THE ANTERIOR ENDOSCOPIC TRANSNASAL APPROACH TO PETROUS APEX LESIONS
Introduction
The petrous apex is bounded by the bony labyrinth and internal carotid artery (ICA) anteriorly, the posterior cranial fossa and Dorello’s canal (cranial nerve VI) posteriorly, the middle cranial fossa and Meckel’s cave superiorly, and the jugular bulb and inferior petrosal sinus inferiorly.1
The petrous apex is uncommonly tangled by disease, the involved pathologies are cholesterol granuloma, effusion, petrous apicitis or osteomyelitis, petrous bone cholesteatoma, mucocele, chondromas, chondrosar-comas, arachnoid cysts, vascular malformations, meningiomas and metastases which are extremely rare.2
The clinical symptoms of pathologic processes of the petrous apex are often vague but may include diplopia, hearing loss, vertigo, headaches, and facial nerve weakness. Hearing loss and vestibular abnormalities may present as the lesion enlarges and encroaches on the internal auditory canal. Petrous apicitis may present as Gradenigo’s syndrome with a sixth cranial nerve palsy.3,4
PACG is the most common benign, cystic lesion of unknown etiology. Many theories have been postulated for its formation. The most accepted one is the ‘obstruction-vacuum’ theory, which entails obstruction of the petrous apex air cell outflow tracts, with consequent development of a vacuum, leading to transudation of blood with hemoglobin into the apex cells and cholesterol liberation that stimulate a foreign-body reaction resulting in granuloma formation.5
The diagnosis of a cholesterol granuloma can often be made on the basis of its radiologic appearance, as expansile and erosive mass with well-defined margins on computerized tomography (CT). They have a high intensity on both T1 and T2-weighted magnetic resonance imaging.6
There are two plans in managing the petrous apex cholesterol granuloma: the wait-and-see policy and surgical treatment. The first option is suggested to asymptomatic patients who are diagnosed incidentally by imaging and the symptomatic patients that have poor general conditions. These patients are followed by a series of radiologic evaluations with MRI/CT. The surgical treatment is recommended to patients with symptomatic disease and patients having cranial nerve affection.7
Several approaches have been proposed in literature according to the situation and expansion of the lesion through the lateral skull base and the transnasal-transsphenoidal route.9–11 We describe our experience in the treatment of three cases with PACG via a navigation-guided transnasal route in the main university hospital of Alexandria.
Patients and methods
Ethical considerations
A retrospective study was conducted, after the approval of the Institutional Review Board (IRB) of Alexandria University Hospital, on the charts of three patients (two females and one male) with petrous apex cholesterol granuloma managed using the endoscopic anterior transsphenoidal approach at the Department of Otorhino-laryngology – Head & Neck Surgery, Alexandria Main University Hospital, from January 2006 to December 2011. An informed consent from all the patients was taken prior to surgery after they were fully informed about the details of the surgical procedure.
Diagnosis and pre-operative evaluation
Careful history and complete otorhinolaryngological examination including endoscopic nasal examination using a Karl Storz 4 mm 0° rigid nasal endoscope was performed in all cases. A thorough physical examination to assess the patient’s general condition and to exclude any other associated lesions was also done prior to surgery.
After endoscopic evaluation, radiological imaging studies to localize the defect in the form of multi-detector computed tomography (MDCT) with ultra-thin 1-mm cuts, bone and soft-tissue settings, with multi-planar reconstruction, CT carotid angiography and magnetic-resonance imaging (MRI) high resolution coronal T2-weighted sequences were done. Complete pre-operative routine laboratory investigations were also carried out on all patients.
Surgical technique
The surgical procedure was done under controlled hypotensive general anesthesia. The surgery was performed with the patient lying supine; head slightly extended and rotated 15° to the right. Intra-operatively, the GE InstaTrak™ 3500 electromagnetic navigation system (General Electric Company, GE Healthcare) was used in all cases. The head, face and anterior aspect of the thigh were sterilized and covered with sterile surgical drapes. Nasal decongestant cottonoids impregnated with Oxymetazoline 0.05% and Xylocaine were applied in both nasal cavities for ten minutes before surgery started. We prefer to perform endoscopic transnasal surgery via both nasal fossae using the ‘four-hand’ technique, in which two surgeons work simultaneously inside the nose after connecting the nasal endoscope to a high-definition video camera and a video monitor.
The surgery was commenced via the endonasal route, sphenoidotomy was performed on both sides as laterally as possible. A posterior septal window was created by removing the posterior part of the bony nasal septum to allow working through both nostrils. In some cases, partial superior turbinectomy and resection of the tail of the middle turbinate were necessary. The optic nerve, the carotid canal buttresses, planum sphenoidal and clival recess were visualized as landmarks.
The petrous apex is situated deep between the horizontal and vertical segments of the petrous ICA. The horizontal portion of the ICA runs parallel and deep to the Eustachian tube and the mandibuler nerve. The ICA turns vertically at the second genu at the level of the clival recess. The vidian artery and its course through the pterygoid canal are useful and reliable landmarks for locating the second genu of the ICA. Large expansile lesions of the petrous apex that expand medially into the sphenoid sinus were easily recognized and create a window for access between the brainstem dura and ICA at the level of the clival recess.
The overlying mucosa is stripped, and the bone overlying the cyst is thinned with a three-mm coarse diamond burr. Drilling started along a vertical plane to avoid injury to the ICA, the bone was thinned out and the rest was removed with a one-mm angled Kerrison rongeur, and the lesion was completely exposed. The cyst wall was opened with a sickle knife, the chocolate content erupting under pressure was evacuated with suctions, curettes, and repeated irrigation. The orifice created was then enlarged as much as possible to establish the necessary aeration and avoid recurrence. There was no need to use any stents in the cyst cavity.
All cases were given an intravenous antibiotic chemoprophylaxis (third-generation cephalosporin) that started on the day of surgery and continued for seven days post-operatively. Patients and parents were given strict instructions to avoid straining or nose blowing for a minimum period of one month and were given stool softeners during this period. The patients were monitored for any CSF leak, signs of meningitis, hemorrhage, neurologic complications. Nasal packing was removed on the second or third post-operative day, and the patient was discharged. The patients were followed up weekly for the first month and then every two weeks for another month. Complete healing usually took place after four to eight weeks. Radiologic follow up was performed at three, six, and 12 months and after that yearly.
Cholesterol granulomas are benign, cystic lesions filled with brownish-yellow fluid, lipids and cholesterol crystals. The term granuloma indicates a foreign body, a giant cell inflammatory reaction to blood degradation products. It can be found inside air cells of temporal bone, that is, middle ear, mastoid, and less commonly in PA air cells.12
These lesions may remain clinically silent for a long time and become symptomatic if adjacent neurovas-cular structures become involved. A CT scan is essential to assess bone erosion, and MRI scans should be performed, as it shows high-signal intensity on both T1- and T2-weighted images. Such imaging is therefore essential to assess the feasibility of different surgical approaches as well as to distinguish the lesion from other possible PA pathologies.13,14
In literature, several approaches have been proposed by neurosurgeons and neurotologists through the lateral skull base and transnasal-transsphenoidal route.15,16 However, the choice of surgical approach is based on pre-operative hearing status, location, extension of the lesion, relationship with neurovascular structures, and anatomical variations. Regarding treatment for PACGs; different surgical strategies are used to perform marsupialization of the cyst cavity and establish pneumatization using preformed petrous apex air cell tracts. However, rates of revision surgery for PACG vary from 14% to 16%.5,8,10
The most common approaches to use in petrous apex in a hearing ear include transcanal infracochlear, infralabyrinthine, suboccipital, and middle cranial fossa approaches. These procedures require advanced technological skill and can lead to complications associated with intracranial procedures, such as sensorineural hearing loss, vestibular injury, facial nerve damage, cerebrospinal fluid leak, or meningitis.17–19
A well-pneumatized sphenoid sinus facilitates identification of important landmarks, especially the course of the internal carotid artery in order to avoid inadvertent injury and complete removal of disease. When there is a medial expansion of the cholesterol granuloma into the sphenoid sinus, the surgery is straightforward with minimal technical difficulty and risk. Also, because of the recent advances in minimally invasive surgery, powered instrumentation and intra-operative image-guidance systems, skull-base endoscopy has led to new treatment options for petrous apex lesions and precise removal of the lesion with minimal surgical risk.20–22
Theoretically, stenosis of the opening created with an endoscopic approach can occur. Many surgeons claimed that the use of a Silastic stent to maintain the patency of the drainage tract may helps prevent recurrence of the granuloma.6–10 We did not use any stenting in our group of cases and no recurrence rate was obtained during a follow-up period of six years. The placement of a stent may be of help when used in lateral approaches away from any possible source of infection, but when using the anterior endonasal approach, the risk of infection and a reaction to the stent as a foreign body is still high. Another point to consider is that the endoscopic approach allows for easy post-operative follow up of the surgical site.
Possible complications of the endoscopic surgery include injury of the neurovascular structure, especially ICA, and cerebrospinal fluid leak. But these can be avoided with adequate surgical technique, knowledge of anatomic relationships, recognition of anatomic variations, and the use of intra-operative navigation. However, a narrow window between the brainstem and ICA has been considered a relative contra-indication for the transsphenoidal approach.23,24
Conclusion
This transsphenoidal endoscopic surgical procedure is an appropriate approach for the drainage of cholesterol granulomas involving the petrous apex. It avoids craniotomy and shortens recovery with minimal post-operative symptoms and decreased hospitalization time.
References
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Address for correspondence: Mohamed M.K. Badr-El-Dine, MD, Professor of Otolaryngology, Faculty of Medicine, University of Alexandria, Egypt. mbeldine@yahoo.com
Cholesteatoma and Ear Surgery – An Update, pp. 329–332
Edited by Haruo Takahashi
2013 © Kugler Publications, Amsterdam, The Netherlands