Greater Superficial Petrosal Nerve Research Articles

Internal Acoustic Meatus Localization During Anterior Petrosectomy: A Novel Technique

Anterior petrosectomy demands localization of the internal auditory canal (IAC) for safe bone drilling and maximum exposure. Various techniques have been described in the literature, each with shortcomings. We propose a new technique to localize the internal acoustic meatus (IAM) using more consistent anatomical landmarks. The study was done in three phases. In phase-I (radiological), computed tomography scan heads of fifty patients (100 sides) were analyzed. Arcuate eminence-Greater Superficial Petrosal Nerve bifurcation angle(Garcia-Ibanez technique), Arcuate eminence-IAC angle(Fisch technique) and a new angle formed between foramen ovale (FO) and foramen spinosum (FS) line, and FS and IAM line (FO-FS-IAM angle) was measured. The mean, standard deviation, and variance were calculated. In phase-II (cadaveric), the FO-FS-IAM angle was measured on five (10 sides) dry skulls. In phase-III (clinical), the IAM was localized using the FO-FS-IAM angle in 13 patients. The mean angle between arcuate eminence and Greater Superficial Petrosal Nerve (Garcia-Ibanez technique) was 126.20±11.63°(range 106-156) with a variance of 135.20. The mean bifurcation angle was 63±5.81°(range 53-78). By the Fisch technique, the mean arcuate-IAM angle was 73.5±11.70°(range 51-105) with a variance of 137.18. By our technique, the mean FO-FS-IAM angle was 94.72±5.89°(range 84-108). The variance was 34.73. The mean FO-FS-IAM angle on dry skulls was identical (95±1.97°) to our radiological measurements. This angle was reproduced reliably in clinical cases for localizing the IAM during anterior petrosectomy. The FO-FS-IAM angle variance was much lower than the analogous angles measured by Garcia-Ibanez and Fisch techniques, making it a more reliable and effective tool for localizing the IAM.

Surgical Closure of the Eustachian Tube Through Middle Fossa and Transmastoid Approaches: A Pilot Cadaveric Anatomy Study.

Cerebrospinal fluid rhinorrhea after temporal bone surgery involves drainage from the Eustachian tube (ET) into the nasopharynx, causing significant patient morbidity. Variable anatomy of the ET accounts for failures of currently used ET obliteration techniques. To describe the surgical anatomy of the ET and examine possible techniques for ET closure through middle fossa (MF) and transmastoid approaches. We described the surgical anatomy of the ET from the MF and transmastoid approaches in 5 adult cadaveric heads, measuring morphometric and surgical anatomy parameters and establishing targets for definite ET obliteration. The osseous ET measured an average of 19.53 mm (±1.56 mm), with a mean diameter of 2.24 mm (±0.29 mm). The shortest distance between the greater superficial petrosal nerve and the ET junction was 6.61 mm (±0.61 mm). Shortest distances between the ET junction and the foramen spinosum and posterior border of the foramen ovale were 1.09 mm (±0.24 mm) and 2.03 mm (±0.30 mm), respectively. Closure of the cartilaginous ET may be performed by folding it in on itself, securing it by packing, suturing, or surgical clip ligation. Definite obliteration of the cartilaginous ET appears feasible and the most definite approach to eliminate egress of cerebrospinal fluid to the nasopharynx using the MF approach. This technique may be used as an adjunct to skull base procedures where ET closure is planned.

Schwannomas of the greater superficial petrosal nerve – case series, discussion of surgical techniques, and review of literature

Facial nerve schwannomas account for about 0.8% of all petrous mass lesions. Schwannomas of the greater superficial petrosal nerve (GSPN) are a rare subtype with few case-reports up to date. A retrospective analysis of clinical outcomes, radiographic findings and postoperative complication between June 2007 and December 2020 was performed. Four cases of GSPN schwannomas were reported. The presenting symptoms were facial nerve palsy and hearing loss. Imaging studies showed a subtemporal mass on the anterosuperior aspect of the petrous bone, in one case with extraordinary petrous bone and mastoid infiltration and destruction. Three cases were removed through a subtemporal extra- or intradural approach, one case via a combined pre- and retrosigmoid approach. Improvement of facial nerve palsy occurred in one case; new hearing loss was observed in another case. Xeropthalmia was a short-term temporary deficit in three cases. Short- to mid-term follow-up of the patients has not shown any tumor recurrence. GSPN schwannomas are rare entities presenting with heterogenous symptoms. Our surgical findings emphasize safe resection. Complete remission is possible by GTR. Since the small data set limits the expressiveness of statements regarding standard of care and alternative therapy options, additional data is needed.

Microsurgical Anatomy of the Petrous Part of the Temporal Bone

For a surgeon to become skilled at skull base surgery, they should have mastered the three-dimensional anatomy of the petrous part of the temporal bone. The anatomy encountered during surgery is demonstrated from the superior, posterior, and lateral aspects of the petrous bone. The landmarks of the superior aspect of the petrous bone are the third division of the trigeminal nerve, the petrous ridge, the arcuate eminence, the greater superficial petrosal nerve, and the internal carotid artery. Drilling of the rhomboid area surrounded by these structures results in the exposure of the internal auditory canal and the posterior fossa dura. A key landmark of the posterior surface of the petrous bone is the dural fovea which marks the apex of the endolymphatic sac. After a dura flap is raised in a "U" shape just beyond the fovea, the internal auditory canal is opened to resect an intacanalicular portion of a vestibular schwannoma. Mastoidectomy is then performed from the lateral aspect of the petrous bone. Drilling of the mastoid leads to the exposure of the sigmoid sinus, mastoid antrum, fallopian canal, and lateral semicircular canals. Knowledge of the precise surgical anatomy of the petrosal bone is required to perform safe and secure skull base surgery.

Excision of Greater Superficial Petrosal Nerve Schwannoma Via a Pure Endoscopic Endonasal Approach.

Greater superficial petrosal nerve (GSPN) schwannomas are an exceedingly rare nerve sheath tumor. The current literature search was conducted using Medline and Embase database by key search terms. Only 31 cases have been reported in the literature so far. Facial palsy, hearing loss, and xerophthalmia accounted for 48.4% (15), 41.9% (13), and 29% (9) of all cases, respectively. The middle cranial fossa approach was used in all previous reports. A retrospective review of 2 GSPN schwannomas patients treated by endoscopic endonasal approach (EEA) in our center was collected. Clinical records, including clinical features, pre- and postoperative images, surgery, and follow-up information, were reviewed. In all cases, clinical features including facial numbness and headache were found, with tinnitus in case 1, hearing loss, xerophthalmia in case 2. Imaging studies showed a solid mass that originated in the anterior of the petrous bone. Two patients were treated by EEA. Furthermore, no recurrence was found during the follow-up period (15-29 months) in both of the 2 cases after the operation. Complete resection of GSPN schwannomas can be achieved via the pure EEA. Endoscopic endonasal approach for radical removal of tumors is safe and feasible.

Suprameatal-transzygomatic root endoscopic approach to the geniculate ganglion: an anatomical and radiological study.

To describe the suprameatal-transzygomatic root endoscopic approach (STEA) to the geniculate ganglion (GG), the labyrinthine facial nerve (FN) and epitympanum. The feasibility and limits of the STEA, maintaining the integrity of the ossicular chain, were analysed. Ten human cadaveric ears were dissected. Step-by-step description of the technique and relevant measurements were taken during the approach. The visualization and surgical working field on the anterior and posterior medial epitympanum, GG, greater superficial petrosal nerve, the labyrinthine FN and suprageniculate area were evaluated. The range of motion through the approach and the rate of the decompression of the GG and the labyrinthine portion of the FN were assessed as well. CT-scan measurements were compared with those obtained during the dissection. A complete exploration of the epitympanum was possible in every specimen. Decompression of the GG and first portion of the FN was achieved without any trauma to the ossicular chain in nine ears. The endoscope movements were mainly limited by the distance between bony buttress-short process of the incus-tegmen. The working space, during GG and labyrinthine FN decompression, was limited by the distance between malleus head-medial epitympanic wall and malleus head-GG. Radiologic measurements were consistent with those obtained during the dissections. The STEA is a promising minimally invasive approach for decompression of the GG and FN's labyrinthine portion. The applications of this corridor include the exploration and surgery of the medial epitympanum, preserving the ossicular chain.

Objective evaluation of gustatory function after surgery for vestibular schwannoma: A pilot study

ObjectiveTo evaluate the gustatory function before and after vestibular schwannoma (VS) surgery. MethodsIn this retrospective study, we evaluated the gustatory function of 12 patients who underwent VS surgery at Tsukuba University Hospital between 2012 and 2018. Gustatory function was examined using electrogustometry before VS surgery and 3 months, 6 months and 1 year after surgery. Electrogustometry was tested at the area mapped to the chorda tympani nerve, glossopharyngeal nerve and greater superficial petrosal nerve (GSPN). Intergroup mean comparisons of the threshold were performed using a one-way analysis of variance (ANOVA) followed by the Bonferroni post-hoc test. ResultsThe gustatory function mapped to the chorda tympani nerve was significantly disturbed 6 months after the surgery as compared with the preoperative function (p = 0.033) and that the dysfunction recovered at 1 year. However, gustatory function mapped to the glossopharyngeal nerve and greater superficial petrosal nerve (GSPN) was not impaired. ConclusionThe gustatory function mapped to the chorda tympani nerve is impaired after surgery for VS. The dysfunction peaked at 6 months after surgery, and recovered within 1 year.

3D Exoscope Navigation-Guided Approach to Middle Cranial Fossa.

To test the feasibility and efficacy of a 3D exoscope navigation-guided middle cranial fossa (MCF) approach to the internal auditory canal (IAC); to potentially obviate the need to use dissection landmarks and instead, use the navigation probe as a guide to find structures and drill down to the IAC. Cadaveric dissection of six temporal bones. Computed tomography temporal bone was performed with fiducials on each specimen before the dissection to employ the navigation system. Using a 3D exoscope with navigation by Synaptive (Toronto, Ontario, Canada), the MCF approach was performed. Navigation accuracy, ability to identify critical structures, and ability to drill out the IAC successfully. All six specimens had the IAC successfully drilled out using the 3D exoscope. All dissections were performed with navigation and did not require dissecting out the greater superficial petrosal nerve and superior semicircular canal. One specimen used landmark dissection to confirm the IAC after navigation had been used to locate the IAC first. Navigation accuracy mean was 1.86 mm (range, 1.56-2.05 mm). A 3D exoscope navigation-guided MCF approach to the IAC is feasible without landmark dissection.

The Anterolateral Triangle: Implications for a Transnasal Prelacrimal Approach to the Floor of the Middle Cranial Fossa.

The anterolateral triangle enclosed by the foramen rotundum and foramen ovale constitutes part of the floor of the middle cranial fossa (MCF). To assess the feasibility of a transnasal prelacrimal approach for accessing the floor of MCF via an anterolateral triangle corridor and to determine the extent of maximal exposure while safeguarding neurovascular structures. A transnasal prelacrimal approach was performed in 5 cadaveric specimens (10 sides). Following the identification of foramen rotundum and foramen ovale, the bony ridge between 2 was drilled to expose the MCF. The temporal lobe dura was then elevated laterally, and the distances from foramen ovale to the respective borders of the area of the MCF window were measured using a surgical navigation device. The MCF was exposed with a 0° scope in all specimens also exposing significant landmarks including the middle meningeal artery, greater superficial petrosal nerve, superior petrous sinus, and arcuate eminence. Average distances from foramen ovale to the anterior, posterior, and lateral exposed borders were 22.86 ± 1.87 mm, 27.24 ± 0.94 mm, and 24.23 ± 1.61 mm, respectively. The average area of exposed MCF window was 554.12 ± 60.22 mm2. Preservation of vidian nerve, greater palatine nerve, lateral nasal wall, and nasolacrimal duct was possible in all 10 sides. It is feasible to access the floor of MCF via an endoscopic transnasal prelacrimal approach with seemingly low risk.

Stuck in the Middle: Nervus Intermedius‐Related Neuropathologic Imaging Spectrum

The nervus intermedius is a complex nerve that traverses the cerebellopontine angle and is associated with a wide range of pathologies for which imaging plays a crucial diagnostic role. Cerebellopontine angle masses or neurovascular compression may directly involve the nervus intermedius. Alternatively, pathologies that involve branches of the nervus intermedius may present with symptoms referable to the nervus intermedius, including sinonasal tumors, perineural tumor spread, or viral reactivation such as in Ramsay Hunt syndrome. Overlapping innervation with branches of the trigeminal, glossopharyngeal, and vagus nerves can confound diagnosis and/or lead to mislocalization, which may result in delayed diagnosis or inappropriate therapy. This review article provides an in-depth overview of nervus intermedius anatomy and physiology, and the wide spectrum of pathologies that can involve the nervus intermedius or its branches, with an emphasis on clinical relevance.Learning Objective: To understand the normal anatomy and physiology of the nervus intermedius as well as the clinical relevance and imaging findings of the neuropathologic spectrum of disease referable to the nervus intermedius and its branches: the greater superficial petrosal nerve, the chorda tympani, and the sensory auricular branch.

Intradural Transpetrosectomy for Petrous Apex Meningiomas.

ObjectiveThis study aimed to assess the surgical results of the intradural transpetrosectomy for petrous apex meningiomas (PAMs). In addition, we describe the methods and techniques used to expose and manage superior petrous vein and greater superficial petrosal nerve. MethodsThe authors conducted a retrospective study of 16 patients with PAMs operated by the senior author via the intradural transpetrosectomy between February 2012 to May 2017. We reviewed patient data regarding the general characteristics, surgical technique and surgery-related outcomes and adopted a combined follow-up strategy of clinic and telephone contacts to evaluate postoperative complications. ResultsSimpson grade I and II resection was performed in 10 out of 16 cases (62.5%), and grade III resection were reported in the remaining six cases (37.5%) with no resultant mortality. The mean Karnofsky Performance Status score was 85.6 preoperatively and improved to 91.9 postoperatively, with a mean follow-up period of 34.4 months (range, 6–66 months). Tumor recurrence was found in two patients and they underwent the second surgical operation. ConclusionPAMs could be completely resected by the intradural transpetrosectomy with an improved survival rate and postoperative life quality. Superior petrous vein and greater superficial petrosal nerve should be managed properly in avoidance of postoperative complications. Finally, most meningioma inside cavernous sinus or adhered to brainstem could be totally removed without postoperative complications.

Detectability of minute temporal bone structures with ultra-high resolution CT

ObjectiveComputed tomography (CT) is the imaging tool of choice in the diagnosis of temporal bone lesions. With the recent progress in imaging technology, CT with higher spatial resolution (Ultra-high resolution CT) has become available in the clinical setting. The purpose of this study is to evaluate the visibility of small temporal bone structures using ultra-high resolution CT. Material and methodsThe visibility of 27 minute temporal bone structures on ultra-high resolution CT images was evaluated. Non-helical axial scans were performed in 18 normal hearing ears without previous otologic diseases. Visibility was scored by an experienced radiologist and otologist. ResultsMinute temporal bone structures including the ossicular chain, the crus of the stapes, the greater superficial petrosal nerve, and the anterior malleolar ligament were clearly visualized on ultra-high resolution CT. The stapedius muscle tendon and the chorda tympani exiting the posterior canaliculus and coursing medial to the malleus could be visualized. ConclusionUltra-high resolution CT provides good visualization of small temporal bone structures in normal subjects.

Middle Fossa Approach for Resection of an Intracanalicular Vestibular Schwannoma.

Objective This video was aimed to demonstrate the middle fossa approach for the resection of an intracanalicular vestibular schwannoma. Design Present study is a video case report. Setting The operative video is showing a microsurgical resection. Participant The patient was a 59-year-old man who presented with worsening headache and right-side hearing loss. He was found to have a right intracanalicular vestibular schwannoma. After weighing risks and benefits, he chose surgery to remove his tumor. Since his hearing remained “serviceable,” a middle fossa approach was chosen. Main Outcome Measures Pre- and postoperative patient photographs evaluated the muscles of facial expression as a marker for facial nerve preservation. Results A right middle fossa craniotomy was performed which allowed access to the floor of the middle cranial fossa. The greater superficial petrosal nerve (GSPN) and arcuate eminence were identified. Using these two landmarks, the internal acoustic canal (IAC) was localized. After drilling the petrous bone, the IAC was unroofed. The facial nerve was identified by stimulation and visual inspection and the tumor was separated from it with microsurgical dissection. In the end, the tumor was fully resected. Both the facial and cochlear nerves were preserved. Postoperatively, the patient experienced no facial palsy and his hearing is at baseline. Conclusion With radiosurgery gaining increasing popularity, patients with intracanalicular vestibular schwannomas are frequently treated with it, or are managed with observation. The middle fossa approach is therefore becoming a “lost art,” but as demonstrated in this video, remains an effective technique for tumor removal and nerve preservation. The link to the video can be found at: https://youtu.be/MD6o3DF6jYg .

Microsurgical Resection of a Ventral Pontine Cavernoma via Supratrigeminal Zone by Anterior Transpetrosal Approach: 2-Dimensional Operative Video.

Brainstem cavernomas with recurrent bleeding and gradual neurological deterioration should be considered an indication for surgical treatment. However, surgery is challenging for cavernous hemangiomas located in the ventral part of the pons. In such cases, safe surgical access to the brainstem is limited and obtaining a good surgical field, regardless of the approach selected, is often difficult. Here, we show a 73-year-old man with a history of 3 episodes of intracranial bleeding associated with a cavernous hemangioma located in the right ventral pons. The hemangioma was removed via the supratrigeminal zone of the brainstem using an anterior transpetrosal approach (ATPA). ATPA was first described in 1985 for upper petroclival lesions by Kawase T.1 This approach requires epidural subtemporal procedures to expose the petrous apex adequately. The petrous apex must be totally resected and the dura of the temporal lobe and posterior fossa is then cut to ligate the superior petrosal sinus and tentorium. In this procedure, the most important things are to preserve the internal carotid artery (C2 segment) and greater superficial petrosal nerve (GSPN). To identify the GSPN, facial nerve integrity monitor (Medtronic Inc, Dublin, Ireland) is very useful. In the extradural bone removal, Sonopet Ultrasonic Aspirator (Stryker Ltd, Portage, Michigan) is a very excellent surgical tool for avoiding the injury of the internal carotid artery. As demonstrated by Cavalcanti DD2, ATPA is particularly useful for accessing lesions located in the upper ventral pons via the supratrigeminal zone because it provides a wide and shallow surgical field above the trigeminal nerve without requiring retraction of the cerebellum. We received written informed consent from the patient for this publication.

Key anatomical landmarks for middle fossa surgery: a surgical anatomy study.

Middle fossa surgery is challenging, and reliable surgical landmarks are essential to perform accurate and safe surgery. Although many descriptions of the middle fossa components have been published, a clinically practical description of this very complex anatomical region is lacking. Small structure arrangements in this area are often not well visualized or accurately demarcated with neuronavigation systems. The objective is to describe a "roadmap" of key surgical reference points and landmarks during middle fossa surgery to help the surgeon predict where critical structures will be located. The authors studied 40 dry skulls (80 sides) obtained from the anatomical board at their institution. Measurements of anatomical structures in the middle fossa were made with a digital caliper and a protractor, taking as reference the middle point of the external auditory canal (MEAC). The results were statistically analyzed. The petrous part of the temporal bone was found at a mean of 16 mm anterior and 24 mm posterior to the MEAC. In 87% and 99% of the sides, the foramen ovale and foramen spinosum, respectively, were encountered deep to the zygomatic root. The posterior aspect of the greater superficial petrosal nerve (GSPN) groove was a mean of 6 mm anterior and 25 mm medial to the MEAC, nearly parallel to the petrous ridge. The main axis of the IAC projected to the root of the zygoma in all cases. The internal auditory canal (IAC) porus was found 5.5 mm lateral and 4.5 mm deep to the lateral aspect of the trigeminal impression along the petrous ridge (mean measurement values). A projection from this point to the middle aspect of the root of the zygoma, being posterior to the GSPN groove, could estimate the orientation of the IAC. In middle fossa approaches, the external acoustic canal is a reliable reference before skin incision, whereas the zygomatic root becomes important after the skin incision. Deep structures can be related to these 2 anatomical structures. An easy method to predict the location of the IAC in surgery is described. Careful study of the preoperative imaging is essential to adapt this knowledge to the individual anatomy of the patient.

The transcription factor Phox2b distinguishes between oral and non-oral sensory neurons in the geniculate ganglion.

Many basic characteristics of gustatory neurons remain unknown, partly due to the absence of specific markers. Some neurons in the geniculate ganglion project to taste regions in the oral cavity, whereas others innervate the outer ear. We hypothesized that the transcription factor Phox2b would identify oral cavity-projecting neurons in the geniculate ganglion. To test this possibility, we characterized mice in which Phox2b-Cre mediated gene recombination labeled neurons with tdTomato. Nerve labeling revealed that all taste neurons projecting through the chorda tympani (27%) and greater superficial petrosal nerves (15%) expressed Phox2b during development, whereas non-oral somatosensory neurons (58%) in the geniculate ganglion did not. We found tdTomato-positive innervation within all taste buds. Most (57%) of the fungiform papillae had labeled innervation only in taste buds, whereas 43% of the fungiform papillae also had additional labeled innervation to the papilla epithelium. Chorda tympani nerve transection eliminated all labeled innervation to taste buds, but most of the additional innervation in the fungiform papillae remained. Some of these additional fibers also expressed tyrosine hydroxylase, suggesting a sympathetic origin. Consistent with this, both sympathetic and parasympathetic fibers innervating blood vessels and salivary glands contained tdTomato labeling. Phox2b-tdTomato labels nerve fascicles in the tongue of the developing embryo and demonstrates a similar stereotyped branching pattern DiI-labeling.

Intraspinosum Middle Meningeal Artery Ligation: A Simple Technique to Control Bleeding in the Middle Fossa During the Anterior Transpetrosal Approach.

Although the greater superficial petrosal nerve (GSPN) is an important landmark of the anterior transpetrosal approach (ATPA), bleeding from the interdural space around the foramen spinosum (FS), the GSPN, and the foramen ovale impedes the identification of the GSPN, during epidural dissection in the ATPA. To describe the technique of intraspinosum middle meningeal artery (MMA) ligation, which enables us to control bleeding from the interdural space. During epidural dissection, we identified the FS and partially drilled the lateral side of the FS. Next, we cut the convergence site of the neurovascular structures such as the MMA, middle meningeal vein, and the meningeal branch of the mandibular nerve with the periosteal dura within the FS and continued dural detachment epidurally to expose the petrous apex. Bleeding control around the FS and postoperative facial nerve paresis were assessed for 96 patients treated with the ATPA. Additionally, histological study was performed around the FS using Masson's trichrome stain. In all cases, in which this technique was used, bleeding from the interdural space was well controlled and no persistent facial nerve paresis was identified. In the histological study, we confirmed that the MMA, the middle meningeal vein, and the meningeal branch of the mandibular nerve converged into the FS and many venous channels existed in the interdural space around the FS and the foramen ovale. Intra-FS MMA ligation is an effective method for control of bleeding from the interdural space of the middle fossa during the ATPA.

Selective Deletion of Sodium Salt Taste during Development Leads to Expanded Terminal Fields of Gustatory Nerves in the Adult Mouse Nucleus of the Solitary Tract.

Neural activity plays a major role in the development of sensory circuits in the mammalian brain. To date, there has been no direct test of whether taste-elicited neural activity has a role in shaping central gustatory circuits. However, recently developed genetic tools now allow an assessment of how specific taste stimuli, in this case sodium salt taste, play a role in the maturation of the terminal fields in the mouse brainstem. We found that the specific deletion of sodium salt taste during development produced terminal fields in adults that were dramatically larger than in control mice, demonstrating for the first time that sodium salt taste-elicited activity is necessary for the normal maturation of gustatory inputs into the brain.

Decompression of the tympanic and labyrinthine segments of the facial nerve by middle cranial fossa approach: an anatomic study.

Peripheral facial palsy is characterized by the permanent or temporary interruption of facial muscle function. The middle cranial fossa (MCF) approach has been used to decompress the facial nerve (FN) when hearing needs to be preserved. In this work, we describe a technique for decompressing the FN through the MCF approach, which allows the direct exposure of the labyrinthine and entire tympanic segment of the FN, with preservation of inner ear function. Twenty cadavers heads were used in this study. The reference landmarks used were the middle meningeal artery, greater superficial petrosal nerve, arcuate eminence, inferior petrosal sinus and meatal plane following the petrous apex from its most anterior and medial portion. The tympanic segment of the FN presented, on average, a total length of 11 ± 0.67mm to the right and 11.5 ± 0.60mm to the left. The longitudinal lengths of the bone window in the tegmen tympani were 16.8 ± 1.67mm to the right and 16.8 ± 1.20mm to the left. The cross-sectional lengths of the bone window in the tegmen tympani were 5.5 ± 1.20mm and 5.0 ± 1.75mm to the right and left sides, respectively. The average value of the elliptical area formed by the longitudinal and transversal lengths of the bone window made in the tegmen tympani was 72.5 ± 22.5mm(2) to the right and 65.9 ± 30.3mm(2) to the left. The proposed technique can be used for the surgical decompression of the tympanic, labyrinthine and meatal segments of the FN through the MCF in addition to reducing the surgical time and the risk to patients.

Clinical Anatomy of the Lesser Petrosal Nerve

Context: The human lesser petrosal nerve (LPN) is a branch of the glossopharyngeal nerve (IX), with contributions from the facial (VII) and vagus (X) nerves. Its formation and course are highly variable and complicated. The purpose of this article was to review the literature regarding the clinical anatomy of the LPN. Evidence Acquisition: The existing literature regarding this nerve was critically reviewed, with emphasis on its clinical significance. Results: The LPN conveys the preganglionic parasympathetic fibers derived from the superior and inferior salivary nucleus. It is composed of fibers from the tympanic branch of the IX, the nervus intermedius of the VII, and the auricular branch of the X. The fibers from the nervus intermedius and the auricular branch of the X separate from the VII as the communicating branch, which then joins the tympanic branch of the IX to form the LPN. The LPN leaves the middle ear and enters the middle cranial fossa through canaliculus innominatus. It runs under the dura in its own groove. In the infratemporal fossa, it reaches the otic ganglion. The postganglionic parasympathetic fibers distribute mainly to the parotid gland. Combined damage to the greater superficial petrosal nerve (GSPN) and the LPN is associated with face hyperemia and profuse salivation from the parotid gland (following atropine administration), lacrimation (crocodile tears syndrome), and mucus nasal secretion. These phenomena are explained by the development of an ephaptic relation between the damaged nerves. An understanding of the relationships of the LPN will reduce the likelihood of confusing it with the GSPN during surgical approaches to the middle cranial fossa. Conclusions: The LPN is anatomically one of the most complicated nerves in humans. Quite thin and small, it follows a variable and complicated course to serve primarily the preganglionic part of the parasympathetic innervation of the parotid gland. Its clinical significance results mainly from its close relation to the GSPN on the floor of the middle cranial fossa.