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reduce misdiagnosis, such as changes related to free fat grafts used in prior reconstruction.

Scar and other high signal tissues may not be easily discernable from recurrent disease. Changes on serial examinations, after an early postoperative baseline study, may be the only characteristic features of residual pathology [43]. MRI also enables differentiation of tumor from retained secretions.

Magnetic resonance angiography or CT angiography 33 (Fig. 33.2) [36] can be used to assess the structure of me- dium-to-large arteries in patients when erosion of the sphenoid and clivus has occurred. The relationship between the basilar arteries and ICAs to pathology is crucial in this area. Although conventional angiography is not routinely performed, it may verify the functional integrity of the circle of Willis, the extent of any carotid artery

compromise, and differentiate aneurysm from tumor.

Endocrine and Hypothalamic Considerations

Even with the best preoperative imaging, the relationship between tumor and intracranial structures can be difficult to demonstrate. It is extremely difficult to evaluate before surgery whether some tumors are extra-arachnoi- dal, extrapial-subarachnoidal, or partially intraparenchy- mal-subpial [16]. This weighs heavily on considerations to obtain complete resection. Parasellar pathologies such as craniopharyngiomas may often encase the pituitary

Aldo C. Stamm, João Flávio, and Richard J. Harvey

stalk or involve the hypothalamus. Resection of the pituitary stalk carries considerable morbidity with hormone replacement and reproductive dysfunction for adults, and has an even greater impact on growth and development for children. Hypothalamic injury may result in severe, crippling and life-threatening sequelae, such as adipsia, morbid obesity, sleep disturbances, and behavioral and cognitive disorders [56]. The decision to attempt complete tumor removal when resection or injury to these structures is inevitable should be discussed with the patient prior to surgery and not left to an intraoperative dilemma when such circumstances arise [17]. Careful preoperative assessment with an endocrinologist, within an MDT, for pituitary and hypothalamic dysfunction is essential in the operative planning for these patients [40, 48, 56].

Instrumentation

Endoscopic SBS is highly dependant on specialized instrumentation and its absence is an absolute contraindication to surgery. Dissection instruments and drills that are appropriately long enough to perform dissection beyond the sphenoid are essential. Similarly, high-quality endoscopes and video equipment are required. It is not appropriate to perform endoscopic SBS without camera equipment. An entire operative team needs to be visually informed of the state of surgery. A second surgeon, for bimanual dissection, and theater staff should be actively involved. The ability to maintain hemostasis and

Fig. 33.3  Endoscopic skull-base surgery equipment. a 5.2-mm and 4-mm endoscopes. b Image-guidance systems. c Long bi-

a workable operative field during prolonged surgery is a demanding aspect of extended endoscopic surgery. Long endoscopic bipolar forceps and hemostatic materials such as Surgicel or Avatine are essential to this process (Fig. 33.3) [28].

Previous Radiotherapy

Precise knowledge of previous radiotherapy fields will have significant impact on reconstructive options. In irradiated tissue, multilayered free graft repair of skull-base defects has a high dehiscence rate in our experience and elsewhere [45]. Reconstruction of the irradiated skull base almost always demands vascularized tissue. Pedicled mucoperiosteal and mucoperichondrial flaps are used for reconstruction. Radiotherapy may also thicken the pia­ arachnoid tumor interface, obscuring dissection planes, and contribute to a greater risk of neural injury [43].

polar forceps. d Long protected drill shafts. (Reproduced with permission from Centro de ORL, Sao Paulo, Brazil)

Surgical Techniques

General Principles

■The medial orbital wall, orbital apex, and prechiasmal optic nerve axis is a key landmark in revision SBS.

■Dissection should always proceed from known to unknown.

Endoscopic dissection in a previously operated skull base can be challenging due to the loss of traditional surgical landmarks. The use of image guidance has gained increasingly popularity since early reports of its use [6]. Improving the accuracy of image guidance has an associated learning curve [55] and occasional use may prove frustrating to the unfamiliar. Fusion MRI and CT guidance may provide more significant information for the surgeon operating on the skull base with extensive bone loss and altered soft-tissue structures [34]. However, detailed

knowledge of the endoscopic anatomy of the skull base can not be substituted by image guidance [51]. The revision endoscopic skull-base surgeon must have an exquisite knowledge of the anatomy and is referred to two anatomical series by Jho and Ha [22–24] and Kassam et al. [29, 30] for a review of the relevant endoscopic relationships.

A planned staging of resection in cases of extensive benign skull-base tumors may be appropriate when pathologies involve critical structures or neurovascular planes [14]. This approach may assist with venous hemostasis, especially within the clivus.

preserve the arachnoid tissue and vessels – even for vessels much smaller than 1 mm in diameter.

The technical difficulties posed by reoperation in the anterior fossa, parasellar region, and posterior fossa are often the result of meningeal inflammation associated with previous dissection. The arachnoid can be diffusely tenacious and opalescent, which complicates the establishment of microdissection planes and may hinder the identification of vital structures. Where subtotal tumor removal with possible reoperation is planned, it may be preferable to resist dissection in the neural plane. Reoperation of a previously undissected tumor–nerve interface is typically more effective than attempting to reestablish a previously developed plane [43].

Staging the Resection

Hemostasis

■The most important hemostatic technique, especially in venous bleeding, may be patience.

The principles of hemostasis in endoscopic SBS differ little from those of the microsurgical era. Prevention of bleeding is obviously the best solution. Tumor debulking, extracapsular sharp dissection, and countertraction using gentle suction still form the foundation of cerebrovascular control [28]. Standard neurosurgical bayonets are often not appropriate via the long surgical corridor of endoscopic SBS. Specialized instrumentation, as discussed previously, is essential. Examples of hemostatic techniques are demonstrated in Table 33.2.

Operative Basics

■Adrenaline-soaked cottonoids are used during the surgery but are replaced with saline cottonoids when intradural dissection proceeds.

Revision Endoscopic Skull-Base Surgery

the areas of surgical access for 10 min before the surgical procedure. If septectomy or mucosal flaps are planned, the septum is infiltrated with lidocaine with epinephrine 1:100.000. When the surgery includes the pterygopalatine and infratemporal fossa, the region of the sphenopalatine foramen is infiltrated with approximately 2.0 ml of the same concentration solution using an angulated 25-gauge spinal needle after first aspirating.

Avoiding Complications in Revision

Endoscopic SBS

295

a previous repair adherent in the prechiasmatic position. Secondly, the anterior cerebral vessels may be adherent to the previous repair of a transplanum approach. If the arteries are adherent to fat or fascia then it may be prudent to leave an island of scar tissue on the vessel rather than attempt dissection (Fig. 33.4). Finally, the vasculature of the pituitary may be easily damaged if there is scar tissue involving the stalk. Most importantly, a recurrent superior hypophyseal artery may lie within the vasculature of the pituitary stalk and injury can result in optic nerve or pituitary injury (Fig. 33.5) [33, 65].

There are well established techniques for closing CSF leaks [68, 69]. The endoscopic management with free grafts is the first option for small defects (<1 cm) in primary and revision cases [18, 37, 41]. However, possible failure can be avoided by identification of benign intracranial hypertension, which is often characterized by empty sellae, multiple skull-base defects, or a broadly attenuated skull base. These patients and may require additional interventions, such as lumbar drains or CSF diversion, for success [52].

Transplanum/Transsphenoidal Surgery

Endoscopic revision surgery for pituitary adenoma is almost the standard care in many centers [5]. There are three important implications of previous surgery in this area. Firstly, the optic chiasm may lie superior or inferior to its original position and will often have fat from

The position of the ICA can be difficult to locate in revision SBS. Previous extensive bone removal can leave a long segment of the ICA in soft tissue. The ICAs usually remain in a lateral position after previous displacement by pathology (Fig. 33.6). Intraoperative micro-Doppler ultrasound can be used to help locate the vessels in such cases [10]. Prior radiotherapy, especially in chordoma, may make surgical planes difficult to identify. The role of CT angiography may be important in defining pathology from prior reconstruction (mainly fat) and the basilar arterial system (Fig. 33.2).

Reconstructive Options

■The ability to close large skull-base defects is perhaps the second greatest challenge to endoscopic SBS, after the management of cerebrovascular structures.

■Multilayered reconstruction with pedicled mucosal flaps is the key to closing large skull-base defects.

A variety of reconstructive materials have been used (Table 33.3). The use of vascularized pedicled flaps has been the most significant advancement in our institution to reconstruct major skull-base defects (Fig. 33.7, Video 33.1). Pedicled mucosal flaps have been well described for a variety of reconstructive procedures such as septal perforation repair [47, 53], reconstructive rhinoplasty [2, 42], and choanal atresia repair [11, 58]. However, the use of vascularized mucosal flaps to repair large skull-base defects [19] or congenital defects [64] has been described only recently. Along with other centers, with endoscopic skull-base experience, we discourage the use of free bone grafts and synthetic materials (i.e., titanium mesh) as these may lead to poor healing and formation of sequestra [26].

Free fat grafts are used to fill dead space and form a buttress for a subdural fascial graft. This is covered with a combination of pedicled mucoperiosteal/chondrial flaps.

Fibrin tissue glue is used to secure the repair. Gelfoam is layered to the area, followed by gauze packing. The packing is supported by a Foleys balloon catheter (Fig. 33.8).

Postoperative Care

If the procedure is intradural, recovery is performed with neurological observations in high dependency. CT is performed out our institution on the first postoperative day for evidence of hemorrhage. Antibiotics are used perioperatively and continued postoperatively while nasal packing remains in situ. Packing is left in place for 7–14 days as most grafts are adherent in bone in 1 week [50]. The onset of diabetes insipidus is monitored with serum and urine sodium/osmolality measurements. Patients are confined to bed/chair rest with toilet privileges for 48 hrs, have 30 ° head elevation, and avoid straining, Valsalva maneuvers, and nose blowing. Lumbar drains are not used unless there is an additional comorbidity such as raised intracranial hypertension or prior radiotherapy.

33

Fig. 33.8  A cross-section of the completed repair. 1 Fat, 2 subdural fascia, 3 mucosal flaps, 4 fibrin glue, 5 Gelfoam, 6 anti- biotic-soaked gauze, 7 balloon catheter. (Reproduced with permission from Centro de ORL, Sao Paulo, Brazil)

Discharge usually occurs at 3–5 days postoperatively and an MRI scan is performed early for baseline assessment. This is important as postsurgical MRI signaling is often difficult to interpret [1].

Complications and Outcomes

■Major complications:

1.Death.

2.Infectious (meningitis, ventriculitis, subdural abscess).

3.Intracranial bleeding (arachnoid or subdural).

4.Endocrine disturbances (diabetes insipidus, pituitary).

5.Neurological (cranial nerve deficits, cerebrovascular accidents, epilepsy, hypothalamic dysfunction).

6.Pneumocephalus.

Endoscopic repair of CSF leaks is generally accepted as the standard of care. Success approaches 95% even with revision cases [21]. However, the incidence of many other skull-base pathologies is low. Most centers with endoscopic skull-base teams have gained their experience and skill by treating a diverse group of pathologies. Many of the surgical steps and techniques are common between lesions, but generating large populations for similar lesions is difficult. International collaborations, such as those for neoplastic disease, demonstrating an 88% 5-year survival for selected malignant skull-base pathologies, will be necessary to accrue sufficient patient numbers [38]. Out-

comes for olfactory neuroblastoma have been the most widely reported, with survival rates in excess of 80% at about 3-year follow-up [7, 63]. Outcomes of recurrent chordoma, with or without proton beam radiotherapy, vary between 26% and 75% [15, 17, 62]. The results for recurrent craniopharyngioma vary even more, depending on the philosophy of the treating surgical team [25].

Conclusion

Endoscopic SBS has both neurosurgical and otorhinolaryngological origins. The ability of the surgical team to access the entire ventral skull base endoscopically greatly benefits patients with a variety of benign and malignant pathologies. Endoscopic revision SBS presents an even more challenging set of problems for treatment. The management of these complex problems should be firmly established within an MDT. Absolute familiarity with endoscopic techniques, the ability to control nasal vasculature, reconstruct skull-base defects, and manage cerebrovascular structures should be available to the operative team. These skills combined with a detailed knowledge of endoscopic skull-base anatomy, and its distortion from disease, serve as a foundation for addressing the pathology of the skull base.

Tips and Pearls

■The intercarotid distance, height of the sphenoid sinus, and position of sellar should be evaluated on CT to assess the dimensions for a transnasal craniotomy.

■Bleeding from the intercarvenous sinuses can be troublesome. Surgicel packing and patience will control most venous bleeding. Persistent manipulation often hinders hemostasis.

■Venous hemostasis should be achieved prior to intradural dissection.

■The removal of remaining mucosa from the bone of the skull base prior to reconstruction will avoid mucocele formation.

■Do not use excessive tissue glue as this will lead to potential barriers between reconstructive layers.

■Tight packing of the reconstructed area can occlude the vascular flow of pedicled grafts and should be avoided.

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