Surgery : Part I
Informed Consent
As emphasized throughout this book, sinonasal tumors are rare, present late, and are often difficult to cure. Patients and their families must understand this from the outset so that a strong relationship of trust is developed. It is important that they understand the rationale for all the treatment options, the chances of success, and the potential complications that accompany them so that a genuinely informed consent may be taken. The increased availability of information means that patients can choose to be involved in the decisions about their treatment to a much greater extent than in the past; but with that power comes responsibility, so it is important that the consequences of a particular choice are fully discussed. This of course can be difficult and the extent of patient involvement will differ from person to person. However, doctors should always be prepared to discuss their expertise in dealing with the specific condition and be prepared to involve other colleagues if appropriate.
In discussing a particular operation such as the choice between an open craniofacial resection and an endonasal endoscopic technique, it may be appropriate to obtain consent for both procedures in case the tumor is found to be more extensive than indicated by preoperative imaging. As Wolfgang Draf has so wisely remarked, “the operation must fit the tumor, not the tumor made to fit a particular operation.”
Endonasal Endoscopic Surgical Approaches
The introduction of endoscopic endonasal surgery in the 1980s, underpinned by access to CT and then MRI, revolutionized our approach to the diagnosis and management of virtually all rhinological conditions. Beginning with inflammatory and infective conditions, it was rapidly extended to the interfaces with the orbit and skull base, encouraging cross-specialty interaction and leading to the development of new techniques particularly for repair of dura and orbital periosteum. It was thus a natural progression to the resection of benign sinonasal tumors and then, albeit with some trepidation, to malignant tumors. Similarly, it became clear that disease arising outside the sinuses might be accessed via endonasal routes, beginning with the pituitary and extending to cranial and orbital lesions. The collaboration of rhinological surgeons with neurosurgeons and ophthalmologists has proved beneficial for all concerned, not least the patients, who may avoid some of the morbidity of conventional external approaches and, as a consequence, often enjoy shorter hospital stays. This in turn has led to a new genre of surgery—neuroendoscopic or minimal access skull base surgery that is based on detailed anatomical studies of the skull base anatomy from an endoscopic perspective, the use of new instrumentation and intraoperative image guidance, and often two senior surgeons or more working together, depending on the complexity of the case.
As a consequence, the anterior, middle, and posterior cranial fossae can now be reached using extended endonasal approaches (EEAs).1,2 These techniques have been developed in several centers around the world, which to some extent has led to the concentration of some of these rare pathologies. The feasibility and the safety of these approaches is now well established and has been published widely (Table 19.1).3–13 However, not all tumors can be resected by endoscopic endonasal approaches and it is important that the full range of surgical procedures and other therapies is available in managing these difficult and generally rare conditions.
One of the major criticisms of EEAs is the often piecemeal nature of the resection. However, anyone undertaking any form of major sinonasal surgery will know that after removal of the main specimen, further surrounding tissue is almost always removed. As long as all the tumor is excised and clear margins are obtained, which can be confirmed with frozen section, there is no hard evidence that piecemeal resection is detrimental to cure.14 Indeed it has been argued that the visualization afforded by the endoscope significantly improves complete resection and is a reason for combining endoscopic techniques with an open approach if the latter is undertaken. The concept of an “en bloc” resection, originally conceived in relation to colon cancer, may not be justifiably applied to the sino-nasal area. The term “debulking” should also be regarded with some circumspection as it implies that there will be residual tumor at the end of this process. This should definitively not be the aim in most instances, unless the situation is palliative or some degree of decompression is sought—for example, of the orbit—while obtaining tissue for diagnosis. Resection with intent to cure should be the guiding principle via whatever approach is appropriate. A much more appropriate term, coined by Piero Nicolai, Paolo Castelnuovo, and colleagues, is “tumor disassembly.”
The limits of EEA are constantly changing, although factors such as the histology, the extent of disease, and its relationship to major neurovascular structures and invasion of dura, brain, and eye are important determining factors as well as the experience of the surgeon and the facilities of the institution and not forgetting factors related to the patients themselves.13 Access to the lesion with minimal manipulation of normal neurovascular structures while maintaining good visualization and hemostasis15 is critical, and the ability to manage vascular complications and to perform the necessary reconstruction16–18 after resection is essential for optimal surgical results (Fig. 19.1). Ultimately the same oncological principles must be applied, irrespective of the surgical approach.
Technique
The details of the various EEAs are widely available in the literature but it is helpful to consider them in the three broad categories described by Nicolai, Castelnuovo, and colleagues19:
Endonasal endoscopic resection (EER)
EER with transnasal craniectomy (ERTC)
Cranioendoscopic resection (CER)
EER may be used for all tumors involving the nasal cavity and paranasal sinuses that reach the skull base but do not require extensive skull base removal or dural resection. ERTC encompasses those tumors that have involved and/or transgressed the skull base with contact or focal infiltration of the dura. It should also be considered for tumors such as olfactory neuroblastoma, where the olfactory tract is likely to be involved. Finally, there are those tumors that have extensively involved the skull base or dura, particularly with lateral extension over the orbital roof and/or brain involvement, where the endoscope may assist a conventional craniofacial resection with or without a facial incision (CER).
Adequate Access
A common mistake is to think of resection via an EEA as somehow smaller. It is true that there may be less collateral damage of normal tissue, but the actual resection of tumor and its margin will be comparable to that achieved via an open approach. However, adequate access and visualization of the operative field is mandatory. Thus, for tumors involving the maxillary sinus, an endoscopic medial maxillectomy should be undertaken to allow complete subperiosteal dissection of tumor and removal of mucosa and any involved bone. For sellar and skull base lesions, a binarial approach is frequently utilized to allow for a two-surgeon, three- or four-hand technique.20 Bimanual dissection is facilitated by bilateral nasal access, often combined with some form of posterosuperior nasal septectomy as it provides the necessary space for instrument manipulation and movement of the scope and improves the angle for dissection. Out-fracture or removal of some of the structures on the lateral wall, for example, inferior and middle turbinates, may be needed to provide a wider access to the posterior and superior nasal cavity and skull base as well as to confirm complete excision and absence of field-change in the case of certain malignant tumors.
Many surgeons advocate extending the septectomy into the frontal sinuses (Draf III) so that this area may be readily visualized postoperatively and similarly wide bilateral sphenoidotomies are usually performed.21 These may be extended laterally to the level of the pterygoid plates and lateral wall of the sphenoid sinus, superiorly to the planum sphenoidale and inferiorly to the floor of the sphenoid sinus. Even if the lateral wall is not involved, a middle meatal antrostomy is often recommended either as part of staging or to optimize postoperative visualization and to avoid secondary inflammation/infection particularly if radiotherapy will be given.
Resection
The extent of the tumor resection should be the same whether undertaken endoscopically, using a microscope, or with the naked eye. The main difference is the necessity in many cases to endoscopically debulk the lesion, although it may still be possible to circumnavigate it, taking a cuff of normal mucosa and mucoperiosteum and removing the tumor as one piece. This will be determined by the position, size, and consistency of the lesion. A small osteoma can be removed in its entirety; a large one will need to be drilled out from within and “imploded.” Tumor removal may involve suction, powered instrumentation (debriders), drills, through-cutting forceps, and ultrasonic aspiration. Intracranial lesions in particular will require sequential capsular mobilization, extracapsular dissection of neurovascular structures, coagulation, and then removal of the capsule.
The stages of EER/ERTC have been divided into six main steps (Figs. 19.2 and 19.3)19,22:
Tumor debulking or disassembly
Septal resection
Opening of adjacent sinuses (usually including Draf III, total ethmoidectomy, medial maxillectomy, and median sphenoidotomy) and wide field removal of nasal and sinus mucosa and periosteum
Removal of bone adjacent to tumor—lamina papyracea, skull base
Removal of the orbital periosteum, dura, olfactory bulbs, and tracts if tumor is adjacent, adherent, or infiltrating
Repair and reconstruction of the skull base and orbit
When CER is undertaken, four phases have been defined:
Endoscopic
Transcranial
Simultaneous removal of the “ethmoid box” from above and below
Skull base reconstruction
The concept of endoscopic endonasal modules based on anatomical corridors has been widely popularized by Kassam, Carrau, and colleagues using the sphenoid sinus as the pivot point for the sagittal and coronal planes (Table 19.2).1,2,14,23 The sagittal plane modules extend from the frontal sinus to the second cervical vertebra, enabling access through the crista galli, planum, tuberculum, dorsum sella, and clivus. The EEA approaches in the coronal plane are divided into anterior, middle, and posterior, corresponding to the relevant cranial fossae.
Transcribriform Approach
The transcribriform approach1 is the approach most often utilized for sinonasal neoplasia affecting the anterior skull base, although it may also be used to repair CSF leaks, remove meningoencephaloceles, and access benign intracranial tumors such as olfactory groove meningiomas. This approach can be performed unilaterally or bilaterally. Its anterior limits are the crista galli and the frontal sinuses (i.e., transfrontal approach), the posterior limit is the planum sphenoidale. Laterally, it is bounded by the roof of the ethmoid sinus (fovea ethmoidalis) and medial orbital wall (lamina papyracea).
A complete fronto-ethmo-sphenoidectomy may be performed together with resection of the anterior nasal septum from the skull base. This allows complete staging of the disease in cases of malignancy and allows excellent visualization of the postoperative cavity. If not already performed, large middle meatal antrostomies will avoid subsequent maxillary sinusitis, particularly if radiotherapy will be given.
The lamina papyracea can be removed together with orbital periosteum if required (see Management of the Orbit, below). The ethmoidal arteries (AEA and PEA) can be identified, coagulated and transected medial to the lamina papyracea, aiding devascularization of the tumor (as may the sphenopalatine vessels). A frontal sinusotomy may be undertaken depending on the extent of disease and the exposure required. This is often a Draf III (or endoscopic Lothrop), which includes the bilateral removal of the sinus floors and intersinus septum, or just an ipsilateral resection may suffice (Draf II).21
The skull base may then be removed using osteotomies around the cribriform plate, or by drilling away the bone after removal of the nasal mucosa, or by thinning the bone to facilitate piecemeal resection together with coagulation of ethmoidal vessels and olfactory filaments. Once the cribriform plate has been removed, the crista galli is drilled/dissected out. Dural prolongations on either side of the crista need to be coagulated as they carry CSF and/or venous channels.
The exposed dura is coagulated and incised on each side of the falx and the tumor is removed by approaching from each side, exposing the free edges of the falx. After coagulation of the falx and any feeding vessels arising from the associated arteries, the dura is incised and the rest of the tumor is removed. Ideally, dura anterior to the tumor–brain junction is not opened, to prevent frontal lobe herniation. Considerable care is now required using gentle countertraction and sharp dissection, especially if dissection of the upper extent of the tumor involves the interhemispheric fissure, as the A2 and frontopolar arteries will be draped over the tumor surface. Similarly the dissection inferoposteriorly may bring one into close contact with the optic nerves and the anterior communicating artery. If there is any concern that safe excision from below cannot be accomplished, the decision should be made to proceed to an open craniofacial approach, ideally at that time, and patients should provide consent for both procedures if there is any doubt.
Transsellar Approach
The transsellar approach1 is primarily used for pituitary pathology such as pituitary adenomas and Rathke cleft cysts. The endoscope affords a panoramic view, ensuring complete tumor removal. In the event of cavernous sinus extension, the medial cavernous wall can be examined from within the sella. Since the carotid siphon is usually displaced anteriorly, the space between the posterior clinoid and the siphon offers an ideal corridor to enter the cavernous sinus. A considerable literature may be found on this approach, which is beyond the scope of this book.13
Transtuberculum/Transplanum Approach
Extrasellar pituitary adenomas with suprasellar extension, meningiomas and select craniopharyngiomas require a combined transsellar/transplanum approach1 with removal of the tuberculum. This allows one-stage removal of the entire tumor with direct visualization.
Transclival Approach
The clivus can be divided into three portions along the rostral-caudal direction.23 The upper third includes the dorsum sella and posterior clinoids down to the level of Dorello′s canal. The middle third extends from Dorello′s canal down to the jugular foramen. The lower third extends from jugular foramen through the cervicomedullary junction and foramen magnum. Indications include the surgical treatment of meningiomas, chordomas, and chondrosarcomas, which are the most common tumors in this region.
Transodontoid and Foramen Magnum/Craniovertebral Approach
Exposure of the foramen magnum and odontoid requires additional soft tissue removal following the panclival module and may be utilized for surgery on the odontoid itself, for recurrent nasopharyngeal carcinoma, and for access to structures within the foramen magnum and cervical spinal cord down to the level C1-C2. Caudal exposure is limited by the inability to move the instruments beyond the nasal bones anterosuperiorly and the hard palate posteroinferiorly. The line connecting these two points is defined as the nasopalatine line (NPL). The NPL accurately predicts the most inferior extent of an endoscopic endonasal approach.23–25
Anterior Coronal Plane: Supraorbital and Transorbital Approaches
In the supraorbital approach, the medial wall of the orbit is removed and the orbital soft tissues are displaced to visualize the orbital roof. The transorbital approach is used for intraconal lesions that are inferior and medial to the optic nerve. Access is gained between the inferior and medial rectus muscle with preservation of extraocular muscle function.
Middle Coronal Plane
These approaches are defined by their relationship to the petrous carotid artery.2 Infrapetrous approaches give access to the medial petrous apex and the petroclival junction, whereas the suprapetrous approaches give access to the inferior and superior cavernous sinus as well as the infratemporal/middle fossa.
Medial Petrous Apex Approach
Large bilateral sphenoidotomies are undertaken followed by removal of the basipharyngeal fascia from the face of the sphenoid down to the clivus. The sphenoid floor is then drilled down to the clival recess and the clivus itself may also be partially removed if needed. The posterior wall of the maxillary sinus is accessed via a large middle meatal antrostomy and the posterior wall is removed to expose the pterygopalatine fossa. The sphenopalatine arteries are identified and coagulated at the foramen, remembering that there may be up to 11 branches.26 The base of the pterygoid plate is exposed by elevation of the soft tissues of the pterygopalatine fossa and the vidian canal (pterygoid canal), identified just lateral to the junction of the sphenoid floor with the medial pterygoid plate (MPP). The canal is important as lesions such as angiofibroma often involve it and from there infiltrate the basisphenoid. The canal also leads directly to the anterior genu of the internal carotid artery (ICA) as its petrous portion turns up to form the vertical paraclival ICA.
The medial pterygoid plate may be drilled medial and inferior to the vidian canal while following it posteriorly, toward the foramen lacerum. After identifying the anterior genu of the ICA, the lateral and superior part of the MPP can be removed. To access the petrous apex, drilling of the bone covering the paraclival carotid may be required if the ICA needs to be mobilized laterally.27 Greater access can also be provided by drilling a portion of the lateral clivus at its junction with the petrous apex.
Petroclival Approaches
Kassam and colleagues have described extending the medial petrous apex approach, by drilling the vidian canal circumferentially and following it back to the anterior genu of the ICA.28,29 The anterior genu of the ICA represents the lateral margin of this approach and is the most important landmark. The bone overlying the genu, the horizontal petrous, and the vertical paraclival segments of the ICA can be removed to uncover the carotid, allowing its lateral displacement. The medial portion of the clivus may then be safely drilled after identification of the anterior genu of the ICA. The lateral portion of the clivus at the petroclival junction is drilled up to the clival recess of the sphenoid. The cavernous sinus represents the superior boundary of this exposure, and the middle fossa the lateral boundary.
Inferior Cavernous Sinus/Quadrangular Space Approach
This is an extension of the petroclival approach. Removal of the posterior wall of the maxillary antrum is extended laterally until the maxillary branch (V2) of the trigeminal nerve is identified traveling superiorly toward the foramen rotundum. The MPP is drilled inferiorly and medially to the vidian canal. Next, the bone between the vidian canal and V2 is drilled away, accepting that this bony corridor narrows progressively as it deepens. Removal of this bone gives access to the quadrangular space that is defined by the parasellar ICA medially, V2 and dura of middle cranial fossa laterally, the horizontal petrous ICA inferiorly, and the sixth cranial nerve superiorly. Bone covering the horizontal petrous ICA, the anterior genu, and parasellar ICA may need to be removed if mobilization of the carotid is required. Access to the inferior cavernous sinus is gained by opening the dura from the genu of the ICA (medial) toward the V2 (lateral).
Superior Cavernous Sinus Approach
This module requires a similar amount of bone removal and ICA exposure as for the inferior cavernous sinus module. However, before incising the dura, the medial margin of the ICA in the sella should be identified so that it can be protected during this maneuver. The dural incision is begun directly over the superolateral portion of the cavernous sinus and performed in a medial-to-lateral direction. If, as is often the case, the cavernous sinus has thrombosed, little venous bleeding occurs during initial opening but this can dramatically change once the tumor is removed. This approach has been used for tumors unresponsive to medical treatment or radiosurgery and for patients with established cranial nerve deficits.30
Infratemporal Approach
Once the medial pterygoid plate has been dissected, the vidian canal has been identified, and the maxillary antrostomy completed, the plate is removed flush with the middle cranial fossa and foramen rotundum. The internal maxillary artery and its branches must be identified and ligated and the anterior genu of the ICA and horizontal petrous segment of the ICA identified before tumor removal commences. Dissection may be extended laterally until the lateral pterygoid plate is identified, and this may also be drilled rostrally until flush with the middle cranial fossa and foramen ovale. Bleeding from the pterygopalatine venous complex can be profuse and it may be necessary to pack the area and perform further resection at a later date, after the venous complex has thrombosed.
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