Suboccipital retrosigmoid surgical approach for internal auditory canal--a morphometric anatomical study on dry human temporal bones

Suboccipital retrosigmoid craniotomy with removal of posterior wall of internal auditory canal is preferred by many surgeons operating on acoustic neuromas, as it is a simple and safe approach. To study the topographic landmarks of the posterior surface of the temporal bone. We studied the surgical anatomy of 224 dry adult human temporal bones, measured the various distances on posterior wall of petrous bone relevant for suboccipital surgical approach to internal auditory canal. The internal auditory canal (IAC) lies within 32-44?mm from posterior wall of sigmoid sulcus and within 3-8?mm from the superior border of petrous bone. The point corresponding to highest point of jugular bulb was found between 4 and 9?mm away from the inferior border of IAC. The maximum distance found between bony orifice of vestibular aqueduct and IAC was 14?mm and the minimum distance was 6?mm.The vertical diameter of IAC ranged between 3 and 7?mm. These parameters may help the surgeons for better exposure of internal auditory canal and for avoiding damage to vital surrounding structures.     

A temporal bone study of posterior semicircular canal resection for exposure of the internal auditory canal (PSCC resection)

Partial resection of the labyrinth is becoming accepted as a means of improving access to the internal auditory canal and central skull base neoplasms. In this investigation, an infralabyrinthine approach was performed on 20 temporal bones. The dissection was extended by transection of the endolymphatic duct, then excision of the posterior semicircular canal. The maximal lateral exposure of the internal auditory canal (IAC) was measured after each manoeuvre. Resection of the posterior semicircular canal increased lateral exposure in 7/20 specimens to an average 61% of the length of the IAC. Posterior canal resection improved superior exposure and increased the circumference of exposure in all specimens.     

Surgical exposure of the fundus of the internal auditory canal: Anatomic limits of the middle fossa versus the retrosigmoid transcanal approach

Objective: To define the anatomic limitations and advantages of the middle cranial fossa and the retrosigmoid transcanal approaches in the exposure of the fundus of the internal auditory canal (IAC). Study Design: A series of 15 cadaver temporal bone specimens were dissected and the measurements of the lateral recess of the IAC were made with a millimeter rule and rounded to the nearest quarter millimeter. Methods: Retrospective case review, surgical observation, review, and measurements recorded from magnetic resonance scans. Surgical observations and measurements recorded from cadaver specimens. Results: These results were compared with historical studies of the retrosigmoid transcanal approach. The results utilizing a combination of these approaches to remove acoustic neuromas at a tertiary referral center during the preceding 11 years are also presented. Previous studies have shown that for the retrosigmoid transcanal approach, it is impossible to expose 3 to 4 mm of the lateral recess of the IAC without violating the vestibule and/or the endolymphatic duct. This has led some authors to advocate the middle cranial fossa approach to the IAC when hearing preservation is a consideration. The current study shows that the falciform crest obscures the inferior half of the fundus. This creates a pocket that cannot be visualized, which on average is 1.82 × 2.33 mm. Conclusion: The fundus of the IAC cannot be completely exposed without violating the labyrinth through either the posterior fossa or middle fossa approach. The clinical implications of these studies are unknown at this time. Low recurrence rates are achieved with both approaches. The anatomic limitations of both approaches must still be considered when planning or performing these approaches, to minimize the risk of recurrence.     

Partial labyrinthectomy approach for brainstem vascular lesions.

Conventional wisdom has typically dictated that the bony labyrinth is an inviolate structure. This notion, however, was successfully challenged following the introduction of the partial labyrinthectomy approach, which was primarily used for the surgical management of cerebellopontine and petrous apex meningiomas. In this article, we discuss an extension of the technique of partial labyrinthectomy in a series of patients that has been used for the treatment of brainstem vascular lesions. We believe that this technique provides superior exposure to the brain stem when compared with conventional retrosigmoid and retrolabyrinthine approaches while reducing the inherent morbidity seen in transotic or petrosectomy approaches.     

部分迷路切除的应用解剖学观察及意义

目的探讨经部分迷路切除手术到达内听道和桥小脑角区的应用解剖及临床意义。方法对25个成人湿尸头经乳突分别切除上半规管和后半规管,再向深部削除岩部骨质,观察对岩尖、内听道及桥小脑角区暴露情况。结果选择性切除上半规管或／和后半规管的迷路部分切除术可到达岩尖和暴露部分内听道,不损及面神经和蜗神经,桥小脑角区显露改善。结论部分迷路切除人路可用于某些岩尖、桥小脑角或内听道占位病变的治疗。     

The transmastoid partial labyrinthectomy approach to medial skull base lesions

INTRODUCTION: It has long been thought that surgical disruption of the membranous labyrinth invariably results in sensorineural hearing loss and balance dysfunction. Recent evidence suggests that the inner ear can withstand such manipulation without loss of function. The technique of transmastoid partial labyrinthectomy has recently been described as a means of providing access to lesions of the medial skull base by removing part of the labyrinth and at the same time attempting to preserve hearing and vestibular function of the lateral semicircular canal (LSCC) and otolithic organs. PROCEDURE: An extended cortical mastoidectomy is performed and the posterior and middle cranial fossa dura are exposed widely. The posterior and superior semicircular canals are occluded at their ampullated ends and at the crus commune, and then resected. The LSCC and vestibule are left undisturbed. The petrous apex is removed and the medial end of the internal auditory canal is exposed. Posterior cranial fossa dural flaps are raised allowing access to the brainstem, petro-clival area and cerebellopontine angle. Temporal and suboccipital craniotomies can be performed, as required. RESULTS: Four patients underwent this procedure by a joint Otolaryngological-Neurosurgical team for access to the following lesions: three intra-axial pontine cavernomas and a basilar artery aneurysm. The preliminary hearing and balance results are discussed. CONCLUSIONS: The partial labyrinthectomy approach provides improved access to certain lesions of the medial skull base and requires less brain retraction compared with the retrolabyrinthine approach. It also has the potential to preserve serviceable hearing.     

内镜下迷路后入路小脑脑桥角及内耳门区手术的实验解剖

目的 测量比较内耳门后唇至乙状窦前、后缘的距离;迷路后间隙与乙状窦距外耳道后壁距离的相关性,为经迷路后入路内镜下小脑脑桥角区及内耳道微创手术提供解剖学依据.方法 10％甲醛固定的成人头颅标本（正常完整颅底）15例（30侧）,性别不限,乳突轮廓化,迷路骨骼化,乙状窦全程解剖.①测量内耳门后唇至乙状窦前、后缘的距离;②测量...     

Using greater superficial petrosal nerve and geniculate ganglion as the only two landmarks for identifying internal auditory canal in middle fossa approach

The middle fossa approach is a surgical technique indicated for acoustic neuroma with advantages of complete tumor removal and hearing preservation. Various methods have been developed for identifying internal auditory canal (IAC). Here, we describe a new method, which uses greater superficial petrosal nerve (GSPN) and geniculate ganglion (GG) as the only two landmarks to identify IAC. In this study, the surgical anatomy and relations between GSPN, GG, petrous ridge, and IAC were measured on 20 temporal bone specimens and 40 HRCT scans of normal inner ear structures. The temporal bone study showed that the GSPN is nearly parallel to the petrous ridge, with an average angle of about 6 degrees. The line perpendicular to the GSPN from the tip of the GG to the petrous ridge reaches at the porus acousticus, with an average distance of 12.95 mm. The temporal bone HRCT scan study revealed that the length from the tip of the GG to the midpoint of the IAC portion on the line perpendicular to the petrous ridge is about 9.9 mm. We applied this method on 20 temporal bones by drilling the point away from the tip of the GG about 9.9 mm on a line angled with the GSPN about 96 degrees. All IACs were safely identified without damaging the cochlea, the labyrinthine portion of the facial nerve, or the vestibule. In conclusion, the GSPN and GG can be the only two landmarks for safely identifying the IAC without injury to the inner ear structures in the middle fossa approach.     

A comparison of retrosigmoid IAC, retrolabyrinthine, and middle fossa vestibular neurectomy for treatment of vertigo

A new procedure, the retrosigmoid internal auditory canal (IAC) vestibular neurectomy has been developed and presented. It involves a 3-cm retrosigmoid craniotomy removing the posterior wall of the IAC to the singular canal, with transection of the superior vestibular nerve and posterior ampullary nerve. This produces a complete denervation of the vestibular labyrinth and preserves the patient's hearing. All ten patients with Meniere's disease had their vertigo cured. Hearing was preserved to within 11 dB of the preoperative pure tone average in 9 of 10 cases. There were no serious complications, no cases of facial paralysis, and no cases of total hearing loss. These results compare favorably with the MFVN and the RVN. The retrosigmoid IAC vestibular neurectomy is an important improvement in the evolution of vestibular neurectomy for the treatment of vertigo.     

Enhancing hearing preservation in endoscopic-assisted excision of acoustic neuroma via the retrosigmoid approach

Surgeons using the operating microscope are able to make use of numerous landmarks described for the lateral limits of dissection to preserve hearing in acoustic neuroma surgery via the retrosigmoid approach. Similar landmarks for hearing preservation described specifically for the endoscopic-assisted technique, are lacking. By analysing computed tomography (CT) scans of temporal bones, it was observed that to reach within 3 mm of the lateral end of the internal auditory meatus (IAM) via a 3 cm retrosigmoid craniotomy, drilling should be up to about 3 mm medial to the opening of the vestibular aqueduct. It was hypothesized that in surgery, by keeping 3 mm medial to the opening of the vestibular aqueduct, the integrity of inner ear structures would be preserved. This hypothesis was tested in 30 temporal bones and was found to be true. In addition, the lateral end of the IAM up to the transverse crest could be viewed by the 30-degree rigid angled endoscope. This landmark could, therefore, be utilized in the endoscopic-assisted technique to predict the optimal amount of bone to be removed at a stage before the internal auditory meatal dura is opened when the intact dura affords added protection to the meatal contents during drilling. Well designed dural flaps on the posterior petrous bone could be created by making a longitudinal incision not more than 7 mm from the superior border of petrous bone and a transverse incision at least 17 mm from sigmoid. These flaps minimize injury to the endolymphatic sac and protect the cochlear nerve and vasculature that when damaged, may result in hearing loss.     

Anatomical study of presigmoid-retrolabyrinthine approach based on temporal bone high-resolution CT

Background: The surgical approach of acoustic neuroma includes translabyrinthine, transcranial fossa, suboccipital retrosigmoid sinus, and presigmoid retrolabyrinthine approach.

Aims/Objective: To provide the anatomical basis for the surgical selection of presigmoid retrolabyrinthine approach by measuring the anatomical parameters of retrolabyrinthine space of the petrous bone by high-resolution CT.

Material and methods: A retrospective study of 208 high-resolution CT (HRCT) images of 104 patients examined in our hospital were analyzed retrospectively. Forty-nine males and 55 females were included in this study. Lines were drawn on the HRCT to measure the morphological data for pre-operational assessment.

Result: Morphological data were retracted from HRCT, for preoperational assessment.

Conclusion and significance: Using the standard postprocessing images of temporal bone HRCT can predict the size of the retrolabyrinthine space and the degree of exposure to the inner auditory canal, providing an important anatomical index for the choice of presigmoid retrolabyrinthine approach.     

How to perform microscopic/endoscopic resection of large petrous apex lesions

The endoscope and microscope can be used conjointly in certain sites, such as middle ear cholesteatoma or for resection of cerebellopontine angle tumours. Petrous apex tumours are classically accessed via a lateral otological approach, or, for the most anterior tumours, via an endonasal endoscopic approach. Surgical access via a lateral incision is limited inferiorly by the superior bulb of the internal jugular vein, medially by the labyrinth, facial nerve and internal auditory canal, superiorly by the dura mater, and laterally by the internal carotid artery. Via an anterior endonasal approach, the corridor formed by the internal carotid artery and the paraclival dura limits access to the posterior part of the petrous apex, restricting this approach to certain cholesterol granulomas or small cholesteatomas. None of these approaches, on its own, is sufficient in the case of an extensive petrous apex lesion. The objective of this technical note is to describe the combined microscopic/endoscopic approach comprising sequential use of the microscope and the endoscope via a lateral approach for the management of large petrous apex lesions.     

Meningioma of the internal auditory canal

The great majority of tumors that arise in the internal auditory canal are schwannomas of the eighth cranial nerve (acoustic neuromas). Meningiomas constitute the second largest group of posterior fossa tumors. Meningiomas arise from arachnoid villae, the apparatus responsible for cerebrospinal fluid absorption, in proximity to a major vein or dural sinus in most cases. Arachnoid villae are also present along neural foramena at the base of the skull. They have been observed histologically in the internal auditory canal (IAC), and are the probable site of origin of meningiomas in this location. Larger cerebellopontine angle meningiomas occasionally possess a significant intracanalicular component; however, these lesions usually originate from the meningeal lining of the posterior petrous face adjacent to the sigmoid, superior petrosal, or inferior petrosal sinuses and prolapse into the IAC. Two meningiomas have recently been observed that extensively involved the IAC, one of which arose from the lining of the IAC. The clinical manifestations of these meningiomas mimicked those of acoustic neuromas. Preoperative radiographic studies, including magnetic resonance imaging, were unable to differentiate these from acoustic neuromas. Meningiomas have a higher rate of recurrence than acoustic neuromas and should be excised with surrounding dura and several millimeters of subjacent bone. Meningiomas that extensively involve the IAC have a tendency to invade the inner ear and the deeper portions of the temporal bone. In meningiomas that involve the lateral portion of the IAC, consideration should be given to exenteration of the cochlea and semicircular canals.     

Cochlear schwannoma removed through the external auditory canal by a transcanal exclusive endoscopic technique

Surgical approaches to the inner ear and internal auditory canal (IAC) are widely known and extensively recorded. The most popular can be classified as retrosigmoid, transmastoid‐translabyrinthine, and middle cranial fossa approaches. For the first time, an exclusive endoscopic approach to the IAC is described here, used to remove a cochlear schwannoma involving both the IAC and labyrinth. The operation provided a direct transcochlear intradural approach from lateral to medial and from external to internal auditory canal, without any external incision. The pathology was totally removed, and the postoperative outcome of the facial nerve was grade II (House‐Brackmann grading system) at 3‐month follow‐up. Laryngoscope, 123:2862–2867, 2013     

Exclusive endoscopic transcanal approach to lateral skull base lesions: Institutional experience of 3 cases

Introduction:Majority of petrous bone and lateral skull base pathologies are benign in nature.The complex anatomy usually warrants an extensive approach with associated morbidity.Case summary:Two cases of petrous bone cholesteatoma(1 congenital cholesteatoma with facial palsy and 1 acquired cholesteatoma)and a case of glomus tympanicum were treated with exclusive endoscopic transcanal approach.The cases of petrous cholesteatoma were addressed with trans-promontorial and infra-cochlear approaches.The mean operative time was approximately 140 min.No CSF otorrhoea was noticed in the post-operative period.The average period of hospital stay was 3.7 days.Conclusion:In the subset of cases with limited benign disease an endoscopic trans-canal approach is a better alternative to an external approach.It decreases operative time,blood loss,chance of meningitis,morbidity and hospital stay.The lack of depth perception is a major hurdle which can be come over by experience in endoscopic middle ear surgery.This approach can create direct access to cochlea/petrous apex/internal auditory canal(IAC)/Supra-geniculate ganglion region.     

Vidian canal: analysis and relationship to the internal carotid artery

OBJECTIVES: The purpose of this study is to describe the anatomy and relationships of the vidian canal to known endonasal and skull base landmarks. This will allow the endoscopic skull base surgeon to safely approach the anterior genu of the petrous carotid artery during expanded endonasal approaches to the skull base. STUDY DESIGN: The study is a prospective cohort study. METHODS: Axial, coronal, and sagittal computed tomography scans of the paranasal sinuses and skull base of 44 patients were examined. Individuals with known skull base pathology were excluded. Measurements included the length of the vidian canal, the relationship of the vidian canal to the anterior genu of the petrous carotid artery, and the type of pneumatization of the sphenoid sinus as it pertains to foramen rotundum and the vidian canal. In addition, we will focus on the relationship of the vidian canal to the sphenopalatine foramen and base of the medial pterygoid plate. RESULTS: The degree of pneumatization of the sphenoid sinus is highly variable. The mean length of the vidian canal is 18 mm (10-23 mm). The vidian canal is found entirely within bone in 27% to 30% of scans reviewed. The anterior genu of the petrous internal carotid artery is found superior-medial to the vidian canal in 44 of 44 of the CT scans reviewed. The vidian canal runs medial to lateral in 93% to 98% of patients studied. CONCLUSIONS: As a result of this study the endoscopic skull base surgeon has a number of anatomical landmarks and measurements that may be helpful in safely localizing the anterior genu of the petrous internal carotid artery during expanded endonasal approaches to the skull base.     

Surgical anatomy of the petrous canal and posterior cranial fossa in relation to hearing preservation in surgery of acoustic neuroma

The suboccipital (retrosigmoid) and the middle fossa routes are recommended for preservation of hearing in surgery for acoustic neuroma. We carried out a comparative study of the critical distances and bony landmarks on 520 petrous bones. Unlike the transtemporal route, the suboccipital approach offers no landmarks for identification of the common crus, the vestibule or the facial nerve; the lateral portion of the internal auditory canal is not always seen. The fundus can be seen in only 50% of bones without opening the labyrinth.     

Surgical anatomy of the internal auditory canal. A temporal bone dissection study

The suboccipital fossa approach to the fundus of the internal auditory canal (IAC) at acoustic neurinoma surgery was investigated in 32 temporal bones. A microdissection was done under the operating microscope in a specially constructed holder so that the surgeon's exposure and angles of view through the craniotomy were mimicked. It was possible to obtain an unobstructed view of the transverse crest and the vestibular nerves in all specimens without the bony labyrinth being opened in the process. A prerequisite was that, as the posterior wall of the IAC was removed, drilling did not extend lateral to a line running through the midpoint of the craniotomy to the transverse crest. The distances of major structures from the posterior and superior pyramid surface were measured, using a special impression technique that made it possible to measure the thickness of the bony layer removed.     

Invasive cerebrospinal fluid cysts and cephaloceles of the petrous apex.

OBJECTIVE: To describe the presentation, diagnostic evaluation, and surgical management of petrous apex cerebrospinal fluid (CSF) cysts and cephaloceles. STUDY DESIGN: Retrospective case review. SETTING: Tertiary referral center. PATIENTS: Six patients with symptomatic CSF cysts or cephaloceles. INTERVENTION(S): All patients underwent operative intervention. MAIN OUTCOME MEASURE(S): Presentation, imaging characteristics, operative findings, surgical approach, resolution of symptoms, and complications. RESULTS: Six patients presented with various neurotologic symptoms including vertigo, otalgia, diplopia, meningitis, hearing loss, and retroorbital headaches. Four lesions were centered within the anterior petrous apex and were classified as a cephalocele originating from Meckel's cave. The remaining two lesions were arachnoid cysts that involved the posterior petrous apex. Cysts and cephaloceles both demonstrated bone erosion on computed tomography and were hyperintense on T2-weighted magnetic resonance imaging and isointense or hypointense on T1-weighted magnetic resonance imaging. A variety of surgical approaches was used to treat these lesions. Preoperative symptoms were improved in five of six cases. One patient developed a postoperative CSF leak that resolved with conservative measures. CONCLUSION: Petrous apex CSF cysts and cephaloceles may present with a variety of neurotologic symptoms. Imaging often helps narrow the differential diagnosis, but these lesions can still be confused with other erosive skull base lesions such as cholesterol granulomas, epidermoids, or tumors. Optimal treatment of symptomatic posterior petrous apex CSF cysts is marsupialization via a posterior fossa approach (i.e., retrosigmoid or retrolabyrinthine). A middle fossa approach with obliteration of the anterior petrous apex may be used to treat symptomatic CSF cephaloceles arising from Meckel's cave.     

内镜下迷路后入路小脑桥脑角区解剖学研究

目的探讨内镜下迷路后入路小脑桥脑角区解剖标志与定位方法。方法在10例（20侧）成人头颅标本上模拟内镜下迷路后入路手术,观察内听道与桥脑小脑角区各组颅神经之间的关系,并测量相关数据。结果以外半规管水平上的后半规管后缘为标志点：后半规管后缘距内耳门后缘（15.89±1.61）mm,距三叉神经下缘（27.43±3.25）mm,距舌咽神经上缘（19.39±2.57）mm;后半规管后缘-内耳门后缘连线与后半规管后缘-舌咽神经上缘连线的夹角为16.78°±2.06°,后半规管后缘-内耳门后缘连线与后半规管后缘-三叉神经下缘连线的夹角为16.25°±2.88°。结论内镜下迷路后入路小脑桥脑角区手术具有损伤小,暴露清晰,多角度观察等优点,对于显微外科手术是一种有效的辅助手段。