Anterior Subfrontal Approach - Tumor Removal

In 1954, Smith reported the first anterior craniofacial resection in a patient presenting with a tumor arising in the frontal sinus.[1] Ketcham et al subsequently reported the first series of patients treated with an anterior craniofacial resection for tumors arising in the ethmoid sinuses.[2] This seminal report included the indications, morbidity, and outcome of the procedure and included a systematic description of the surgical technique.

The oncologic principles of anterior craniofacial resection as described by Ketcham involves an en bloc resection of the tumor, including the ethmoid sinuses, superior nasal septum, and floor of the anterior cranial fossa, corresponding to the interorbital area (ie, anterior craniofacial resection) or extended laterally to include part of the bony orbit or its soft tissue contents (ie, anterolateral craniofacial resection).[3]

Subsequent reports included larger series of patients and multiple modifications of Ketcham's original surgical technique. These latter reports incorporated technical advances brought to craniofacial surgery by Tessier, such as the use of the subfrontal technique adopted for oncologic surgery by Derome.[4] These modifications improved the visualization of the tumor, facilitating its total removal, and decreased, although did not eliminate, the morbidity related to brain retraction. Recently, endoscopic and endoscopic-assisted techniques have been adopted to extirpate selected tumors that traditionally have been resected using a subfrontal approach.

As opposed to a craniofacial resection, the endoscopic resection does not involve an en bloc resection. However, it is still founded on a complete resection of the tumor, preferably corroborated by intraoperative frozen section analysis. In well-selected patients, endoscopic endonasal resection, however, should yield oncologic outcomes that are equivalent to those of traditional subfrontal approaches.[5]

Frequency

From the head and neck surgeon's standpoint, the anterior skull base is affected most commonly by tumors arising in the paranasal sinuses; the neurosurgical experience will be biased toward tumors that arise from the anterior cranial fossa. In either case, these tumors may be resected using a completely endoscopic or an endoscopic-assisted approach according to their extension. Tumors that extend lateral to the meridian of the orbit, invade the soft issues of the orbit, the maxillary sinus, the anterior wall of the frontal sinus, or the facial skin require an open approach. Other tumors, such as those arising in the skin or orbits, may also require an anterior craniofacial resection via a subfrontal approach.

Malignant tumors of the sinonasal tract comprise approximately 3% of the malignancies that arise in the upper aerodigestive tract. Overall, sinonasal tumors are most commonly diagnosed in white males (the male-to-female ratio is 2:1) during the fifth to the seventh decades of life. Approximately 10% of tumors that arise in the sinonasal tract originate in the ethmoid and/or frontal sinuses and are likely to involve the anterior cranial base.

Most series of patients with malignancies arising in the ethmoid sinuses demonstrate a preponderance of squamous cell carcinoma (SCCA). However, in the authors' experience, the histopathology of the ethmoid sinuses is equally divided between SCCA and other malignancies, such as adenoid-type carcinomas, sarcomas, and melanomas. This may be a reflection of the referral base, as European series demonstrate a preponderance of intestinal-type adenocarcinomas. Malignancies of the frontal sinuses, which are extremely rare, comprise an equal number of SCCA and adenoid cystic carcinoma. The sellar and parasellar areas are affected by tumors such as chordomas, chondrosarcomas, invasive pituitary adenomas, and meningiomas that, as previously stated, also may require a subfrontal approach.

Several reports have associated malignant tumors of the paranasal sinuses with exposure to industrial fumes, mining industry pollutants, and wood dust. Specifically, individuals who work with nickel demonstrate an incidence of SCCA and anaplastic carcinoma that is 250 times higher than in the general population. These tumors have a latent period of 18-36 years.

Woodworkers exposed to hardwood dust show an increased incidence of adenocarcinoma of the ethmoid sinuses, while woodworkers exposed to softwood dust demonstrate an increased incidence of SCCA, anaplastic carcinoma, and adenocarcinoma. Workers in the leather tanning industry also demonstrate an increased incidence of epithelial malignancies of the sinonasal tract. Other industrial exposures with an increased incidence of sinonasal cancer include mineral oils, chromium and chromium compounds, isopropyl oils, lacquer, paint, soldering and welding materials, and radium dye paint.

Tobacco smoking, which is a recognized pathogenetic factor for SCCA of the upper aerodigestive tract, does not appear to play a significant role in the genesis of these tumors. However, some have suggested the possibility of an additive effect between softwood dust and tobacco smoking.

In general, the most common symptoms and signs produced by tumors arising in the sinonasal tract are similar to the symptoms produced by inflammatory disease (ie, chronic sinusitis). Nasal obstruction, anosmia, facial pressure or pain, epistaxis, and nasal discharge are the most common complaints. Thus, the diagnosis commonly is delayed as the patient seeks attention and/or receives treatment for sinusitis for an extended period. In addition, approximately 10% of patients with these tumors are asymptomatic. Even patients with advanced sinonasal tumors invading the anterior cranial fossa and frontal lobe may have subtle neurologic symptoms that may be easily overlooked.

A detailed physical examination should pay special attention to the sinonasal tract, orbits, and cranial nerves and include a nasal endoscopy. Sensory dysfunction of the first or second division of the trigeminal nerve is more common in patients presenting with malignant neoplasms of the paranasal sinuses than in patients with inflammatory disease of the paranasal sinuses, providing an important clue regarding the nature of the patient's problem.

Orbital findings, such as deficits of extraocular muscle movements, chemosis, or proptosis, should alert the physician to the possibility of a neoplasm. Similarly, loose dentition or a mass effect in the cheek, nose, forehead, palate, or gingivobuccal sulcus, which commonly presents as ill-fitting dentures, also should raise suspicion for presence of a sinonasal neoplasm. Although tumors of the paranasal sinuses are commonly advanced at the time of their diagnosis, they usually are confined to the local site and rarely present with cervical lymphadenopathy. Nonetheless, a detailed examination of the neck is mandatory.

A surgery that involves the resection of the skull base is usually performed with curative intent. A subfrontal approach is the preferred open technique to resect the anterior cranial base because it diminishes the retraction of the frontal lobes, thus decreasing the possibility of edema, contusion, or necrosis of the brain.

As previously mentioned, tumors that do not involve the skin, the soft tissues of the eye, or the anterior table of the frontal sinus and those that do not require an orbital exenteration or total maxillectomy and do not extend lateral to the optic nerves or the meridian of the orbit are amenable to an endoscopic resection.

Thorough understanding of the surgical anatomy of the nasal cavity, paranasal sinuses, orbits, and anterior cranial cavity is critical to predict the pattern of spread of tumors arising in the frontal and ethmoid sinuses and to enable their safe and complete removal. This article offers a brief summary of the anatomy of the sinonasal tract and skull base pertinent to the subject. For more information about the relevant anatomy, see Nasal Anatomy, Nasolacrimal System Anatomy, Paranasal Sinus Anatomy, Olfactory System Anatomy, Facial Bone Anatomy, Facial Nerve Anatomy, and Facial Nerve Embryology. The reader is also encouraged to review the cited references and anatomy textbooks for further details.

Embryology

The midfacial skeleton first appears at week 2.5 of embryonal development, when a mass of neural crest cells starts to migrate around the optic capsule and enter the first branchial arch to form the maxilla. A second mass of cells travels over the frontonasal process into the medial regions of the face to form the framework for the developing nose and paranasal sinuses. Once the bony framework is fully developed, aeration of the sinuses starts as invaginations arising from the middle meatus and sphenoid bone. Thus, the sinonasal tract develops in close association with structures derived from the first branchial arch, the orbits, and the anterior skull base. The ethmoid and maxillary sinuses are the first to develop, followed by the sphenoid sinus and, lastly, by the frontal sinus.

Nasal cavity

The nasal cavity can be visualized as a quadrangular corridor that is narrower at the top and divided into right and left compartments by a midline septum. It communicates with the exterior through an anterior opening, the nares, ie, nostrils. Posteriorly, it opens into the nasopharynx through the posterior choanae. Its external pyramidal shape reflects its skeletal support, which is composed of the paired nasal bones and the upper and lower lateral nasal cartilages as they surround the pyriform aperture.

The most anterior part of the nasal cavity, namely, the vestibule, is covered by skin that contains adnexal structures. Except for the most superior third, the rest of the nasal cavity is lined by pseudostratified ciliated epithelium (ie, respiratory epithelium). Olfactory epithelium (containing the sensory endings of the olfactory nerve) covers the nasal vault.

The walls of the nasal fossae include the nasal septum medially, the horizontal portion of the maxillary bone and palatine bone inferiorly, and the inferior turbinates and ethmoid bones laterally. Superiorly, the nasal fossae are confined by the cribriform plate and the rostrum of the sphenoid sinus as it slants posteroinferiorly toward the nasopharynx. The nasal septum is formed by the perpendicular plate of the ethmoid bone posterosuperiorly, the vomer posteroinferiorly, and the septal or quadrangular cartilage anteriorly. The suture formed by the junction of the perpendicular plate of the ethmoid bone and the vomer leads to the rostrum of the sphenoid sinus, thus providing a useful surgical landmark.

The cartilaginous septum (ie, anterior septum) is attached to the upper lateral cartilages and nasal bones along the dorsum of the nose. Thus, the posterior end of the nasal septum abuts the rostrum of the sphenoid sinus superiorly and has a free edge exposed to the nasopharynx inferiorly. Superiorly, the perpendicular plate of the ethmoid bone is continuous with the cribriform plate. Inferiorly, the nasal septum articulates with the maxillary crest in a tongue-in-groove fashion, stabilized by a dense layer of fibrous adhesions.

The lateral nasal wall separates the nasal fossae from most of the paranasal sinuses and contains their drainage ostia. It is formed superiorly and anteriorly by the nasal bones, the nasal process of the frontal bone, and the frontal process of the maxilla. Superiorly and posteriorly, it is formed by the ethmoid bone. Posteriorly, the wall is completed by the vertical process of the palatine bone and the medial plate of the pterygoid process. The sphenopalatine foramen, which is the passage for the corresponding neurovascular bundle and the posterior nasal artery, is formed by the most cephalic junction of these 2 bony areas. During surgery, the sphenopalatine foramen can be identified posteriorly in line with the posterior tip of the middle turbinate, just posterior to the back wall of the maxillary sinus and at a height level that is equivalent to that of the superior third of the back wall of the antrum.

The lateral wall supports 3-4 projecting scrolls of bone, ie, the conchae or turbinates. The inferior turbinate is an independent bone, whereas the middle and superior turbinates are part of the ethmoid bone. A thick mucous membrane containing a venous plexus with erectile properties covers the inferior and middle turbinates, while the superior and (infrequently found) supreme turbinates are covered by olfactory epithelium. The air spaces beneath them, the meati, are named according to the corresponding turbinate. The anterior third of the inferior meatus contains the ostium of the nasolacrimal duct. The anterior area of the middle meatus contains the frontonasal recess.

Inferior and posterior to the frontal recess, the surgeon can find the uncinate process, the ethmoid bulla, and the semilunar hiatus, which is located between these 2 structures. The nasofrontal recess receives the drainage of the frontal sinus, whereas the infundibulum receives the drainage of the anterior ethmoidal and maxillary sinuses. The superior meatus is short, and its mucous membrane (medial aspect) is mostly olfactory epithelium containing the sensory cells of the olfactory nerves. Posterior ethmoid cells usually drain into the superior meatus.

Sensory afferent fibers to the mucous membranes of the nasal cavities are supplied by the anterior ethmoidal and infratrochlear nerves coming from the nasociliary nerve (V1), the infraorbital nerve, the anterior superior alveolar nerve, pterygopalatine nerves (branches from V2), and the greater petrosal nerve from cranial nerve [CN] VII. Sympathetic innervation derives from branches traveling along the internal carotid artery through the deep petrosal nerve, then via the vidian nerve. Parasympathetic nerves travel in the nervus intermedius of CN VII, then in the greater petrosal nerve to reach the nose through branches of the pterygopalatine ganglion.

Blood to the posteroinferior nasal area is supplied by the internal maxillary artery and the anteroinferior area by branches of the facial artery, both branches from the external carotid artery, while the superior nasal area is supplied by the ethmoid arteries, which are terminal branches from the internal carotid artery. Venous drainage begins as plexuses in the turbinates that form veins that parallel the pathway of the arterial irrigation to then connect with the pterygoid venous plexus or the superior ophthalmic vein.

Lymph drains out of the nasal cavity running posteriorly from the vestibule toward the choanae, passing over the lateral nasal wall to a pretubal plexus, and then passes above and below the eustachian tube toward the posterior pharyngeal wall (ie, retropharyngeal nodes). These nodes drain into the deep jugular chain at the level of the carotid bifurcation. Small lymphatic branches may run upward from the lateral nasal wall toward the upper jugular lymph nodes. Lymphatics of the nasal vestibule run toward the submental and submandibular areas.

Ethmoid sinus

The ethmoid labyrinth consists of 3-18 cells per side that are connected in the midline by the cribriform plate. Each side is divided into an anterior and posterior group of cells based on the attachment of the middle turbinate to the lateral nasal wall (ie, basal lamella). Anterior cells drain into the anterior portion of the hiatus semilunaris. Posterior cells drain into the superior meatus. The lateral wall of the ethmoid sinuses is contiguous to the orbital cavity, and anterior ethmoid cells frequently communicate with the orbit through dehiscences in the lamina papyracea.

Furthermore, posterior ethmoid cells may "invade" the sphenoid sinus to be in close relation to, or even surround, the optic canal (ie, Onodi cells), which also may be dehiscent. Anterior, posterior, and, frequently, middle ethmoid neurovascular bundles pierce the medial orbital wall (ie, lamina papyracea) in their route to the ethmoid cells and then into the vertical lamina of the cribriform plate to reach the anterior cranial fossa. Their foramina can be identified close to the level of the frontoethmoidal suture, which therefore constitutes a reliable surgical landmark.

The anterior ethmoidal artery exits the orbit at a retrobulbar level and between the superior oblique and medial rectus muscles just posterior to the anterior wall of the bulla ethmoidalis. The posterior artery exits the orbit just anterior to the rostrum of the sphenoid. The lacrimal sac and duct and the soft tissues of the anterior and inferior area of the medial orbit may be in close relation to the most anterior ethmoid cells (ie, agger nasi cells).

The roof of the ethmoid sinuses is contiguous to the frontal sinus laterally and anteriorly, to the anterior cranial fossa laterally and posteriorly (ie, fovea ethmoidalis), and to the cribriform plate medially. Although variable, the bottom of the cribriform plate is located approximately just above the level of an imaginary horizontal line joining the medial canthi. Intranasally, it can be identified as the level of the highest attachment of the middle portion of the middle turbinate. Posteriorly, the ethmoid cells may extend into the floor of the middle cranial fossa and may extend lateral and/or superior to the sphenoid sinus.

Blood to the ethmoid sinuses is supplied by the posterolateral nasal artery (a branch of the sphenopalatine artery) and by the anterior and posterior ethmoidal arteries. Sensory innervation of the anterior and middle cells comes from the anterior ethmoidal nerve (V1). Posterior cells are supplied by branches of the pterygopalatine nerve (V2).

Frontal sinus

The frontal sinuses are paired cavities within the diploic frontal bone with frondlike pneumatization and asymmetric shape and size. Their anterior wall is contiguous with the soft tissue of the forehead. The posterior wall is shared with the anterior cranial fossa. The floor corresponds to the roof of the orbit and anterior ethmoid cells. The supraorbital neurovascular bundle supplies sensory and vascular supply and drainage to the frontal sinuses.

Maxillary sinus

The maxillary antrum is the largest of the paranasal sinuses. It is a pyramidal cavity with its apex extending into the body of the zygoma and its base at the lateral wall of the nose. The maxillary sinus walls are contiguous with other anatomic regions of the mid face, and the sinus shares its roof with the orbital cavity. This bony wall is pierced by the infraorbital canal, which communicates with the inferior orbital fissure. Its floor, which is formed by the alveolar process of the maxilla, lies 1-1.5 cm inferior to the floor of the nose and is in close relation with the first to third molars. The anterior wall is contiguous with the soft tissues of the mid face. The posterior and posterolateral walls of the maxillary sinus are contiguous with the pterygopalatine and infratemporal fossae, respectively. The medial wall of the antrum corresponds to the lateral wall of the nasal cavity and contains the drainage ostium at its highest aspect.

Arterial supply to the antrum comes from branches of the sphenopalatine artery, the terminal branch of the internal maxillary artery. Sensory innervation derives from the infraorbital and pterygopalatine nerves of V2. Venous and lymphatic drainage routes travel through the drainage ostium to join their nasal and ethmoidal counterparts at the lateral nasal wall as they travel toward the posterior choana.

Sphenoid sinus

The sphenoid sinus usually is divided into two asymmetric cavities by a bony intersinus septum. Its anterior wall bulges into the nasal cavity and contains the drainage ostium, which may be found at the sphenoethmoidal recess above and posterior to the middle turbinate. The anterior wall of the sphenoid sinus is approximately 9 cm from the anterior nasal spine. However, the overlap between the range of the distances between the nasal spine and its anterior and posterior walls is significant. Thus, distance is an unreliable anatomic reference.

Inferiorly, the sphenoid sinus is contiguous with the nasal and nasopharyngeal cavities. Posteriorly, it abuts the clivus, which separates it from the pons and the basilar artery. Superiorly, it borders the middle cranial fossa, the hypophysis, and the optic chiasm. The lateral wall abuts the cavernous sinus, the optic nerves, and CN V1, III, IV, and VI, which are en route to the superior orbital fissure. Dehiscences of the lateral wall may leave any of these structures exposed to the interior of the sinus. The posterior ethmoid arteries and branches from the sphenopalatine vessels provide arterial blood supply and venous drainage to the sphenoid sinus. Sensory innervation comes from the pterygopalatine ganglion.

Orbital cavity

The orbit shares three of its walls with the paranasal sinuses. Its medial wall corresponds to the lateral wall of the ethmoid sinus. It bears, from anterior to posterior, the nasolacrimal sac lying on the lacrimal bone (ie, lacrimal fossa), the anterior and posterior ethmoidal arteries, the trochlea, and the optic nerve with its foramen at the apex of the orbital cavity. Its inferior wall corresponds to the roof of the maxillary sinus.

The orbital cavity bears the infraorbital fissure and infraorbital neurovascular bundle. The infraorbital fissure is continuous with the pterygomaxillary fissure, thus providing access to the infratemporal fossa laterally or to the pterygopalatine fossa medially. The superior wall is contiguous with the ethmoid or frontal sinuses and with the anterior cranial fossa. As previously stated, the superior orbital fissure serves as a passage for CN V1, III, IV, and VI and represents a potential pathway to the middle cranial fossa. The lateral wall is contiguous with the temporal fossa anteriorly to laterally. Posteriorly and medially, it is contiguous to the middle cranial fossa.

Scalp

The scalp comprises six different layers, which include the skin, subcutaneous tissue, frontalis muscle, galea, areolar tissue, and periosteum. By convention, the term pericranium refers to the combination of the periosteum and the areolar tissue. Vessels and sensory nerves supplying the scalp are superficial to the galea.

Anterior cranial fossa

The floor of the anterior cranial fossa comprises the frontal, ethmoid, and sphenoid bones. Laterally, the floor of the anterior cranial cavity corresponds to the roof of the orbits, while, centrally, it corresponds to the vault of the nasal cavity and the fovea ethmoidalis. The floor of the anterior cranial cavity is concave, with the medial or central area (ie, cribriform plate) located at a lower level than the lateral area. A slant from anterior (higher) to posterior (lower) is noted.

At the central anterior skull base, the most prominent structure is the cribriform plate, which contains multiple foramina, through which the olfactory filaments pass into the nasal cavity. Branches of the anterior ethmoid artery penetrate the vertical wall of the cribriform plate. This area is the weakest point of the anterior skull base. Anterior to the cribriform plate and just posterior to the foramen cecum is a tooth-shaped prominence, the crista galli. In children, the foramen cecum, anterior to the crista galli, may contain a vein that connects to the superior sagittal sinus. The planum sphenoidale denotes the area posterior to the cribriform plate, and its posterior aspect marks the posterior boundary of the anterior cranial fossa. The average distance between the foramen cecum and the tuberculum sella ranges from 28-50 mm, with an average distance of 42.5 mm.

Hematogenous metastasis, invasion of the cavernous sinus or internal carotid artery, bilateral invasion of the orbits (ie, soft tissues), optic nerves, or optic chiasm by a high-grade malignant tumor are contraindications for a craniofacial surgery under most circumstances. Lymphoreticular lesions, such as lymphoma and plasmacytoma, are best treated with nonsurgical therapies. Other contraindications include patients who refuse surgery or patients who are poor surgical candidates due to comorbidities.

Laboratory studies are recommended based on clinical history and are only necessary to exclude endocrine, electrolyte, or coagulation disorders. Preoperative evaluation of these potential problems is critical because they can significantly affect outcome and perioperative management.

According to the extent of the tumor and/or resection, vascularity of the tumor, risk of vascular injury, and preoperative hematocrit, the patient is typed and cross-typed for 2-6 units of packed red blood cells (PRBC).

Imaging using CT scan and/or MRI is recommended to delineate the extent of the tumor, especially in areas that are not amenable to endoscopic examination, such as the cranial cavity, orbit, other paranasal sinuses, and soft tissues of the face, pterygopalatine, and infratemporal fossa.

CT scanning is superior to MRI in defining the bony boundaries, as depicted in the image below.

Use of contrast during CT scanning can help estimate the vascularity of the tumor and demonstrates its relationship to the great vessels and other neurovascular structures such as dura, brain, and cranial nerves.

MRI usually is reserved for patients presenting with invasion of soft tissues, most importantly orbit and brain, as depicted in the images below.

MRI does not use ionizing radiation and better defines the soft tissue interfaces, demonstrates perineural spread, and differentiates tumor from retained secretions within the paranasal sinuses. For these reasons, MRI is the preferred method to monitor areas that are not amenable to clinical examination. Despite superior soft tissue definition, MRI may not distinguish scar or reconstructive flaps from tumor. This dilemma is elucidated by performing biopsy or sequential imaging to monitor changes or growth and thus corroborate the presence or absence of tumor.

Positron emission tomography (PET) may help to identify the presence of metastatic or recurrent tumor that may escape detection by clinical examination or CT and MRI. Fusion of a PET with a CT or MR provide an anatomic and metabolic correlate which helps to clarify the presence or absence of tumor in complex areas, such as the skull base.

Angiography rarely is necessary during evaluation of patients presenting with tumors of the sinonasal tract and usually is reserved for patients presenting with vascular tumors in which embolization is being considered. Angiography is important for patients who present with sellar or parasellar lesions that approximate, enclose, or invade the internal carotid artery.

When necessary, the vascular anatomy of the affected area (ie, sphenoid sinus invasion) can be assessed by noninvasive methods such as MR angiography (MRA) or CT angiography (CTA), reserving intra-arterial angiography for those patients in whom embolization of the tumor is being considered.

Patients who may need the sacrifice of the internal carotid artery or its branches are studied preoperatively with a cerebral blood-flow test, such as the angiography-balloon occlusion–xenon-CT scan test (ABOX-CT).

Single-photon emission computed tomography (SPECT) with balloon occlusion and transcranial Doppler also provides a reasonably accurate assessment of the adequacy of the blood supply provided by the contralateral internal carotid artery to the ipsilateral cerebral hemisphere. All these studies, however, usually are performed under very controlled circumstances and do not provide information about the status of the cerebral blood flow under stress conditions such as hypotension or hypoxia. In addition, these tests cannot predict embolic phenomena.

A metastatic workup including CT scan of the chest and abdomen and a bone scan is recommended for patients presenting with tumors that metastasize hematogenously, such as sarcomas, melanomas, or adenoid cystic carcinomas.

Transnasal endoscopic biopsy is the method of choice for sampling tumors of the paranasal sinuses. The authors prefer to defer biopsy until the imaging workup is completed; this avoids interference from surgical artifact caused by the biopsy or by nasal packing, which is often required after sampling a vascular tumor. A punch biopsy often can be performed in the office. However, vascular tumors that require multiple or extensive biopsies (ie, lymphomas, sarcomas, neuroendocrine tumors) are better obtained in the operating room.

Patients with sarcomas of the sinonasal tract that invade the dura are advised to undergo a lumbar spinal tap for cytologic analysis. These patients should undergo an MRI of the brain and spine to exclude meningeal carcinomatosis or drop metastasis.

Generally, chemotherapy is recommended for palliation of unresectable tumors or as part of combination therapy with radiation therapy (as a radiosensitizer), or as induction therapy of rapidly growing tumors, such as sinonasal undifferentiated carcinomas (SNUC) or poorly differentiated esthesioneuroblastomas or neuroendocrine carcinomas.

Combination therapy, including surgery and radiation, commonly is used because of the extent of the tumors at presentation and the impossibility of resection with true wide margins. The issue of whether preoperative external irradiation is better than postoperative external irradiation remains controversial. Most surgeons prefer to refer the patient for radiation therapy postoperatively (3-6 wk after surgery) because the cure rate offered by either regimen seems similar but increased technical difficulty and potentially greater morbidity are associated with surgery of irradiated tissues.

Surgical planning aims to facilitate a complete resection of the tumor and an adequate reconstruction with minimal morbidity and sequelae. A surgical approach is chosen based on surgeon or patient preferences and on tumor extent, vascularity, and relationship to neurovascular structures. The extirpative phase usually begins with exposure of the tumor. An adequate exposure facilitates a complete resection, preserving normal tissue and protecting important neurovascular structures such as the brain, carotid artery, and cranial nerves.

Finally, the reconstruction should restore the separation of the cranial cavity and the upper aerodigestive tract and provide an adequate cosmetic and functional rehabilitation.

A subfrontal approach facilitates exposure and resection of the cephalic boundary of the tumor with less brain retraction than a transcranial approach (bifrontal craniotomy). It also facilitates the reconstruction of the skull base and preserves the cosmetic profile of the craniofacial region, thus meeting most of the previously mentioned surgical criteria. Endoscopic approaches are associated with less brain manipulation and no brain retraction; and in very select patients, the endoscopic approach offers the possibility of preserving olfaction. Nonetheless, not all tumors are amenable to an endoscopic resection.

Perioperative prophylactic antibiotics for 48 hours, sequential compression stockings (ie, prevention of pulmonary embolism), and a secure airway are critical components of the perioperative management of patients requiring an anterior skull base resection for tumors. In general, patients undergoing an anterior skull base resection do not require a tracheotomy. The authors prefer an airway provided by an endotracheal tube wired to a premolar or molar tooth at the beginning of the surgery. The patient usually is extubated at the end of the surgery. However, a tracheotomy is recommended if the patient requires a microvascular free flap reconstruction. Ultimately, the decision to perform a tracheotomy should take into consideration the available personnel and facilities in each institution and the experience of the surgical team.

An anterior subfrontal approach usually involves a combination of incisions used to expose the intracranial and extracranial components of the tumor. A bicoronal incision provides access to the upper face and cranium, and the resultant scar is hidden inside the hairline, as depicted in the 1st image below. A lateral rhinotomy, degloving gingivobuccal incisions, or endoscopy-guided intranasal incisions (endoscopic assisted) are used to complement the cranial exposure, as depicted in the last two images below. In selected patients, such as those presenting with tumors that invade the skin, the incisions can be performed directly at the margins of the tumor.

Intraoperative navigational devices may improve the precision of incisions, craniotomies, and facial osteotomies, limiting the need for wide exposure of important anatomic structures around the tumor. During intraoperative navigation, the surgeon uses a virtual rendering of the tumor and its surrounding anatomy to guide removal, eliminating the need for conspicuous and lengthy incisions or extensive dissection of normal tissues.

The bicoronal incision divides the scalp at the level of the vertex, following a true bicoronal plane extending from the top of one auricle to the top of the other, as depicted in the 1st image above. When the surgical exposure should extend below the level of the glabella, the surgeon may increase the arc of rotation of the bicoronal scalp flap by extending the incision inferiorly, following the preauricular crease down to a level corresponding to the tragal cartilage. Carry the incision through the subcutaneous tissue, galea, and superficial temporal fascia laterally and through the pericranium centrally (ie, between the temporalis muscles). Then, elevate the scalp in a subpericranial plane transecting the pericranium at its junction with the deep temporal fascia, around the superior border of the temporalis muscle (ie, temporal line).

Once the supraorbital rims have been exposed, the supraorbital neurovascular bundle is dissected from the supraorbital notches, as depicted in the image below. When a true supraorbital foramen is present, it may be opened inferiorly using a 3 to 6mm osteotome and mallet. This maneuver allows mobilization and inferior retraction of the supraorbital neurovascular bundles and dissection of the periorbita from the superior or medial orbital walls. Thus, the bicoronal approach exposes the superior cranium and frontal area, glabella, nasal bones, temporalis muscles and temporal fossae, and the superior two thirds of the orbits.

Plan a craniotomy according to the extent of the lesion as a bifrontal craniotomy, a transfrontal sinus craniotomy, or a craniotomy that follows the margins of the tumor (ie, when the frontal bone has been invaded) as depicted in, as depicted in the 1st two images below. The craniotomy cuts also can be extended laterally for tumors that extend into the orbit or infratemporal fossa or inferiorly to include the orbital rims (ie, subfrontal approach as a monobloc bone graft). Alternatively, the supraorbital block is removed separately from the craniotomy, as depicted in the last three images below. This facilitates inclusion of the posterior orbital roofs in the supraorbital block bone graft.

A lateral rhinotomy may be used to expose the medial maxilla, providing ample exposure for the resection of tumors that extend into the ethmoid sinuses and lateral nasal wall. During the opening of the lateral rhinotomy, the medial attachment of the nasal ala is preserved to prevent subsequent ala retraction and deformity. The subcutaneous tissue and muscles deep to the ala also are preserved. This preserves the alar soft tissue support and enhances the postoperative cosmesis, preventing contraction. The perialar extension of the lateral rhinotomy is not necessary for tumors that are located in the superior sinonasal tract, such as ethmoid or nasal vault tumors.

Gingivobuccal degloving incisions can be used in combination with the bicoronal incision to avoid facial incisions. However, in general, approaching the ethmoid sinuses through a degloving approach is somewhat cumbersome because the cheek flaps are tethered by the infraorbital neurovascular bundles. All the intranasal incisions and osteotomies can be performed using endoscopic guidance, avoiding any type of facial or intraoral incision. The most common osteotomies for the en bloc resection of these tumors correspond to those used for a medial maxillectomy, combined with resection of the cribriform plate and upper septum.

Endoscopic resection

In the late 1990s, we stopped using a lateral rhinotomy, as most tumors amenable to this approach are also amenable to an endoscopic or endoscopic-assisted approach. The cranial extent may be removed using a traditional subfrontal approach (endoscopic assisted) or a completely endoscopic endonasal approach.

During a pure endoscopic approach, the tumor is debulked and then removed following a sequential layered resection. The middle turbinates are removed and then bilateral maxillary windows, bilateral sphenoidotomies, and a Draf III frontal sinusotomy are completed. These steps expose the tumor origin completely and help to identify the position of the lamina papyracea and the skull base. Removal of the lamina papyracea allows the control of the ethmoidal arteries, enhancing hemostasis and tumor devascularization, and serves as an additional resection margin. The tumor origin is then removed in layers sequentially: first the tumor and mucoperiosteum, then the bone, and then the dura and intradural tumor. Adequacy of the resection of each layer is corroborated by frozen-section analysis.

Contraindications to a pure endoscopic approach include dural involvement that extends lateral to the level of the midorbital roof, intraorbital extension, involvement of the anterior table or lateral recess of the frontal sinus, and tumor extension into facial or orbital soft tissues. Relative contraindications include gross brain parenchyma involvement and tumor extension to the lateral wall of the maxillary sinus and infratemporal fossa.

Nicolai et al reported on patients with malignant tumors of the sinonasal tract and anterior skull base treated with a pure endoscopic approach (n=134) or cranio-endoscopic technique (n=50). The authors concluded that patients with (1) minimal dural involvement and (2) tumor not involving the orbit, nasolacrimal duct, anterior wall of the maxillary sinus, and without massive intracranial extension or dural extension lateral to the orbit are candidates for an endoscopic endonasal approach. They also reported a statistically significant difference in the 5-year disease-specific survival between patients treated with pure endoscopic surgery versus combined cranio-endoscopic surgery (91.4% vs 58.8%).[6]

Due to the rarity of sinonasal tumors, no prospective studies comparing the results of endoscopic surgery versus craniofacial resection are available. Eloy at al compared retrospectively the results of endoscopic approach (n=18) versus open anterior craniofacial resection (n=48).[7] Because the difference in overall survival between the 2 groups was not statistically significant, the authors concluded that early- and intermediate-stage anterior skull base malignancies are safely and successfully treated with an endoscopic approach using proper oncologic principles.

Hanna et al reported on 120 patients treated for sinonasal cancer with endoscopic surgery alone or in combination with frontal craniotomy. The authors conclude that in well-selected patients and with proper use of adjuvant therapy, endoscopic resection results in acceptable oncologic outcomes.[8]

Carrau et al published a series of 20 patients with malignant tumors of the sinonasal cavity involving the skull base. In this cohort, 19 patients were alive without evidence of disease at a median follow-up of 22 months (range, 11-46 mo).[9]

Reports on individual histologic tumors are focused on esthesioneuroblastomas. Folbe et al reported on a multicenter study of 23 patients with esthesioneuroblastoma. In this cohort, 26.3% of the patients were Kadish stage C. The authors conclude that Kadish stage C tumors can be effectively treated using pure endoscopic techniques followed by radiation without sacrificing local control.[10] Results from a meta-analysis on 361 patients with a diagnosis of esthesioneuroblastoma by Devaiah et al suggest that endoscopic surgery is a valid approach, with survival rates comparable to open surgery.[11]

When analyzing the literature, one should consider that all available studies are retrospective; thus, they reflect the surgeons’ biases regarding the selection of the surgical approach. In general, endoscopic series comprise patients with less extensive tumors; thus, the groups are not comparable. Nonetheless, one can conclude that endoscopic and endoscopic-assisted surgeries are as effective in treating well-selected tumors of the anterior skull base as a traditional craniofacial approach.

Reconstruction

A pericranial flap is the most common technique to restore the separation of the cranial cavity from the upper aerodigestive tract following a subfrontal approach (as depicted in the images below). Elevate the pericranium as a vascularized flap based on the supraorbital vessels. Ensure that the flap created can adequately cover defects that include the cribriform plate, fovea ethmoidalis, and planum sphenoidale (and occasionally the medial orbit).

The authors prefer to elevate the pericranial flap after completion of the extirpative phase of the surgery to avoid desiccation of the flap or accidental tearing or avulsion during resection of the tumor. Following repair of any dural defect, place the pericranial flap beneath the brain and supraorbital and craniotomy bone grafts. Stabilize the craniotomy and orbital bone grafts with titanium alloy adaptation plates, as depicted in the images below. Titanium alloy plates are preferred to wires or sutures because of their superior stability. However, cost and availability may dictate the use of wires and/or sutures.

Reconstruction after endoscopic resection

Patients who undergo an endoscopic resection are most often reconstructed with the Hadad-Bassagaisteguy flap (pedicled nasoseptal flap). The entire mucoperiosteum of one side of the nasal septum is harvested pedicled on the posterior septal arteries. Two parallel incisions are made, one 1-2 cm below the olfactory sulcus and the other at the junction of the floor of the nose and the nasal septum. These incisions can be modified and performed lower and more lateral, respectively, in deference to oncologic margins. The inferior incision is extended to follow the free edge of the posterior septum and to follow the posterior choanae toward the lateral nasal wall. The superior incision crosses the rostrum of the sphenoid sinus at the level of its natural ostium.[12]

Kassam et al reported on 75 patients who underwent endoscopic extended approaches who were reconstructed with the pedicle nasoseptal flap. The authors report a decreased rate of cerebrospinal fluid (CSF) leak from 33% to 4% with the use of the pedicle nasoseptal flap.[13] Zanation et al prospectively studied the use of the nasoseptal flap for reconstruction of skull base defects associated with high-flow leaks. The authors report a 94% success rate.[14]

Other pedicle flaps have been described as alternatives for skull base reconstruction when the pedicled nasoseptal flap is not available. These flaps include transfrontal pericranial flap, in which a pericranial flap may be harvested (endoscopic assistance or via bicoronal incision) and transposed to the defect through an osteotomy at the nasion. Others include the transpterygoid temporoparietal fascia flap,[15, 16] inferior turbinate flap,[17] middle turbinate flap,[18] and palatal flap.[19, 20] A systematic review of endoscopic repair of large skull base defects revealed that vascularized flaps had a lower CSF leak rate than free grafts (6.6 vs 15.6%, respectively), and, therefore, the wide armamentarium of pedicled flaps should be used for endoscopic repair of skull base defects.[21]

Transfer the patient to a neurosurgical intensive care unit (NICU) for continuous cardiac, respiratory, and neurologic monitoring. Stay at the NICU varies but usually extends for 48 hours.

Patients undergo a CT scan with contrast within 24 hours of surgery to detect intracranial complications, such as hematoma, tension pneumocephalus, or brain contusion. Other monitoring is discussed in Complications.

For oncologic follow-up care, the authors advise the patient to return to the outpatient office for clinical examination every 6-8 weeks for the first year, every 8-12 weeks for the second year, every 12-18 weeks for the third year, every 6 months for the fourth and fifth years, and yearly thereafter. Patients may also require debridement of intra nasal crusting that forms until the nasal epithelium regenerates. Imaging of the skull base and brain is an integral part of follow-up care for areas not amenable to clinical examination. The authors prefer to use MRI 3, 6, 12, and 18 months after the surgery and then yearly. Yearly chest radiographs also are advised. This follow-up regimen is adjusted to the nature and aggressiveness of the tumor, use of adjunctive radiation and/or chemotherapy, and patient characteristics such as compliance, reliability, and distance of residence from the hospital/office.

Wound

Scalp necrosis

Necrosis of the scalp flap is rare. Patients who have been irradiated preoperatively and who also undergo a galeal flap or galeopericranial flap procedure are at risk for this complication because elevation of the flap superficial to the galea compromises the blood supply to the remaining scalp. Prolonged use of hemostatic clamps at the scalp (eg, Raney clamps) also can result in necrosis. Debridement and reconstruction using posteriorly based scalp flaps often are required to close the resultant defect.

Wound infection

Infection of the bone and/or soft tissue is most commonly the result of faulty technique (with inadequate separation of the cranial or orbital bone grafts from the sinonasal tract) or a noncompliant patient. Necrosis of the scalp exposing the bone grafts, although rare, also can lead to a wound infection. Correction of the primary problem (eg, communication with the sinonasal tract, loss of flap), debridement (usually requiring the removal of the bone flaps), and prolonged antibiotics for osteomyelitis (45 d, guided by culture and sensitivities) are the treatments of choice.

Postoperative bleeding

Postoperative bleeding is usually self-limited or easy to control with the use of topical vasoconstrictors and/or packing with hemostatic materials or self-expanding sponges. Significant postoperative bleeding most commonly arises from a branch of the internal maxillary or anterior ethmoidal arteries. If easily identifiable, the vessel may be clipped under endoscopic assistance. Angiography with embolization is reserved for patients in whom the bleeding site is not readily apparent, such as patients who underwent a reconstruction using a microvascular free flap.

Postoperative bleeding from branches of the internal carotid artery (eg, ethmoidal, ophthalmic) is not usually amenable to embolization and may lead to intracranial hematomas, requiring surgical exploration.

Intracranial

Tension pneumocephalus

Intracranial air under pressure acts as a space-occupying lesion that compresses the brain parenchyma, causing neurologic deficits, such as lethargy, disorientation, slow mentation, or hemiparesis. A CT scan without contrast can help confirm the diagnosis, as depicted in the image below. Initial treatment consists of aspiration of the air using a needle placed through a burr hole or osteotomy gap. In rapidly deteriorating or unstable patients, this measure can be lifesaving. Recurrent tension pneumocephalus is rare and is usually associated with inadequate cranionasal separation (ie, loss of the reconstructive flap) or a noncompliant patient who repeatedly blows the nose. Recurrent pneumocephalus may require bypassing the airway (ie, tracheotomy, intubation) and/or surgical exploration to close any communication between the cranial cavity and the sinonasal tract.

Cerebrospinal fluid leak

Postoperative cerebrospinal fluid (CSF) leaks after traditional techniques are initially managed conservatively with bed rest, stool softeners, and a lumbar drain (50 mL q6-8h). Persistence of the leak beyond 1 week indicates need for surgical repair. However, surgical exploration may be indicated as an initial therapy if loss of the reconstructive flap or dehiscence of the dural repair is suspected.

Patients with postoperative CSF leaks after endoscopic approaches are taken back to the operating room immediately. Usually, the leak is limited to a small area in which the graft failed to take or was displaced by the pulsation of the brain.

Meningitis/abscess

Meningitis, like pneumocephalus, CSF leak, and osteomyelitis, is usually the result of inadequate separation of the cranial cavity from the sinonasal tract. However, meningitis can occur in the absence of a CSF leak, and its presentation may be atypical due to use of perioperative prophylactic antibiotics. A CT scan followed by a lumbar puncture can help confirm the diagnosis. The treatment of choice is intravenous antibiotic therapy with adequate CSF penetration. Persistent communication between the cranial cavity and the upper aerodigestive tract should be closed as soon as the patient is stable enough to tolerate the surgery.

Management of intracranial/cerebral abscesses is similar to treatment of meningitis. However, abscesses usually require drainage. Epidural abscesses usually require the removal of contaminated free bone grafts. This creates a deformity that can be corrected in a secondary surgery.

Cerebral edema/contusion

This complication usually occurs as a result of overenthusiastic brain retraction, as depicted in the image below. Systemic corticosteroids, correction of hemodynamic problems, and electrolyte/fluid balance are essential to avoid further brain injury brought by the parenchymal swelling and subsequent increased intracranial pressure. Consider medical prophylaxis for seizures in the presence of a contusion of the brain parenchyma or if brain had to be removed as part of the oncologic surgery.

Orbital

Epiphora

A dacryocystorhinostomy (DCR) diminishes the incidence of epiphora after resection of the medial maxilla. DCR is performed by marsupializing the lacrimal sac upon its transection from the lacrimal duct. Occasionally, a DCR closes, requiring lacrimal stenting (eg, Crawford tubes) or even a revision DCR. Another cause of epiphora is failure to restore the medial canthus, causing laxity and failure of the lacrimal pump mechanism. Similarly, a lax lower eyelid caused by paralysis of the facial nerve or failure to fix the lateral canthus may lead to lagophthalmos and epiphora. Tarsal strip surgery and lateral canthopexy are indicated to resolve this problem.

Extraocular muscle limitation

Diplopia caused by dissection of the trochlea, postoperative edema, or removal of the orbital walls occurs in most patients but is self-limited, lasting fewer than 4 weeks. However, physicians should consider other causes for diplopia.

Reconstructive grafts over the orbital walls may entrap the medial, lateral, or inferior rectus muscles, resulting in restriction of the range of motion and leading to diplopia. Intraorbital dissection, such as that required when the periorbita is resected, or surgery of the cavernous sinus may injure the motor innervation of these muscles. A forced duction test helps to differentiate these problems.

Enophthalmos

Enophthalmos is the result of expansion of the volume of the orbital cavity due to resection of the orbital walls and is more pronounced if the periorbita is injured or resected. Preventing this complication by reconstructing the orbital walls with autogenous bone or titanium mesh (ie, rigid reconstruction), which is depicted in the image below, is best.

Blindness

Unexpected blindness after an anterior craniofacial resection is the result of injury to the optic nerve or its blood supply. High-dose steroids and immediate optic nerve decompression are indicated.

Endocrine/electrolyte abnormalities

Endocrine abnormalities

Hyponatremia (serum sodium < 130 mg/dL) can be produced by excessive fluid replacement or by the syndrome of inappropriate antidiuretic hormone (SIADH), which usually is caused by cerebral edema. SIADH is usually self-limited and may be treated by fluid restriction. Neurologic symptoms, such as disorientation, irritability, changes in consciousness or mentation, and seizures, require administration of hypertonic (3%) sodium chloride solution.

Conversely, ischemia or traction injury to the hypothalamus may lead to diabetes insipidus (DI), which is caused by insufficient production of the antidiuretic hormone. DI is manifested by the inability to concentrate urine, leading to the voiding of large volumes, hypernatremia, and hypovolemia. Serum sodium greater than 145 mg/dL and a urine specific gravity greater than 1.020 mg/dL confirm the diagnosis. Aggressive fluid replacement and aqueous vasopressin (2.5 U q4h) is the initial treatment.

Closely monitor patients with diabetes mellitus, especially if corticosteroids are being administered. Regular insulin, administered following a sliding scale, is commonly required to control the glycemia.

Electrolyte deficits

Other electrolyte disorders, such as hypocalcemia, hypomagnesemia, and hypophosphatemia, may be encountered in patients who require extensive skull base surgery. Replacement of these electrolytes should be immediate, using calcium gluconate 10% (10 mL at < 1 mL/min), phosphate solution (10-15 mmol of sodium phosphate in 250 mL of 5% dextrose solution over 6 h), and magnesium sulphate (2-4 g in 100 mL of isotonic sodium chloride solution over 30 min). Because of the length of some cranial base surgeries, these electrolyte deficiencies may develop intraoperatively or during the immediate postoperative period. This is especially true in patients requiring transfusion of more than 5 units of PRBC.

The prognosis of lesions that require a subfrontal approach for their resection mostly depends on histologic diagnosis and the completeness of the resection. On one side of the spectrum, high-grade sarcomas and melanomas have a dismal prognosis because of their propensity for early metastasis (ie, < 10% of patients alive and without disease at 5 y). Conversely, adenocarcinomas have an excellent prognosis (ie, >75% of patients alive and without evidence of disease at 5 y). Patients with SCCA have a 5-year survival rate of 60%. Adenoid cystic carcinoma of the skull base is somewhat unpredictable but behaves more aggressively than adenoid cystic carcinomas in other parts of the head and neck (eg, salivary gland).

Use of endoscopic techniques to complement or replace traditional approaches is rapidly expanding. Intraoperative navigational devices (computer-assisted surgery) and high-definition monitors and cameras, customized instruments, and new endovascular neurosurgery techniques that allow intraoperative control of the intracranial vasculature will contribute to the advancement of these techniques. Recent advances include combining expanded endonasal approaches with a transoral robotic assisted approach for extensive skull base tumors.[22] Furthermore progress in imaging has lead to the development of virtual surgical planning as well as augmented reality, where a three-dimensional image of critical structures is superimposed onto the endoscopic surgical view.[23]

Adjunctive techniques, such as brachytherapy, radiosurgery, intra-arterial chemotherapy, and chemotherapy combined with radiation, may have a role in treatment of these lesions. However, the role of these treatments remains undefined. Reports are mainly anecdotal, and their use should be limited to controlled protocols, palliative cases, or poor surgical candidates for whom conventional therapy has failed.