Acta Neurochir (2011) 153:1161–1167 DOI 10.1007/s00701-011-1010-9
HOW I DO IT
How I do it: epidural anterior petrosectomy Pierre-Hugues Roche & Vincent F. Lubrano & Rémy Noudel
Received: 30 March 2011 / Accepted: 31 March 2011 / Published online: 27 April 2011 # Springer-Verlag 2011
Abstract Background Among the potential approaches to access the petroclival area, epidural anterior petrosectomy (EAP) appears to be the most direct and conservative transpetrous route. In this article, we aim to detail the relevant surgical steps necessary to perform EAP in a reproducible and safe manner. Method The temporo-pterional bone flap is tailored to access the floor of the middle fossa and expose the foramen ovale and foramen spinosum. Elevation of the dura covering the upper surface of the petrous apex is conducted medially toward the level of the petrous ridge. Identification of the landmarks of the rhomboid fossa delineates the limits of the drilling zone (necessary for removal of the petrous apex)—beneath Meckel’s cave and just anterior to the anterior margin of the internal auditory meatus. The tentorium is divided at its free edge and is followed by opening of the posterior fossa dura. Conclusion Epidural anterior petrosectomy is a conservative trans-petrous approach that offers an excellent direct surgical corridor for exposure of disease processes involving Meckel’s cave, the petroclival area and the ventrolateral pons.
Electronic supplementary material The online version of this article (doi:10.1007/s00701-011-1010-9) contains supplementary material, which is available to authorized users. P.-H. Roche (*) : R. Noudel Service de Neurochirurgie, CHU Marseille Nord, APHM, Université de la Méditerrannée, Chemin des Bourelly, 13915 Marseille Cedex 20, France e-mail:
[email protected] V. F. Lubrano Service de Neurochirurgie, CHU Toulouse, Université de Toulouse-Paul Sabatier, Toulouse, France
Keywords Petrous bone . Meningioma . Skull base neoplasms . Trigeminal ganglion . Pons . Clivus Abbreviations CSF Cerebrospinal fluid EAP epidural anterior petrosectomy GG geniculate ganglion GSPN great superficial petrosal nerve IPS inferior petrosal sinus IAC internal auditory canal SOF superior orbital fissure SPS superior petrosal sinus
Introduction In the last 4 decades, the field of skull base surgery has been enriched by the development of a large variety of trans-petrous approaches. Because of their sophistication and an increased risk of injury to intra-petrous neurootologic structures, these approaches require of the surgeon an excellent background in anatomy combined with advanced knowledge of the petrous bone anatomy. Specific team education and training are mandatory before undertaking most transpetrous approaches. Furthermore, collaboration with an expert neuro-otologist is essential for most of these trans-petrous approaches. It is our experience that the epidural anterior petrosectomy (EAP) offers the advantage of a suitable exposure of the petroclival region and related areas [7, 8] without the prerequisite of mandatory neuro-otological input. As a skull base approach, EAP offers direct access to the posterior fossa through multiple corridors (from the middle to the posterior fossa). This extends to the ventral brain stem and requires no traction of
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the cerebellum with no interposition of critical neural structures. Hence, it facilitates the management of disease (e.g., tumor) from the site of origin. Classical indications for EAP arising from these principles are summarized in Table 1, and the prerequisites necessary to perform the procedure are shown in Table 2. In this technical study we describe a stepwise approach to EAP and discuss its fields of applications along with its limitations.
Operative technique Positioning of the patient and general settings The patient is positioned supine with the head rotated approximately 80° toward the opposite side (maintained in a 3-pin Mayfield head clamp) (Fig. 1A). Care should be taken to avoid contralateral jugular vein compression. If the head is rotated at 90°, it should be borne in mind that the external auditory canal (EAC) projects at the vertical line of the internal auditory canal (IAC). The surgeon should be positioned in front of the vertex. Another field is prepared and draped to harvest abdominal fat for closure. Antibiotics are administered in the operating room. Consideration may be given to steroid administration preprocedure. Neurophysiological monitoring includes monitoring of the facial (VII) and abducens (VI) nerves. Auditory-evoked brain stem responses should be monitored when hearingpreservation surgery is being attempted. Perioperative CSF lumbar drainage and neuronavigation are optional. Communication with the anaesthetist is important throughout the procedure.
Table 1 Classical indications for EAP
Table 2 Necessary prerequisites for performing the procedure Prerequisites for epidural anterior petrosectomy Knowledge Excellent background in anatomy [2, 9] Surgical literature [5, 7, 8] Skull base education program Technical skills Training for skull base approaches in the anatomy laboratory Clinical reasoning Relevant complaints and symptoms suggesting cranial nerves and/or brain stem involvement Radiological reasoning (CT and MR) Location, insertion, main extension of the tumor Main diagnosis hypothesis (tumor texture, adherences, etc.) Checking of nerves and vessels shift Individual variations of pneumatisation of the petrous bone air cells and intrapetrous neuro-otologic structures(CT) Venous drainage pattern of the brain (MR angiography) Patient information The surgeon should have explained clearly to the patient the principles of this type of surgery, expected results and individual risks This information should be based on existing literature as well as the surgeon’s own experience Patient safety Surgical tools and material checking Operative checklist (WHO)
Soft tissue dissection The skin incision is carried out following a reverse question mark (Fig. 1B). This starts 1 cm anterior to the tragus at the
Indications for epidural anterior petrosectomy Indications • Intrapetrous diseases, which can develop and continue to be epidural (even when they reach very large sizes) ○ Anterior petrosal cysts (epidermoid or cholesterine) ○ Chordomas and chondrosarcomas •Petroclival and Meckel’s cave tumors ○ Meningiomas ○ Trigeminal schwannomas Intracisternal dermoid and epidermoid cysts Potential indications Lateral and ventral pontine intra-axial diseases (cavernous malformations and tumors)
Contra-indications Considering the limitations of the exposure offered by the approach, the following targets are not suitable: • Tumor originating medial to the groove of the IPS (pure clival tumors) • Tumors originating lower than and behind the IAC • Large tumor extension to the lower cranial nerves • Midbrain and medulla oblongata diseases
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Fig. 1 Illustrative operative case of an epidural anterior petrosectomy on the right side. A Head is rotated toward the opposite side, and the reverse question mark skin incision starts from the pretragal area. B The temporopterional bone flap is achieved with an inferior margin (burr hole) just above the root of zygoma. C After elevation of the dura from the middle fossa, the landmarks of the rhomboid fossa are
indicated by the dotted line. The black line corresponds to the GSPN, the red one to the arcuate eminencia, the blue one to the petrous ridge and SPS, and the green one to the posterior border of V3 and Meckel’s cave. D Drilling is carried out with a diamond drill at the anterior part of the rhomboid fossa under V3 and Meckel's cave, medial to the carotid artery, lateral to the petrous ridge
level of the zygomatic arch and runs above the external ear, ending in the frontal region. This incision can be modified following the extent of the drilling that is required. The fronto-temporal pericranial flap is dissected separately in two layers, and the temporal muscle is detached with its deep aponeurosis and reflected anteroinferiorly.
Superficial drilling
Bony step One burr hole is made above the root of zygoma and is usually sufficient to allow a safe detachment of the dura from the inner table of the bone flap (Fig. 1B). A temporopterional craniotomy is undertaken reaching the floor of the middle fossa downward. The lesser sphenoid wing is drilled with a 5-mm diamond drill. The contours of the bone flap stay inside a cuff of temporal muscle that has been left on the calvaria for better reinsertion of the muscle at the end of surgery. The temporo-pterional bone is preserved in sterile saline for replacement at the end of the operation.
The drilling of the pterion is conducted by flattening the lateral wall of the orbit in order to identify the external margin of the superior orbital fissure (SOF). Elevation of the dura from the anterior part of the floor of the middle fossa is conducted laterally to medially and posteriorly. It is now possible to identify the external margins of the foramen rotundum, foramen ovale and foramen spinosum successively. The 180° external borders of these foramina are skeletonized. Coagulating and dividing the middle meningeal artery a few millimeters above the spinosum is necessary. The SOF, the maxillary (V2) and the mandibular (V3) branches of the trigeminal nerve are now identified. The next step is to peel and elevate the dura propria that covers Meckel’s cave under high magnification. This step is required to translocate V3 anteriorly and then to expose the true petrous apex that lies under Meckel’s cave [4]. It is not unusual to experience
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some venous bleeding from the posterior margin of the foramen ovale. This is due to bridging veins that connect the lateral cavernous sinus with the pterygoid venous plexus in the infratemporal fossa. Such bleeding is easily controlled by gentle packing with small pieces of oxidized cellulose. Upon elevating the dura behind V3, the great superficial petrosal nerve (GSPN) is identified. Being detached from the dura using a sharp dissector preserves the nerve. The GSPN running over the horizontal intra-petrous carotid artery leads to the geniculate ganglion (GG). Its exact location is easily checked using a neurostimulator (0.3 to 0.5 mA). It is noteworthy that the bony roof of the horizontal intrapetrous carotid is frequently dehiscent, thereby requiring the use of a diamond drill while flattening the middle fossa until the carotid landmarks have been clearly identified. Deep drilling: the anterior petrosectomy While proceeding to elevate the dura, the surgeon reaches the petrous ridge medially and behind V3 (Fig. 1C). The limits of the rhomboid fossa are now delineated: the petrous ridge medially, posterior border of V3 anteriorly, GSPN laterally and arcuate eminence posteriorly [1]. The rhomboid fossa can be divided into two areas by a vertical straight line drawn from the GG toward the petrous ridge. This line represents the external landmark of the roof of the internal auditory canal. Anterior to the line is the pre-meatal area, which corresponds to the posteromedial middle fossa triangle (also known as Kawase's triangle). Posterior to the line is the retro-meatal area, which does not need to be drilled in the regular approach. At this point, we recommend unroofing the internal auditory canal. Indeed, it is necessary to at least expose the dura of the anterior border of the porus, because this point corresponds to the posterior limit of the EAP approach. However, attempting to skeletonize the whole length of the canal, and particularly the fundus, may damage the GG and the first turn of the cochlea more in the depth. Once the landmarks of the pre-meatal triangle have been identified, drilling of the petrous apex is undertaken (Fig. 1D). The drilling is facilitated by a high level of pneumatization of the petrous pyramid in some cases; in others, the fatty aspect of the bone is usually helpful. Approaching the cortical bone of the inner surface, close to the dura of the posterior petrous bone, more cautious drilling is needed to avoid opening the dura prematurely. Indeed, an early and inappropriate opening jeopardizes the structures the dura protects. Inferiorly, the drilling is conducted until the bluish tinge of the inferior petrosal sinus (IPS) is seen. If a tear occurs in the IPS, there is always abundant bleeding, and gentle packing of the sinus lumen should be carried out with small pieces of oxidized cellulose. Such an event can be prevented by preoperative
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embolization of the sinus, though the proximity of the abducens nerve may lead to the risk of a subsequent palsy following this technique. It is sometimes quite difficult to reach the extreme tip of the petrous apex; in that situation, upward retraction of Meckel’s cave is useful. Once the drilling is complete, meticulous hemostasis of the dura and the epidural space is achieved before opening the dura. Opening of the dura Optimal opening of the dura has to fit with the bony exposure in order to avoid undue retraction of the temporal lobe and a restricted corridor (Figs. 2 and 3). Care should be taken to proceed in a stepwise manner to avoid damage of the underlying cranial nerves, excessive bleeding of the venous sinuses and closure problems. Horizontal sectioning of the dura is carried out above the superior petrosal sinus (SPS), from Meckel’s cave anteriorly to the retro-meatal field. An excessive posterior opening puts the vein of Labbé at jeopardy. Then, horizontal sectioning of the posterior fossa dura is carried out just inferior and parallel to the SPS, from the porus trigeminus to the anterior margin of the auditory meatus. Attention should be paid to the trigeminal sensory root, which can be laterally displaced at the vicinity of the dura, and hence the nerve can be damaged while cutting the dura under the SPS. Coagulation and transverse sectioning of the SPS allow sectioning of the tentorium toward its free edge. The surgeon has to keep in mind the orientation of the tentorium while performing this step. Indeed, when the sectioning is too oblique posteriorly, the working distance increases, and more temporal retraction and damage to bridging veins may occur. Conversely, when the sectioning is too close to the
Fig. 2 Sketch of a right EAP once the drilling has been done. The dura is cut above and parallel to the SPS. The SPS (blue) is then coagulated and divided. The dotted line shows the method of division of the dura of the posterior sinus between the SPS and IPS. The tentorium is divided as far as the free edge with preservation of the trochlear nerve
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strips of fat or fascia because this area is usually rather thin and can be sometimes dehiscent. The dura is stitched at the boundaries of the bone flap as well as at its central part to prevent postoperative epidural hematoma. The bone flap is repositioned and maintained with titanium plates. Drainage of the epidural space should be avoided to avoid creating a CSF channel and predisposing the patient to postoperative leaks. Re-application and suturing of the temporal muscle are done with absorbable sutures. Skin suturing is carried out in two layers. Postoperative course and instructions from the surgeon
Fig. 3 Anterior petrosectomy, cadaver head dissection on the right side. Blue tetragon represents the posterior compartment of the cavernous sinus. Red triangle corresponds to Glasscock’s triangle. The right arrow shows the horizontal segment of the intrapetrous carotid. The white arrowhead indicates the IPS. The curved arrow displays the porus trigeminus and entry of Meckel’s cave
cavernous sinus, the trochlear nerve may be injured. Suture stitches at both edges of the cut section and traction elevation of the threads widen the operative field. At this point in surgery, tentorial resection can be performed if invaded by a tumor. The approach is now achieved and the operative field is focused on the cisternal part of the trigeminal nerve as well the ventral and lateral pons, as illustrated by Figs. 4 and 5. Closure At the end of surgery, watertight stitched closure of the dura is usually hampered by its resection and retraction by coagulation. Therefore, the use of an abundant abdominal fat graft is probably the best option to cover the defect. The fat is divided into several pieces of various sizes. One plugs the bony defect created by the petrous apex resection. The other pieces cover the dural defect and are maintained with fibrin glue. It is advised to overlay the superior surface of the petrous bone at the level of the tegmen tympani with Fig. 4 Operative view (illustrative case) of an EAP while the dura is open. A The lateral pons is exposed as well as the sensitive root of the trigeminal nerve. Note the yellow coloration (black arrow) at the level of the nerve indicating a recent bleeding. B The (mulberry-like) cavernous malformation has been approached under the trigeminal nerve and is now exposed at the pial surface
During the 24 h following surgery, the patient is observed in an intensive care unit, and a postoperative CT scan (without contrast) is done. Low-molecular-weight heparin is started the day after surgery to prevent thromboembolic complications. It is recommended that all Valsalva-related maneuvers be avoided to prevent CSF leaks. Postoperative checks of the cranial nerves should be carried out with particular attention to the trigeminal and facial nerves in order to avoid ocular complications such as corneal anesthesia and eye dryness. The use of special tissues for closure, including fat, should be clearly explained to the patient and written in the operative chart to avoid any misinterpretation of the postoperative baseline MR. Optional additional petrous bone removal and combined approaches The following additional steps or procedures are usually not necessary for a regular anterior petrosectomy, but may be considered as options on a case-by-case basis depending on the extent of the disease. –
Drilling laterally to the horizontal segment of the ICA in Glasscock’s triangle is undertaken if it is necessary to mobilize the carotid artery.
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Fig. 5 MRI of the operative case shown in Fig. 4. The preoperative MRI (A and B) shows recent bleeding of a cavernous malformation located at the right ventrolateral surface of the pons. Early postoperative MRI (C
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Deroofing of the entire IAC may be performed to open the dura and remove a piece of tumor that extends inside the meatus. Drilling the posterior part of the rhomboid fossa just in front of the arcuate eminence in addition to the roof of the IAC gives access to tumor extension behind the IAC [6]. An orbitozygomatic deposit can be done to get a wider view to the supratentorial compartment and to expose the lateral midbrain. An epidural temporopolar transcavernous middle fossa approach, which requires elevation of the dura propria from the lateral wall of the cavernous sinus [3], can be undertaken to remove the intracavernous part of a tumor (Fig. 3). A combined petrosectomy, in which a retrolabyrinthine mastoidectomy is required, is usually proposed for large tumors extending laterally and downward [10].
and D) shows the approach (right EAP) filled by fat that plugs the petrous and dural defects. Note the total resection of the malformation
Table 3 Pearls Pearls 1. Tailor the temporo-pterional bone flap toward the temporal fossa 2. Identify the key reliable landmarks that delineate the rhomboid fossa before drilling 3. Optimize the dura opening at the size of the bony exposure 4. Ensure venous epidural hemostasis usingoxycellulose and temporary neuro-cottonoid application 5. Consider the risk of damage to the following structures during the approach: GG, GSPN, IAC, carotid, cochlea and the trochlear nerve 6. Despite a lack of systematic prediction, venous complications and postoperative temporal lobe edema is preempted by ensuring meticulous protection during surgery 7. EAP (like any skull base approach) requires careful closure to avoid CSF leaks, for which we consider fat grafts to be the best option
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Conclusion The epidural anterior petrosectomy is one of the safest and most useful skull base approaches to appropriately expose the petroclival area. EAP can be achieved in a relatively short time by the neurosurgeon, providing he has acquired sufficient technical skills and competences in skull base surgery. Pearls that summarize the key points are shown in Table 3. Nevertheless, surgeons should be aware that EAP is just an approach, and that tumor resection carries its own difficulties depending on the tumor texture and adhesion to the vascular and neural structures. A neurosurgeon has to consider alternative approaches or combined procedures to gain access to those lesions whose insertions and/or extensions do not fit the indications for EAP.
Conflicts of interest None.
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