How should an image‑guided navigation system be used during endoscopic sinus and skull‑base ENT surgery?

Image-Guided Navigation in Endoscopic Sinus and Skull Base ENT Surgery

Image-guided navigation systems should be used selectively during endoscopic sinus and skull base surgery—specifically in complex cases with distorted anatomy, revision surgery, massive polyposis, or when operating near critical structures like the orbit, optic nerve, or skull base—using either electromagnetic or optical tracking systems with CT-based registration to achieve submillimeter to 2mm accuracy. 1

Indications for Navigation System Use

Navigation systems are not recommended for routine, straightforward endoscopic sinus surgery but should be reserved for specific high-risk scenarios: 1, 2

• Revision surgery where normal anatomical landmarks are distorted or absent 2
• Massive recurrent polyposis that obscures typical anatomical references 2
• Abnormal anatomy including sphenoethmoidal (Onodi) air cells that increase risk of optic nerve or carotid artery injury 1
• Skull base procedures requiring precise localization near the clivus, sphenoid sinus wall, or orbital apex 2
• Tumor biopsies from specific anatomical locations where millimeter-level precision is required 2
• Frontal skull base access where proximity to intracranial structures demands real-time confirmation 3

Technical Implementation and System Types

Registration and Accuracy Standards

The registration process creates a one-to-one relationship between the operative field and imaging data, with accuracy within 2mm considered acceptable for safe endoscopic sinus surgery: 1

• Electromagnetic tracking systems and optical tracking systems are the two major platforms available 1
• Mean localization error ranges from 1.1-2.5mm across validated systems, which is sufficient for safe navigation near critical structures 2, 4
• Registration accuracy of 0.70mm mean target registration error has been achieved with video-based tracking methods in research settings 5

Preoperative CT Protocol

Non-contrast sinus CT is the imaging modality of choice for navigation system integration: 1

• CT provides optimal delineation of complex ethmoidal anatomy, ostiomeatal unit, and anatomic variations 1
• The CT dataset is imported into the navigation system for image-based guidance during surgery 1
• Fine-cut CT protocols optimize registration accuracy and intraoperative visualization 6

Intraoperative Workflow

Navigation adds 15-52 minutes to total operating room time depending on the system used: 2, 4

• Optical tracking systems (e.g., Stealth Station) require approximately 17 minutes additional preparation time 4
• Real-time MRI-based systems require approximately 52 minutes additional setup but provide updated imaging during surgery 4
• In 94% of cases, navigation provides accurate anatomical localization with less than 2mm error 2

Advantages and Safety Benefits

Navigation systems provide real-time information of instrument location relative to critical structures, reducing surgical risks: 1

• Surgeons report increased confidence and perceived safety factor in 100% of complex cases 2
• The system enables identification of surgical sites when normal landmarks are compromised 2
• Particularly valuable for visualizing the relationship between instruments and the optic nerve, carotid artery, and skull base 1, 3

Limitations and Contraindications

Navigation is not advised for surgeons unfamiliar with standard endoscopic sinus surgery techniques: 2

• The system is a surgical adjunct, not a replacement for anatomical knowledge and endoscopic skill 2
• For experienced endoscopists, navigation is valuable specifically in complex procedures 2
• Some real-time MRI systems require MR-safe instruments, limiting available surgical tools 4
• Registration accuracy can degrade with significant tissue manipulation or CSF leak during surgery 1

Emerging Technologies

Novel trackerless navigation using 3D endoscopy and simultaneous localization and mapping (SLAM) algorithms shows promise: 7

• SLAM-based systems achieve 1.38mm registration error without external tracking equipment 7
• These systems reconstruct high-fidelity 3D surface models directly from stereoscopic endoscopic video 7
• Video-based tracking maintains submillimeter accuracy (0.70mm mean) in validation studies 5
• This approach may improve surgical efficiency and economy of motion by eliminating bulky external trackers 7

Common Pitfalls to Avoid

• Do not rely solely on navigation without confirming anatomical landmarks through direct endoscopic visualization 2
• Do not use navigation as a substitute for proper surgical training in endoscopic techniques 2
• Do not assume registration remains accurate throughout the entire procedure—verify periodically with known anatomical landmarks 1
• Do not proceed with surgery if registration error exceeds 2mm—re-register or convert to standard technique 1, 2