Endoscopic endonasal approaches to the skull base pathology have developed and evolved dramatically over the past 2 decades, particularly with collaboration between neurosurgery and otolaryngology physicians. These advances have increased significantly the use of such approaches beyond just resection of pituitary adenomas, including a variety of skull base pathologies. As the field has evolved, so has our understanding of the complications accompanying endoscopic skull base surgery, as well as techniques to both avoid and manage these complications. These are discussed here.
Key points
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Expanded endoscopic resection of pituitary and complex skull base pathology requires an understanding of medical and surgical complications unique to these surgical techniques.
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Common medical complications include anterior and posterior pituitary dysfunction and meningitis; other medical complications such as venous thromboembolism or pneumonia are rare.
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Common surgical complications include vascular injury, cerebrospinal fluid fistula owing to reconstruction failure, cranial nerve injury, and infection/meningitis.
Introduction
The use of endoscopic endonasal approaches (EEA) to the skull base pathology has evolved significantly over the past 2 decades. Development of the 2-surgeon collaboration between neurosurgery and otolaryngology physicians for the endoscopic resection of pituitary adenomas has led to significant innovation and expansion of this approach to various skull base pathologies. As indications have expanded, surgeons have begun to define the expected incidence of common complications and adopted techniques to avoid or manage these adverse outcomes. With expansion of endoscopic approaches to more challenging tumors (ie, malignancies, intradural pathology), it is imperative that fundamental skull base principles are not short changed for the sake of performing an approach. In this article we review the complications and common pitfalls of the EEA for complex cranial base pathology.
Introduction
The use of endoscopic endonasal approaches (EEA) to the skull base pathology has evolved significantly over the past 2 decades. Development of the 2-surgeon collaboration between neurosurgery and otolaryngology physicians for the endoscopic resection of pituitary adenomas has led to significant innovation and expansion of this approach to various skull base pathologies. As indications have expanded, surgeons have begun to define the expected incidence of common complications and adopted techniques to avoid or manage these adverse outcomes. With expansion of endoscopic approaches to more challenging tumors (ie, malignancies, intradural pathology), it is imperative that fundamental skull base principles are not short changed for the sake of performing an approach. In this article we review the complications and common pitfalls of the EEA for complex cranial base pathology.
Endocrinologic complications
The most frequent postoperative systemic complications relate directly to the manipulation or disruption of the normal hypothalamic–pituitary axis. Diabetes insipidus (DI), the syndrome of inappropriate antidiuretic hormone release, and panhypopituitarism consequently occur almost exclusively in those populations of patients in which the pituitary gland, stalk, or hypothalamus are involved in either the pathology or the surgical corridor. These can be classified further pathophysiologically as perturbations of anterior gland (secretory function) or posterior gland (osmostat function).
Many studies have suggested equivalent rates of postoperative sodium dysregulation in microscopic and endoscopic pituitary surgery, approximating 11% to 14% in a recent metaanalysis. Risk factors for developing postoperative DI (either transient or permanent) include tumor size, young age, and pathology involving the posterior gland or stalk, that is, Rathke’s cleft cyst or craniopharyngioma. Pars intermedia tumors and cystic adenomas likely confer an intermediate increase in risk, as does surgical exploration of the posterior gland and intraoperative traction on the pituitary stalk. These perturbations often manifest within the first 48 to 72 hours after surgery. However, delayed postoperative hyponatremia occurs in approximately 15% of cases, peaking between 1 and 2 weeks after surgery, leading to readmission in 6.4% of cases.
Management of postoperative sodium fluctuations starts with vigilant attention to laboratory values, often by checking serum sodium and urine specific gravity every 6 hours for the first 2 to 3 days after surgery, and checking serum sodium on a postoperative clinic visit. The syndrome of inappropriate antidiuretic hormone release is most often mild and managed by fluid restriction and free water deprivation; rare refractory or severe cases may require hypertonic infusion. DI may likewise be mild and managed by drinking free water to thirst, or may require desmopressin by various routes. By carefully educating patients on the signs and symptoms of sodium imbalance and the avoidance of excessive free water on discharge, it may be possible to reduce the incidence of delayed postoperative hyponatremia requiring readmission. Last, the surgeon must be mindful of the possibility of the so-called triple phase response, which encompasses the syndrome of inappropriate antidiuretic hormone release, transient DI, and delayed postoperative hyponatremia.
Hypopituitarism after pituitary surgery likewise has not been shown to differ significantly between microscopic and endoscopic approaches, in approximately 3% to 6% of cases. Adrenal crisis after such surgery can be fatal, although this can be avoided easily with judicious use of preoperative, intraoperative, and postoperative steroid administration. Preoperative low fasting morning cortisol should alert the surgeon that stress dose steroid administration on induction of anesthesia and subsequent taper to a maintenance dose may be indicated. Fasting morning cortisol should likewise be monitored while patients are in house, with cortisol repletion in cases where it is low. Any clinical suspicion for adrenal crisis should prompt swift response to administer steroids because a delay could be life threatening. After cortisol, repletion of thyroid hormone may also be considered, though the longer half-lives of thyroid hormone and other anterior gland hormones make their administration less critical in the immediate postoperative period.
Perioperative antibiotics and meningitis
The use of perioperative antibiotics for EEA to skull base and pituitary tumors has been carried over from data relating to open skull base procedures. As the use of the EEA becomes more widely adopted, data specific to these populations are beginning to emerge. Intuitively, one would expect the majority of infections to arise from the repetitive passage of surgical instruments via the nonsterile nasal passageways. As such, the organism most commonly isolated in culture-positive sinusitis is Staphylococcus aureus and suggests that the perioperative usage of narrow spectrum antibiotic coverage of gram-positive bacteria is prudent. A study looking at perioperative infections in a population undergoing EEA for various skull base pathologies demonstrated no cases of postoperative meningitis when giving cefazolin or vancomycin (penicillin allergic patients) in the 24-hour perioperative period.
A quantitative analysis of 2005 patients undergoing expanded EEA, excluding transsellar approached for pituitary adenomas, revealed an incidence of postoperative meningitis of 1.8%. In the subgroup experiencing a postoperative cerebrospinal fluid (CSF) leak, the incidence increased to 13%. This was compared with 0.1% of those without postoperative leak ( P <.01). Independent risk factors for postoperative infection include male sex, history of prior craniotomy or endonasal surgery, ventriculoperitoneal shunt and higher complexity intradural procedures.
These data suggest that the overall rate of postoperative meningitis in patients undergoing EEA to the skull base is low. Additional precautions may be taken for those patients with these risk factors, including use of broader spectrum perioperative coverage, tight control of perioperative glucose for diabetics, preoperative nasal cultures to reveal resistant organisms, and inclusion of antibiotics in operative irrigation solution.
Other medical complications
Expanded endoscopic endonasal surgery is generally well-tolerated, with shorter operating room times, duration of stay, and lower rates of medical complications than transcranial approaches. Patients with Cushing’s disease undergoing surgical treatment are at higher risk for many systemic complications, likely because of the far-reaching adverse effects of long-term hypercortisolemia on the body. In general, postoperative medical complications not directly related to the surgery itself (ie, endocrinopathies) are uncommon.
Venous thromboembolism (VTE) is rare in the population of patients undergoing EEA, and is more likely to occur in patients who are older or have underlying coagulopathy or peripheral vascular disorders. Postoperative neurologic complications, CSF leak, electrolyte imbalances, and cardiopulmonary complications are also associated with VTE, likely because these increase patient immobility and hospital duration of stay. Mechanical prophylaxis with sequential compression boots and early and frequent ambulation are used in most cases unless contraindicated. The use of chemoprophylaxis is controversial, and surgeons must consider the risk of VTE against the risk of postoperative hematoma; as such, it is usually reserved for patients with Cushing disease or other conditions that place them at higher risk.
The incidence of pneumonia is similarly lower after endoscopic approaches to the sellar region than transfrontal approaches, occurring in fewer than 0.6% of patients overall. There is, as expected, an association with older age and presence of congestive heart failure or chronic pulmonary disease. Incentive spirometry can be used to reduce the risk of pneumonia in these populations.
Cranial neuropathies
Incurring a neurologic insult from EEA surgery can increase duration of stay, immobility, and lead to further medical complications. A large series of 800 patients undergoing EEA for skull base pathology demonstrated a low overall risk for transient (2.5%) and permanent (1.8%) worsening of neurologic deficit. Ultimately, ideal approach selection (ie, transcranial vs EEA for paramedian skull base pathology) along with thoughtful and meticulous microsurgical dissection ensure optimal cranial nerve outcomes with any skull base resection.
Patients harboring anterior cranial fossa, sellar, and parasellar skull base lesions often present with visual deficits. Studies examining resection of pituitary lesions with preexisting visual complaints demonstrate equivalent postoperative outcomes, comparing microscopic approaches with EEA, with respect to stability or improvement of visual symptoms. There was no demonstrable increased risk for worsening vision. Key factors to preservation and improvement of vision include minimizing nerve manipulation, relieving mechanical pressure at any tethering points, and preservation of vascular supply. Often a neglected artery, the superior hypophyseal branches of the supraclinoid internal carotid artery (ICA) provide arterial supply to the optic chiasm and cisternal segments of the optic nerve. Understanding the arachnoidal relationship of these branches to the growth pattern of the target lesion is critical to avoiding ischemic injury to the optic apparatus. With regard to the management of relief of mechanical pressure of the nerves, lessons learned from the surgical resection of tuberculum meningiomas are useful. Several studies have demonstrated that unroofing of the optic canal by transcranial approach or decompression via EEA leads to improvement of visual symptoms in a majority of cases, and is a critical step in surgically managing tuberculum sellae or planum sphenoidale meningioma with intracanalicular extension into the optic canal. Typically, early canal decompression during the course of the operation provides optimal immediate postoperative outcomes. A review article by Raza and colleagues indicates roles for both endoscopic and transcranial skull base approaches in providing optimal visual outcomes and rates of resection depending on the size of tumor, involvement of the anterior communicating artery perforators, and pattern of optic canal extension (ie, superior vs inferior to the nerve).
Extension of EEA laterally as performed in medial cavernous sinus, transclival, petrous apex and Meckel’s cave and infratemporal fossa approaches can carry additional risk to the VIth cranial nerve. Detailed anatomic knowledge of the relationship of the 6th nerve to the cavernous carotid as the nerve transitions through its intracranial (interdural, gulfar, and cavernous) segments ( Fig. 1 ) can help to avoid inadvertent injury. Specific landmarks such as the vertebrobasilar junction for transclival approach, the lateral segment of the ICA and sellar floor for medial petrous apex approach, and V2 for Meckel’s cave approach allow for reliable localization. Intraoperative electromyographic monitoring of the VIth cranial nerve has been described and can provide additional warning during exposure and dissection.
