Tag: Retrosigmoid approach

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The Mastoid Foramen and Mastoid Emissary Vein Canal as Surgical Landmarks for Mastoid Pneumatization During Retrosigmoid Approach

Operative Neurosurgery 31:74–84, 2026

This study investigates the anatomical, radiological, and intraoperative relationships between the mastoid foramen (MF), mastoid emissary vein canal (MEVC), and mastoid air cell (MAC) pneumatization to improve planning and safety of the retrosigmoid approach (RSA). It reports measurements from cadaveric specimens, high-resolution CT of 100 patients, and surgical outcomes from 54 RSA procedures, linking MF/MEVC positions with pneumatization grades.

Key findings show the MF and MEVC are reliably posterior to MACs in most cases, with higher pneumatization grades correlated with shorter MF‑MAC and mMEVC‑MAC distances. Preoperative radiological assessment of these landmarks guided burr hole placement and border‑sealing techniques, reducing intraoperative MAC openings and postoperative complications.

Goal Assess whether the mastoid foramen (MF) and mastoid emissary vein canal (MEVC) can predict mastoid pneumatization and guide safer retrosigmoid approach (RSA) craniectomy planning.

Methods Combined anatomic dissection/drilling (2 dry temporal bones; 2 formalin-fixed heads), radiology (100 high‑resolution CTs; Han grade 1–4), and surgical review (54 RSA cases with complication tracking).

Classification & measures MF labeled “posterior” vs “anterior” to the most posterior mastoid air cell (MAC); MEVC labeled type 1 (posterior to MACs) vs type 2 (within MACs); quantified MF‑MAC distance and minimal MEVC‑MAC (mMEVC‑MAC) distance.

Key anatomy pattern MF was posterior to MACs in 99.4% of CT sides; MEVC was posterior to MACs in 88.0% (i.e., type 2 “within MACs” in the remainder).

Pneumatization relationships Higher Han pneumatization grades were associated with shorter MF‑MAC and mMEVC‑MAC distances (both P < .001), and these two distances were strongly correlated (r = 0.741, P < .001).

Age association Mastoid pneumatization grade decreased with age (inverse correlation, P < .001).

Surgical risk signal Intraoperative MAC opening occurred in 5.6% (3/54), and all had Han grade 4 pneumatization with type 2 MEVC (“within” MACs).

Clinical outcome No major intraoperative complications were reported; only one CSF wound leak (1.9%) occurred postoperatively and resolved with lumbar drainage.

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Dural and cranial reconstruction techniques in retrosigmoid craniotomy: key factors associated with CSF leaks in 225 patients

Neurosurg Focus 58(2):E8, 2025

This study evaluated the effectiveness of various dural closure and bone reconstruction techniques in preventing CSF leakage following retrosigmoid craniotomy for cerebellopontine angle (CPA) tumors. The goal was to identify whether newer combinations of reconstructive materials offer any advantage in reducing CSF leaks and improving surgical outcomes.

METHODS The authors conducted a retrospective review of 225 patients who underwent a retrosigmoid craniotomy for CPA neoplasms between January 2018 and August 2024. Patient demographics, intraoperative reports, and postoperative complications were analyzed. Various reconstructive methods, including the use of TachoSil, HydroSet, autologous or heterologous dural patches, and bone flap repositioning, were compared. CSF-related complications such as CSF leakage, infections, and postoperative hydrocephalus were systematically evaluated.

RESULTS CSF leakage occurred in 31% of cases (n = 69), while CSF infections and postoperative hydrocephalus were noted in 6% and 7% of patients, respectively. HydroSet combined with bone flap repositioning significantly reduced CSF leakage (p = 0.008), as did the combination of HydroSet and heterologous dural patches (p = 0.007). TachoSil did not show a significant reduction in CSF leakage. Craniectomy with titanium mesh or heterologous cranioplasty was not associated with any CSF leaks. No other single or combined techniques showed significant associations with CSF leakage.

CONCLUSIONS HydroSet in combination with bone reconstruction and heterologous patches demonstrated superior outcomes in reducing CSF leaks. TachoSil did not significantly affect leakage rates, with less definite results. Refining surgical techniques and selecting appropriate materials for dural and bone reconstruction may help reduce complications and improve patient outcomes in CPA tumor surgeries using the retrosigmoid approach.

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Endoscopic Retrolabyrinthine Craniotomy for Exposure of the Trigeminal Nerve Root Entry Zone

Operative Neurosurgery 27:464–470, 2024

Exposure of the root entry zone (REZ) of the trigeminal nerve (TN) for microvascular decompression is commonly obtained with a retrosigmoid approach, with or without endoscopic assistance. We hypothesized that adequate exposure of the TN REZ could be obtained through an endoscopic retrolabyrinthine (RL) approach. We aim to quantify exposure of the REZ of the TN using endoscopic RL approach, with and without drilling of the suprameatal tubercle of the internal auditory canal.

METHODS: Surgical dissection was performed bilaterally on 3 embalmed cadaveric human heads at the anatomy laboratory of the House Institute. Heads were scanned for volumetric analysis using 3D Slicer software both before and after dissection. Extent of exposure was quantified in 2 ways: first, by assessment of the surgeon’s ability to visualize 16 predetermined anatomic landmarks with the endoscope and second, we estimated the “working” area by placing fiducials under the fully endoscopic view and calculating the resultant 3D volume.

RESULTS: Using the standard endoscopic RL approach, anaverageof 13.8 landmarks (range 12-16) was visualized. The estimated working volume exposed by the RL on each side of each head varied from 189.28 to 527.85 mm3 . Drilling of the suprameatal tubercle provided both increases in landmark visualization and, on average, an additional 55 mm 3 of working volume.

CONCLUSION: The endoscopic RL approach is a viable alternative to the standard retrosigmoid approach. Potential advantages of the RL include a more lateral trajectory that minimizes the need for cerebellar retraction and a shorter working distance and shallower angle to the cerebellopontine angle. Potential disadvantages include longer surgery time, increased technical difficulty of exposure, and potential for cerebrospinal fluid leak and or hearing loss.

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The auricula as a new surgical landmark for the transverse-sigmoid-sinus-transition

Brain and Spine 4 (2024) 102757

The transverse-sigmoid-sinus-transition constitutes an important landmark during a retrosigmoid craniotomy. Due to anatomical variations, the location is highly variable. Landmarks for identification of the anterior border of the sigmoid sinus have been described extensively, such as the mastoid notch, digastric point, external auditory meatus and crux of the helix curvature. There is a paucity of landmarks for the identification of the posterior border, however.

Research question: We examined the relationship between the transverse-sigmoid-sinus-transition and the mostposterior-part-of-the-auricula.

Material and methods: We performed a retrospective analysis of one-hundred patients (38 males and 62 females) who underwent cerebral MRI examinations at Antwerp University Hospital (Belgium). Using Brainlab®, the transverse-sigmoid-sinus-transition and most-posterior-part-of-the-auricula coordinates were calculated and compared. Left and right sides were compared in both the anteroposterior and craniocaudal axis.

Results: Mean age was 56.4 ± 16.1 years. Mean MPPA-TSST-distance in the anteroposterior direction was − 1.93 mm (right) and − 1.96 mm (left). Mean MPPA-TSST-distance in the craniocaudal direction was − 5.16 mm (right) and − 5.04 mm (left).

Discussion and conclusion: The transverse-sigmoid-sinus-transition seems to be located more anterior and caudal with respect to the most-posterior-part-of-the-auricula, meaning that it can be considered a save landmark. A correction of five mm needs to be applied in order to identify the inferior border of the transverse sinus. Left/ right and gender had no significant influence. The most-posterior-part-of-the-auricula can be considered a fast and practical anatomical landmark for identification of the transverse-sigmoid-sinus-transition, without affecting operative fluency, especially during an emergency craniotomy.

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Subclassification of Koos grade 4 vestibular schwannoma: insights into tumor morphology for predicting postoperative facial nerve function

J Neurosurg 140:127–137, 2024

OBJECTIVE Koos grade 4 vestibular schwannoma (KG4VS) is a large tumor that causes brainstem displacement and is generally considered a candidate for surgery. Few studies have examined the relationship between morphological differences in KG4VS other than tumor size and postoperative facial nerve function. The authors have developed a landmark-based subclassification of KG4VS that provides insights into the morphology of this tumor and can predict the risk of facial nerve injury during microsurgery. The aims of this study were to morphologically verify the validity of this subclassification and to clarify the relationship of the position of the center of the vestibular schwannoma within the cerebellopontine angle (CPA) cistern on preoperative MR images to postoperative facial nerve function in patients who underwent microsurgical resection of a vestibular schwannoma.

METHODS In this paper, the authors classified KG4VSs into two subtypes according to the position of the center of the KG4VS within the CPA cistern relative to the perpendicular bisector of the porus acusticus internus, which was the landmark for the subclassification. KG4VSs with ventral centers to the landmark were classified as type 4V, and those with dorsal centers as type 4D. The clinical impact of this subclassification on short- and long-term postoperative facial nerve function was analyzed.

RESULTS In this study, the authors retrospectively reviewed patients with vestibular schwannoma who were treated surgically via a retrosigmoid approach between January 2010 and March 2020. Of the 107 patients with KG4VS who met the inclusion criteria, 45 (42.1%) were classified as having type 4V (KG4VSs with centers ventral to the perpendicular bisector of the porous acusticus internus) and 62 (57.9%) as having type 4D (those with centers dorsal to the perpendicular bisector). Ventral extension to the perpendicular bisector of the porus acusticus internus was significantly greater in the type 4V group than in the type 4D group (p < 0.001), although there was no significant difference in the maximal ventrodorsal diameter. The rate of preservation of favorable facial nerve function (House-Brackmann grades I and II) was significantly lower in the type 4V group than in the type 4D group in terms of both short-term (46.7% vs 85.5%, p < 0.001) and long-term (82.9% vs 96.7%, p = 0.001) outcomes. Type 4V had a significantly negative impact on short-term (OR 7.67, 95% CI 2.90–20.3; p < 0.001) and long-term (OR 6.05, 95% CI 1.04–35.0; p = 0.045) facial nerve function after surgery when age, tumor size, and presence of a fundal fluid cap were taken into account.

CONCLUSIONS The authors have delineated two different morphological subtypes of KG4VS. This subclassification could predict short- and long-term facial nerve function after microsurgical resection of KG4VS via the retrosigmoid approach. The risk of postoperative facial palsy when attempting total resection is greater for type 4V than for type 4D. This classification into types 4V and 4D could help to predict the risk of facial nerve injury and generate more individualized surgical strategies for KG4VSs with better facial nerve outcomes.

 

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Micro‑Doppler for venous sinus localization in approaches to the cerebello‑pontine angle

Acta Neurochirurgica (2023) 165:3467–3472

Main anatomical landmarks of retrosigmoid craniotomy are transverse sinus (TS), sigmoid sinus (SS), and the confluence of both. Anatomical references and guidance based on preoperative imaging studies are less reliable in the posterior fossa than in the supratentorial region. Simple intraoperative real-time guidance methods are in demand to increase safety.

Methods This manuscript describes the localization of TS, SS, and TS-SS junction by audio blood flow detection with a micro-Doppler system.

Conclusion This is an additional technique to increase safety during craniotomy and dura opening, widening the surgical corridor to secure margins without carrying risks nor increase surgical time.

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Surgical management of large cerebellopontine angle meningiomas: long-term results of a less aggressive resection strategy

J Neurosurg 138:1630–1639, 2023

Cerebellopontine angle (CPA) meningiomas present many surgical challenges depending on their volume, site of dural attachment, and connection to surrounding neurovascular structures. Assuming that systematic radical resection of large CPA meningiomas carries a high risk of permanent morbidity, the authors adopted an alternative strategy of optimal resection followed by radiosurgery or careful observation of the residual tumor and assessed the efficiency and safety of this approach to meningioma treatment management.

METHODS This single-center retrospective cohort study included 50 consecutive patients who underwent surgery for meningioma between January 2003 and February 2020.

RESULTS The most common main dural attachments of the meningiomas were posterior (42%) and superior (26%) to the internal auditory meatus. The suboccipital retrosigmoid route was the most routinely used (92%). At the last follow-up examination, 93% of the patients with normal preoperative facial nerve (FN) function retained good House-Brackmann (HB) grades of I and II, whereas 3 patients (7%) displayed intermediate HB grade III FN function. Hearing preservation was achieved in 86% of the patients who presented with preoperative serviceable hearing, and recovery after surgery was achieved in 19% of the patients experiencing preoperative hearing loss. In order to preserve all cranial nerve function, gross-total resection was obtained in 26% of patients. Of the 35 patients who had undergone subtotal resection, 20 (57%) had been allocated into a wait-and-rescan treatment approach and 15 (43%) underwent upfront Gamma Knife surgery (GKS). The mean postoperative tumor volume was 1.20 cm 3 in the upfront GKS group and 0.73 cm 3 in the waitand-rescan group (p = 0.08). Tumor control was achieved in 87% and 55% of cases (p < 0.001), with a mean follow-up of 85 and 69 months in the GKS and wait-and-rescan groups, respectively. The 1-, 5-, and 7-year tumor progression-free survival rates were 100%, 100%, and 89% in the GKS group and 95%, 59%, and 47% in the wait-and-rescan group, respectively (p < 0.001).

CONCLUSIONS Optimal nonradical resection of large CPA meningiomas provides favorable long-term tumor control and functional preservation. Adjuvant GKS does not carry additional morbidity and appears to be an efficient adjuvant treatment.

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Presence of a fundal fluid cap on preoperative magnetic resonance imaging may predict long-term facial nerve function after resection of vestibular schwannoma via the retrosigmoid approach

J Neurosurg 138:972–980, 2023

Preservation of neurological function is a priority when performing a resection of a vestibular schwannoma (VS). Few studies have examined the radiographic value of a fundal fluid cap—i.e., cerebrospinal fluid in the lateral end of a VS within the internal auditory canal—for prediction of postoperative neurological function. The aim of this study was to clarify whether the presence of a fundal fluid cap on preoperative magnetic resonance images has a clinical impact on facial nerve function after resection of VSs.

METHODS The presence of a fundal fluid cap and its prognostic impact on long-term postoperative facial nerve function were analyzed.

RESULTS A fundal fluid cap was present in 102 of 143 patients who underwent resection of sporadic VSs via the retrosigmoid approach. Facial nerve function was acceptable (House-Brackmann grade I–II) immediately after surgery in 82 (80.4%) patients with a fundal fluid cap and in 26 (63.4%) of those without this sign. The preservation rate of facial nerve function increased in a time-dependent manner after surgery in patients with a fundal fluid cap but plateaued by 3 months postoperatively in those without a fundal fluid cap; the difference was statistically significant at 12 months (96.1% vs 82.9%, p = 0.013) and 24 months (97.1% vs 82.9%, p = 0.006) after surgery. The presence of a fundal fluid cap had a significantly positive effect on long-term facial nerve function at 24 months after surgery when tumor size and intraoperative neuromonitoring response were taken into account (OR 5.55, 95% CI 1.12–27.5, p = 0.034).

CONCLUSIONS Neuromonitoring-guided microsurgery for total resection of VSs is more likely to be successful in terms of preservation of facial nerve function if a fundal fluid cap is present. This preoperative radiographic sign could be helpful when counseling patients and deciding the treatment strategy.

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Sacrifice or preserve the superior petrosal vein in microvascular decompression surgery

J Neurosurg 138:390–398, 2023

In microvascular decompression (MVD) surgery through the retrosigmoid approach, the surgeon may have to sacrifice the superior petrosal vein (SPV). However, this is a controversial maneuver. To date, high-level evidence comparing the operative outcomes of patients who underwent MVD with and without SPV sacrifice is lacking. Therefore, this study sought to bridge this gap.

METHODS The authors searched the Medline and PubMed databases with appropriate Medical Subject Heading (MeSH) terms and keywords. The primary outcome was vascular-related complications; secondary outcomes were new neurological deficit, cerebrospinal fluid (CSF) leak, and neuralgia relief. The pooled proportions of outcomes and OR (95% CI) for categorical data were calculated by using the logit transformation and Mantel-Haenszel methods, respectively.

RESULTS Six studies yielding 1143 patients were included, of which 618 patients had their SPV sacrificed. The pooled proportion (95% CI) values were 3.82 (0.87–15.17) for vascular-related complications, 3.64 (1.0–12.42) for new neurological deficits, 2.85 (1.21–6.58) for CSF leaks, and 88.90 (84.90–91.94) for neuralgia relief. The meta-analysis concluded that, whether the surgeon sacrificed or preserved the SPV, the odds were similar for vascular-related complications (2.5% vs 1.5%, OR [95% CI] 1.01 [0.33–3.09], p = 0.99), new neurological deficits (1.2% vs 2.8%, OR [95% CI] 0.55 [0.18–1.66], p = 0.29), CSF leak (3.1% vs 2.1%, OR [95% CI] 1.16 [0.46–2.94], p = 0.75), and neuralgia relief (86.6% vs 87%, OR [95% CI] 0.96 [0.62–1.49], p = 0.84).

CONCLUSIONS SPV sacrifice is as safe as SPV preservation. The authors recommend intentional SPV sacrifice when gentle retraction fails to enhance surgical field visualization and if the surgeon encounters SPV-related neurovascular conflict and/or anticipates impeding SPV-related bleeding.

 

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Indication for a skull base approach in microvascular decompression for hemifacial spasm

Acta Neurochirurgica (2022) 164:3235–3246

A thorough observation of the root exit zone (REZ) and secure transposition of the offending arteries is crucial for a successful microvascular decompression (MVD) for hemifacial spasm (HFS). Decompression procedures are not always feasible in a narrow operative field through a retrosigmoid approach. In such instances, extending the craniectomy laterally is useful in accomplishing the procedure safely. This study aims to introduce the benefits of a skull base approach in MVD for HFS.

Methods The skull base approach was performed in twenty-eight patients among 335 consecutive MVDs for HFS. The site of the neurovascular compression (NVC), the size of the flocculus, and the location of the sigmoid sinus are measured factors in the imaging studies. The indication for a skull base approach is evaluated and verified retrospectively in comparison with the conventional retrosigmoid approach. Operative outcomes and long-term results were analyzed retrospectively.

Results The extended retrosigmoid approach was used for 27 patients and the retrolabyrinthine presigmoid approach was used in one patient. The measurement value including the site of NVC, the size of the flocculus, and the location of the sigmoid sinus represents well the indication of the skull base approach, which is significantly different from the conventional retrosigmoid approach. The skull base approach is useful for patients with medially located NVC, a large flocculus, or repeat MVD cases. The long-term result demonstrated favorable outcomes in patients with the skull base approach applied. Conclusions Preoperative evaluation for lateral expansion of the craniectomy contributes to a safe and secure MVD.

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Retrolabyrinthine transsigmoid approach to complex parabrainstem tumors in the posterior fossa

J Neurosurg 136:1097–1102, 2022

The surgical management of large and complex tumors of the posterior fossa poses a formidable challenge in neurosurgery. The standard retrosigmoid craniotomy approach has been performed at most neurosurgical centers; however, the retrosigmoid approach may not provide enough working space without significant retraction of the cerebellum. The transsigmoid approach provides wider and shallower surgical fields; however, there have been few clinical and no cadaveric studies on its usefulness. In the present study, the authors describe the transsigmoid approach in clinical cases and cadaveric specimens.

METHODS For the clinical study, the authors retrospectively reviewed the medical records and operative charts of patients who had been surgically treated for parabrainstem tumors using the transsigmoid approach between 1997 and 2019. They analyzed patient demographic and clinical data, as well as surgical and clinical outcomes. In the cadaveric study, they compared the surgical views obtained in different approaches (retrosigmoid, presigmoid, retrolabyrinthine, and transsigmoid) and measured the sigmoid sinus width at the level of the endolymphatic sac and the distance between the anterior edge of the sigmoid sinus and the endolymphatic sac on 35 sides in 19 cadaveric specimens.

RESULTS A total of 21 patients (6 males and 15 females) with a mean age of 42.2 (range 15–67) years were included in the clinical study. Eleven patients had meningioma, 7 had vestibular schwannoma, 2 had hemangioblastoma, and 1 had epidermoid cyst. Gross-total, near-total, and subtotal removal were achieved in 7 (33.3%), 3 (14.3%), and 11 (52.4%) patients, respectively. In the cadaveric study, 19 cadaveric specimens were used. The sigmoid sinus was cut in the middle, and the incision was extended from the retrosigmoid to the presigmoid dura. The dura was then retracted upward and downward like opening a door. The results indicated that this technique can widen the operative field anteriorly by approximately 2 cm as compared to the retrosigmoid approach and provides a better view anterior to the brainstem.

CONCLUSIONS The transsigmoid approach is useful for complex parabrainstem tumors in the posterior fossa because it provides a wider and shallower operative view with less retraction of the cerebellum. This enables safer tumor removal with less damage to important structures in the posterior fossa, resulting in better operative and clinical outcomes.

 

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Retrosigmoid transhorizontal fissure approach to lateral pontine cavernous malformation

J Neurosurg 136:205–214, 2022

The retrosigmoid (RS) approach is a classic route used to access deep-seated brainstem cavernous malformation (CM). The angle of access is limited, so alternatives such as the transpetrosal presigmoid retrolabyrinthine (TPPR) approach have been used to overcome this limitation. Here, the authors evaluated a modification to the RS approach, horizontal fissure dissection by using the RS transhorizontal (RSTH) approach.

METHODS Relevant clinical parameters were evaluated in 9 patients who underwent resection of lateral pontine CM. Cadaveric dissection was performed to compare the TPPR approach and the RSTH approach.

RESULTS Five patients underwent the TPPR approach, and 4 underwent the RSTH approach. Dissection of the horizontal fissure allowed for access to the infratrigeminal safe entry zone, with a direct trajectory to the middle cerebellar peduncle similar to that used in TPPR exposure. Operative time was longer in the TPPR group. All patients had a modified Rankin Scale score ≤ 2 at the last follow-up. Cadaveric dissection confirmed increased anteroposterior working angle and middle cerebellar peduncle exposure with the addition of horizontal fissure dissection.

CONCLUSIONS The RSTH approach leads to a direct lateral path to lateral pontine CM, with similar efficacy and shorter operative time compared with more extensive skull base exposure. The RSTH approach could be considered a valid alternative for resection of selected pontine CM.

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Large and small vestibular schwannomas: same, yet different tumors

Acta Neurochirurgica (2021) 163:2199–2207

Vestibular schwannomas (VS) present at variable size with heterogeneous symptomatology. Modern treatment paradigms for large VS include gross total resection, subtotal resection (STR) in combination with observation, and/or radiation to achieve optimal function preservation, whereas treatment is felt to be both easier and safer for small VS. The objective is to better characterize the presentation and surgical outcomes of large and small VS.

Methods We collected data of patients who had surgically treated VS with a posterior fossa diameter of 4.0 cm or larger (large tumor group, LTG) and smaller than 1.0 cm in cisternal diameter (small tumor group, STG). Statistical significance was defined as p < 0.05.

Results LTG included 48 patients (average tumor size: 44.9 mm) and STG 38 (7.9 mm). Patients in STG presented more frequently with tinnitus and sudden hearing loss. Patients in LTG underwent more STR than STG (50.0% vs. 2.6%, p < 0.0001). LTG had more complications (31.3% vs. 13.2%, p = 0.049). Postoperative facial nerve function in STG was significantly better than LTG. STG had better hearing preoperatively (p < 0.0001) and postoperatively than LTG (p = 0.0002). Postoperative headache was more common in STG (13.2% vs. 2.1%, p = 0.045). The rate of recurrence/progression needing treatment was not statistically different between the groups (12.5% in LTG vs. 7.9% in STG, p = 0.49). Those patients who required periprocedural cerebrospinal fluid diversion had higher risk of infection (20.8% vs 4.8%, p = 0.022).

Conclusion Large and small VS present differently. LTG showed more unsatisfactory outcomes in facial nerve function and postoperative hearing despite maximal efforts undertaken toward function-preservation strategy; however, similar tumor control was achieved.

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Impact of C‑shaped skin incision on surgical operability in the retrosigmoid approach: when a good start is half of the job

Acta Neurochirurgica (2021) 163:2155–2163

The retrosigmoid approach (RSA) is one of the routes of choice to approach tumors and vascular lesions of the cerebellopontine angle. Among different types of skin incisions and soft tissue dissection techniques, the most widely used variants comprise the straight/lazy S-shaped and the C-shaped incisions. Several reports discuss advantages in terms of functional and clinical outcomes of the C-shaped incision, but scientific considerations about the critical impact of this kind of incision on surgical operability are still extremely limited.

Object Authors comparatively analyze the advantage provided by C-shaped incision in RSA in terms of anatomic exposure and surgical operability, compared with straight/lazy S-shaped one.

Methods A comparative microanatomical laboratory investigation was conducted. The operability score (OS) was applied for quantitative analysis of surgical operability.

Results C-shaped incision, providing a significant reduction of the overall working distance (–13%) together with an overall increase of the maneuverability area (+ 204.9%), did improve the conizing effect on the surgical corridor. It optimized overall maneuverability of surgical instruments, in terms of angle of attack (+ 27.7%), as well as maneuverability arc (+ 122%), on the entire surgical field. C-shaped incision ensured good operability on all surgical targets (OS ranging from 2 to 3), most significantly improving surgical maneuverability at the porus trigeminus and internal acoustic meatus.

Conclusion C-shaped incision in the RSA significantly improves anatomic exposure and surgical operability as compared with straight/lazy S-shaped incision.

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Nervus intermedius and the surgical management of geniculate neuralgia

J Neurosurg 131:343–351, 2019

Geniculate neuralgia (GN) is an uncommon craniofacial pain syndrome attributable to nervus intermedius (NI) dysfunction. Diagnosis and treatment can be challenging, due to the complex nature of ear sensory innervation, resulting in clinical overlap with trigeminal neuralgia (TN) and glossopharyngeal neuralgia (GPN).

METHODS A retrospective review of a prospective neurosurgical database at our institution was performed, 2000–2017, with a corresponding systematic literature review. Pain outcomes were dichotomized as unfavorable for unchanged/worsened symptoms versus favorable if improved/resolved. Eight formalin-fixed brains were examined to describe NI at the brainstem.

RESULTS Eleven patients were surgically treated for GN—9 primary, 2 reoperations. The median age was 48, 7 pa- tients were female, and the median follow-up was 11 months (range 3–143). Seven had ≥ 2 probable cranial neuralgias. NI was sectioned in 9 and treated via microvascular decompression (MVD) in 2. Five patients underwent simultaneous treatment for TN (4 MVD; 1 rhizotomy) and 5 for GPN (3 MVD; 2 rhizotomy). Eleven reported symptomatic improvement (100%); 8 initially reported complete resolution (73%). Pain outcomes at last contact were favorable in 8 (73%)—all among the 9 primary operations (89% vs 0%, p = 0.054). Six prior series reported outcomes in 111 patients.

CONCLUSIONS GN is rare, and diagnosis is confounded by symptomatic overlap with TN/GPN. Directed treatment of all possible neuralgias improved pain control in almost all primary operations. Repeat surgery seems a risk factor for an unfavorable outcome. NI is adherent to superomedial VIII at the brainstem; the intermediate/cisternal portion is optimal for visualization and sectioning.

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Endoscopic microvascular decompression for hemifacial spasm associated with the vertebral artery

Acta Neurochir (2018) 160:157–159

Microvascular decompression (MVD) of hemifacial spasm (HFS) associated with the vertebral artery (VA) shows higher rates of incomplete cure and complications compared to non-VA-related HFS.

Method Purely endoscopic MVD for VA-associated HFS via a retrosigmoid keyhole was performed. Neurovascular conflicts by a directly offending artery and VA around the root exit zone of the facial nerve were clearly demonstrated under 30° endoscopic view without significant cerebellar retraction. The VA and directly offending artery were safely transposed with preservation of perforators under excellent view.

Conclusion Endoscopic MVD offers reliable decompression for VA-associated HFS with minimal invasiveness.

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Fully endoscopic retrosigmoid approach for posterior petrous meningioma and trigeminal microvascular decompression

Fully endoscopic retrosigmoid approach for posterior petrous

Acta Neurochir (2015) 157:611–615

Cerebellopontine angle tumor resection and cranial nerve microvascular decompression are usually performed with the aid of the surgical microscope. The endoscope is commonly used as an adjuvant.

Method A retrosigmoid craniectomy is done. Upon dural opening, the endoscope is inserted into the operative field along the petrotentorial junction. Cerebrospinal fluid drainage provides a wider space for introduction of the endoscope and surgical instruments. Traditional microsurgical techniques are used during the entire procedure.

Conclusion A fully endoscopic retrosigmoid approach is a safe and effective procedure for cerebellopontine angle tumor resection and cranial nerve microvascular decompression.

Key points

• Careful examination of preoperative studies is needed to identify anatomical peculiarities.

• Patient positioning: the head must be gently flexed and its vertex gently tilted toward the floor.

• Neurophysiologic monitoring and intraoperative navigation.

• Craniectomy: partial exposure of the transverse and sigmoid sinuses.

• Curvilinear dural incision reflected laterally to minimize the risk of sinus injury.

• Opening the cerebellomedullary cistern for CSF drainage and cerebellar relaxation.

• Dynamic endoscopy enhances depth perception and must be performed by a team with experience in endoscopic intracranial surgery.

• Traditional microsurgical techniques have to be applied during the entire operation.

• Multilayer reconstruction, including watertight dural closure.

• Meningiomas causing brainstem shift are not suitable for endoscopic resection.

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A combined dual-port endoscope-assisted pre- and retrosigmoid approach to the cerebellopontine angle

A combined dual-port endoscope-assisted pre- and retrosigmoid approach to the cerebellopontine angle- an extensive anatomo-surgical study

Neurosurg Rev (2014) 37:597–608

The use of the endoscope in the cerebellopontine angle (CPA) has been suggested to minimize cerebellar retraction and reduce the size of the craniotomy. 3D endoscopy combines the benefits of conventional 2D endoscopy with the added benefit of stereoscopic perception, though improved visualization alone does not guarantee improved surgical maneuverability and a better surgical outcome. We propose a new combined dual-port endoscope-assisted pre- and retrosigmoid approach to improve visualization and accessibility of the CPA with shortened distances and increased surgical maneuverability of neurovascular structures.

We analyze surgical exposure and maneuverability of this approach and compare it with the surgical microscopic and a conventional single-port endoscope-assisted retrosigmoid approach. This combined pre- and retrosigmoid approach was performed on eight cadaveric heads (16 sides). The endoscopic probe was inserted through the presigmoid surgical port while surgical manipulation was performed through the retrosigmoid corridor. The CPA was divided into three compartments, from medial to lateral, the anteromedial, and the middle and the posterolateral. The microscope provided good visualization of the posterolateral and middle compartments, whereas poor visualization was offered of the anteromedial compartment. The dual-port endoscopic approach dramatically improved visualization and surgical maneuverability of the anteromedial compartments, clivus, and related neurovascular structures. Additionally, the 3D endoscope allowed for a better understanding of the surgical anatomy of the CPA and improved visualization of structures located in the anteromedial compartments towards the midline.

This approach allowed for full realization of the benefits of endoscopic-assisted technique by improving surgical access and maneuverability.

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Suprajugular extension of the retrosigmoid approach

Suprajugular extension retrosigmoid approach

J Neurosurg 121:397–407, 2014

Jugular foramen tumors often extend intra- and extracranially. The gross-total removal of tumors located both intracranially and intraforaminally is technically challenging and often requires a combined skull base approach. This study presents a suprajugular extension of the retrosigmoid approach directed through the osseous roof of the jugular foramen that allows the removal of tumors located in the cerebellopontine angle with extension into the upper part of the foramen, with demonstration of an illustrative case.

Methods. The cerebellopontine angles and jugular foramina were examined in dry skulls and cadaveric heads to clarify the microsurgical anatomy around the jugular foramen and to define the steps of the suprajugular exposure.

Results. The area drilled in the suprajugular approach is inferior to the acoustic meatus, medial to the endolymphatic depression and surrounding the superior half of the glossopharyngeal dural fold. Opening this area exposed the upper part of the jugular foramen and extended the exposure along the glossopharyngeal nerve below the roof of the jugular foramen. In the illustrative case, a schwannoma originating from the glossopharyngeal nerve in the cerebellopontine angle and extending below the roof of the jugular foramen and above the jugular bulb was totally removed without any postoperative complications.

Conclusions. The suprajugular extension of the retrosigmoid approach will permit removal of tumors located predominantly in the cerebellopontine angle but also extending into the upper part of the jugular foramen without any additional skull base approaches.

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Classification of the Superior Petrosal Veins and Sinus Based on Drainage Pattern

Classification of the Superior Petrosal Veins and Sinus Based on Drainage Pattern

Operative Neurosurgery 10:357–367, 2014

The increasing number of reports of complications after sacrificing the superior petrosal veins, the largest veins in the posterior fossa, has led to a need for an increased understanding of the anatomy of these veins and the superior petrosal sinus into which they empty.

OBJECTIVE: To examine the anatomy of the superior petrosal veins and their size, draining area, and tributaries, as well as the anatomic variations of the superior petrosal sinus.

METHOD: Injected cadaveric cerebellopontine angles and 3-dimensional multifusion angiography images were examined.

RESULTS: The 4 groups of the superior petrosal veins based on their tributaries, course, and draining areas are the petrosal, posterior mesencephalic, anterior pontomesencephalic, and tentorial groups. The largest group was the petrosal group. Its largest tributary, the vein of the cerebellopontine fissure, was usually identifiable in the suprafloccular cistern located above the flocculus on the lateral surface of the middle cerebellar peduncle. The medial or lateral segment of the superior petrosal sinus was absent in 40% of cerebellopontine angles studied with venography.

CONCLUSION: The superior petrosal veins and their largest tributaries, especially the vein of the cerebellopontine fissure, should be preserved if possible. Obliteration of superior petrosal sinuses in which either the lateral or medial portion is absent may result in loss of the drainage pathway of the superior petrosal veins. Preoperative assessment of the superior petrosal sinus should be considered before transpetrosal surgery in which the superior petrosal sinus may be obliterated.

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