Development of minimally invasive approaches has become a significant driver across surgical specialties in recent years. Purely endoscopic resections with proper attention to oncologic margins are now possible, with the potential benefit of decreased perioperative morbidity and improved cosmesis compared with traditional open transfacial or craniofacial approaches. Efforts to reduce perioperative morbidity and mortality have been applied with increasing sophistication in the most complex anatomic regions of the human body, including the head and neck. These efforts have resulted in an expanded role of purely endoscopic approaches to the paranasal sinuses, the anterior skull base, and the anterior cranial fossa. This article reviews the current understanding and available literature regarding the diagnosis and management of complications associated with endoscopic anterior skull base surgery.
Development of minimally invasive approaches has become a significant driver across surgical specialties in recent years, with the goal of reducing patient morbidity while maintaining good outcomes. The potential trade-off between recovery times or patient satisfaction and eradication of disease is of utmost importance. Efforts to reduce perioperative morbidity and mortality have been applied with increasing sophistication in the most complex anatomic regions of the human body, including the head and neck. These efforts have resulted in an expanded role of purely endoscopic approaches to the paranasal sinuses, the anterior skull base, and the anterior cranial fossa.
The routine use of functional endoscopic sinus surgery (FESS) in the management of chronic infectious and inflammatory sinus disease has led to significant improvements in endoscopic skills and surgical technology. Application of endoscopic surgery to the treatment of sinonasal tumors was initially confined to benign lesions, such as inverted papilloma and osteomas. Recently, endoscopic indications have expanded to include sinonasal malignancies and skull base neoplasms. This finding has been supported by advances in surgeon experience, advances in computer-guided technology, angled drills, and proven techniques for skull base reconstruction. Purely endoscopic resections with proper attention to oncologic margins are now possible, with the potential benefit of decreased perioperative morbidity and improved cosmesis compared with traditional open transfacial or craniofacial approaches.
However, literature in this emerging field is still developing. Evidence used in surgical and perioperative management has been derived from retrospective case series. Lack of specific protocols and limited experience with perioperative management of patients with sinus disease have the potential to significantly inhibit further advances in the routine and safe application of purely endoscopic skull base techniques. In particular, cases in which intracranial extent is present, obligating the surgeon to enter the anterior cranial fossa and reconstruct the skull base, demand nothing short of a complete understanding of the critical structures encountered in the approach and the potential morbidity of this work. This article reviews the current understanding and available literature regarding the diagnosis and management of complications associated with endoscopic anterior skull base surgery.
Operative procedures
As endoscopic skull base surgery has become feasible and widespread, otorhinolaryngologists have become increasingly involved. This involvement has expanded the required knowledge base of this specialty, particularly with regard to neurologic and endocrinologic issues in the perioperative period. Given that prevention is the best strategy for management of complications in any surgery, a review of the extended endoscopic approaches is an important first step and allows for an anatomic understanding of the clinical data. A brief summary of each of the common extended endoscopic approaches is included in this article and forms the basis for the detailed discussion of complications, prevention, and management decisions that follows.
Endoscopic Transsphenoidal Approach
The endoscopic transsphenoidal approach (TSA) represents a natural extension or modification of the traditional microscope-assisted TSA. By obviating complete nasal septal detachment and sublabial or columellar incisions, the surgeon may potentially reduce the incidence of rhinologic or cosmetic sequelae, such as septal perforation, nasal obstruction, palate or dental anesthesia, and obvious scars. Data regarding the efficacy and safety of endoscopic TSA have been almost uniformly supportive, showing adequate and safe tumor resection. Direct comparisons of microscopic and endoscopic approaches have been less common and have had differing results. Some investigators have shown reduced operative time, hospital stay, and patient-reported postoperative discomfort. A lower incidence of lumbar drain requirement and postoperative cerebrospinal fluid (CSF) leak has also been found in a study, relative to traditional sublabial and transseptal approaches.
As it is most commonly performed, the endoscopic approach to the sella is made via a partial posterior septectomy followed by a wide bilateral opening of the sphenoid rostrum. Connecting the ostia of each sphenoid sinus and then removing the bone inferiorly to the level of the sphenoid sinus floor places the underside of the bony sella turcica and clival recess in direct view. An appreciation of the lateral extent of the sphenoid sinus and the thickness of the bony covering of the internal carotid artery (ICA) and optic nerve is crucial. Tumor resection is then accomplished by removal of the thin bone of the sella and gentle dissection of the adenomatous portion of the gland from the normal residual adenohypophysis anteriorly and neurohypophysis posteriorly. If the arachnoid is sufficiently damaged, a CSF leak may be present and should be repaired with a multilayer technique.
Transcribriform Approach
The transcribriform approach is used for lesions involving the midline anterior skull base, which is anterior to the sphenoid rostrum at the level of the cribriform plate of the ethmoid bone. This extremely thin bony roof separates the ethmoid air cells from the anterior cranial fossa and contains the olfactory fillae as they extend inferiorly from the olfactory bulbs. Lesions in this area include paranasal sinus tumors with skull base or transcranial extension, such as esthesioneuroblastomas, adenocarcinomas, squamous cell carcinomas, or mucosal melanomas among others.
In contrast to the TSA, transcribriform approaches require significant paranasal sinus work either for initial debulking, as in tumor resections, or to adequately expose lesions primarily at the bony skull base. A variety of adjunct procedures may be required for oncologic concerns. These procedures include opening of the paranasal sinuses to ensure complete circumferential tumor-free margins, with the addition of endoscopic medial maxillectomy for cases with significant inferior and lateral extent. Maxillectomy may necessitate complete removal of the lamina papyracea for gross tumor involvement or as a margin in the case of malignancy. Hemostasis is crucial when working with the orbital contents. The proportion of nasal septum that must be removed is variable but is frequently substantial. Unilateral or bilateral middle turbinectomies are also required in most cases.
Anterior skull base lesions with a minimal extent of paranasal sinus or lying entirely within the anterior cranial fossa require wide opening of the ethmoid air cells, ligation of the anterior ethmoid arteries, partial septectomy, and careful skeletonizing of the ethmoid roof. Image guidance is helpful in such cases and aids the surgeon to identify the extent of the lesion and delineate the portion of bony skull base to be removed (like a trapdoor for olfactory or tuberculum meningiomas). In cases in which there is significant intracranial disease, preoperative magnetic resonance imaging (MRI) is used to assess parenchymal involvement, although the difference between displacement and invasion of the pia mater may be subtle. With pial invasion, microneurosurgical techniques are required for resection and thus increase the risk for neurovascular complications. To date, resections of frontal lobe lesions have been limited to minimal corticectomy; deeper involvement is an indication for a traditional open approach via craniotomy.
Anteriorly, the cribriform plate terminates at the posterior wall of the frontal sinus. When the lesion or margin of resection reaches this point, additional complex paranasal sinus work is required to ensure a functional and safe frontal sinus. An endoscopic modified Lothrop procedure (Draf III) is performed, resulting in a common, large frontal sinus outflow tract. Resection of the mass and reconstruction of the skull base may then proceed posteriorly from the common frontal recess.
Transplanum-Transtuberculum Approach
For lesions involving or overlying the planum sphenoidale and tuberculum sellae, a transplanum-transtuberculum approach is used. The initial steps are similar to an endoscopic TSA, but after the wide sphenoidotomy, entry through the skull base is accomplished more superiorly and anteriorly. Removal of the bone anterior to the sella turcica results in exposure of the optic chiasm and pituitary stalk, requiring careful dissection and thoughtful use of electrocautery. Significant morbidity may follow the minutest manipulation of these structures or their fragile vascular supply, which may be encountered directly in the operative field or on the tumor surface. In addition, care should be taken to avoid entry into the cavernous sinus, which may result in persistent venous bleeding and significantly compromise visualization.
Durotomy in this area creates a high-volume, high-flow CSF leak by opening the suprasellar or chiasmatic cistern. This condition is further complicated by the abnormal 3-dimensional geometry of the resulting defect, which is somewhat trapezoidal but with a bend in the middle. Reconstruction typically relies on a flat plane and a layered technique, as in the cribriform area. This added dimension makes skull base repair complex and tenuous, although pedicled septal mucosa rotation flaps have been used with frequent success.
Tuberculum sellae and olfactory groove meningioma are the most common lesions that have been treated via a transplanum-transtuberculum approach. Other lesions may be treated via a modified transplanum-transtuberculum approach to achieve suprachiasmatic control, including Rathke cleft cysts and craniopharyngiomas.
Transclival Approach
The clivus is the midline bony structure of variable thickness formed by the sphenoid and occipital bones, which lies inferior to the sella and slopes to the foramen magnum. The transclival approach is used in the case of clival mass lesions, most commonly including chordomas but may also include chondrosarcomas and other rare tumors. Because of its more inferior location, less paranasal sinus work is required in this approach. The theoretical risk of CSF leak is also reduced significantly, because the ethmoid roof, planum sphenoidale, and sella are generally avoided. Entry into the CSF space at this level would require passage through the entire bone and entry into the prepontine cistern or craniocervical junction or the dissection of sella turcica, in addition.
Circumferential dissection around a clival tumor may proceed from within the sphenoid sinus, with removal of the posterior and inferior sinus walls. For smaller or more inferior lesions, minimal sphenoid work may be required or a nasopharyngeal approach could be used. In the case of a larger or more superior lesion, the transclival approach has been combined with endoscopic TSA.
Endoscopic Approach to the Petrous Apex
Minimally invasive approaches to the petrous apex are also possible via the anterior corridor through the sphenoid sinus and have been used primarily for endoscopic treatment of cystic and inflammatory lesions, such as cholesterol granuloma and petrous apicitis. After creation of a wide sphenoidotomy, identification of the anterior wall of the cystic lesion is achieved with image guidance, noting also the relative position of the optic nerve and ICA. These lesions may then be opened widely and allowed to drain via the sphenoid sinus into the nasopharynx, occasionally with the aid of a temporary Silastic stent (Dow Corning, Midland, MI, USA). Some investigators have used this approach for solid lesions as well, including smaller chordomas and chondrosarcomas. Accurate and continually updated image guidance with careful intraoperative mapping of the petrous portion of the ICA is essential in this approach. For larger lesions, specific anatomic considerations of the temporal bone may become important or a combined endoscopic anterior and traditional lateral skull base procedure may be necessary.
Review of complications
The anterior skull base is a complex anatomic region, which contains crucial sensory and neurovascular structures in extremely close proximity. The breadth and severity of potential perioperative complications of endoscopic surgery is thus significant. Overall, major complication rates in endoscopic approaches are consistently reported as less than 10%, with some smaller series reporting around 20%. Perioperative deaths are exceedingly rare in endoscopic skull base approaches, with only 3 reported in the literature to date. This rarity represents a significant improvement over the reported perioperative morbidity and mortality of traditional open craniofacial resection, which was 35% to 50% and 5% to 10%, respectively. In addition, a meta-analysis showed the perioperative mortality rate for endoscopic TSA as 0.24%. Although the different types of lesions and the extent of dissection make it impossible to compare endoscopic TSA and extended endoscopic approaches, the reported morbidity and mortality data are encouraging. Lastly, the inherent bias in morbidity and mortality statistics, which result from surgeon preference and from factors intrinsic to specific lesions (eg, size, lateral extent, parenchymal involvement), must be acknowledged. These differences make direct comparisons of open and endoscopic approaches difficult and encourage cautious interpretation of clinical series.
In this section, the cause, incidence, and basic management of potential complications in endoscopic skull base surgery are reviewed in reference to the relevant skull base and neuroanatomy. The discussion is organized by anatomic location or organ system, with reference to specific approaches where applicable.
Sinonasal Complications
All endonasal surgery inherently involves the risk for nasal mucosa injury and postoperative bleeding. Synechiae occur when opposing mucosal surfaces are abraded or lacerated and are commonly formed between the septum and turbinates, particularly in endoscopic TSA in which the turbinates remain in the operative corridor. Postoperative airway obstruction attributable to anterior adhesions is experienced as greater inspiratory resistance or change in nasal airflow direction. As with most complications of nasal surgery, prevention of adhesions by careful surgical technique is the best strategy. Epistaxis, the most common postoperative complication of FESS, also occurs after endoscopic skull base surgery. This complication should be treated with packing or cautery according to severity, after endoscopic localization of the source. Significant epistaxis should be taken seriously, because it may indicate a major vessel bleed or intracranial bleed.
A variable extent of paranasal sinus work is required in endoscopic endonasal approaches, frequently including ethmoidectomy, sphenoidotomy, and frontal sinusotomy. Although these surgical procedures are used for access of margins, they also affect the function of the sinuses. Similar to standard FESS, disruption of the sinus mucosa, obstruction of the sinus outflow, or the retained bony fragments and debris may result in sinusitis. A severe case of chronic frontal sinusitis after endoscopic resection was described by Unger and colleagues and required FESS and subsequent osteoplastic flap. The incidence of acute or chronic rhinosinusitis after endoscopic anterior skull base surgery is not known, although patient-specific factors, including previous history of sinus disease or allergy, may predict postoperative difficulty. This feature underscores the importance of meticulous technique during the intranasal portion of the approach.
Not only particularly in the frontal sinus but also in the ethmoid region, obstruction of sinus outflow with continued mucus production may result in a mucocele. As this material accumulates, increased pressure within the cell results in an expansile lesion of the sinus with bony remodeling. Treatment involves endoscopic drainage and wide opening of the involved sinus. Although not directly reported in most studies, Nicolai and colleagues noted 2 mucoceles in 134 cases (1.5%). With mucocele formation in the area of a previously resected neoplasm, directed biopsies should be done to rule out residual or recurrent tumor. Mucoceles of any origin may recur, although endoscopic approaches are proved effective even in the most complicated lesions.
Finally, atrophic rhinitis is a significant concern when the paranasal sinus approach to the skull base requires removal of a large portion of the mucosal surface. Atrophic rhinitis is a condition characterized by thick crusting, persistent rhinorrhea, foul smell or taste, and a paradoxic sensation of nasal airway obstruction. Although atrophic rhinitis is more common with resection of the inferior turbinates, it may also occur in cases with bilateral middle turbinectomy and subtotal septectomy. Alterations in sinonasal physiology may predispose the patient to bacterial rhinitis with distinct flora such as Klebsiella ozaenae . Chronic crusting and poor nasal function has been reported in at least one-third of patients undergoing endoscopic skull base surgery, although the incidence may be even higher, because many studies do not comment on this issue. Postoperative external beam radiation therapy may increase the likelihood of atrophic rhinitis in this group by delaying mucosal healing and promoting atrophy of glandular elements and cilia. Symptomatic improvement is achieved by routine humidification, nasal irrigations, improved nasal hygiene, and topical antibiotics, but no curative treatment exists for this complication.
Orbital and Optic Nerve Complications
Orbital hematoma is a familiar and fortunately rare complication of FESS, with a reported incidence of less than 1%, and thus it is a potential complication in endoscopic skull base approaches. Vascular injury leads to bleeding within the orbit, resulting in proptosis, elevated pressures, and subsequent ischemic damage of the optic nerve and retina. This injury may be venous, frequently from the orbital fat, or arterial, in the case of anterior or posterior ethmoid artery injury. If a developing orbital hematoma is suspected, elevated intraocular pressure (normally 10–20 mm Hg) confirms the diagnosis. Initial conservative measures include massage, administration of mannitol, and intravenous steroids. With rapidly expanding hematoma or pressures greater than 40 mm Hg, the surgeon must urgently decompress the orbit via lateral canthotomy. Identification and control of the source of hemorrhage may then be proceeded.
Although the incidence of orbital hematoma in endoscopic skull base surgery is not defined, it is likely similar to or somewhat less than in FESS. One case has been reported in the literature on endoscopic skull base surgery. In endoscopic approaches in which orbital work is required, this generally entails removal of a significant portion of the lamina papyracea and exposure of the periorbita. Bleeding due to this exposure is more easily appreciated than that resulting from inadvertent puncture, as in FESS. In addition, optic nerve ischemia is less likely to occur in cases in which the lamina has been removed, because hematoma expands into the nasal cavity rather than building pressure within the orbit proper. Particularly in transcribriform approaches, early ligation of the anterior or posterior ethmoid arteries may be indicated.
The optic nerve may be injured directly, accidentally by surgical instrumentation, or indirectly, as was discussed in the case of orbital hematoma earlier. A thorough review of the current literature on endoscopic skull base failed to reveal a case of permanent blindness secondary to direct optic nerve injury, although the risk should be assumed to be equal to or greater than in FESS in cases in which posterior ethmoidectomy, wide sphenoidotomy, and wide exposure of the optic nerve or chiasm is required ( Fig. 1 ). Careful review of the preoperative imaging reveals anatomic variations that may place the optic nerve at greater risk, including Onodi cells (present in 10% of the population) and a dehiscent optic nerve in the sphenoid sinus (present in 4%). One case of blindness attributed to vascular injury has been reported after resection of a multiply recurrent and multiply operated craniopharyngioma. No proven treatment exists for restoring vision after optic nerve transection. For incomplete injury, including inadvertent bipolar cautery, some investigators have advocated intravenous steroids and optic nerve decompression, although evidence of efficacy is lacking.
Medial rectus injury is a severe but rare complication of FESS, reported in less than 0.5% of cases. The incidence of this complication in endoscopic skull base surgery is not known, but a review of the current literature did not find a reported case. The mechanism of injury typically involves direct penetration of the lamina papyracea and periorbita, with subsequent contusion, disruption, or transection of muscle fibers. This injury results in eye movement abnormalities, including diplopia and strabismus. Medial rectus injury occurs most frequently in ethmoidectomy, given the thinness of the lamina and its proximity to the ethmoid air cells. Anatomic variants in this region and use of powered instruments seem to increase the risk and severity of injuries. Treatment of medial rectus injury is extremely difficult and requires an oculoplastic expert. Depending on the degree of muscle loss, reapproximation, transposition grafts, and more advanced techniques have been used. Results are however poor in many cases.
Ophthalmoplegia
Extraocular movement deficiency may also complicate endoscopic skull base approaches as the result of injury to the abducens or oculomotor nerve. These cranial nerves, along with the trochlear nerve and first division of the trigeminal nerve, traverse the cavernous sinus and, in some extended parasellar approaches, may be found in the endoscopic operative field. During dissection, these nerves may be accidentally stretched, cauterized, or transected. The abducens nerve is most commonly affected, resulting in the typical ipsilateral lateral gaze palsy. This injury has been reported in the resection of parasellar, suprasellar, and clival lesions. However, many midline skull base lesions present with oculomotor abnormalities, most, but not all, of which improve after surgery.
Hyposmia and Anosmia
Decreased sense of smell is a common occurrence after endoscopic skull base surgery. In the immediate postoperative period, most patients have some degree of hyposmia secondary to nasal packing. True hyposmia is evident after packing removal and debridement. Although hyposmia is frequently transient after TSA or transclival approaches, transcribriform and transplanum-transtuberculum approaches may lead to permanent hyposmia or anosmia. These approaches involve extensive removal of the nasal septum, superior turbinate, or cribriform plate, with concomitant injury to or excision of the olfactory fillae. In the case of esthesioneuroblastoma, some investigators have argued for routine excision of the olfactory bulbs even in absence of gross involvement, given the cause of the tumor. This excision obviously results in anosmia, and although this result is expected, patients must be counseled to avoid an unpleasant surprise postoperatively. Other investigators have posited avoidance of anosmia as an advantage of endoscopic approaches over craniofacial resection.
Infectious Complications
Acute bacterial sinusitis may be common after endoscopic skull base surgery, particularly, given the degree of mucosal disruption and presence of foreign bodies (packing) in the resection cavity. For example, Unger and colleagues reported acute sinusitis in 4 of 14 (29%) patients who underwent endoscopic resection and adjuvant Gamma Knife (Elekta Inc, Stockholm, Sweden) radiation therapy for esthesioneuroblastoma. Batra and colleagues reported 15 cases of acute sinusitis after 200 TSAs (7.5%), including 10 cases of sphenoid sinusitis—five of which required revision surgery. Acute sinusitis must be treated quickly and aggressively, to avoid ascending infection and compromise of the healing–skull base reconstruction. Whenever possible, culture should be taken under endoscopic guidance before initiation of broad-spectrum empiric antibiotics. Subsequently, coverage may be tailored to culture results and sensitivities.
Intracranial infection may result from contamination during endoscopic skull base surgery or ascending infection via the skull base defect. Postoperative meningitis is relatively rare, with only a handful of cases reported. Some of the larger series report an incidence of less than 1%. Although the small number of cases makes statistical analysis impossible at this point, it is noteworthy that no cases of meningitis have been reported in the literature on transclival approaches. Lack of cases of meningitis is likely because of the infrequency of dural disruption in this area and the location of the resection bed in the posterior-most aspect of the sinonasal cavity.
Localized suppurative infection may also complicate endoscopic skull base approaches in the form of epidural abscess, subdural empyema, or intraparenchymal abscess. These are rare events because sterile technique and perioperative antibiotics dramatically reduce the risk in immunocompetent patients. Frontal lobe abscess has been reported in 2 cases, from different investigators, each after endoscopic resection of a large transcranial esthesioneuroblastoma. A high degree of suspicion is required in the case of smaller collections, because computed tomography (CT) may be nondiagnostic in up to 30% of cases. Culture results typically reveal methicillin-resistant Staphylococcus aureus , gram-negative rods, or polymicrobial infections. This complication requires formal craniotomy for drainage and possible revision of the skull base reconstruction, in addition to culture-specific intravenous antibiotics with CSF penetration. All grossly infected allograft materials should be removed at the time of surgery.
Neurovascular Injury, Hemorrhage, and Permanent Deficits
Injury of the ICA or the delicate intracranial vessels at the anterior skull base is perhaps the most feared operative complication in endoscopic surgery. Morbidity in such cases may range from blindness to pituitary apoplexy to stroke with permanent neurologic sequelae. Gentle dissection, judicious use of cautery, and traditional microneurosurgical technique are required to reduce vascular injury. Modern hemostatic agents, such as fibrin glue, concentrated thrombin, and microfibrillar collagen, are invaluable. In addition, employment of the “2 nostrils 4 hands” technique provides for constant and stable visualization by allowing the primary surgeon to use both hands, while the second surgeon holds the endoscope and a second suction device.
Intraoperative injury of the ICA is a rare but potentially lethal complication in endoscopic skull base surgery. Only two cases have been reported to date. The first involved a recurrent, previously operated, and irradiated chordoma. ICA rupture was contained endonasally, without craniotomy or neurointerventional procedures, and no long-term dysfunction resulted. The second case occurred during resection of a clival chordoma with cavernous sinus extension and was also controlled endoscopically; however, a pseudoaneurysm developed and required postoperative endovascular treatment. No permanent deficits resulted, although this case highlights the need for delayed postoperative angiography to rule out or treat a potentially dangerous pseudoaneurysm.
In endoscopic approaches including intracranial work, particularly in the parasellar region and with transplanum-transtuberculum approaches, injury of the circle of Willis is possible ( Fig. 2 ). Tearing of the anterior cerebral artery or anterior communicating artery may result in significant subarachnoid hemorrhage (SAH), intraparenchymal hemorrhage (IPH), or intraventricular hemorrhage (IVH). Ability to control bleeding in these vessels endonasally in the event of laceration or rupture may mean life or death for the patient, and most investigators stress the need for significant experience before tackling lesions with significant intracranial extension. Although each case should involve preoperative consent and preparation for potential conversion to open craniotomy, in reality this would take too much time in the event of an intracranial arterial bleeding.
Review of the literature reveals four cases of significant ICH, with two cases each involving tuberculum sellae meningiomas and clival chordomas. In the first case, the patient had developed a postoperative CSF leak, which required a trial of lumbar drainage and 3 subsequent endoscopic repairs. After the final surgery, the patient’s condition unexpectedly and rapidly declined. CT scan demonstrated a severe IVH of the third and fourth ventricle, and the patient expired. In the second case, a delayed postoperative bleed from a frontopolar artery pseudoaneurysm presented as epistaxis, which resulted in IPH and necessitated a frontal craniotomy for control followed by embolization, and the patient was left with permanent cognitive deficit and hemiparesis. In the third case, a brainstem hemorrhage after resection of a clival chordoma was reported by Stippler and colleagues, resulting in quadriparesis and lower cranial nerve deficits. In the fourth case, a diffuse SAH occurred after chordomas resection in the series by Zhang and colleagues.
Neuroendocrine and Electrolyte Derangement
Postoperative neuroendocrine derangement may complicate any surgery of the anterior and middle skull base and may be difficult to manage. These disorders result from surgical manipulation of the pituitary gland or sacrifice of a portion of its vasculature. This fact is well known in the neurosurgical community and has been a staple of postoperative care for patients with pituitary adenoma. In its most extreme form, injury may result in panhypopituitarism, with the requirement of lifelong hormone supplementation in some patients. Although more common in open procedures, this may occur in even minimally invasive surgery of the sella or parasellar and suprasellar regions. Partial anterior pituitary dysfunction is also possible and frequently results in deficiency in systemic cortisol levels secondary to decreased adrenocorticotropic hormone secretion.
Isolated neurohypophyseal dysfunction is more common than panhypopituitarism and leads to either diabetes insipidus (DI) or, less commonly, the syndrome of inappropriate antidiuretic hormone secretion (SIADH). DI may be transient or permanent and is the result of deficient antidiuretic hormone (ADH, also called vasopressin) secretion. DI manifests as increased output of dilute urine (specific gravity <1.005) and concomitant hypovolemia. Loss of free water increases the serum sodium concentration. The resulting hypernatremia may be significant and at higher levels can lead to mental status change, seizures, cardiovascular collapse, and significant decline. Treatment initially involves intravenous hypotonic fluid but may necessitate extrinsic hormone replacement in the form of desmopressin, a synthetic analogue of ADH, which is delivered subcutaneously or as a nasal spray. DI with or without hypocortisolemia has been particularly prevalent in endoscopic resection of craniopharyngiomas, although preoperative endocrine abnormalities are also more common in these patients. In some cases, DI may be permanent, requiring lifelong therapy.
SIADH after surgery for pituitary adenoma in the sella or suprasellar compartments has been described. SIADH after other endoscopic skull base approaches is exceedingly rare, with only 1 case presented in the literature to date. SIADH results from continued secretion of ADH despite decreasing serum sodium concentration, which is normally detected by the hypothalamus as a change in osmolality. However, renal excretion of sodium is maintained and the urine is very concentrated. Patients are generally euvolemic. Diffuse edema does not occur, and urine output may be normal to low. Sodium levels less than 120 mEq/L are characterized by nausea and vomiting, headache, drowsiness, and stupor. As sodium concentration declines further, generalized seizures become a significant concern. SIADH must be distinguished from cerebral salt wasting, in which hyponatremia results from increased renal excretion of sodium rather than from increased free water retention. This increased excretion of sodium leads to hypovolemia with increased urine output and therefore should not be managed with fluid restriction.
CSF Leak and Pneumocephalus
Reported postoperative CSF leak rates have been widely divergent to date, although review of the literature suggests that leak rates decrease over time. Some series have reported notably high rates, in the range of 40%, whereas others have reported no leaks. At least part of this variance is related to imprecise terminology reflecting the extent of the surgery. It is expected that resection of sinonasal tumors that extend to the skull base but do not directly involve the bone or dura result in fewer CSF leaks than in cases with true transcranial or intracranial work. However, this distinction is frequently unclear in the literature, thus making interpretation and comparison of results somewhat less straightforward. In recent years, with improved surgical techniques, reconstructive algorithms, and available materials, CSF leak rates in transcranial endoscopic approaches have decreased dramatically. Most investigators now report postoperative CSF leak in less than 20% of cases with bony skull base and dural entry.
In planning the skull base reconstruction, it is important to consider the geometry and location of the defect, as well as the pathologic condition. Close review of the endoscopic literature shows that leak rates are widely divergent across anatomic locations. The lowest incidence of postoperative leak is found in transcribriform cases, the highest rates were reported in the transplanum-transtuberculum approach, and very low to intermediate rates were reported in the transclival approach. In addition, CSF-leak risk seems to be greater after resection of craniopharyngiomas. In each case, familiarity with a variety of reconstructive materials and local flaps, such as the pedicled septal mucosa rotation flap (Hadad-Bassagasteguy flap), provides the best opportunity for success of the primary repair.
Extensive surgery around the sella and planum sphenoidale results in a wide opening of the suprasellar or chiasmatic cistern. This space holds a relatively large volume of CSF, particularly when compared with the minimal amount in the subarachnoid space under the frontal lobes, where communication is created during transcribriform approaches. In addition, repairs in this area have a complex geometry, where the force of gravity acts against the surgeon’s efforts at watertight closure. Lastly, whereas repair of the cribriform plate may be assisted by the weight of the frontal lobes on the reconstruction, no such support mechanism is possible from within the sphenoid sinus or the sella. Repair of the skull base defect by this approach is therefore prone to failure. This fact is evidenced by the significant postoperative CSF leak rate encountered by other surgeons using this approach, including 62% in the meningioma series by Gardner and colleagues and 33% in the series by de Divitiis and colleagues. Studies involving extended TSA or suprasellar work have reported postoperative CSF leak rates of 10% to 30%.
Reconstruction failure most often presents as CSF leak but may also result in pneumocephalus. Regardless of the surgical approach, opening of the cranial vault always results in the trapping of a small amount of air. In some cases, however, this volume may expand postoperatively, usually in conjunction with a CSF leak. Significant gas volumes may lead to tension pneumocephalus, in which intracranial structures are compressed, blood flow is inhibited, and herniation is possible. Tension pneumocephalus is a very rare complication of endoscopic skull base surgery but has been reported in 1 case, although no craniotomy was required. Tension pneumocephalus in endoscopic approaches could potentially result from a 1-way valve effect at the site of a dehiscent skull base reconstruction ( Fig. 3 ). Pressure changes during nasal inspiration, coughing, or sneezing may overcome the dehiscent repair, entering the intracranial space. This air then becomes trapped by the increasing pressure on repair from the inside.
