Ryosuke Tomio

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

IntroductionThe 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.MethodsWe 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.ResultsFacial 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.ConclusionsGSPN 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.

Primary dural closure and anterior cranial base reconstruction using pericranial and nasoseptal multi-layered flaps in endoscopic-assisted skull base surgery

IntroductionDural and anterior cranial base reconstruction is essential in the surgical resection of a craniofacial tumor that extends from the paranasal sinuses to the subdural space. Watertight reconstruction of vascularized tissue is essential to prevent postoperative liquorrhea, especially under conditions that prevent wound healing (e.g., postoperative irradiation therapy).MethodWe successfully treated two cases of olfactory neuroblastoma by endoscopic-assisted craniotomy with primary dural closure and anterior cranial base reconstruction using a multi-layered flap technique. Dural defects were closed using temporal fascia or fascia lata in a conventional fashion, immediately after detaching the subdural tumor, in order to isolate and prevent contamination of subdural components and cerebrospinal fluid (CSF) from the tumor and nasal sinuses. Tumor removal and anterior cranial base reconstruction were performed without any concern of CSF contamination after dural closure by craniotomy and endoscopic endonasal approach (EEA). Vascularized pericranial flaps (PCF) and nasoseptal flaps (NSF) were used simultaneously as doubled-over layers for reconstruction.ResultsThe tumor was completely removed macroscopically and the anterior cranial base was reconstructed in both cases. CSF leak and postoperative meningitis were absent. Postoperative and irradiation therapy courses were successful and uneventful.ConclusionsThis multi-layered anterior cranial base reconstruction consisted of three layers: a fascia for dural plasty and double-layered PCF and NSF. This surgical reconstruction technique is suitable to treat craniofacial tumors extending into the subdural space through the anterior cranial base dura mater.

Pathological Location of Cranial Nerves in Petroclival Lesions: How to Avoid Their Injury during Anterior Petrosal Approach

Objectives Numerous surgical approaches have been developed to access the petroclival region. The Kawase approach, through the middle fossa, is a well-described option for addressing cranial base lesions of the petroclival region. Our aim was to gather data about the variation of cranial nerve locations in diverse petroclival pathologies and clarify the most common pathologic variations confirmed during the anterior petrosal approach. Method A retrospective analysis was made of both videos and operative and histologic records of 40 petroclival tumors from January 2009 to September 2013 in which the Kawase approach was used. The anatomical variations of cranial nerves IV-VI related to the tumor were divided into several location categories: superior lateral (SL), inferior lateral (IL), superior medial (SM), inferior medial (IM), and encased (E). These data were then analyzed taking into consideration pathologic subgroups of meningioma, epidermoid, and schwannoma. Results In 41% of meningiomas, the trigeminal nerve is encased by the tumor. In 38% of the meningiomas, the trigeminal nerve is in the SL part of the tumor, and it is in 20% of the IL portion of the tumor. In 38% of the meningiomas, the trochlear nerve is encased by the tumor. The abducens nerve is not always visible (35%). The pathologic nerve pattern differs from that of meningiomas for epidermoid and trigeminal schwannomas. Conclusion The pattern of cranial nerves IV-VI is linked to the type of petroclival tumor. In a meningioma, tumor origin (cavernous, upper clival, tentorial, and petrous apex) is the most important predictor of the location of cranial nerves IV-VI. Classification of four subtypes of petroclival meningiomas using magnetic resonance imaging is very useful to predict the location of deviated cranial nerves IV-VI intraoperatively.

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

OBJECT 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 quantitatively evaluate the safety of Kawase triangle as an anatomical landmark. METHOD We 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. RESULTS Drilling 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. CONCLUSION The 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.

Grüber's ligament as a useful landmark for the abducens nerve in the transnasal approach

OBJECT Extended endoscopic transnasal surgeries for skull base lesions have recently been performed. Some expert surgeons have attempted to remove tumors such as chordomas, meningiomas, and pituitary adenomas in the clival region using the transnasal approach and have reported abducens nerve injury as a common complication. There have been many microsurgical anatomical studies of the abducens nerve, but none of these studies has described an anatomical landmark of the abducens nerve in the transnasal approach. In this study the authors used cadaver dissections to describe Grübers ligament as the most reliable landmark of the abducens nerve in the transnasal transclival view. METHODS The petroclival segment of the abducens nerve was dissected in the interdural space-which is also called Dorellos canal, the petroclival venous gulf, or the sphenopetroclival venous confluence-using the transnasal approach in 20 specimens obtained from 10 adult cadaveric heads. RESULTS The petroclival segment of the abducens nerve clearly crossed and attached to Grübers ligament in the interdural space, as noted in the transnasal view. The average length of the dural porus to the intersection on the abducens nerve was 5.2 ± 1.0 mm. The length of the posterior clinoid process (PCP) to the intersection on Grübers ligament was 6.4 ± 2.6 mm. The average width of Grübers ligament at the midsection was 1.6 ± 0.5 mm. CONCLUSIONS Grübers ligament is considered a useful landmark, and it is visible in most adults. Thus, surgeons can find the abducens nerve safely by visualizing inferolaterally along Grübers ligament from the PCP.

Visualization of the electric field evoked by transcranial electric stimulation during a craniotomy using the finite element method.

BACKGROUND Transcranial MEP (tMEP) monitoring is more readily performed than cortical MEP (cMEP), however, tMEP is considered as less accurate than cMEP. The craniotomy procedure and changes in CSF levels must affect current spread. These changes can impair the accuracy. The aim of this study was to investigate the influence of skull deformation and cerebrospinal fluid (CSF) decrease on tMEP monitoring during frontotemporal craniotomy. METHODS We used the finite element method to visualize the electric field in the brain, which was generated by transcranial electric stimulation, using realistic 3-dimensional head models developed from T1-weighted images. Surfaces of 5 layers of the head were separated as accurately as possible. We created 3 brain types and 5 craniotomy models. RESULTS The electric field in the brain radiates out from the cortex just below the electrodes. When the CSF layer is thick, a decrease in CSF volume and depression of CSF surface level during the craniotomy has a major impact on the electric field. When the CSF layer is thin and the distance between the skull and brain is short, the craniotomy has a larger effect on the electric field than the CSF decrease. COMPARISON WITH EXISTING METHOD So far no report in the literature the electric field during intraoperative tMEP using a 3-dimensional realistic head model. CONCLUSION Our main finding was that the intensity of the electric field in the brain is most affected by changes in the thickness and volume of the CSF layer.

Aggressive change of a carotid-cavernous fistula in a patient with Ehlers–Danlos syndrome type IV

The authors report a rare case of a carotid-cavernous fistula (CCF) secondary to Ehlers–Danlos syndrome (EDS) type IV which showed an aggressive angiographical change. A 59-year-old woman presented with headache, right pulsatile tinnitus, and diplopia on the right side. The diagnostic angiography demonstrated a right CCF. Accordingly transarterial embolization of the fistula was attempted 5 days later. The initial right internal carotid angiography showed an aneurysm on the petrous portion of the internal carotid artery (ICA) which was not recognized in the diagnostic angiography. Spontaneous reduction of the shunt flow and long dissection of the ICA were also revealed. The aneurysm was successfully occluded with coils, and only minor shunt flow was shown on the final angiogram. EDS type IV was diagnosed with a skin biopsy for a collagen abnormality. After the operation, the stenosis of the right ICA gradually progressed, although there was no recurrence of the CCF. Interventional treatment for patients with EDS can cause devastating vascular complication. We should be aware of the possibility of EDS type IV when a spontaneous CCF shows unusual angiographical change because early diagnosis of EDS type IV is crucial for determination of the optimum treatment option.

Procalcitonin as an Early Diagnostic Marker for Ventriculoperitoneal Shunt Infections

BACKGROUND Procalcitonin (PCT) has been considered a more reliable marker than others because of its specificity for bacterial infection. METHODS Case report and review of the literature. RESULTS A 50-year-old male was diagnosed with subarachnoid hemorrhage, intraventricular hemorrhage, and intracerebral hemorrhage. We performed a ruptured aneurysm clipping and left unilateral external ventricular drainage. We also performed ventriculoperitoneal (VP) shunt placement in the course; however, VP shunt infection was indicated by fever, increased C-reactive protein concentration and leukocytosis. The cerebrospinal fluid culture showed methicillin-resistant Staphylococcus epidermidis but the serum PCT concentration was quite low. CONCLUSIONS Although PCT is considered a more reliable serological marker of bacterial meningitis in several reports, the serum PCT concentration did not reflect the bacterial VP shunt infection that was present in our case.

Immunoglobulin G4-related intracranial inflammatory pseudotumours along both the oculomotor nerves

We report the first documented case of IgG4-related inflammatory pseudotumours (IPTs) along the bilateral oculomotor nerves. A man in his 60s complained of decreased vision. He exhibited bilateral optic nerve atrophy without any extraocular movement deficits. MRI revealed enhanced masses that reached from the bilateral cavernous sinus to within the bilateral orbits. The tumours extended along the lines of the bilateral oculomotor nerves. The patients serum level of IgG4 was high, 147 mg/dl. A biopsy specimen showed inflammatory cell-rich lesions against a collagenous stroma. Immunostaining revealed infiltration of CD138-positive plasma cells, which were mainly IgG and IgG4 positive. The IgG4/IgG ratio was greater than 0.4. These factors led us to a diagnosis of IgG4-related IPTs. Oral administration of prednisolone (30 mg/day) was started 3 months after the operation and continued for 6 months with gradual tapering. The tumour was significantly reduced by prednisolone.

Comprehensive genetic characterization of rosette-forming glioneuronal tumors: Independent component analysis by tissue microdissection

A rosette‐forming glioneuronal tumor (RGNT) is a rare mixed neuronal‐glial tumor characterized by biphasic architecture of glial and neurocytic components. The number of reports of genetic analyses of RGNTs is few. Additionally, the genetic background of the unique biphasic pathological characteristics of such mixed neuronal‐glial tumors remains unclear. To clarify the genetic background of RGNTs, we performed separate comprehensive genetic analyses of glial and neurocytic components of five RGNTs, by tissue microdissection. Two missense mutations in FGFR1 in both components of two cases, and one mutation in PIK3CA in both components of one case, were detected. In the latter case with PIK3CA mutation, the additional FGFR1 mutation was detected only in the glial component. Moreover, the loss of chromosome 13q in only the neurocytic component was observed in one other case. Their results suggested that RGNTs, which are tumors harboring two divergent differentiations that arose from a single clone, have a diverse genetic background. Although previous studies have suggested that RGNTs and pilocytic astrocytomas (PAs) represent the same tumor entity, their results confirm that the genetic background of RGNTs is not identical to that of PA.