Complications of Endoscopic Endonasal Skull Base Surgery




Abstract


Background


Endoscopic endonasal skull base surgery (ESBS) has gained significant popularity over the last decade. However, there is a significant learning curve associated with these approaches and many potential complications, depending on the region and increasing with the complexity of the pathology.


Methods


This chapter is designed to review the complications associated with ESBS and review anatomic and technical details to prevent such complications.


Results


The internal carotid artery (ICA) provides one of the major limitations to lateral access for midline endonasal approaches. Avoidance and management of ICA injury remains critical for performing safe ESBS. In addition, the cranial nerves in the cavernous sinus and various cranial base foramina (optic canal, foramen rotundum and ovale, Dorello’s canal and the hypoglossal canal) create the lateral limits for ESBS. There are well defined anatomic landmarks for each of these, providing the keys to their safe identification and preservation.


Cerebrospinal fluid leak remains the most common complication following ESBS, but has been dramatically decreased through the development and use of vascularized flaps and multilayered reconstruction.


Conclusions


ESBS is fraught with potential complications, but these can be largely avoided and the advantages of the approach preserved through detailed anatomic understanding and a healthy respect for the significant learning curve, both anatomic and technical.




Keywords

endoscopy, skull base, carotid injury, cranial nerve injury, learning curve, CSF leak

 




Highlights





  • Cerebrospinal fluid leak remains the most common complication of endoscopic endonasal skull base surgery, but this has decreased dramatically with the use of vascularized nasoseptal flaps.



  • Lumbar drains have been shown to decrease the risk of cerebrospinal fluid leak after endonasal skull base surgery, primarily for larger anterior and posterior fossa defects.



  • Major vascular injury can be controlled during endoscopic ESBS, but it often requires immediate endovascular evaluation and/or treatment.



  • Nasal instrumentation should be avoided in the postoperative period unless under direct endoscopic visualization.



  • There is a significant learning curve with endonasal skull base surgery that should be respected to keep complication rates low.





Background


Endoscopic endonasal skull base surgery (ESBS) has seen a dramatic increase in adoption since its introduction and development over the last two decades. Initially used only for pituitary tumors, the approach has expanded significantly to include the entire ventral skull base. However, multiple articles have demonstrated that there is a significant learning curve with these approaches, with improved resection and decreased complication rates such as cerebrospinal fluid (CSF) leak over time. In addition, the introduction of vascularized flaps such as the nasoseptal flap has significantly improved the reconstruction of the skull base after these approaches.


With all skull base approaches, nerve and vascular injury make up the remainder of the majority of complications. In general, endonasal approaches were developed to allow wide and well-visualized anterior access for tumors that originate in the midline or paramedian skull base and displace involved neurovascular structures laterally. Respecting this concept in approach selection, as well as the learning curve, helps minimize neurovascular complications.




Anatomic Insights


The anterior cranial base slopes inferiorly from anterior to posterior with varying degree. During exposure, care should be taken not to violate the skull base during anterior to posterior dissection, especially during maneuvers such as middle turbinate resection. Excessive head extension during positioning may alter the trajectory and predispose to anterior skull base injury during exposure.


A thorough understanding of vascular and neural anatomy is critical for navigating the skull base. The internal carotid artery (ICA) is a key anatomic landmark for orientation and classification of endonasal approaches ( Fig. 36.1 ). Endonasal landmarks include:




  • The Eustachian tube lies medial to the parapharyngeal ICA as it enters the skull base.



  • The vidian nerve is located just inferior and lateral to the foramen lacerum ICA, and it crosses over the horizontal petrous ICA to connect with the greater superficial petrosal nerve (GSPN).



  • The pterygoid process marks the medial plane of the foramen lacerum and the pterygo-sphenoidal fissure (between pterygoid process and sphenoid sinus floor) and attaches posteriorly to the foramen lacerum ICA.



  • The middle clinoid process, when present, is located between the cavernous ICA and the clinoidal ICA.



  • The “medial optic-carotid recess (OCR)” is a landmark for the clinoidal segment of the ICA and dural ring.



  • The lateral OCR is located laterally between the clinoidal ICA and optic canal.




Fig. 36.1


Endoscopic endonasal view of a cadaver dissection showing the segments of the internal carotid artery (ICA) that create the lateral limit of many endonasal approaches. DR, Dural ring confluence; FL, foramen lacerum; PC, paraclival ICA; Pet, horizontal petrous ICA; PPh, Parapharyngeal ICA; PS, parasellar ICA; VN, vidian nerve.


Sphenopalatine artery anatomy ( Fig. 36.2 ) is critical to understand for a multitude of reasons. It can be a source of postoperative epistaxis after pituitary surgery, is the key supply for the nasoseptal (posterior nasal artery) and other posteriorly based flaps, and must be dissected and managed to access the pterygoid canal and base of the pterygoid for transpterygoid approaches.




Fig. 36.2


Endoscopic endonasal view of the right pterygopalatine fossa showing the sphenopalatine artery (SPA) and key posterior nasal artery (PNA) branch. The latter provides blood supply to the vascularized nasoseptal flap and can also be a source of postoperative epistaxis when sacrificed.


Limitations for the endoscopic endonasal approach (EEA) are largely laterally located or displaced nerves and/or arteries. Crossing the plane of nerves defeats the main advantage of an endoscopic endonasal corridor, which is avoidance of neurovascular manipulation. Understanding these limitations and the anatomy of the cranial nerves in these key locations is critical for avoiding injury.


In the suprasellar space, the optic nerves enter the dural sheath of the optic canal at the medial aspect of the optic strut/lateral OCR. The canal can be widely decompressed by carefully drilling all bone overlying the medial canal. A suprasellar dural opening can be extended laterally to the medial falciform ligament above the optic nerve, to avoid injury to the ophthalmic artery, which often originates on the medial supraclinoidal ICA or loops medially before travelling to its usual position, just inferior to the optic nerve, until it crosses superiorly more distally.


The sella is limited laterally by the ICA, but tumors can be dissected from the various compartments of the cavernous sinus, named based on their relationship to the genu of the cavernous ICA. The superior compartment (where most medially originating tumors extend) is related to the third cranial nerve, whereas the posterior and inferior compartments only have segments of the abducens nerve (CN VI). The lateral compartment contains segments of all cavernous cranial nerves (III, IV, V1, and VI). Though III and IV are generally ensheathed in the lateral cavernous wall dura, entrance into this compartment is generally reserved for aggressive tumors or those with symptoms indicative of oculomotor nerve involvement.


The midclivus is bounded laterally by the petrous apex, Dorello’s canal, and the abducens nerve. This nerve is most likely to be injured during any transclival approach, so understanding its anatomy is essential. CN VI exits the brainstem at the vertebrobasilar junction and runs obliquely up to Dorello’s canal, which runs behind the upper half of the paraclival ICA. There is a venous channel, the inferior petrosal sinus, immediately below the nerve, which can be a conduit for tumor growth. “Gardner’s triangle” is a medial anatomic triangle providing access to the petrous apex. It is bounded superiorly by the abducens nerve, anteriorly by the paraclival ICA, and inferiorly by the petroclival synchondrosis.


The lateral limitation in the lower clivus, below the foramen lacerum, is the hypoglossal canal and nerve. Extending exposure to this landmark increases access by 50%. Immediately above the canal lies the medial jugular tubercle and below it, the medial occipital condyle. Inferior extension of dissection beyond the tip of the odontoid process may cause craniocervical instability, especially if the anterior ring of C1 is disrupted.



Red Flags





  • Prior endonasal surgery increases risk of nasoseptal flap necrosis.



  • Chondroid tumors (chordoma and chondrosarcoma) have the highest risk of ICA injury.



  • Growth hormone–secreting tumors are associated with ICA ectasia and increased risk of injury.



  • Recurrent tumors, especially after radiation therapy, have an increased risk of both neural and vascular injury.



  • Nonadenomas invading the cavernous sinus are at much higher risk than adenomas for nerve and artery injury during cavernous sinus dissection.



  • Coronal plane (paramedian) approaches have an increased risk of complications, especially ICA injury.






Prevention


Important aspects of prevention of complications during ESBS include preoperative preparation; a careful understanding of the normal anatomy from an endonasal perspective; proper imaging (computed tomography [CT] angiography) to assess the circle of Willis; evaluation of nasal structures if the patient has had prior endonasal surgery; and full evaluation of hormonal and ophthalmologic function preoperatively.


Intraoperatively, the use of image guidance and Doppler probes provides accurate localization of the ICA to avoid injury. Electromyography (EMG) (both free-running and stimulated) can help identify motor cranial nerves and is associated with lower risk of postoperative loss of function ( Fig. 36.3 ). In addition, team surgery (two surgeons, 3–4 hands) has significant advantages with respect to visualization, dynamic endoscopy, and microsurgical dissection, as well as avoidance and management of complications. A second surgeon will often notice impending complications when the other does not. Two surgeons (especially from different specialties) will often focus on different aspects, thereby increasing the likelihood of complication avoidance.


Jun 29, 2019 | Posted by in NEUROSURGERY | Comments Off on Complications of Endoscopic Endonasal Skull Base Surgery

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