06mm2 of the abducens nerve was exposed by endoscopy, but 366.84 ± 30.30mm2 of the abducens nerve could not be exposed by microscopy; moreover, there was a significant difference in the area of exposure between the two (P < 0.001). At 3 degrees of bone removal, the endoscopic exposure area was 875.92 ± 31.87mm2, the microscopic exposure area was 699.26 ± 48.00mm2, and the abducens nerves were exposed. There were significant differences between the two areas (P < 0.001). However, the difference between the 2-degree endoscopic exposure area and the 3-degree microscopic exposure area was studied by using paired t tests, and there was no difference (P > 0.05). When the same degree of the Kawase triangle bone was removed, the extent of endoscopic exposure of the petroclival core area was significantly greater than the extent of microscopic exposure. At 2 degrees of bone removal, an endoscopic application can maximally expose the petroclival core area, thus reducing the probability of exposure damage to the ICA and abductor nerve.

Purely endoscopic subtemporal keyhole anterior transpetrosal approach to access the petrous apex region: surgical techniques and early results.

The anterior transpetrosal approach using a microscope to provide wider access to the petrous apex region has been described for radical resection of lesions of the middle and posterior skull base. The microscopic anterior transpetrosal approach (mATPA) requires a wide craniotomy and meticulous epidural procedures to minimize temporal lobe retraction. Recently, the clinical application of transcranial endoscopic keyhole approaches for minimally invasive surgery has been steadily expanding. In this study, the details of the purely endoscopic subtemporal keyhole ATPA (eATPA) for petrous apex lesions are described and its initial results are reported. Between May 2022 and May 2023, the authors performed eATPA in 10 patients with petrous apex lesions, of which 6 were meningiomas, 3 were trigeminal schwannomas, and 1 was epidermoid cyst. The surgical procedure of the purely eATPA is as follows. After a small temporal craniotomy, the endoscopic procedure is started. The anterior rim of the petrous bone and Meckel's cave are exposed via an intradural subtemporal approach. The lesion is removed with additional drilling of Kawase's triangle, cutting the superior petrosal sinus, opening Meckel's cave, and cutting the tentorium. The authors also compared the outcomes of mATPA versus eATPA for consecutive cases of petrous apex lesions. Gross-total resection was achieved in 8 of the 10 patients. The average operative time was 4 hours 13 minutes. There were 3 cases of transient abducens nerve palsy and 1 case of trochlear nerve palsy in the postoperative period. No new-onset motor deficits or CSF leakage was noted in any of these patients. Only 1 patient exhibited postoperative asymptomatic temporal lobe edema. The Karnofsky Performance Scale (KPS) scores remained unchanged or improved for all patients postoperatively. Compared with mATPA, eATPA achieved a similar extent of resection and comparable postoperative KPS scores with a significantly shorter mean operative time, much smaller temporal craniotomy, and thus less mean blood loss during surgery with lower rates of new-onset temporal lobe edema in the postoperative period. An eATPA allows a direct route to access Meckel's cave and posterior cranial fossa lesions similar to conventional mATPA, with shortening the operative time and reducing the risk of postoperative temporal lobe edema. This eATPA is considered one of the new surgical techniques that can be expected to develop in the future.

Microsurgical Resection of a Petroclival Epidermoid Cyst Using an Anterior Petrosectomy Approach: 2-Dimensional Operative Video.

Epidermoid cysts are rare, benign lesions that result from inclusion of ectodermal elements during neural tube closure.1 Cysts are composed of desquamated epithelial cells and restrict diffusion on magnetic resonance imaging (MRI).2,3 Symptoms are attributable to anatomic location.4,5 In this video, we illustrate the surgical treatment of an epidermoid cyst located in the right cerebellopontine angle, petrous apex, and Meckel's cave. The patient, a 33-yr-old female with right-sided V1 trigeminal hypoesthesia, underwent surveillance imaging for 2 yr. However, she developed progressive V1 and V2 trigeminal hypoesthesia and imaging revealed enlargement of the lesion. Therefore, surgical resection was pursued. The patient consented to the procedure. The patient underwent a right middle fossa craniotomy and anterior petrosectomy. After identifying the greater superficial petrosal nerve and cutting the middle meningeal artery as it exited foramen spinosum, Kawase's triangle was drilled, and the dura over Meckel's cave and the subtemporal dura were opened. The lesion was resected, taking care to preserve the trigeminal nerve and the basilar artery. A retrosigmoid craniotomy was then fashioned. The cyst and its capsule were dissected off the brainstem and cranial nerves utilizing natural corridors between the trigeminal and vestibulocochlear nerves as well as between the facial and lower cranial nerves. Gross total resection was confirmed on postoperative MRI, and she was discharged home on postoperative day 5. Three months after surgery, she underwent formal pinprick testing, which revealed 95% loss of sensation in V1, 20% loss in V2, and normal sensation in V3. Three-month postoperative MRI showed no residual tumor.

The modified method of locating related bony structures in intradural anterior transpetrosal approach

Objective To explore the improved method of precisely locating related bony structures in intradural anterior transpetrosal approach. Methods On the 10 dry skulls, the highest point of arcuate eminence (A), the petrous apex (P), the most lateral point of groove for the greater petrosal nerve (B), foramen spinosum (C), foramen ovale (D), trigeminal impression (E) and t foramen lacerum (F)were marked. Using point A as reference point and the line AP as the baseline, the distances of AB, AC, AD, AE and AF and the angles of ∠BAP, ∠CAP, ∠DAP, ∠EAP and ∠FAP were measured. Samples were analyzed by mean and standard deviation, and the data on both sides were compared by t test. Results 1．AB: (11.61±2.31) mm (left), 10.44±2.31 mm (right), t=1.084; AC: (23.14±3.07) mm (left), (21.08±2.67) mm (right), t=1.596; AD: (24.95±2.82) mm (left), (24.38±3.44) mm (right), t=0.408; AE: (18.98±3.11) mm (left), (19.21±3.09) mm (right), t=-0.164; AF: (29.68±2.62) mm (left), (29.25±2.77) mm (right), t=0.725. 2. ∠BAP: (49.15±12.10)° (left), (52.78±14.27)° (right), t=-0.624; ∠CAP: (43.98±6.95)° (left), (48.73±8.02)° (right), t=-1.418; ∠DAP: (38.68±4.81)° (left), (41.48±3.14)° (right), t=-1.543; ∠EAP: (21.93±5.29)° (left), (25.94±6.43)° (right), t=-1.523; ∠FAP: (15.96±2.78)° (left), (17.20±3.44)° (right), t=-0.882. There were no significant differences between the left and right sides (P>0.05). Conclusion Using point A and P as referent indexes, the bony structures which represent the corresponding nerves and blood vessels can be precisely located for grinding Kawase triangle via intradural anterior transpetrosal approach. Key words: Intradural anterior transpetrosal approach; Arcuate eminence; Petrous apex; Location

Intradural Combined Transpetrosal Approach for Primary Pontine Hemorrhage

The standard combined transpetrosal approach (CTPA) is fundamentally an epidural approach that has been quite successfully practiced for many decades. However, it has some disadvantages, such as cosmetic problems, difficulties with custom-tailored petrosectomy, and cerebrospinal fluid leakage, as it is a complicated epidural procedure. We describe here a case of primary pontine hemorrhage via intradural CTPA (iCTPA), which is a modified technique of CTPA and includes intradural anterior petrosectomy and partial posterior petrosectomy without mastoidectomy and skeletonization of the sigmoid sinus. A 63-year-old woman with primary pontine hemorrhage underwent surgery via iCTPA to improve postoperative functional outcomes. After the temporal craniotomy without mastoidectomy and skeletonization of the sigmoid sinus, Kawase's triangle and Trautmann's triangle were identified from the intradural space. Resection of Kawase's triangle and partial resection of Trautmann's triangle were performed to approach the frontotemporal surface of the pons. The hematoma was irrigated and totally removed after corticotomy on the pons. The postoperative symptoms of the patient improved within 2 weeks without surgical complication. The intradural approach allows for custom-tailored petrosectomy and is more straightforward than the epidural route, although it can injure the vein of Labbé. Moreover, it can also reduce cosmetic problems and cerebrospinal fluid leakage. iCTPA could provide enough working space for the frontolateral surface of pontine and petroclival lesions without the need for mastoidectomy and skeletonization of the sigmoid sinus.

Anterior petrosal approach: The safety of Kawase triangle as an anatomical landmark for anterior petrosectomy in petroclival meningiomas

ObjectAnterior petrosectomy through the middle fossa is a well-described option for addressing cranial base lesions of the petroclival region.To access posterior fossa through middle fossa, we quantitatively evaluate the safety of Kawase triangle as an anatomical landmark. MethodWe reviewed pre- and postoperative Multi-Slice CT scan (1mm thickness) of patients with petroclival meningioma between Jan 2009 and Sep 2013 in which anterior petrosectomy was performed to access the posterior fossa part of the tumor. The distances between drilling start and finish edge to the vital anatomical skull base structures such as internal auditory canal (IAC) and superior semicircular canal and petrous apex (petrous part of the carotid artery) were measured and analyzed. ResultsDrilling entrance length is directly related with tumor size. The distances between anatomical structures and drilling points decrease with increasing tumor size, but it always remains a safe margin between drilling points and IAC, internal carotid artery (ICA), and semicircular canals in axial and coronal views. ConclusionThe Kawase triangle is shown to be a safe anatomical landmark for anterior petrosectomy. The described landmarks avoid damage to the vital anatomical structures during access to the posterior fossa through middle fossa, despite temporal bone anatomical variations and different tumor sizes.

Anterior Transpetrosal Approach Combined with Partial Posterior Petrosectomy for Petroclival Meningiomas with Posterior Extension

An anterior transpetrosal approach (ATPA) is suitable for treating upper petroclival lesions. However, the limit of the ATPA is reached when the tumor extends posterolaterally over the internal auditory canal (IAC) along the petrous edge. In such cases, ligation of the posterior part of the superior petrosal sinus (SPS) is necessary. To overcome this limitation, we combined the ATPA with a partial posterior petrosectomy in 8 patients who had petroclival meningiomas extending posterolaterally over the IAC. We resected only the Trautmann triangle in addition to the Kawase triangle to secure the space to ligate the posterior portion of the SPS. Because the tympanic cavity and bony labyrinth of the ear were not exposed, we were able to preserve hearing function and lower the risk of cerebrospinal fluid leakage. Furthermore, this approach enables easy ligation of the SPS and the tentorium posterior to the tumor attachment. This combined technique also allows visualization of the petrosal vein, which is important for surgery of the posterior fossa. Total and near-total tumor removal was achieved in 6 patients (75%) with no permanent complications and no cerebrospinal fluid leakage. Postoperative hearing impairment was not found in any of the patients who underwent this surgery. The ATPA combined with partial posterior petrosectomy is an effective method for removal of complicated petroclival meningiomas that extend posterolaterally over the IAC along the petrous edge.

Usefulness of facial nerve monitoring for confirmation of greater superficial petrosal nerve in anterior transpetrosal approach.

The greater superficial petrosal nerve (GSPN) is especially important in anterior transpetrosal approach (ATPA) as the most reliable superficial landmark of Kawase's triangle. The GSPN can be considered as the superficial lateral border of anterior petrosectomy on the middle fossa to avoid internal carotid artery (ICA) injury. Although experienced operators can find the GSPN, its confirmation is not always easy to achieve. We introduce our recent GSPN confirmation methods using facial nerve monitoring. In 10 recent cases, antidromic GSPN stimulation and free-running facial muscle electromyography (EMG) monitoring were performed. Facial nerve evoked-EMG by antidromic GSPN stimulation confirmed the location of the GSPN course with precision in all cases. Free-running facial muscle EMG informed the mechanical stress of facial nerves through the GSPN. There was no postoperative facial palsy or dry eye in these cases. GSPN confirmation and preservation are not always easy to achieve. These monitoring methods are useful for the confirmation of the GSPN, which is a landmark for safe extradural anterior petrosectomy, and for the preservation of the GSPN itself.

The Safety of Kawase Triangle as an Anatomical Landmark for Anterior Petrosectomy in Petroclival Meningiomas

Objective: Anterior petrosectomy through the middle fossa is a well-described option for addressing cranial base lesions of the petroclival region. To access posterior fossa through middle fossa we evaluate quantitatively the safety of Kawase triangle as an anatomical landmark. Methods: We reviewed pre- and postoperative CT scans of patients with petroclival meningioma between January, 2009 and September, 2013 in which anterior petrosectomy were performed to access the posterior fossa part of the tumor. The distances between drilling start edge and drilling finish edge to the vital anatomical skull base structures such as internal carotid artery (IAC) and superior semicircular and petrous apex also drilling entrance length in coronal and axial views were measured and analyzed. Results: Drilling entrance length is directly related with tumor size. The distances between anatomical structures and drilling points decrease with increasing tumor size but always a safe margin remains between drilling points and internal auditory canal, internal carotid artery and semicircular canals in axial and coronal views. Conclusion: Kawase triangle is a safe anatomical landmark for anterior petrosectomy. Staying in such triangle avoid damages to the vital anatomical structures while accessing posterior fossa via middle fossa.

Volumetry and analysis of anatomical variants of the anterior portion of the petrous apex outlined by the kawase triangle using computed tomography.

Background Anterior petrosectomy has become an increasingly used approach for petroclival lesions. This study measures the volume and the anatomical variants of the anterior portion of the petrous apex outlined by the Kawase triangle using computed tomography (CT). Methods This was a transversal retrospective study. We assessed the anterior petrous apex portion outlined by the Kawase triangle in consecutive patients > 18 years of age from CT scans of temporal bone stored in an archive system. The volumetry was performed on a workstation. Results A total of 154 petrosal apex were analyzed in 77 patients (36 men). The average volume of the region outlined by the Kawase triangle was 1.89 ± 0.52 cm(3). The volume average in men was 2.01 ± 0.58 cm(3), and the average in women was 1.79 ± 0.41 cm(3). Intra- and interobserver agreement were both excellent, and there was little variance. Nineteen petrous apex demonstrated anatomical variations. In 18 cases it was pneumatized, and in one case a vascular or nerve-like structure was identified, a report we did not find in the literature. Conclusion The volumetry of the petrous apex anterior portion outlined by the Kawase triangle can be made by CT with excellent intra- and interobserver agreement and reproducibility. There are anatomical variants in this region that are relevant to surgery.

Quantitative Analysis of “Kawase's Triangle” versus “Modified Anterior Petrosectomy (MAP) Rhomboid” Approach for Extended Middle Cranial Fossa Lesions Extending into Posterior Cranial Fossa

Objective: Extended middle cranial fossa approach with transtentorial extension (Kawase's Triangle approach) is an established operative technique for anterior petrosectomy. We used cadaveric model and performed computerized quantitative analysis to compare 'Kawase's' and 'Modified Anteior Petrosectomy (MAP) ie Dolenc's + Kawase's' approach for lesions around petroclival region.

The Subtemporal Interdural Approach to Dumbbell-Shaped Trigeminal Schwannomas: Cadaveric Prosection

Successful resection of dumbbell-shaped trigeminal schwannomas via a subtemporal interdural approach requires an understanding of both the anatomy related to the bone dissection of the petrous apex (Kawase's triangle or quadrilateral) and meningeal anatomy. We studied the meningeal anatomy related to this approach and describe the dural incisions and stepwise mobilization. Meningeal anatomy around Meckel's cave and porus trigeminus was examined during the subtemporal interdural anterior transpetrosal approach in both sides of 15 cadaveric heads. Histological study of the Meckel's cave region was performed in two cadaveric heads. The Gasserian ganglion and trigeminal roots have two layers of dura propria on their dorsolateral surface: an inner layer from the posterior fossa dura propria that constitutes the dorsolateral wall of Meckel's cave and an outer layer from the dura propria of the middle fossa. The cleavage plane between these two layers continues distally as the cleavage plane between the epineural sheaths of the trigeminal divisions and the dura propria of the middle fossa. This cleavage plane serves as the anatomic landmark for the interdural exposure of the contents of Meckel's cave. The superior petrosal sinus is sectioned at the medial aspect of Kawase's triangle and reflected along with the porus trigeminus roof. Understanding the critical meningeal architecture in and around Meckel's cave allows experienced cranial neurosurgeons to develop a subtemporal interdural approach to dumbbell-shaped trigeminal schwannomas that effectively converts a multiple-compartment tumor into a single-compartment tumor. Dural incisions and stepwise mobilization complements our previous description of the bony dissection for this approach.

Custom-tailored transdural anterior transpetrosal approach to ventral pons and retroclival regions

The extradural anterior petrosectomy approach to the pons and midbasilar artery (mid-BA) has the main disadvantage that the extent of resection of the petrous apex cannot be as minimal as desired given that the surgical target field is not visible during bone removal. Unnecessary or excessive drilling poses the risk of injury to the internal carotid artery, vestibulocochlear organ, and seventh and eighth cranial nerves. The use of a custom-tailored transdural anterior transpetrosal approach can potentially avoid these pitfalls. A technique for a transdural anterior petrosectomy was developed in the operating theater and anatomy laboratory. Following a subtemporal craniotomy and basal opening of the dura mater, the vein of Labbé is first identified and protected. Cerebrospinal fluid ([CSF] 50-100 ml) is drained via a spinal catheter. The tent is incised behind the entrance of the trochlear nerve toward the superior petrosal sinus (SPS), which is coagulated and divided. The dura is stripped from the petrous pyramid. Drilling starts at the petrous ridge and proceeds laterally and ventrally. The trigeminal nerve is unroofed. The internal acoustic meatus is identified and drilling is continued laterally as needed. The bone of the Kawase triangle toward the clivus can be removed down to the inferior petrosal sinus if necessary. Anterior exposure can be extended to the carotid artery if required. It is only exceptionally necessary to follow the greater superior petrosal nerve toward the geniculate ganglion and to expose the length of the internal acoustic canal. The modified transdural anterior petrosectomy exposure has been used in nine patients-two with a mid-BA aneurysm, two with a dural arteriovenous fistula, one with a pontine glioma, three with a pontine cavernoma, and one with a pontine abscess. In one patient with a mid-BA aneurysm, subcutaneous CSF collection occurred during the postoperative period. No CSF fistula or approach-related cranial nerve deficit developed in any of these patients. There was no retraction injury or venous congestion of the temporal lobe nor any venous congestion due to the obliteration of the SPS or the petrosal vein. The custom-made transdural anterior petrosectomy appears to be a feasible alternative to the formal extradural approach.

Extended middle fossa approach: quantitative analysis of petroclival exposure and surgical freedom as a function of successive temporal bone removal by using frameless stereotaxy

Conventional wisdom regarding skull base surgery says that more extensive bone removal equals greater exposure. Few researchers have quantitatively examined this assertion, however. In this study the authors used a frameless stereotactic system to measure quantitatively the area of petroclival exposure and surgical freedom for manipulation of instruments with successive steps of temporal bone removal. With the aid of high-power magnification and a high-speed drill, 12 cadaveric specimens were dissected in four predetermined, successive bone removal steps: 1) removal of the Kawase triangle; 2) removal of the Glasscock triangle; 3) removal of the cochlea together with skeletonization of the anterior internal auditory canal; and 4) inferior displacement of the zygoma. Step 1 offered 62 +/- 43 mm2 of exposed petroclival area, with 84 +/- 69 mm2 of surgical freedom; Step 2, 61 +/- 22 and 76 +/- 58 mm2; Step 3, 128 +/- 47 and 109 +/- 87 mm2; and Step 4, 135 +/- 38 and 102 +/- 69 mm2, respectively. The middle fossa approach provided a means surgically to expose the petroclival area. When examined quantitatively by using a frameless stereotactic device, the authors determined that the removal of the cochlea and skeletonization of the anterior internal auditory canal (Step 3) provided the most significant increase in both exposure and surgical freedom. Removal of the zygoma improved neither exposure nor surgical freedom.

Selective indications for the management of extensive anterior epitympanic cholesteatoma via combined transmastoid/middle fossa approach.

Cholesteatoma that is present in the anterior epitympanic space may extend medially along the supralabyrinthine route to the geniculate ganglion, labyrinth, and cochlea and medially toward Kawase's triangle and the anterior petrous apex. Superiorly it may erode into the middle fossa. Contemporary microsurgical techniques allow for optimal management of these lesions with minimal morbidity, provided that the irregular and complex osteology of the petrous base is understood. The objective of the study was to review the relevant regional anatomy, pathobiology, and current algorithm used in treatment of this select patient population using a combined transmastoid/middle fossa (TM/MF) approach. A retrospective review was performed of all clinical and radiographic data from patients undergoing combined TM/MF management of extensive anterior epitympanic cholesteatoma between July 1984 and June 1998. Data from physical examinations, preoperative imaging studies, and operative findings and other relevant data were tabulated and analyzed for patients undergoing TM/MF management of cholesteatoma. Of 488 patients with cholesteatoma treated by the otological service between 1984 and 1998, 11 patients underwent TM/MF exposure and removal of anterior epitympanic cholesteatoma. Total cholesteatoma removal was accomplished in six patients. In three patients, because of facial nerve involvement, labyrinthine fistulae, or internal carotid artery involvement, open-cavity surgery was performed. In two patients, residual or recurrent cholesteatoma was exteriorized at "second-look" procedures. In this small cohort of patients the majority had extension to the arcuate eminence, geniculate ganglion, or Kawase's triangle or had "blue-lining" of the cochlea or labyrinth. To a lesser degree, the middle ear and mastoid contents were involved. Further facial nerve dysfunction or sensorineural hearing loss was not noted after surgery. Selective TM/MF removal of cholesteatoma provides an optimal route for removing complex cholesteatoma in patients with intact sensorineural function and medial cholesteatoma extension.