Skull Base Tumors Treatment & Management

The goal of therapeutic intervention is to maximize the patient’s functional outcome while minimizing morbidity. A team approach to treatment is often required. Specialists involved in the diagnosis and treatment of patients with skull base lesions include the following:

• Oncologist/neuro-oncologist

• Radiation oncologist

• Neurologist

• Neurophysiologist

• Ophthalmologist/neuro-ophthalmologist

• Oral/maxillofacial surgeon

• Otorhinolaryngologist

• Plastic surgeon

• Neurosurgeon

Treatments may include medical intervention, radiation therapy, surgical intervention, or a combination thereof. A tissue diagnosis is generally required prior to medical or radiation therapy. Chemotherapy can be used as a primary or adjunctive treatment of many skull base tumors.

Radiation therapy or stereotactic radiosurgery can also be used to primarily treat a skull base tumor or can be used as adjuvant therapy after surgical resection.

Of 42 patients who underwent image-guided intensity-modulated radiotherapy (IG-IMRT) for skull base chordoma or chondrosarcoma, 5-year overall survival rates and local control rates were 85.6% and 65.3% for chordoma patients and 87.8% and 88.1% for chondrosarcoma patients. Ten patients progressed locally, 8 of whom were chordoma patients and 2 chondrosarcoma patients. Both chondrosarcoma failures were in higher-grade tumors (grades 2 and 3), and none of the 8 patients with grade 1 chondrosarcoma failed. Gross total resection and age were predictors of local control in the chordoma and chondrosarcoma patients, respectively. ^[21]

Surgical approaches for skull base tumors include the following: modified orbitozygomatic, pterional, middle fossa, retrosigmoid, far lateral craniotomy, and midline suboccipital craniotomy. ^{[2, 1, 3, 4]}

Typically, complete surgical extirpation of osteomas is curative; if the mass is large, skull reconstruction may be necessary. For chondromas, symptomatic lesions are treated with radical resection that extends back to normal bone margins to prevent recurrence. Even after optimal treatment of the primary tumor, most patients with chordoma have local and/or metastatic recurrences that cannot be cured. Conventional chordoma is unresponsive to cytotoxic chemotherapy. Molecular therapies (including imatinib, sorafenib, and EGFR inhibitors) have been introduced but have had limited impact on disease outcome. ^[22]

Complete surgical resection of hemangioma is curative. Radiation therapy is sometimes recommended for incompletely resected or multiple tumors (particularly in the spine), but it is of uncertain efficacy. Incidentally found hemangiomas should be managed conservatively.

For dermoid and epidermoid tumors of the skull, surgical treatment is usually indicated for symptomatic or progressive lesions. These lesions often involve a communication between the skin and the intracranial cavity through a tract that should be visualized in any surgical resection.

Because of the high rate of progression of plasmacytoma plasma cell tumors to multiple myeloma, a conservative surgical approach with aggressive radiotherapy may achieve the greatest response with the lowest morbidity. In easily accessible lesions, optimal treatment includes complete surgical resection followed by radiation therapy. Systemic evaluation to rule out systemic disease should continue for at least one year after the initial diagnosis.

For paragangliomas, catecholamine secretion can be diagnosed with urine or serum studies. In functional tumors, secretion must be blocked prior to surgical intervention to prevent a hypertensive crisis. Surgery offers the best chance of cure or extended control of the disease. Despite being histologically benign, local invasiveness often leads to recurrence after partial resection, even when followed by radiotherapy. Radiosurgery can be used to decrease tumor volume and provide local disease control.

For chondrosarcoma, surgical resection followed by fractionated conformal radiation therapy and surgery with further therapy, when indicated, have both been associated with 5-year survival rates of more than 90%. ^{[23, 24]}

For osteogenic sarcoma and fibrous sarcoma, malignant tumors are treated with radical surgical resection with extensive margins, although complete excision is often impossible for lesions at the skull base. Radiotherapy is usually given postoperatively. Charged-particle irradiation, such as proton beam or helium, is particularly effective for chordoma or chondrosarcoma of the skull base and, if available, is the technique of choice. Despite aggressive therapy, recurrence is common. Gross total surgical resection correlates with lower recurrence rates and is the strongest factor in patient survival. ^[25]

Nerve sheath tumors

For vestibular schwannomas, treatment aims to cure the tumor and preserve neurologic function. Surgery using microsurgical techniques is highly effective. Facial nerve function can be preserved in more than 95% of patients with small tumors (< 2 cm) but in less than 50% of patients with tumors larger than 3 cm. Complete resection cures these tumors, and the slow growth rate allows subtotal resection or conservative treatment in some older patients with minimal symptoms. ^[26]  Radiosurgery is an excellent alternative to surgical resection in tumors less than 3 cm in diameter. Local control is achieved in more than 90% of patients, and hearing has been preserved in a greater proportion of patients than after other forms of surgery. However, delayed hearing loss, delayed facial weakness, and delayed trigeminal sensory loss have been reported in some patients 2-3 years after radiosurgery. Radiosurgery prevents surgical morbidity, and, for well-selected patients at an experienced center, it can be the treatment of choice.

Surgical resection is highly successful in providing a cure or long-term control of trigeminal schwannoma. Radiosurgery may also control the disease in some patients.

Meningioma

Many skull base meningiomas are asymptomatic or minimally symptomatic. Given the frequency with which vital structures such as cranial nerves and cerebral vessels are involved, observation is sometimes a prudent strategy. When a skull base meningioma requires treatment, surgical intervention is generally the first line because a complete resection is often curative. Partial resection is the surgical objective for tumors in which complete removal would require an unacceptable risk of neurological injury.

The experience of the individual surgeon and comfort level of the patient are intimately involved in planning the operative goals. Preoperative embolization decreases tumor vascularity and, therefore, intraoperative blood loss. In smaller tumors, embolization may not be required. Advanced imaging techniques such as 3-dimensional reconstruction and intraoperative MRI can greatly assist the surgeon during tumor removal.

Although tumor removal can lead to improvement in some preoperative neurologic deficits, cranial neuropathies are frequently irreversible. Skull base locations such as the medial sphenoid wing, the clivus, the cerebellopontine angle, and especially the cavernous sinus often allow only subtotal resection because of the high risk of injury to adjacent structures such as the internal carotid artery or cranial nerves. Operative morbidity rates associated with skull base meningiomas can be as high as 14% and is significantly riskier than the treatment of convexity lesions. ^[27]

Radiotherapy of skull base meningiomas is indicated in some cases of postoperative residual tumors or tumor recurrence and in some tumors with malignant histology results. Under circumstances of medical instability or anatomic contraindication for surgery, radiotherapy has been used as primary treatment. In meningiomas throughout the intracranial space, tumor regression or stability at 5 and 10 years has been achieved in 95% and 92% of patients, respectively. Radiation has been shown to be very effective as an adjunct in the treatment of tumors that require subtotal resection.

Proton beam radiotherapy delivers heavily charged particles that may be effective in the treatment of deep tumors, while minimizing damage to normal tissue. Radiosurgery delivers focused radiation in one large dose in an attempt to minimize damage to adjacent structures. Radiosurgery is performed with a linear accelerator or gamma rays (gamma knife) as the energy sources and is limited to tumors smaller than 3 cm in diameter. Radiosurgery is particularly useful in older or infirm patients who cannot undergo surgery. Gamma knife radiosurgery alone can provide excellent control. Another approach is stereotactic radiosurgery (SRS), in which radiation is given in multiple small fractions for meningiomas of the cavernous sinus or tumors close to the brainstem. Radiosurgery has become the preferred method for delivering radiotherapy to most patients with meningiomas.

A study of long-term outcomes of SRS treatment for WHO grade I posterior fossa meningiomas (PFMs) reported high tumor control and a low incidence of post-SRS neurologic deficits compared with those obtained using alternativee treatment modalities. Lesion volumetric response at the short-term follow-up of 3 years is predictive of the long-term response at 5 and 10 years. ^[28]

Medical treatment of skull base meningiomas is largely limited to steroid therapy for the short-term treatment of peritumoral edema. Hormone and chemotherapeutics have not met with significant clinical success.

Tumors of the anterior cranial fossa

Nasopharyngeal carcinoma is the most common skull base lesion that requires multidisciplinary surgical management. Complete surgical resection with tumor cure is the operative objective.

The following case is an example of a lesion managed nonsurgically. The patient is a 68-year-old man with squamous cell carcinoma with invasion of his right temporal bone and involvement of his right sigmoid sinus. Surgical excision would require resection of the right sigmoid sinus. Therefore, cerebral angiography (see the image below) was performed, demonstrating no filling in the left transverse sinus. Because the patient had venous drainage that appeared to pass exclusively through the right transverse sinus, balloon test occlusion (BTO) of the sinus was performed.

The balloon catheter was passed from the femoral vein into the right transverse sinus. The balloon was inflated to occlude the sinus (see the first image below). A concurrent angiogram demonstrated no flow in the right or left transverse sinus (see the second image below). The patient was carefully monitored for neurologic changes and experienced headaches that improved upon deflation of the balloon. The BTO demonstrated that surgical resection of the tumor posed a high risk of venous infarct due to impaired sinus drainage, and the patient received palliative radiation therapy.

Malignant Tumors of the Skull Base

As stated above, malignant neoplasms of the skull base require a unique approach to surgical intervention. Pieper et al described an algorithm for choosing the proper operative approach to these tumors. ^[29] The authors divided the lesions into those that involve the anterior skull base, the clivus, or the lateral skull base. Origitano et al added a further contribution regarding the management of malignant lesions of the anterior skull base. ^[30]

The goal of surgery for malignant cranial base masses differs from that of benign lesions in that an oncologic resection, including a margin of normal tissue, is optimal. Adjacent vital normal tissue often limits resection margins. This emphasizes the need for multidisciplinary management of these lesions, taking advantage of advances in radiotherapy and chemotherapeutics.

Anterior skull base

When possible, a tissue diagnosis is established via a minimally invasive biopsy. Extensive resection of malignant lesions of the anterior skull base is performed through an intracranial, extracranial, or combined approach. The 2 most common intracranial approaches are the orbitozygomatic craniotomy and the bifrontal craniotomy, which may be extended to include superior orbital rim osteotomy and nasion resection, as indicated.

Bifrontal craniotomy provides access to the undersurface of the frontal lobe, allowing an extradural subfrontal approach to the floor of the anterior fossa. Extracranial approaches are designed to access a malignant lesion that originated in the nasal or paranasal tissues. Incisions for extracranial approaches may be transfacial or sublabial, the latter of which allows the surgeon to access lesions near the sella turcica or those that involve the clivus. Without the addition of an intracranial component, these approaches may be limited at the superior border of the required resection.

Clivus

Minimally invasive methods to obtain a tissue diagnosis may be appropriate for malignant tumors that involve the clivus, as aggressive resection is not indicated for certain lesions (eg, plasmacytoma, poorly controlled systemic malignancy). Endoscopic biopsy has become a favored approach to achieve this goal.

When aggressive surgical resection is indicated, a subfrontal or transfacial approach, as described above, is commonly used. In addition, lesions confined to the sella turcica or upper third of the clivus may be adequately exposed using a sublabial transsphenoidal approach. Lesions that involve the inferior two thirds of the clivus are more likely to require a sublabial incision and maxillotomy.

Lateral skull base

In their series, the authors note that malignant lesions of the lateral skull base usually originate in the extracranial infratemporal fossa. Neurofibrosarcomas associated with NF-1 or tumors that originate in the parotid gland or paranasal sinuses (via perineural spread) were the most common. Also notable were histologically aggressive meningiomas that had invaded the infratemporal fossa or temporal bone. In a series of 95 patients with lateral skull base malignancies, McGrew et al reported 35 patients with epithelial tumors (eg, squamous cell carcinoma), 28 patients with salivary malignancies (eg, adenocarcinomas), and 32 patients with tumors of mesenchymal origin (eg, chondrosarcoma). ^[31]

The optimal surgical approach to lateral skull base lesions confined to the infratemporal fossa (and possibly the floor of the middle fossa) depends on the anatomy of the region, specifically the relationship of the lesion to the internal carotid artery. For lesions lateral to the internal carotid artery (ICA), a preauricular approach with zygomatic osteotomy may be used. Lesions of the infratemporal fossa lying medial to the ICA are best exposed via mandibulotomy. For all lesions in the infratemporal fossa, proximal and distal exposure and control of the internal carotid artery is prudent.

Lateral skull base malignancies near the jugular foramen or temporal bone may be approached through a postauricular incision and transjugular approach and/or petrosectomy.

Extensive tumors that involve the lateral skull base may require complex reconstructive plans, including free tissue transfers. Optimally, all reconstructive flaps should be planned in the preoperative and perioperative setting. Additionally, the authors emphasize the importance of dural competency in regard to the prognosis of patients with malignant skull base lesions and in regard to the meticulous reconstruction following complex skull base tumor resection. Meticulous dural closure and cranial reconstruction are the surgeon’s best tools in the prevention of the most common complications, which include cerebrospinal fluid (CSF) leak and infection. ^[32]

As described above for meningioma, radiation therapy has been successfully applied as both a primary and an adjunctive modality in the treatment of benign and malignant skull base neoplasms. Among radiosurgical modalities, gamma knife radiosurgery (GKRS) technology is the most thoroughly described (see the image below).

Meningioma

GKRS has been well established in the treatment of meningiomas smaller than 3 cm in diameter. Pollock reviewed 303 patients treated with GKRS. Seventy percent of the lesions were located at the skull base, with an average tumor volume of 7.3 cm³. Following GKRS, 94% of tumors remained stable or decreased in size. Treatment-related complications occurred in 8% of the patients. ^[33]

Vestibular schwannoma (acoustic neuroma)

In a review of treatment options and follow-up of 162 patients treated for vestibular schwannoma, Kondziolka et al described a 70% tumor reduction rate and a 94% tumor control rate using GKRS. They emphasize the use of radiosurgery as a primary treatment modality but recommend open surgical resection for patients with vestibular schwannomas that require brain stem decompression or patients with greater than 3 cm of extracanalicular extension. ^[34]

Subtotal resection followed by GKRS has proven to be a viable treatment option for large vestibular schwannomas, owing to good tumor growth control and facial nerve function preservation, plus the possibility of preserving serviceable hearing and the low number of complications. ^[35]

In a study by Haque et al, 383 patients were treated for an acoustic neuroma by a single surgeon using a facial nerve–sparing paradigm. Larger tumors were treated with initial microsurgical resection, focusing on facial nerve preservation and leaving residual tumor if the facial nerve was determined to be at risk, while smaller tumors and postmicrosurgical tumor regrowth were treated with GKRS. The results from the 151 patients treated with microsurgery showed that facial nerve–sparing microsurgery provided good tumor control (13.2% of patients required radiosurgery for tumor regrowth after microsurgery) with excellent facial nerve preservation rates (97% of patients initially treated with microsurgery had House-Brackmann grade I or II function at last follow-up), showing the efficacy of this facial nerve–sparing paradigm for acoustic neuromas. ^[36]

Pituitary adenoma

In a review of radiosurgical treatment of pituitary adenomas, Witt discussed the dual therapeutic goals of tumor growth control and endocrine cure. His review demonstrated a control of tumor growth in 92-100% of tumors. The goal of endocrine cure was more difficult to assess because consistent definitions of cure have not been established. Based on the criteria defined in each particular study, endocrine cure rates of 0-96% were reported in cases of growth hormone-secreting adenomas and 0-84% in prolactinomas. Witt recommended GKRS as the best option in the treatment of small, medically refractory lesions in surgically inaccessible locations. ^[37]

One significant complication related to radiotherapy or radiosurgery is radiation-induced necrosis. Radiation necrosis may mimic tumor recurrence and can produce significant mass effect through edema (see the image below). Positron emission tomography (PET) can be used to help distinguish radiation necrosis from recurrent tumor. ^{[38, 7]}

Endoscopic surgery

Endoscopic neurosurgery offers a minimally invasive route to specific lesions and is increasingly being implemented as a tool for the biopsy and removal of these lesions. The role of endoscopy in accessing and resecting tumors of the skull base has been evolving since it was first used for the intranasal removal of pituitary tumors. ^[39] Expanding upon the original transnasal approach, many centers have developed different approaches that increase the applicability of endoscopic surgery.

Although prior work in this field has depended on cadaveric studies, case reports, and small case series, larger center experiences are now emerging in the literature. As the field develops, indications continue to expand and outcomes after endoscopic surgery continue to improve. The most common endoscopic skull base procedures include the transsphenoidal approach to sellar lesions, but this may change as other approaches gain popularity.

Advantages of endoscopic skull base surgery include its ability to access areas that a conventional microscope cannot and better visualization with the panoramic endoscopic view. In addition, the endoscope can gain access to many lesions of the skull base with minimal manipulation of neurovascular structures and decreased brain retraction.

Disadvantages of endoscopic surgery compared with more traditional minimally invasive techniques include visualization, difficulty due to the loss of binocular vision, and a moderate risk of CSF leak. In addition, operating in an area where access is limited creates disadvantages in itself, such as limited visualization of the lesion, difficulty inserting and using certain instruments, and difficulty controlling bleeding in the event of a hemorrhagic complication. 

Endoscopic approaches

Traditional approaches to anterior skull base lesions involve a craniotomy, such as the frontal, bifrontal, expanded bifrontal, frontotemporal orbitozygomatic, and transbasal approaches. Although effective, these approaches carry risk of morbidity, including dissection of the temporalis muscle, risk to the frontalis branch of the facial nerve, and creation of an epidural space. Specific endoscopic approaches can avoid these complications through minimally invasive access. ^{[40, 39]}

The endoscopic endonasal approach has become the standard of care because it provides minimally invasive access to a large portion of the skull base, including anterior and middle cranial fossae and sellae and suprasellar and parasellar regions, and it has been associated with lower surgical morbidity and shorter length of hospitalization. ^[41]

Transnasal approaches

Through the transnasal approach, it is possible to perform transcribriform, transclival, and transodontoid approaches. These approaches target lesions of the olfactory groove, the lower two thirds of the clivus, and the odontoid-cervico-medullary junction, respectively. ^[42]

Transsphenoidal approach

This approach is the most commonly used and can be employed in the transsellar, transtuberculum, transplanum, transclival, and transcavernous approaches. These approaches permit access to the sella, supracellar cistern, upper third of the clivus, and the medial cavernous sinus.

Transethmoidal approach

This endoscopic approach is used for access through 3 structures: transfovea ethmoidalis, transorbital, and transsphenoidal. These approaches permit access to lesions of the anterior fossa, orbital apex, and cavernous sinus, respectively, .

Transmaxillary approach

Access through the maxilla must be used to perform a transpterygoidal approach, which permits access to the pterygopalatine fossa, infratemporal fossa, Meckel cave, the petrous apex, the lateral sphenoid sinus, and the lateral cavernous sinus.

Endoscopic surgery of the skull base provides a minimally invasive alternative to open surgery for many specific lesions.

Anterior approaches

As described above, approaches to the anterior skull base can be divided into intracranial, extracranial, and combined approaches. Intracranial approaches often include a bifrontal craniotomy, which may be expanded to include superior orbital osteotomies and removal of the nasion. ^[29] Extracranial routes to the anterior skull base may involve transfacial incisions or sublabial incisions for facial degloving procedures. Operative corridors through the oral cavity may also be achieved. Descriptions of common open surgical approaches with case examples are provided below.

Orbital approaches

The anterior cranial base, which is located behind and above the orbit, can be approached through a pterional craniotomy with orbitozygomatic osteotomy. This exposure also offers access to lesions of the middle cranial fossa, including tumors of the gasserian ganglion and tumors that involve the cavernous sinus. It can also be used to approach selected lesions in the posterior fossa, such as basilar artery aneurysms.

A case example is a 66-year-old man who presented with slowly progressive right eye proptosis and unilateral loss of visual acuity (see the images below). This en plaque meningioma of the sphenoid wing also invaded the orbit and involved the periorbita. It was completely resected using a frontotemporal craniotomy with orbitozygomatic osteotomies.

Nasal cavity (transsphenoidal) approach

Tumors in the sella turcica, including those with limited extension above the diaphragma sella, can be approached through the nasal cavity by a transsphenoidal approach. This is the most commonly used approach to pituitary adenomas. Very large tumors of the sellar and suprasellar region may require a combined surgical approach, including a transsphenoidal approach and pterional craniotomy (see the image below).

A case example is a 69-year-old woman who presented with bilateral deterioration of vision but no other endocrine or cranial nerve symptoms or findings. MRI (see the image above) demonstrated a very large tumor that arose from the sella turcica, with significant suprasellar extension. This tumor required a combined pterional craniotomy and transnasal transsphenoidal approach in order to achieve a gross total resection.

Midface approach

A transfacial approach can be used to resect tumors that range from the paranasal sinuses to the upper one third of the clivus, which forms the anterior wall of the posterior cranial fossa. When mandibular exposure or resection is necessary, the midface can be degloved.

A case example is a 73-year-old man with adenocystic carcinoma of the ethmoid sinuses. T1-weighted MRI (see the first image below) showed tumor involvement of the ethmoid sinuses and floor of the anterior fossa in the region of the cribriform plate. CT scan (see the second image below) showed extension of the mass into the middle fossa, anterior to the temporal lobe. The patient underwent a combined transfacial and transcranial approach for resection of the tumor, with a pericranial graft reconstruction of the dura.

Transoral approach

Tumors of the upper clivus can be approached using a sublabial, transoral, or transpalatal approach. Transoral and transpalatal approaches require an incision in the posterior pharynx. Clival approaches can be extended via a mandibular osteotomy in order to access lesions that involve the odontoid process.

A case example is an 80-year-old woman who presented with double vision and a right sixth nerve palsy. An MRI one year previously had demonstrated no intracranial lesions. MRI on admission (see the image below) demonstrated a clival tumor with growth into the right cavernous sinus. This tumor was subtotally resected using a sublabial approach, above the palate. The patient had no new postoperative deficits. She was further treated with GKRS.

Middle fossa approaches

Lateral approaches to the middle cranial fossa go through the temporal bone to access tumors in the temporal bone, middle ear, pterygoid fossa, gasserian ganglion, cavernous sinus, and middle third of the clivus. The petrosal or presigmoid approach is one example in which areas of the petrous portion of the temporal bone are drilled away, allowing access to the middle fossa. These approaches require navigation through a very small corridor adjacent to structures such as the inner ear and the facial nerve. Make all attempts to avoid damaging these structures if they are still functional.

A case example is a 68-year-old man who presented with a seizure after developing slowly progressive double vision and left-sided hearing loss. An MRI (see the image below) demonstrated a large meningioma that involved the petrous apex and clivus. The lesion caused considerable mass effect on the brain stem. Angiography did not demonstrate vascular supply that was appropriate for embolization. A presigmoid approach was used to achieve a near-total resection. A small amount of residual tumor in the Meckel cave was treated with GKRS.

Posterior approaches

Posterior approaches to the skull base include the extreme or far lateral approach, retromastoid craniotomy, and retrosigmoid/suboccipital craniotomy or craniectomy. An extreme lateral approach exposes the lower third of the clivus, cerebellopontine angle, and petrous surface of the temporal bone. Retromastoid craniotomy and suboccipital craniotomy are used to approach lesions of the cerebellopontine angle and the petrous surface of the temporal bone.

A 23-year-old woman presented with headache and bilateral abducens palsies. T1-weighted MRI (see the first image below) showed a hypointense mass within the posterior cranial fossa that compressed the pons and medulla posteriorly. T2-weighted MRI (see the second image below) demonstrated a hyperintense mass consistent with an epidermoid. The patient underwent suboccipital craniectomy for complete resection of the mass.

A 38-year-old woman presented with chronic headaches and tingling in the fingers of her left hand. MRI scan (see the image below) demonstrated a contrast-enhancing lesion at the foramen magnum, consistent with a meningioma. This tumor was completely resected using a far lateral approach and suboccipital craniotomy with C1 laminectomy.

Complications of surgery at the skull base can be classified into neurologic, wound related, cosmetic, and perioperative.

Neurologic

Neurologic complications include cranial nerve injuries and injury that affects the CNS. The location of the tumor determines which cranial nerves are at risk. Stretch or traction injury, thermal injury due to electrocautery, or sharp transection of nerves can occur. Cranial nerves displaced by or under tension from tumor growth are most vulnerable, but any cranial nerve in or near the operative field is at risk.

Concurrent injury to multiple cranial nerves can be devastating. For example, concurrent injury to cranial nerves V and VII may cause the eye to be both insensate and exposed because of an inability to close the eyelid. This puts the patient at risk for corneal ulceration and infection and, ultimately, loss of the eye. A large cerebellopontine angle tumor, such as a vestibular schwannoma, is an example of a tumor that may damage both cranial nerves V and VII.

Injury to the lower cranial nerves (IX, X, XI, XII) can produce swallowing difficulties and can place the patient at risk for aspiration and pneumonia. Foramen magnum meningiomas and chordomas of the lower clivus can grow near these nerves.

Intraoperative cranial nerve monitoring is designed to alert the surgeon when nerves are at risk of damage. Cranial nerves II-XII can be monitored intraoperatively. The facial nerve is frequently monitored using electromyography (EMG), and the auditory nerve can be monitored with brainstem auditory evoked responses (BAERs).

Hearing loss after surgery for vestibular schwannoma is a concern. In a comparative analysis, Wind et al found that standard audiometry and patient-perceived hearing function evaluation may be helpful in identifying subjective hearing loss after surgery for vestibular schwannoma and could aid in determining further treatment for these patients. ^[43] Rachinger et al determined that the origin of the tumor is of vital importance to the prognosis for cochlear nerve preservation when performing vestibular schwannoma surgery. Of the patients in their study, hearing was preserved in 42% with superior vestibular nerve origin, versus 16% with inferior vestibular nerve origin. ^[44]

Operative morbidities that affect the CNS include the following:

• Cerebrospinal fluid (CSF) leak

• Pneumocephalus

• Intracranial hemorrhage

• Hydrocephalus

• Cerebral contusion

• Meningitis

• Cerebral edema

• Stroke

• Epidural abscess

• Seizures

• Diabetes insipidus

• Altered mental status

• Anosmia

CSF leaks occur if the dura is violated either intentionally or by tumor invasion. They may also result from hydrocephalus. Many areas of the skull base dura are thin and difficult to repair. Dura that lies over the cribriform plate can be troublesome because the olfactory nerves travel through it into the nasal cavity. The use of pericranial flaps to repair holes in the dura decreases the risk of CSF leaks. Other vascularized flaps (eg, temporalis muscle flaps, trapezius muscle flaps, free radial forearm flaps, free rectus abdominis muscle flaps) are used when appropriate. Complications associated with CSF leakage include poor wound healing and meningitis.

Wound related

Wound complications include the following:

• Cellulitis

• Infected cranial bone flap or osteomyelitis

• Oronasal fistula

• Necrosis of a pericranial flap

• Encephalocele

• Crusting of the nasal cavity

Because the nasal cavity may be included in the wound, chronic sinusitis from infection, loss of sinus mucociliary transport, and stenosis of the sinus ostia can occur. In addition, nasal airway stenosis may occur.

Cosmetic

Cosmetic complications include enophthalmos, facial scar, burr hole-related scalp depression, and ocular dystopia. Cosmetic deformity is more likely with anterior surgical approaches because they may involve the orbit or face. After surgery, the position of the eye and the contour of the facial structures should be maintained. Various reconstructive techniques, including free flaps and bony reconstruction with miniplate fixation, have been developed to address these issues.

Perioperative

Intraoperative blood loss may be significant because of the extensive dissection that is sometimes necessary for approaches to the skull base. The scalp, skull, and dura are highly vascular; therefore, blood loss should be monitored closely and blood products should be replaced aggressively.

Because skull base tumors can be any one of many unrelated tumors, outcome and prognosis vary.

Benign tumors, such as meningiomas, can be resected with minimal mortality and acceptable morbidity. In a series of skull base meningiomas by Sekhar, the rate of total excision was 60%, the postoperative mortality rate was 15%, and the postoperative major morbidity rate was 16%. ^[19] Sixty percent of patients developed a new cranial nerve deficit, and 3% of the patients had a recurrence.

Malignant tumors, such as nasopharyngeal carcinoma and esthesioneuroblastoma, can also be controlled with skull base resection. In a study by Levine et al, a survival rate of 82% was obtained with craniofacial resection of esthesioneuroblastoma, compared with a rate of 37% before the technique of skull base resection. ^[45] In a study by Van Tuyl and Gussack, dural invasion was a factor associated with prognosis; when this occurs, prognosis is worse. ^[46]

Published case series reporting postsurgical outcomes for chordoma indicate that locoregional recurrence affects more than 50% of patients treated with macroscopic complete resection with or without radiation therapy. A high proportion of recurrences occur late (after 5 and 10 years), requiring long-term follow-up. ^[47]

Forty-one patients with esthesioneuroblastomas treated at UCLA were retrospectively studied to profile clinical presentation and treatment results. The 5-year recurrence-free survival (RFS) and overall survival (OS) were 54% and 82%, respectively. Modified Kadish stage was the only factor that was identified as affecting OS, and tumor grade was the only factor that was shown to have an independent impact on RFS. There was no statistical difference in survival between the surgical approaches chosen, but the endoscopic approach was associated with a decreased length of hospital stay, as well as reduced blood loss, ICU admission, and complications. ^[48]

Hayhurst et al studied benign and malignant skull base lesions in 23 children ranging from 13 months to 15 years who underwent resection. They concluded that children tolerate these procedures well. They experienced minimal surgical morbidity and good long-term success in controlling the tumor and in functional outcomes. Adjuvant treatment was sometimes required. ^[49]