Retrosigmoid Keyhole Approach Research Articles

A novel theory for rapid localization of the transverse-sigmoid sinus junction and “keyhole” in the retrosigmoid keyhole approach: micro-anatomical study, technique nuances, and clinical application

To determine a rapid and accurate method for locating the keypoint and “keyhole” in the suboccipital retrosigmoid keyhole approach. (1) Twelve adult skull specimens were selected to locate the anatomical landmarks on the external surface of the skull.The line between the infraorbital margin and superior margin of the external acoustic meatus was named the baseline. A coordinate system was established using the baseline and its perpendicular line through the top point of diagastric groove.The perpendicular distance (x), and the horizontal distance (y) between the central point of the “keyhole” and the top point of the digastric groove in that coordinate system were measured. The method was applied to fresh cadaveric specimens and 53 clinical cases to evaluate its application value. (1) x and y were 14.20 ± 2.63 mm and 6.54 ± 1.83 mm, respectively (left) and 14.95 ± 2.53 mm and 6.65 ± 1.61 mm, respectively (right). There was no significant difference between the left and right sides of the skull (P > 0.05). (2) The operative area was satisfactorily exposed in the fresh cadaveric specimens, and no venous sinus injury was observed. (3) In clinical practice, drilling did not cause injury to venous sinuses, the mean diameter of the bone windows was 2.0–2.5 cm, the mean craniotomy time was 26.01 ± 3.46 min, and the transverse and sigmoid sinuses of 47 patients were well-exposed. We propose a “one point, two lines, and two distances” for “keyhole” localization theory, that is we use the baseline between the infraorbital margin and superior margin of the external acoustic meatus and the perpendicular line to the baseline through the top point of the digastric groove to establish a coordinate system. And the drilling point was 14.0 mm above and 6.5 mm behind the top point of the digastric groove in the coordinate system.

Applying the Full Endoscopic Keyhole Technique to CPA Lesions: A Single-Center Study.

In recent years, endoscopy has become an increasingly common tool used during neurosurgical procedures. However, its application in treating cerebellopontine angle (CPA) lesions has not progressed as rapidly. In this study, the authors present their initial experience with surgically treating CPA lesions using a fully endoscopic keyhole retrosigmoid approach. They conducted a retrospective analysis of clinical data from patients who underwent endoscopic keyhole CPA surgery at their center between May 2017 and April 2022. They provide a comprehensive explanation of this method and an overview of the strategies that have been developed to achieve better clinical outcomes. The study included 107 patients, consisting of 10 cases of vestibular schwannoma, 21 cases of epidermoid cyst, 32 cases of trigeminal neuralgia, and 44 cases of hemifacial spasm. The authors analyzed the clinicodemographic details of the patients. Among the 31 tumor cases, gross total resection was achieved in 25 patients (80.6%), while near-total resection was performed in 6 patients (19.4%). In patients with trigeminal neuralgia, facial pain resolved in 31 out of 32 patients (96.9%). Similarly, facial convulsions disappeared or were relieved in all 44 patients (100%) with hemifacial spasms after the operation. Postoperative complications included facial nerve paresis (n=9, 8.4%), with improvement observed in 6 cases during follow-up, transient facial hypoesthesia (n=3, 2.8%), cerebrospinal fluid rhinorrhea (n=3, 2.8%), transient abducens paresis (n=1, 0.9%), and postoperative hemorrhage (n=1, 0.9%). Endoscopy provides improved deep illumination and, combined with close-up observation, enhances the visualization of structures within the CPA region. The fully endoscopic keyhole technique is a safe and effective method for managing CPA lesions.

Keyhole retrosigmoid approach without watertight dural closure - Evaluation of a minimalistic approach.

The retrosigmoid craniotomy is a versatile surgical approach to the cerebellopontine angle though cerebrospinal fluid leak remains a concern, with a reported prevalence of 0-22 %. A host of closure materials and strategies have been proposed to achieve a watertight dural closure to varying degrees of success. We review our series of keyhole retrosigmoid craniotomies and describe our simple, standardized method of closure without watertight dural closure. A retrospective review of all retrosigmoid craniotomies performed by the senior author was completed. Closure was achieved by placing an oversized piece of gelatin in the subdural space. The dura is grossly approximated. An oversized sheet of collagen matrix is placed as an overlay followed by gelatin sponge in the craniectomy defect held in place with titanium mesh. The superficial layers are approximated. The skin is closed with a running sub-cuticular suture followed by skin glue. Patient demographics, cerebrospinal fluid leak risk factors, and surgical outcomes were determined. A total of 114 patients were included. There was one case (0.9 %) of CSF leak, which resolved with placement of a lumbar drain for 5 days. The patient had one defined risk factor (morbid obesity, BMI 41.0kg/m2). Obtaining a watertight dural layer closure has been the generally accepted strategy in preventing CSF leaks in a traditional retrosigmoid approach. In keyhole retrosigmoid approaches it may not be necessary by utilizing a simple gelfoam bolstered collagen matrix onlay technique potentially improving outcome measures including operative time.

Precise Localization in Craniotomy With a Retrosigmoid Keyhole Approach: Microsurgical Anatomy and Clinical Study.

ObjectiveWe aimed to explore a method of precise localization within craniotomy based on skull anatomical landmarks via the suboccipital retrosigmoid approach.MethodCraniometric measurements were taken from 15 adult dry skulls and eight cadaver head specimens. In the anatomical study, the keypoint corresponded to the transverse-sigmoid sinus junction's corresponding point on the external surface of the temporal mastoid process, eight cadaveric heads underwent a simulated craniotomy using the suboccipital retrosigmoid approach. The center of the burr hole is precisely oriented 12 mm vertically above the top point of the mastoid groove based on the line between the infraorbital margin and the upper edge of the external auditory canal. Clinical application was verified in clinical surgery by evaluating the accuracy, safety, rapidity, and minimal invasiveness of the procedure in 29 patients.ResultNo venous sinus injuries were observed. Within clinical application, 29 patients underwent craniotomy using the suboccipital retrosigmoid approach. The operative area was clearly exposed in all patients and the microsurgical anatomy of the intracranial region after the dura mater incision was satisfactory. No venous sinus ruptures were observed. The average craniectomy time was 27.02 ± 0.86 min. The diameter of the bone window was 1.7–2.9 cm.ConclusionWe conclude that the method can ensure safe, accurate, and rapid craniotomy with good vision while avoiding injury to the venous sinus.

Developing a Method to Precisely Locate the Keypoint During Craniotomy Using the Retrosigmoid Keyhole Approach: Surgical Anatomy and Technical Nuances.

Objective: To explore the precise location of the keypoint during craniotomy using the retrosigmoid keyhole approach.Methods: This study included 20 dry skulls and 10 wet cadaveric specimens. On the inner surface of dry skulls, the junction between the inferior margin of the transverse sinus (ITS) and the posterior margin of the sigmoid sinus (TSJ) was marked. The keypoint (D) was identified as the TSJ's corresponding point on the external surface of the temporal mastoid process (MP). The distance from the keypoint to the top point of the digastric groove, mastoidale, and asterion were noted (AD, BD, CD, respectively). A method to accurately locate the keypoint was developed based on these relationships. The developed method was used on the wet cadaveric specimens to evaluate its accuracy, safety, rapidity, and minimal invasion.Results: No significant difference was found between the AD, BD, and CD of the left and right sides. The drilling point was oriented on a straight line 12 mm above the top point of digastric groove, perpendicular to the Frankfort horizontal plane (FHP). In the cadaveric specimens, the operative area was clearly exposed. No venous sinus rupture occurred. The average craniotomy time was 28.74 ± 3.89 min.Conclusions: A potentially safe, accurate, and rapid craniotomy procedure was developed with the added advantage of preserving the visibility of the operating field and preventing venous sinus injury.

The Efficacy and Safety of

Objective: Microvascular decompression (MVD) surgery has been accepted as a minimally invasive surgical modality for the treatment of hemifacial spasm (HFS). However, the size of the bone window does not match the concept of minimally invasive. This study is aimed at evaluating the efficacy and safety of <2 cm micro-keyhole MVD.Methods: A total of 148 patients with HFS diagnosed in the First Affiliated Hospital of Chongqing Medical University from January 1, 2019, to July 1, 2020, who underwent MVD in the neurosurgery department of the hospital were collected. Surgery was performed by a retrosigmoid keyhole approach with the bone hole diameter <2 cm, which was named micro-keyhole MVD. The efficacy and safety of the micro-keyhole MVD were evaluated by statistical analysis of the efficacy of the micro-keyhole MVD and the incidence of postoperative complications.Results: The effect of micro-keyhole MVD was satisfying (cure or partial remission) in 97.2% (n = 144). The failure and recurrence rates were 2.7% (n = 4) and 0.6% (n = 1), respectively. Among them, immediate facial palsy, delayed facial palsy, hearing loss, and cerebrospinal fluid (CSF) leakage were found in 0.6% (n = 1), 8.1% (n = 12), 4.7% (n = 7), and 1.3% (n = 2). Only one patient developed cerebellar infarction, which was complicated by “moyamoya disease.” The micro-keyhole MVD in the treatment of HFS can achieve a high remission rate and reduce the incidence of surgical complications.Conclusion: Micro-keyhole MVD is a safe and effective minimally invasive treatment for HFS. This technique does not increase the incidence of cranial nerve injury. Meanwhile, it reduces the incidence of CSF leakage and hearing loss (HL).

Endoscopic retrosigmoid keyhole approach in cerebellopontine angle tumors. A surgical cohort

Introduction and objectivesTo determine the safety and efficacy of endoscopic keyhole surgery in patients with cerebellopontine angle tumours. Materials and methodsThis was a retrospective study of patients with cerebellopontine angled tumours treated by fully endoscopic retrosigmoid keyhole approach in a tertiary centre during a period of four years. Preoperative, transoperative and postoperative variables were analysed. ResultsA number of 40 patients were included. The age average was 49.4 years and male/female proportion was 0.4–1. We found 31 vestibular schwannomas (77.5%), five meningiomas (12.5%), two cholesteatomas (5.0%) and two metastases (5.0%). Vestibular schwannomas Hannover type IIIb, IVa and IVb predominated. The surgical resection was total or near-total 92.5% of patients. Hearing preservation rate was 62.5% and acceptable facial function nerve function rate was 80% after six months. Hospital stay was 7.5 days. The total or near total resection and functionally preservation rate was high. Complications were unusual. ConclusionsEndoscopic retrosigmoid keyhole approach represented a safe and efficient procedure in selected patients with cerebellopontine angle tumours.

How I do it: endoscopic microvascular decompression for glossopharyngeal neuralgia.

Microvascular decompression (MVD) for glossopharyngeal neuralgia (GPN) is associated with high complication and incomplete cure rates because of its poor ability to visualize neurovascular conflicts. Fully endoscopic MVD for GPN was carried out through a retrosigmoid keyhole approach. Neurovascular conflicts were clearly demonstrated with a loop of the posterior inferior cerebellar artery (PICA) under a 30° endoscopic view, and no significant cerebellar retraction was observed. The loop of the PICA was safely decompressed and the perforators were preserved while offering an excellent operative view. Endoscopic MVD is a reliable and minimally invasive method for GPN.

Typical trigeminal neuralgia in patients older than 65: Safety and efficacy of microvascular decompression by the retrosigmoid approach

AbstractOBJECT: Incidence of typical trigeminal neuralgia (TN) increases with age and neurologists and neurosurgeons frequently observe patients with this disorder at the age of 65 or more. Microvascular decompression (MVD) of the trigeminal root entry zone in posterior cranial fossa is the only etiological therapy for typical TN with the highest efficacy and durability of all treatments. This procedure is associated with possible risks (cerebellar hematoma, cranial nerve injury, stroke, and death) not seen with the alternative ablative procedures. Thus, the safety of MVD in the elderly remains non definitively demonstrated. This study was conducted to determine whether MVD is a safe and effective treatment in elderly patients with TN in comparison to younger patients.METHODS: In this retrospective study, 25 patients older than 65 (mean age 70.1 ± 3.7 years) and 32 aging &lt;65 (mean age 51.1 ± 6.2 years) underwent MVD by key-hole retrosigmoid approach for Type 1 TN (typical) or Type 2a TN (typical chronicized) from November 2011 to November 2016. A 75 y-o patient had Type 2b TN (atypical) versus 3 nonelderly patients were excluded. Elderly and younger groups were compared in relation to outcome and complication data.RESULTS: At a mean follow-up 23.0 ± 5.5 months, 22 old patients (88%) reported a very good outcome without necessity of any medication for pain, versus 28 (87,5%) of the younger group. Twenty elderly patients with Type 1 TN were compared with 24 younger patients with Type 1 TN, and no significant difference in outcomes was found (p &gt; 0.05). Five elderly patients with Type 2a TN were compared with 8 younger patients with Type 2a TN, and no significant difference in outcomes was noted (p &gt; 0.05). There was one case of CSF leak and one case of cerebellar hematoma both in the younger cohort. Mortality was zero in both groups.CONCLUSIONS: On the basis of our experience and of the international literature, age itself seems not to represent a major contraindication against MVD for TN. Keywords: Elderly, Microvascular Decompression, Retrosigmoid approach, Trigeminal neuralgia, Tic douloureux

Keyhole retrosigmoid approach for large vestibular schwannomas: strategies to improve outcomes.

OBJECTIVE There are numerous treatment strategies in the management for large vestibular schwannomas, including resection only, staged resections, resections followed by radiosurgery, and radiosurgery only. Recent evidence has pointed toward maximal resection as being the optimum strategy to prevent tumor recurrence; however, durable tumor control through aggressive resection has been shown to occur at the expense of facial nerve function and to risk other approach-related complications. Through a retrospective analysis of their single-institution series of keyhole neurosurgical approaches for large vestibular schwannomas, the authors aim to report and justify key techniques to maximize tumor resection and reduce surgical morbidity. METHODS A retrospective chart review was performed at the Centre for Minimally Invasive Neurosurgery. All patients who had undergone a keyhole retrosigmoid approach for the resection of large vestibular schwannomas, defined as having a tumor diameter of ≥ 3.0 cm, were included in this review. Patient demographics, preoperative cranial nerve status, perioperative data, and postoperative follow-up were obtained. A review of the literature for resections of large vestibular schwannomas was also performed. The authors' institutional data were compared with the historical data from the literature. RESULTS Between 2004 and 2017, 45 patients met the inclusion criteria for this retrospective chart review. When compared with findings in a historical cohort in the literature, the authors' minimally invasive, keyhole retrosigmoid technique for the resection of large vestibular schwannomas achieved higher rates of gross-total or near-total resection (100% vs 83%). Moreover, these results compare favorably with the literature in facial nerve preservation (House-Brackmann I-II) at follow-up after gross-total resections (81% vs 47%, p < 0.001) and near-total resections (88% vs 75%, p = 0.028). There were no approach-related complications in this series. CONCLUSIONS It is the experience of the senior author that complete or near-complete resection of large vestibular schwannomas can be successfully achieved via a keyhole approach. In this series of 45 large vestibular schwannomas, a greater extent of resection was achieved while demonstrating high rates of facial nerve preservation and low approach-related and postoperative complications compared with the literature.

Successful Treatment with Microvascular Decompression Surgery of a Patient with Hemiparesis Caused by Vertebral Artery Compression of the Medulla Oblongata: Case Report and Review of the Literature

There are few reports on hemiparesis caused by vascular medullary compression, which can occur because of dolichoectasia of the vertebrobasilar arterial system. In this article, we report a case of vertebral artery compression of the medulla oblongata in a 67-year-old woman. The patient was hypertensive, and she developed hemiparesis and intermittent spasms over 5 years. These spasms had worsened during the last year. Cranial nerve magnetic resonance imaging showed compression of the medulla oblongata by the left vertebral artery. A motor evoked potential (MEP) examination showed abnormal conduction of MEPs of bilateral toe abductors. The patient underwent microvascular decompression surgery under general anesthesia through a retrosigmoid keyhole approach. This operation led to relief of vascular compression and symptomatic improvement. Our case suggests that detailed history, imaging studies, and electrophysiologic studies help lead to a correct and early diagnosis of hemiparesis caused by vascular compression of the rostral ventrolateral medulla. Microvascular decompression surgery improves patient symptoms, and intraoperative electrophysiologic monitoring helps to avoid injury to important adjacent nerves.

Underlay hourglass-shaped autologous pericranium duraplasty in "key-hole" retrosigmoid approach surgery: Technical report.

Background:Cerebrospinal fluid (CSF) leakages represent a major complication of skull base surgery. Watertight dural suture is challenging, and different ways to reinforce it have been proposed. Since 6 months, we use locally harvested autologous pericranium graft for dural repair in retrosigmoid approach.Methods:Retrospectively, we analyzed 27 patients operated on with key-hole retrosigmoid approach from May 2014. In all, autologous pericranium was harvested and inserted as an underlay “hourglass-shaped” plug under the dura plane and stitched to dura. Surgical patch and sealant were used for augmentation. Complications considered were new neurological symptoms, surgical site infections, meningitis, CSF-leaks, and pseudomeningocele.Results:Indications included tumor (16 cases), microvascular decompression (10 cases), and hemorrhagic cerebellar arteriovenous malformation (1 case). Surgical site infections, meningitis, and CSF leaks have never been observed. One neurofibromatosis type 2 patient operated on for large acoustic neuroma developed an asymptomatic pseudomeningocele, disappeared on 3-month magnetic resonance imaging follow-up.Conclusions:In our series, autologous pericranium inserted and stitched as an underlay hourglass-shaped plug, augmented with surgical patch pieces and dural sealant seemed to be safe and effective for dural repair in “key-hole” retrosigmoid approach. With this technique, we obtained low complication rate, similar to the best current results of available literature.

Microsurgical Treatment of Posterior Cerebral Circulation Aneurysms Via Keyhole Approaches

To explore the techniques of microsurgical treatment for posterior cerebral circulation aneurysms via keyhole approaches and assess its feasibility. A total of 27 patients with 28 posterior cerebral circulation aneurysms were treated surgically by keyhole approaches; 24 patients presented with subarachnoid hemorrhage and 3 with headache. Of these 27 patients, 15 patients were treated via the supraorbital keyhole approach, 6 via the retrosigmoid keyhole approach, 3 via the subtemporal keyhole approach, 2 via median suboccipital approach, and 1 via the pterional keyhole approach. Of the 28 posterior cerebral circulation aneurysms, 24 aneurysms were clipped and 4 trapped; 23 aneurysms clipped completely, and 1 had residual aneurysm. Glasgow Outcome Scores at discharge revealed 25 patients had a good recovery; 1 patient was slightly disabled, and 1 patient was severely disabled. Of 15 patients treated via the supraorbital keyhole approach, to make a wider operative space, drilling of anterior clinoid process (2 patients) and posterior clinoid process (3 patients) was performed; posterior communicating artery was cut off (1 patient). For 3 patients with multiple aneurysms, complete occlusion was achieved via the same approach at one-stage. Individualized keyhole approaches for posterior cerebral circulation artery aneurysms are safe and effective. The anterior clinoid process or posterior clinoid process could be drilled to offer a wide operative space for clipping. The use of multiple working windows is very helpful for controlling the parent artery and clipping the aneurysm.

Large Vestibular Schwannoma Resection Through the Suboccipital Retrosigmoid Keyhole Approach

The objective of this study was to retrospectively study the outcomes of large vestibular schwannoma resection through the suboccipital retrosigmoid keyhole approach and emphasize technical details and advantages of surgical resection of large vestibular schwannomas via this approach. From January 2010 to September 2012, 37 consecutive patients (16 men and 21 women) with vestibular schwannoma, 4 cm or greater, received surgical resection through the suboccipital retrosigmoid keyhole approach in our department. Clinical records, radiographic findings, operative summaries, and follow-up data were analyzed retrospectively. The mean age of these patients was 45.1 ± 11.6 years. Thirty-six patients underwent primary keyhole surgical removal, and 1 underwent surgery for residual tumor after gamma knife. Gross total tumor removal was accomplished in 35 patients (94.6%), near total resection in 1 (2.7%), and subtotal resection in 1 patient (2.7%). The facial nerve was anatomically intact in all 37 patients (100%). Facial nerve function was assessed in 6 to 12 months after operation. Good function (House-Brackmann facial nerve grade I-II) was present in 81.1% of the patients, whereas acceptable function (grade III) was present in 11.1%. Cerebrospinal fluid (CSF) leakage that required surgical intervention occurred in only 5.4% of the patients, and meningitis occurred in 8.1%. In addition, 3 patients (8.1%) had hydrocephalus requiring a temporary ventricular diversion. There were no deaths. The suboccipital retrosigmoid keyhole approach is a valid choice for removing large vestibular schwannomas. Through this approach, cerebellopontine angle can be effectively exposed. Skills to protect facial nerve and extensive experience in microsurgical techniques can significantly improve the total resection rate and postoperative facial nerve function. The authors recommend this approach for patients with vestibular schwannomas larger than 3 to 4 cm.

The Keyhole Retrosigmoid Approach to the CPA: Technique and Results

Objectives: Establish the versatility and usefulness of the keyhole retrosigmoid approach to the cerebello-pontine angle (CPA) in various pathologies.

Endoscope-assisted retrosigmoid keyhole approach for cerebellopontine angle: cadaveric study

Conclusion: A 20 mm hole made backwards from the midpoint of the asterion to the mastoid process is suitable for a retrosigmoid keyhole approach with the aid of an endoscope. The endoscope-assisted retrosigmoid keyhole approach can be considered an effective and safe method for removal of vestibular schwannoma. Objective: To investigate the feasibility of the endoscope-assisted retrosigmoid keyhole approach for exposing the cerebellopontine angle (CPA) and internal auditory canal (IAC). Methods: With the aid of an endoscope, we simulated surgical procedures in 30 sides of 15 formalin-fixed cadaver heads. Results: (1) For 24 (80%) sides, the midpoint of the top notch to the mastoid process was in the anterior edge of the sigmoid sinus; for 27 sides (90%) the midpoint of the asterion to the mastoid process was in the posterior edge of the sigmoid sinus. (2) The IAC and CPA were exposed by the retrosigmoid keyhole approach with the aid of the endoscope.

Retrosigmoid Keyhole Approach to the Posterior Cranial Fossa: An Anatomical and Clinical Study

The purpose of this study is to describe the microsurgical anatomic features, as well as the operative technique for the retrosigmoid keyhole (RSK) approach to the posterior cranial fossa. In the anatomical study, 6 cadaveric heads were dissected to simulate the RSK approach. In the clinical study, the records for 15 patients treated using the RSK approach were examined. We found both conventional and RSK procedures expose the regions superior to the anterolateral margin of the tentorium, inferior to the foramen magnum, and medial to the anterolateral pons and medulla. Clinically, total removal was achieved in 13 out of 15 patients. We feel it is a safe, succinct, and minimally invasive alternative to the traditional retrosigmoid approach in selected patients.

Anatomic study to posterior-middle cranial fossa via retrosigmoid keyhole approach

Objective To explore and evaluate the micro-anatomic structure of posterior-middle cra nial fossa in the retrosigmoid keyhole approach for clinical application. Methods Ten formalin-fixed adult cadaver heads of 20 sides were used to apply the retrosigmoid keyhole approach to reach and observe the structure of posterior-middle cranial fossa.Results The retrosigmoid keyhole approach can reach petroclival region from post-lateral aspect and through this approach the lateral potion of cerebellar hemisphere、petrosal bone,CN Ⅴ,Ⅶ,Ⅷ,part of CN Ⅸ-Ⅻ,lateral potion of pons、vertebral artery and anterior inferior cerebellavar artery can be exposed cleady.Resecting part of supra-tubercle of IAM can enlarge the exposure of IAM and CN V.After cutting off the edge of tentorial part of CN Ⅳ and middle cranial fossa can be exposed.Conclusion Through retrosigmoid keyhole approach we can use the small but compatible bone hole to diminish the ineffective exposure of the cerebellum.Meanwhile the wound because of the approach and complication can be cut down.It's an effective,safe and convenience approach in clinical application to resect the tumor mainly located in posterior cranial fossa. Key words: Micro-anatomp; Keyhole approach; Suprameatal; Postenor-middle cranial fossa

Microanatomic study on retrosigmoid keyhole approach

Objective The aim of the present study was to assess the retrosigmoid keyhole approach on a cadaveric model by using a neuronavigation system, and explore its indications. Methods Six cadaveric heads (twelve sides) injected with colored latex were used. The retrosigmoid keyhole approach was followed by the conventional retrosigmoid approach. The exposure areas of petroclivus and brainstem were measured and calculated under stryker frameless stereotactic navigation. Angles of attack for six different target points, which included the Meckle's cave, trigeminal nerve root, internal auditory meatal, facial nerve root, jugular foramen and glossopharyngeal nerve root, were measured. The exposure area and angles of attack between the two approacbes were compared and analyzed by student's t test. Results The retrosigmoid keyhole approach exposes nearly the same anatomic architecture as that of conventional approach, namely, it can expose the area superior to the anteriolateral margin of the tentorium, inferior to the foramen Magnum, medial to the anteriolateral of pons and medulla. The anatomic structure deeply seated in the ispilateral petroclivus can also be observed clearly through the cranial nerve intervals. Exposure area at the petroclivus and brainstem under the retrosignaoid keyhole approach was (304.73±28.93) mm2 and (143.9±31.87)mm2, respectively. The counterpart of the conventional retrosigmoid approach was (346.43 ±42.80) mm2 and (136.05±9.05) mm2, respectively. No statistical difference lies in the exposure area (P > 0.05). The vertical and horizontal attack angles under the conventional approach were wider than those of the keyhole approach at the selected six target points (P < 0.05). Conclusion The retrosigmoid keyhole approach provides similar exposure with that of the conventional retrosigmoid approach, not only can be used in microvascular decompression, also can be used to resect tumors located in cerebellopontine angle, upper petroclivus, middle petroclivus, anteriolateral of midbrain and pons. Key words: Keyhole surgery; Retrosigmoid approach; Cerebellopontine angle; Microanatomy

Keyhole microsurgery for trigeminal neuralgia, hemifacial spasm and glossopharyngeal neuralgia

The aim of the study was to describe and evaluate the efficacy of the keyhole microsurgery to manage patients with trigeminal neuralgia (TN), hemifacial spasm (HFS) and glossopharyngeal neuralgia (GPN). Two hundred and seven patients underwent microvascular decompression (MVD) and neurotomy via retrosigmoid keyhole approach in our department clinic: MVD for trigeminal neuralgia 169 cases, hemifacial spasm 31 cases, glossopharyngeal neuralgia 4 cases and neurotomy for glossopharyngeal neuralgia 3 cases. There was no serious complication such as deaths or infarction in the cerebellum or the brainstem. Complete and partial symptoms relief was obtained in 160 (94.7%) cases and failure 9 (5.3%) cases with MVD for trigeminal neuralgia, postoperatively. Meanwhile, complications occurred in one case with cerebellar hematoma only. The postoperative results of MVD for hemifacial spasm with symptoms relief was noted in 29 (93.5%) cases and failure 2 (6.5%) cases. Postoperative complications occurred in one case with moderate hearing loss, another three cases complained of transient facial paralysis. Symptoms relief achieved in all 7 (100%) cases undergone MVD or neurotomy for glosspharyngeal neuralgia. Postoperative complications occurred in one case with moderate vocal paralysis. We think that microsurgery via retrosigmoid keyhole approach is safe and effective for CPA hyperactive cranial nerve dysfunction syndromes.