Anterior Midline Approaches to the Skull Base

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Chapter 52 Anterior Midline Approaches to the Skull Base

Ivo P. Janecka, Silloo B. Kapadia

Comprehensive oncologic management of neoplasms involving the cranial base is an expanding field. Surgery has emerged as the primary modality of treatment for most tumors in this region, either as a single modality (for benign tumors) or in combination with irradiation and chemotherapy (for most malignant tumors). As with most tumors, the control of the primary site is one of the most important determinants of the ultimate outcome of treated patients, and thus a three-dimensional (3D) tumor resection with histologically clear margins is the primary goal of cranial base oncologic surgery. Extensive resections must be balanced with an acceptable functional and esthetic morbidity. Gross central nervous system involvement or internal carotid encasement in a patient with poor collateral cerebral circulation is considered a relative contraindication to oncologic surgery.

Neoplastic growth affecting the anterolateral skull base often originates from central and paracentral craniofacial anatomic structures (dura, orbit, ethmoid, sphenoid and maxillary sinus, pterygoids, infratemporal fossa, clivus, etc.). Histologically this group of tumors includes a great diversity of cell origin.

The surgical approach to such tumors should accommodate the following features: (1) tumor-specific predilectional neoplastic growth; (2) when feasible, protection of key anatomic structures such as the internal carotid artery (ICA), the optic nerves, and the content of the cavernous sinus and the superior orbital fissure; (3) the best cosmetic result; and (4) the stability of the craniovertebral junction.

The principal goal of an anterolateral approach to the skull base is to achieve an unobstructed view of the midline and paramedian skull base region. Strictly midline lesions of the anterior cranial fossa are treated with craniofacial resection using a low (basal) subfrontal approach combined with a midfacial translocation approach. For small clival (central) skull base lesions, a transoral approach may be satisfactory. For larger lesions, we have combined that with midfacial translocation. Midline lesions extending laterally can be resected through various units of the facial translocation system of approaches.

Anatomic Considerations

The intimate relationship of the skull base to the cranial as well as facial structures requires tissue displacement of one or both of these compartments to reach the desired section of the skull base. It is important to consider the effects of surgery on the normal but surgically manipulated tissues so as to select the most optimal approach. Any operative tissue displacement produces alterations in the anatomy and physiology of affected structures. Such changes have variable consequences when they occur in the neurocranium or the facial viscero-cranium. For example, facial swelling is usually self-limiting, with minimal long-term consequences for the patient. Similar edema, however, may be very deleterious when it involves the neurocranium.

The anterolateral skull base constitutes the floor of the anterior and middle cranial fossa. The proximate paranasal sinuses (ethmoid, sphenoid) with the nasal cavity and the orbits are intimate components of this skull base section.

The proximity of the face to the anterior cranial base gives this region a unique significance. The craniofacial skeleton gives protection to the organs of olfaction and vision and provides support for the configuration of the soft-tissue facial anatomy. This arrangement, however, hinders a direct surgical approach to the cranial base for tumors and requires planning of incisions and osteotomies that respect not only function but esthetics as well.

Anterolateral skull base approaches permit visualization of the surgical anatomy of the skull base that may extend from the ipsilateral temporomandibular joint and geniculate ganglion through trigeminal nerve branches of V3 and V2 as well as the ICA to the cavernous sinus, inferior and superior orbital fissures, and both anterior clinoids with corresponding optic nerves.

Diagnostic Evaluation

Several essential issues guide our evaluation of cranial base neoplasms: (1) tumor biology and its extent, (2) tumor composition, and (3) relationship of the tumor to the ICA and its importance to cerebral circulation (Fig. 52-1).

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FIGURE 52-1 Diagnostic evaluation with imaging. A, Coronal MR with contrast, demonstrating an enhancing midline and paramedian transcranial mass (esthesioneuroblastoma). B, Axial MR with contrast showing involvement of interorbital space. C, Sagittal MR with contrast, outlining the tumor extent into the anterior cranial fossa and its subcranial penetration. D, Coronal CT, bone algorithm, delineating bone destruction of the anterior cranial base and subcranial nasal structures.

Tumor biology is best determined by preoperative histologic evaluation obtained after biopsy. New endoscopic instrumentation permits access to many skull base sites for direct visualization and tissue biopsy, or an open biopsy can be performed. The tumor extent determines the potential for surgical resection of the neoplasm. This is currently best determined by multiplanar CT as well as MRI. Both tests are also very useful in assessing the character of the lesion in terms of its vascular, bony, or soft-tissue content. The location of the ICA, and its contribution to the tumor vascularity as well as the relationship of this vessel to the tumor perimeter, are assessed by MRI, MR angiography, or invasive angiography. The tolerance of the patient to temporary occlusion of the ICA can be evaluated with a series of tests known as temporary balloon occlusion test and xenon blood flow studies.1 These tests permit us to estimate the risk of neurologic deficit with a permanent occlusion in the ICA.

For orbital or periorbital tumors, a detailed neuro-ophthalmologic evaluation is valuable. Not only must the precise level of visual acuity, extent of visual fields, and ocular mobility be ascertained, but the completeness of function or the degree of dysfunction of the superior orbital fissure structures, optic nerve, and lacrimal apparatus should be known as well.

Endocrinologic evaluation is necessary preoperatively and in the follow-up period for tumors of the sellar or parasellar region.

Selected Tumors

Carcinoma

Carcinoma that involves the anterior cranial base originates primarily in the paranasal sinuses, the nose and nasopharynx, or occasionally as a metastatic disease. Carcinoma of the nose and sinuses makes up less than 1% of all malignancies. It carries an overall 30% 5-year survival rate. In general, the prognosis of a patient with a carcinoma is very much related to the histologic type. Anaplastic carcinoma must be differentiated from lymphoma and melanoma with leukocyte common antigen and S-100 protein. Anaplastic carcinoma appears to be a separate entity from poorly differentiated squamous cell carcinoma, which still exhibits some squamous differentiation. It is found more often in women, with occurrence on the left side predominant. Among these patients, 33% develop cervical metastases, but only 70% of these have obvious evidence of bone destruction on radiographs. The survival of patients with anaplastic carcinoma varies with the site of origin. If it occurs in the nose, the 5-year survival rate is 40%. If it originates in the sinuses, the 5-year survival rate decreases to 15% (see Thorup et al.2).

The signs and symptoms common to most malignancies in the sinus–nose region include nasal obstruction, discharge, epistaxis, facial pain, as well as swelling, proptosis, or cervical node metastases.

The nasal passages and the sinuses are intimately related, permitting tumor to spread easily from one cavity to the other. Therefore, ethmoid sinuses are often involved secondarily by tumor spread from the nasal cavity or the maxillary sinus. This is reflected in the fact that isolated ethmoid carcinomas compose no more than 5% to 20% of all carcinomas involving the ethmoid sinus. The initial symptoms are usually insidious and trivial, accounting for a significant delay of diagnosis from the onset of symptoms. Sixty to 75% of patients with malignant tumors of the ethmoid sinuses do not survive for 5 years. The ethmoid sinus is closely related to the orbit. Both the orbit and the ethmoid sinus are simultaneously involved in 60% of malignant sinus neoplasms, and 45% of the patients are likely to require orbital exenteration. Most sinus tumors arise from the mucous membrane lining that is in continuity with the mucosa of the remaining sinuses, nasopharynx, and lacrimal draining system. The respiratory mucosa of the ethmoid sinus gives rise to two types of neoplasm. The first is squamous cell carcinoma, arising from the metaplastic epithelium. Of all malignant neoplasms of the sinuses, 75% to 95% will be squamous cell carcinomas, and the ethmoid sinus is the second most common site for this neoplasm. The second is a glandular tumor, arising from mucous glands. The submucosal glands give rise to adenocarcinomas or adenoid cystic carcinomas. Adenocarcinoma occurs most frequently in the ethmoid sinus, and its behavior is similar to that of squamous cell carcinoma. There is some suggestion that this tumor is found more frequently among workers in woodworking industries than in the population in general.3 The lymphatic drainage from the ethmoid sinus is into the superior cervical chain and the retropharyngeal nodes. The incidence of metastases at the time of diagnosis is low, but 25% to 35% of patients will eventually develop metastatic disease. Distant metastases may occur in up to 18% of the cases.4

Esthesioneuroblastoma

This is a rare tumor originating from the olfactory epithelium and represents 3% of all intranasal neoplasms. It was originally described by Berger and Luc.5 This tumor has been identified under different terms, including olfactory neuroblastoma, esthesioneurocytoma, and olfactory esthesioneuroblastoma. It arises from cells of neural crest origin and resembles childhood neuroblastoma. The tumor does contain neurosecretory granules and is linked to other neural crest tumors, such as carcinoid, chemodectoma, and pheochromocytoma. It occurs most frequently in the third decade of life and is more common in males. Unilateral nasal obstruction and epistaxis are the most common symptoms. The tumor may fill the nose and paranasal sinuses and involve the cribriform plate.

A staging system has been proposed by Kadish and colleagues that recognizes three stages6:

Stage A: Tumor involves only nasal cavity

Stage B: Tumor extends also to sinuses

Stage C: Tumor extends beyond stage B

However, correlation of tumor extent with prognosis has not been as accurate as the relationship of clear surgical margins.

Esthesioneuroblastoma is known to have a slow but insidious malignant course, and death comes from local recurrence, intracranial invasion, and/or metastatic disease. Differential diagnosis must exclude lymphoma, melanoma, and metastatic neuroblastoma. The characteristic histologic picture includes a fibrillary intercytoplasmic background that on electron microscopy is identified as representing neuronal cell processes. The 5-year survival rate is approximately 50%, with a median survival of 58 months. When the cranial base is invaded, the survival rate drops to about 40%. Long-term recurrence has also been observed 10 to 20 years after the original diagnosis. This tumor is characterized by local persistence and recurrence. There is a 20% to 40% potential that this tumor will metastasize into cervical lymph nodes, lungs, and bones. The current modality of treatment includes a radical resection of the area involved that includes the cribriform plate with or without the attached dura followed by a full course of irradiation and possibly chemotherapy as well.

Nasopharyngeal Carcinoma

Nasopharyngeal carcinoma is a rare tumor among non-Chinese patients, with an incidence of 1 in 100,000 among the North American population as compared with 2 in 100,000 among Chinese, especially those living in the Canton province of the People’s Republic of China. Several etiologic factors have been implicated in the development of nasopharyngeal carcinoma, for example, the Epstein-Barr virus and numerous external inhalation as well as dietary carcinogens. The male-to-female ratio heavily favors male patients (3:1), with an average age of onset of 45 years.

Clinically, the tumor appears to arise primarily at the superior or lateral aspect of the nasopharynx. The symptomatology often includes epistaxis, nasal and Eustachian tube obstruction, and eventual cranial nerve neuropathies (the fifth cranial nerve is most commonly involved). Histologically, these tumors are predominantly poorly differentiated carcinomas with a high propensity for metastatic regional spread, so that at the time of diagnosis, 50% of patients are expected to have regional disease. In the diagnostic evaluation, direct nasopharyngoscopy and biopsy, as well as a CT scan and MRI, provide for full assessment of the primary site. Irradiation is still considered a primary therapeutic modality for the nonkeratinizing squamous cell carcinoma of the primary site and the regional lymph node draining area.7 The cure rate, however, varies tremendously depending on the histologic type of the tumor, stage of the disease, and subsequent therapy. The most frequent recurrence of nasopharyngeal carcinoma is in the neck.8 Reirradiation of recurrent nasopharyngeal carcinoma gives a 5-year cure rate of only 14%, with a high chance of radiation-induced complications. It is important prognostically to separate patients with metastatic nasopharyngeal carcinoma in the neck on the basis of their response to the primary irradiation. If metastatic neck nodes disappeared completely following irradiation, the recurrence rate was only 13%. If nodes persisted throughout the course of irradiation, the recurrence rate was 91%.

With the advent of new approaches to the nasopharynx, surgery is becoming a therapeutic option for the treatment of resectable recurrent nasopharyngeal cancer with expected survival of over 50% (5 years). For tumors with very poor response to the primary radiotherapy (e.g., keratinizing squamous cell carcinoma, adenoid cystic carcinoma), surgery should be considered as the initial treatment.

Fibrous Dysplasia

Fibrous dysplasia is a progressive benign fibro-osseous lesion. Its natural growth is one of gradual expansion beyond its bony margins with concomitant displacement of surrounding soft tissue. It was first described by Lichtenstein in 1938.9 It may be placed into three categories on the basis of its clinical presentation. The monostotic form represents a localized disease to one osseous structure and is the most frequent form (up to 70%). A polyostotic form involves several bones but usually on the same side of the body. Here the frequency ranges from 30% to 50%. The third form is disseminated, in which numerous bones are involved, along with the possibility of extraskeletal developments such as skin pigmentation and precocious puberty. The incidence ranges from 3% to 30%. These individual clinical forms retain their categorization during the course of the disease and do not seem to change from, for example, the monostotic to the polyostotic form. Fibrous dysplasia is more common in females. In the head and neck region (0.5% of all head and neck tumors), it is the maxilla, frontal bone, mandible, and parietal and temporal bones that are most frequently involved. It is of interest that the progression of the disease is often limited after completion of skeletal maturation.10

The clinical symptomatology usually includes swelling at the tumor site with displacement of surrounding soft tissues. For example, diplopia, when present, is usually caused by mechanical displacement of the globe. If the cribriform plate is directly involved, alteration in olfaction can be perceived. Histologic verification can be considered in addition to the clinical and radiographic examination. In the differential histologic diagnosis, fibrous dysplasia may mimic meningioma, and sarcoma is also a possibility. Radiographically, a sclerotic form manifests itself with dense bone. The cystic and pagetoid forms are distinguished radiographically from each other by the greater amount of fibrous component in the former.

Fibrous dysplasia can be treated by surgical resection when functional or esthetic deformity warrants it.11 Full preoperative evaluation should include CT scan, with and without contrast, in the axial and coronal planes with bone algorithms.

Osseous reconstruction of the surgical defect is necessary only when the tumor involves key aspects of the craniofacial skeleton. Autogenous bone graft or alloplastic materials can be used. In the orbital region, most of the fibro-osseous lesions involve the orbital roof. Prolonged ocular displacement by the tumor often produces a secondary concavity in the orbital floor. This must be taken into account, since after orbital tumor removal superiorly, the globe may not return to the expected normal level. Secondary bone grafting of the deformed orbital floor may have to be considered.

Juvenile Angiofibroma

Juvenile angiofibroma is a relatively rare tumor occurring primarily in adolescent boys. The site of origin of the tumor is thought to be the medial pterygoid region. Clinically, the tumor has the potential to involve the nasopharynx, nose, infratemporal fossa, sphenoid, orbit, middle cranial fossa, and cavernous sinus. There is a preferential growth through preformed anatomic fissures and foramina. The symptomatology is one of nasal obstruction with episodes of nasal hemorrhage that can be profound. The diagnostic evaluation usually consists of CT scan and MRI as well as angiography. The CT scan demonstrates classical widening of the pterygopalatine fossa. MRI is assuming a greater importance in the diagnosis of this tumor, its extent, as well as the degree of its vascularity. Angiography determines the blood supply to this lesion, which originates primarily in the external carotid system, usually the internal maxillary or the ascending pharyngeal artery. There may be additional blood supply from the internal carotid system. In the differential diagnosis, angiomatous polyp, pyogenic granuloma, and hemangioma are included in the benign group. Carcinoma, rhabdomyosarcoma, and chordoma should be considered among the malignant tumors.12

The primary treatment has been surgical through a trans-facial or transpalatal approach, or, for extensive cases, craniofacial resection. Because of its vascularity and potential for a recurrence, a complete removal of this tumor should be attempted. The need for preoperative embolization can be determined at the time of the diagnostic angiography as well as from the appearance of tumor vascularity on the MRI scan. However, the potential complications from embolization must be considered and its advantage weighed against the potential risks. Recurrent tumors are usually treated again with surgery (if accessible) or irradiation. Hormonal therapy, originally thought to be beneficial, has not proved to be of significant value. Histologically, this tumor is composed of fibrous stroma and multiple vascular channels without a definite layer of muscularis in the vessel walls.13

Careful postoperative and long-term evaluation of patients with juvenile angiofibromas is important. MRI provides the best modality of clinical assessment. Harrison published a personal series of 44 patients treated by surgical removal in whom there was a 23% incidence of recurrence.14 These 10 patients with recurrent tumor received another operation. Of these 10 patients, 3 developed a second recurrence that was subsequently treated successfully with irradiation.

Chordomas

Chordomas are tumors that are thought to arise from remnants of the notochord, which is the embryonic precursor of the axial skeleton. Chordomas constitute only 1% of all intracranial tumors, and 30% to 40% of all chordomas arise in the skull base area. Chordomas may involve the sphenoethmoidal area, the petrosphenoid synchondrosis, and the cavernous sinus region, the upper, middle, or lower clivus. The symptoms produced depend on the location of the tumor. Patients may develop cranial nerve palsies, brain stem compression, or merely a nasal or nasopharyngeal mass with nasal airway obstruction.

There are two histologic types of chordoma. The chondroid variety demonstrates a cartilaginous matrix histologically and is associated with much better long-term survival. Patients with chondroid chordoma may live as long as 20 to 30 years. The regular variety of chordoma is associated with a poorer prognosis (5-year survival rate of 30% to 50%). Death is usually caused by local recurrence of tumor. Metastasis to distant sites occurs in about 10% of patients and is more common with longer survival periods. Chordomas are relatively radioresistant to standard radiotherapy and do not respond to chemotherapy.

During the last 15 years, two new developments in the treatment of chordomas have occurred that may change the prognosis for cranial base chordomas. First, the advances in cranial base surgery have allowed a more complete resection of chordomas from difficult regions such as the clivus, the petrous apex, and the cavernous sinus. Second, irradiation with high-energy particles, such as proton beams (Bragg peak) or helium ions, has permitted the delivery of large amounts of radiation to a restricted area. The effects of both of these advances will require many years to evaluate, since chordomas are slow-growing tumors. The current management principle consists of surgical removal and postoperative irradiation.15–17

Chondrosarcoma

Since the bones of the cranial base are derived from a cartilaginous matrix through endochondral ossification, 60% to 70% of chondrosarcomas involve the cranial base skeleton. Such tumors may involve any area of the cranial base but have a predilection for the petrosphenoid synchondrosis.

The prognosis of chondrosarcomas in general depends on the histologic grade, which is worse in patients with a poorly differentiated tumor. The majority of cranial base chondrosarcomas are low grade, locally confined for many years. They recur repeatedly after local resection and metastasize rarely.

Similar to the management of skull base chordomas, our present management consists of tumor resection. Irradiation is administered to patients with residual tumor or high-grade chondrosarcoma.

Osseous Meningiomas

Meningiomas of the cranial base area are often associated with hyperostosis of the cranium. In 30% to 50% of cases, such hyperostosis is due to actual tumor invasion into the bone. In the others, it occurs as a reaction to the tumor resulting from increased vascularity. A patient with a hyperostotic bony reaction or tumor may have either a carpet-like “meningioma en plaque” or a globular “meningioma en masse” involving the dura, the periorbita, and the paranasal sinuses. Osseous meningiomas may be discovered when a patient presents with signs and symptoms caused by a globular tumor. With the en plaque variety, such osseous involvement is often the reason for neurologic symptoms, commonly proptosis, extraocular muscle palsies, and visual loss.

Failure to remove the osseous portion of the tumor will result in eventual progression of symptoms. Regrowth of osseous tumor is often slow, permitting conservative surgery in many patients.

Surgery

Several basic principles, well utilized in other surgical areas, are applicable to cranial base tumor surgery. One is simplicity. Even in complex cranial base surgery, the simplicity and thus the proper sequential logic of the procedural steps should be high on the priority list. The second principle is exposure. It is essential that adequate surgical access to the tumor be achieved with good visualization to allow its complete removal and preservation of uninvolved anatomic structures. In particular, the blood supply to the overlying skin and surrounding muscles must be respected during exposure and tumor resection, so as to have adequate and viable soft tissue available for reconstruction. The cranial nerves, if free of neoplastic growth, are preserved or reconstructed following tumor removal.

Craniofacial Resection

This procedure is performed for neoplasms involving the midline anterior cranial base. For example, tumors involving the ethmoid sinuses and cribriform plate would be encompassed by this procedure.

A bicoronal incision is used with removal of the craniofacial skeleton (Fig. 52-2). This incision outlines the distal end of the fronto-parietal scalp flap used for the exposure of the cranium. It is based inferiorly on supraorbital and supratrochlear vessels and laterally on branches of the superficial temporal arteries. It is a broad-based flap. It can include all the layers of the scalp, including the underlying pericranium, or it can be raised at the galeopericranial plane. Anterolateral extensions of this bicoronal incision, in front of each ear, permit reflection of the flap over the face (a greater rotational arch was achieved) and thus unhindered exposure to the cranium, the roof of the orbit, and both zygomatic arches. The frontalis branch of the facial nerve is preserved and reflected inferiorly in a fascial layer with the overlying scalp flap. The supraorbital neurovascular pedicle can be dissected out of its foramen or groove on each side and preserved. The nasion is well exposed, permitting access to both medial orbital walls. Loss of the sense of smell is always a consequence of this approach.

image

FIGURE 52-2 Incisions. A, Markings for bicoronal incision. B, Outline of midfacial and subcranial incisions.

In addition to the bicoronal scalp flap for superior exposure, inferior facial incisions are made (see Fig. 52-2). Several options are available, from a purely midline “face-splitting” incision (from the nasion through the upper lip) to a paramedian incision, a modification of a lateral rhinotomy incision. It is also possible to avoid direct facial skin incisions by performing what is referred to as a “degloving” procedure (a horizontal mucosal incision from one maxillary tuberosity to the other in the gingivolabial sulcus with elevation of all the soft tissues of the face including the nose). This approach, however, provides wide surgical access only at the level of the incision and significantly narrows at the skull base. Optimal visualization at the skull base is not achieved in the majority of cases. Also, reconstruction of the skull base, if needed, is difficult with this approach.

The “exposure osteotomies,” done in a zigzagging fashion, are performed with the intent to remove, as a free graft, the supraorbital bar, usually from one supraorbital nerve to the other. The facial bony segments are displaced following osteotomies, with the attached soft tissues. They may extend from one medial orbit across the nasion to the opposite orbit (usually to the level of the superior orbital nerve on the opposite side). If the orbital content is involved with the tumor, then it becomes part of the specimen. Before tumor extirpation, when needed, the ICA is isolated in the neck. The craniotomy used in this approach is a bifrontal craniotomy. After dural elevation from the anterior cranial fossa, tumor extent is appropriately assessed with preservation of as many uninvolved anatomic structures as possible including cranial nerves and the carotid artery.

The planning for 3D tumor resection should include the natural anatomic boundaries to tumor progression. These include dura, one or both medial walls of the orbit, the cribriform plate, and the nasal septum. A portion of the frontal bone, corresponding to the upper boundary of the interorbital space, is usually removed with the specimen. If the frontal sinus is not involved by the tumor, it is possible to replace the most anterior portion of this bone.

Midfacial Split and Midfacial Translocation

Midfacial split provides a direct access and a unified surgical field at the central cranial base. It is performed utilizing bilateral facial osteotomies and soft-tissue mobilization. It extends in the sagittal plane from the anterior cranial fossa floor and sphenoid sinus to the level of C1. In the axial plane, the surgical reach extends between medial orbits superiorly, through the plane between V2 to the level of the palate. If the tumor demands wider exposure, an extended facial translocation with palatal split can be utilized.18

Incision consists of either a midline or a paramedian nasal incision with supraorbital extensions. If needed, it may continue inferiorly through the upper lip. The uninvolved nasal septum is reflected with one of the lateral composite tissue components. Facial soft tissues are elevated from the nasomaxillary bones to both infraorbital foramina.

The upper end of the nasal incision is extended laterally below the medial eyebrows, exposing the superior and medial orbital rims. Elevation of the periorbita reveals the anterior and posterior ethmoid foramina; cauterization of the ethmoid vascular pedicles is performed. Inferiorly, the nasolacrimal duct is identified and preserved (or repositioned for subsequent dacryocystorhinostomy).

Bone cuts are made from the medial orbit on one side to the other, through the nasion followed by LeFort I osteotomy. Vertical maxillary cuts are made just medial to the infraorbital nerves. The osteotomies in the medial and inferior orbit are then connected. A midline nasal osteotomy completes bony disassembly if a central nasal incision is used; if a paramedian nasal incision is selected, the entire nasal-midfacial complex is rotated laterally as a composite flap on a single soft-tissue pedicle. Nasal cavities and maxillary sinuses are now widely exposed, allowing resection of the medial maxillary walls. Nonessential nasal septum and vomer can be removed or dislocated to one side, providing direct access to the nasopharynx, sphenoid sinus, and clivus.

For more inferior exposure, the procedure is modified (by omitting the LeFort I osteotomy and separating the maxillary segment from the pterygoid plates posteriorly) and splitting the hard palate in the midline. Each hemipalate (still attached to its vascular pedicle and the rest of the maxilla) is then rotated laterally and retracted. The soft palate can also be divided in the midline, giving access to the entire orona-sopharynx and C1–C4 area.

If further inferior exposure is needed, a tranoral-transmandibular approach can be selected.19 For more lateral access, an extended facial translocation18,20 can be added.

Facial Translocation

This approach to the skull base has undergone a significant evolution since its original description in 1989 and now comprises a system of approaches based on a principle of facial disassembly along embryonic planes of fusion.18,20,21 Due to its modular design, it permits great versatility of design and accommodates the surgical needs for limited as well as complex procedures at the skull base. The operative manipulation of cranial base anatomy and pathology, crucial for oncologic surgery, can be tailored with this system of approaches very precisely to a specific skull base tumor. Maximum preservation and functional and esthetic reconstruction of craniofacial anatomy is an integral part of this procedure.

The current underlying principle of skull base approaches is to minimize brain retraction while maximizing skull base visualization reflected in disassembly and displacement of craniofacial bony and soft-tissue anatomy while preserving the intactness of the brain. This concept facilitates 3D tumor resection, tumor margin verification, and functional reconstruction with appropriate esthetic concerns. Facial translocation approach to the skull base through its great versatility contributes to this goal.

In general, surgical treatment of lesions located anterior to the neuroaxis should be done through an anterior approach. This requires selection of a transfacial approach because of the anteroinferior anatomic relationship of the facial viscerocranium to the cranial base.

The advantages of the facial translocation system of approaches include the following:

1. Facial anatomy has developed through the embryonic fusion of nasofrontal, maxillary, and mandibular processes. Normally, the fusion takes place in the midline or in the paramedian region, thus logically presenting optimal lines of “separation” of facial units for a surgical approach, permitting the least consequential displacement.

2. The primary blood supply to the “facial units” is through the external carotid system, which also has a lateral-to-medial direction of flow, thus ensuring viability of displaced surgical units.

3. The midface contains multiple “hollow” anatomic spaces (oronasal cavity, nasopharynx, paranasal sinuses) that facilitate the relative ease of surgical access to the central skull base.

4. Displacement of facial units for an approach to the cranial base offers much greater tolerance to postoperative surgical swelling, as opposed to similar displacement of the content of the neurocranium.

5. Reestablishment of the normal anatomy, following repositioning of the facial units during the reconstructive phase of surgery, has a high degree of functional as well as aesthetic achievement.

However, there are some disadvantages:

1. Contamination of the surgical wound with oropharyngeal bacterial flora.

2. The need for facial incisions with subsequent scar development.

3. Emotional considerations for the patient related to “surgical facial disassembly.”

4. The potential need for supplementary airway management (postoperative endotracheal intubation, temporary tracheostomy).

The listed disadvantages are of much lesser consequence to the patient when viewed from the perspective of the procedure’s overall safety, tumor control potential, and the facilitation of excellent reconstructive options.

In the past, several surgeons worked on achieving additional oncologic exposure of the facial viscerocranium. Barbosa22 expanded exposure for the treatment of maxillary sinus cancer and Altemir23 did the same for the nasomaxillary area access.

Operative Technique

Modular craniofacial disassembly is the principle of the facial translocation approach to the skull base. It is based on the creation of composite facial units that are designed along key neurovascular anatomy and esthetic lines. The individual units merge into larger composites without compromising their function. It is possible to attach eponyms to the technical variations of facial translocation for ease of communication and comparison. Thus we can recognize “mini,” “standard,” “expanded” (vertically, medially, posteriorly), and “bilateral” facial translocation procedures.24 Complementary craniotomies or craniectomies are added to these approaches as necessary to assist with 3D tumor resection.

Minifacial translocation-central is designed to reach the medial orbit, sphenoid and ethmoid sinuses, and the inferior clivus. The port of entry is through the displaced ipsilateral nasal bone, the nasal process of the maxilla, and the medial orbital rim (with an attached medial canthal ligament, the lacrimal duct, and the skin). The skin incision is made along the lateral aspect of the nose and the inferior aspect of the medial eyebrow with a triangular design at the level of the medial canthal ligament to limit potential scar contracture. Osteotomies create a rectangular window with a lateral extent being just medial to the inferior orbital nerve. The entire unit is displaced laterally for surgical exposure. Closure is accomplished with replacement of this composite unit (skin, bone, mucosa). Rigid fixation of the bone is accomplished with microplating. The perimeter of this approach can be further augmented with endoscopic instrumentation.

Minifacial translocation-lateral opens the infratemporal fossa. The incisions run from the inner canthus horizontally in the inferior fornix of the lower eyelid through the lateral canthus to the preauricular area. Here, it joins vertical temporal and preauricular incisions. The frontal branches of the facial nerve are temporarily disconnected through entubulation (see later). The temporalis muscle is reflected inferiorly after displacement of the zygomatic archmalar eminence. The head of the mandible, when needed, may be either displaced or resected.

Standard facial translocation achieves surgical access to the anterolateral skull base. The ipsilateral facial skin (including the lower eyelid) is displaced laterally and inferiorly with the attached underlying maxilla (with or without the hard palate). The nasal incision may extend inferiorly to include an upper lip split. Superior incision continues from the nose to the inferior fornix of the lower eyelid, and again through the lateral canthus horizontally to the preauricular area. In some cases (more anterior tumors), it is possible to conclude the horizontal canthal incision about 1.5 cm beyond the lateral orbital rim after identifying and preserving the most anterior frontal branch of the facial nerve. This point then serves as the point of rotation of the displaced composite unit, providing sufficient surgical space for some paracentral tumors. When the entire extent of the horizontal temple incision is needed, the frontal branches of the facial nerve are identified with a nerve stimulator, placed in silicone tubings, and transected (entubulation). During the reconstruction, only these transected tubings are reconnected, approximating the facial nerve branches, and providing a stable, enclosed milieu for nerve regeneration. Osteotomies correlate to LeFort I or II or the midpalatal lines when the entire maxilla is being displaced. The inferior orbital nerve is electively sectioned along the floor of the orbit, tagged, and repaired at the end of the procedure. Rigid fixation is achieved with mini- and microplates. With this technique of facial translocation, good exposure of the anterolateral skull base is achieved, especially when the infratemporal fossa is involved as well.

Extended facial translocation-medial incorporates the standard translocation unit plus the nose and the medial one half of the opposite face (up to the infraorbital nerve). It can be rotated at the LeFort I level or include the ipsilateral palate and upper lip split. The skin incisions are similar to the standard technique, except that the paranasal incision is made on the contralateral side. The surgical exposure includes the ipsilateral infratemporal fossa and the central and paracentral skull base bilaterally. The entire clivus is accessible, as are the optic nerves, both precavernous ICAs, and the nasopharynx. The wide communication with the infratemporal fossa allows the placement of the temporalis muscle flap for vascularized reconstruction of any skull base defect. Bony fixation of craniofacial osteotomies is done with miniplates and a lag screw for the palate. The occlusal plane is reestablished with the help of an orthognathic splint prefabricated preoperatively. In addition, a full palatal splint is attached to the contralateral stable palate for additional stability and protection of the palatal incision. Temporary silicone intranasal stents are inserted, as are bilateral lacrimal stents.

Extended facial translocation-medial and inferior includes the aforementioned procedure with an inferior extension via mandibular split. The lower lip split incision is performed in a zigzagging fashion to conform to the tension lines of the skin with a horizontal extension into the upper neck. Mandibular osteotomy is performed just medial to the mental foramen. Usually an interdental space is found wide enough to permit placement of a reciprocating saw for the osteotomy. This is performed in a step fashion, which then permits more stable reconstructive reapproximation of the bone. Before performing the osteotomy, it is wise to select an appropriate miniplate for eventual fixation, contour it to the mandible, and create drill holes. This maneuver assists in the reestablishment of a normal occlusion during reconstruction. This extended translocation procedure adds a significant inferior as well as upper cervical surgical access.

Bilateral facial translocation combines complete right and left basic translocation units with or without palatal split. The exposure incorporates both infratemporal fossae, central and the entire paracentral skull base. Both distal cervical ICAs are in view, as is the full clivus. The palatal split permits a reach to the level of C2–C3. If further inferior extension is needed, a mandibular split can be added so a vertical reach to C3–C4 is accomplished. A single temporalis muscle flap is sufficient for the coverage of the surgical defect at the skull base.

Reconstruction

The repair of any dural defect is performed with a pericranial graft harvested posterior to the bicoronal incision. In addition, a pericranial flap, based on supraorbital vessels, is utilized to enclose the cranial cavity and complete the separation of the cranial cavity from the extracranium. The reestablishment of external craniofacial bony continuity is done by replacing any skeleton displaced for exposure. Any surgical defect can be augmented with a split cranial bone graft or a titanium mesh. The most inferior portion of cranial base defects (floor of cranial fossae) is usually not bone grafted (Fig. 52-3). Further soft-tissue repair may include regional muscle transposition (temporalis) or free muscle–skin flap transfer (rectus abdominis or latissimus dorsi myocutaneous flaps).

image

FIGURE 52-3 Postoperative scans. A, Coronal MR with contrast, showing total removal of midline transcranial tumor and soft-tissue–only reconstruction of the anterior cranial fossa. B and C, Sagittal and axial MR revealing the same as A. D and E, Postoperative facial appearance with well-healed incisions.

Complications

Complications of a craniofacial resection can be categorized into fatal and nonfatal groups. Terz and colleagues reported an 11% fatal complication rate in their group of 28 patients. The three deaths in this series resulted from pulmonary embolus, brain injury, and tracheal abscess. In the nonfatal complication group, reported by the same investigators, there were several CSF leaks, meningitis, and osteomyelitis of the bone flap, for a 35% nonfatal complication rate.25

Careful attention to even minor details during the preoperative evaluation, the operation, and the postoperative period can often prevent major complications. For instance, when severe lower cranial nerve dysfunction is expected, a temporary tracheostomy and gastrostomy can prevent aspiration pneumonia and malnutrition. Since many of the initial postoperative problems are neurologic, cardiac, or respiratory, the patient should be observed in a unit with facilities for neurologic and cardiorespiratory intensive care. Because of the close collaboration among neurosurgery, otolaryngology, and plastic surgery, the incidence of postoperative problems following extensive cranial base surgery has been greatly reduced.26

Adjuvant Therapy

External beam irradiation is usually administered as an adjuvant treatment to patients with malignant cranial base neoplasms. The value of such combined therapy (surgery and irradiation) for extensive skull base tumors is unproven at this time in the absence of prospective controlled trials. However, such combined modalities have become a standard in head and neck surgery for extensive neoplasms (T3–T4).

High-energy–focused radiation, with proton beams or helium ions, has been used to treat cranial base chordomas and chondrosarcomas with encouraging results.17

Although benign tumors such as meningiomas and neurilemmomas have been considered radioresistant, recent reports suggest that recurrent or residual tumors can be treated with external beam irradiation, reducing their growth rates.27 However, the deleterious effects of irradiation (carcinogenesis, normal tissue growth retardation) must be kept in mind.

For small benign lesions (<2.5 cm), such as meningiomas or acoustic neurilemmomas, stereotactically focused cobalt radiation has been used. Such “gamma knife” treatments appear to be effective in arresting the growth of tumors in many cases and offer an alternative to surgical treatment.28

In general, chemotherapy for cranial base tumors has not been successful. Tissue assay, performed on a sample of a removed tumor, may offer a potential for finding a more specific chemotherapy drug for each patient. In vitro drug testing on tumor cells is in its infancy and still not a perfect predictor of clinical response. However, treatment with assay “positive” drugs is reported to be more strongly associated with clinical response than is treatment with assay “negative” drugs (Weisenthal Cancer Group, “Functional Tumor Cell Profiling,” Huntington Beach, CA, http://www.weisenthalcancer.com/). We have obtained assays on several skull base tumors. Clinical conclusions cannot be drawn yet at this early stage; these findings could be used only as guidance to planning when chemotherapy option needs be considered.

Case 1: Chordoma of clivus. The tumor assay showed sensitivity to Cisplatin and Ifosfamide.

Case 2: Myxoid fibrosarcoma. The tumor assay showed sensitivity to Gemcitabine+Cisplatin, Gemcitabine+Melphan, Gemcitabine+Melphan+High dose of Tamoxifin.

Case 3: Meningioma, middle and infratemporal fossa. The tumor assay showed sensitivity to Taxol.

Case 4: Chordom of clivus. The tumor assay showed sensitivity to Docetaxel, Gemcitabine+Cisplatin, Gemcitabine+CP+High dose of Tamoxifin, Gemcitabine+Melphan+High dose of Tamoxifin, Vinorelbine+High dose of Tamoxifin.

Case 5: Synovial cell sarcoma of upper neck. The tumor assay showed sensitivity to Doxyrubicin, Gemcitabine+Melphan+High dose of Tamoxifin, Isosfamide.

Case 6: Squamous cell carcinoma, maxilla. The tumor assay showed sensitivity to Bleomycin, Cisplatin, Gemcitabine, Gemcitabine+Cisplatin, Docetaxel, Irinotecan+Cisplatin, Irinotecan+Cisplatin+High dose Tamoxifin, Topotecan+Cisplatin.

Case 5: Neuroendocrine carcinoma, ethmoid sinuses. The tumor assay showed sensitivity to Trimetrexate.

Case 6: Meningioma, orbit, middle, and infratemporal fossae. The tumor assay showed sensitivity to Extramusine, Decarbazine, and Taxanes.

Case 7: Myxoid fibrosarcoma, orbit, infratemporal fossa, skull base. Tumor assay showed sensitivity to Doxil, Doxorubicin, Epirubicin, Gemcittabine, Gemcitabine+Cisplatin, Gemcitabine(+Doxil+High dose of Tamoxifin, Gemcitabine+Isofosfamice(4HI), Gemcitabine+Melphan.

Conclusions

The management of complex cranial base neoplasms by a team approach, combined with other therapeutic advances, has greatly improved the outlook for these patients in the past 15 years. The next decade will witness the consolidation of such advances and the conduction of cooperative and prospective clinical trials to assess further the efficacy of such aggressive approaches in controlling neoplastic disease at the skull base. Patients with extensive cranial base neoplasms often need considerable help with psychological, social, and financial problems. Such problems are best handled with the assistance of psychology, nursing, and social service departments.

The oncologic benefit of cranial base surgery is continuously being assessed. The percentage of patients living disease free after cranial base surgery for malignant disease has increased to 60% to 65% at 5 years. This “overall” percentage (all histologies, all sites) reflects not only the slow biologic aggressiveness of some tumors (e.g., chondrosarcomas, adenoid cystic carcinomas), but also the high aggressiveness of others (e.g., squamous cell and anaplastic carcinomas). Most encouraging is that primary cranial base surgery (done as the initial treatment) has a significantly greater chance of oncologic success than “salvage” procedures following failure of other therapeutic modalities (e.g., non–skull base surgery, radiotherapy).

For most benign tumors, cranial base surgery is the only therapeutic modality and has a high degree of effectiveness.

Key References

Choussy O., Ferron C., Védrine P.O., et al. Adenocarcinoma of ethmoid: a GETTEC retrospective multicenter study of 418 cases. Laryngoscope. 2008;118(3):437-443.

Chung W.Y., Pan D.H., Lee C.C., et al. Large vestibular schwannomas treated by gamma knife surgery: long-term outcomes. J Neurosurg. 2010;113(suppl):112-121.

Durante M., Loeffler J.S. Charged particles in radiation oncology. Nat Rev Clin Oncol. 2010;7(1):37-43.

Ganly I., Patel S.G., Singh B., et al. Complications of craniofacial resection for malignant tumors of the skull base. Report of an International Collaborative Study. Head Neck. 27(6), 2005. 445-r51

Ganly I., Snehal G., Patel S.G., et al. Craniofacial resection for malignant paranasal sinus tumors: report of an International Collaborative Study. Head Neck. 2005;27(7):575-584.

Holzmann D., Reisch R., Krayenbühl N., et al. The transnasal transclival approach for clivus chordoma. Minim Invasive Neurosurg. 2010;53(5):211-217.

Janecka I.P. New reconstructive technologies in skull base surgery. Role of titanium mesh and porous polyethylene. Arch Otolaryngol. 2000;126:396-401.

Janecka I.P., Tiedemann K. Skull base surgery. Philadelphia: Lippincott-Raven, 1998.

Kadish S., Goodman M., Wang C.C. Olfactory neuroblastoma: a clinical analysis of 17 cases. Cancer. 1976;37:1571-1576.

Patel S.G., Singh B., Polluri A., et al. Craniofacial surgery for malignant skull base tumors: report of an international collaborative study. Cancer. 2003;98(6):1179-1187.

Roos D.E., Brophy B.P., Taylor J. Lessons from a 17-year radiosurgery experience at the Royal Adelaide Hospital. Int J Radiat Oncol Biol Phys. 2010 Oct 30. [Epub ahead of print]

Sen C., Triana A.I., Berglind N., et al. Clival chordomas: clinical management, results, and complications in 71 patients. J Neurosurg. 2010;113(5):1059-1071.

Suárez C., Rodrigo J.P., Rinaldo A., et al. Current treatment options for recurrent nasopharyngeal cancer. Eur Arch Otorhinolaryngol. 2010;267(12):1811-1824.

Numbered references appear on Expert Consult.

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26. Patel S.G., Singh B., Polluri A., et al. Craniofacial surgery for malignant skull base tumors: report of an international collaborative study. Cancer. 2003;98(6):1179-1187.

27. Chung W.Y., Pan D.H., Lee C.C., et al. Large vestibular schwannomas treated by gamma knife surgery: long-term outcomes. J Neurosurg. 2010;113(suppl):112-121.

28. Roos D.E., Brophy B.P., Taylor J. Lessons from a 17-year radiosurgery experience at the Royal Adelaide Hospital. Int J Radiat Oncol Biol Phys. 2010 Oct 30. [Epub ahead of print]

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