Key points
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Image guidance is a surgical tool that is widely accepted by endoscopic surgeons and used in most frontal sinus surgeries.
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The use of image guidance can help identify critical structures and distorted anatomic landmarks, increasing the surgeon’s confidence and ability to perform a more complete dissection.
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Image-guided placement of limited external frontal sinusotomy allows access to and management of frontal sinus disease that is beyond the endoscopic reach while avoiding the need for an osteoplastic flap.
Background on image guidance in endoscopic sinus surgery
The use of image-guided surgery (IGS) in endoscopic sinus surgery (ESS) has expanded during the last 2 decades. A 2010 survey of American Rhinologic Society members suggests that more surgeons have access to IGS and are using this technology in a greater percentage of cases compared with a similar survey conducted in 2005. With respect to frontal sinus procedures, 71% of respondents thought there was a relative or absolute indication for its use in primary frontal sinus exploration, 96% in revision frontal sinus exploration, and 98% in modified Lothrop procedures. Although it is well known that IGS is not a substitute for sound anatomic knowledge and clinical decision-making, it may help minimize the risk of injury by verifying the location of vital structures surrounding the paranasal sinuses and assist in a more complete clearance of disease. Logically, this would translate into fewer surgical complications and improved patient outcomes, the former of which was a conclusion of a recent meta-analysis of surgical cohorts with and without IGS in sinus surgery.
Complication rates for ESS have been reported to range from 0.36% to 3.1%. Although all aspects of ESS can present challenges, surgery of the frontal sinus is the most technically demanding. The complex and varied anatomy, acute nasofrontal angle, and proximity to critical structures, such as the olfactory fossa, skull base, vascular structures (anterior ethmoid artery), and orbit contribute to the technical difficulty of frontal recess surgery. In addition, distorted anatomy from chronically inflamed mucosa and absent anatomic landmarks from prior surgery only add to the potential risk. However, IGS has uses well beyond simply avoiding complications. It can facilitate identifying the appropriate location for an external frontal trephine (or minitrephine), mapping an osteoplastic flap, or defining the extent of nasofrontal beak exposure before Draf III sinusotomy. Some procedures, such as an image-guided external biopsy of lateral frontal sinus disease, depend entirely on the IGS technology.
Image-guidance systems typically used in ESS can be either optically based or electromagnetic-based, and consist of a computer workstation, tracking system, and specially designed navigation instruments ( Fig. 1 ). The patient’s image-guidance compatible computed tomography (CT) scan, usually an axial noncontrast CT with 1 mm or thinner cuts, is loaded into the system either by CD-ROM or over a broadband network preoperatively. Once the image guidance is registered to the patient, intraoperative localization of a given navigation instrument is displayed in real time on the patient’s preoperative CT in axial, coronal, and sagittal planes ( Fig. 2 ). Image-guidance accuracy has been shown to be within 2 mm and a variety of frontal sinus navigation instruments have been developed to make it well suited for this type of surgery. Although excellent for general localization or reorienting the surgeon, they are not accurate enough to help with submillimeter decision-making around critical skull base anatomy.
Background on image guidance in endoscopic sinus surgery
The use of image-guided surgery (IGS) in endoscopic sinus surgery (ESS) has expanded during the last 2 decades. A 2010 survey of American Rhinologic Society members suggests that more surgeons have access to IGS and are using this technology in a greater percentage of cases compared with a similar survey conducted in 2005. With respect to frontal sinus procedures, 71% of respondents thought there was a relative or absolute indication for its use in primary frontal sinus exploration, 96% in revision frontal sinus exploration, and 98% in modified Lothrop procedures. Although it is well known that IGS is not a substitute for sound anatomic knowledge and clinical decision-making, it may help minimize the risk of injury by verifying the location of vital structures surrounding the paranasal sinuses and assist in a more complete clearance of disease. Logically, this would translate into fewer surgical complications and improved patient outcomes, the former of which was a conclusion of a recent meta-analysis of surgical cohorts with and without IGS in sinus surgery.
Complication rates for ESS have been reported to range from 0.36% to 3.1%. Although all aspects of ESS can present challenges, surgery of the frontal sinus is the most technically demanding. The complex and varied anatomy, acute nasofrontal angle, and proximity to critical structures, such as the olfactory fossa, skull base, vascular structures (anterior ethmoid artery), and orbit contribute to the technical difficulty of frontal recess surgery. In addition, distorted anatomy from chronically inflamed mucosa and absent anatomic landmarks from prior surgery only add to the potential risk. However, IGS has uses well beyond simply avoiding complications. It can facilitate identifying the appropriate location for an external frontal trephine (or minitrephine), mapping an osteoplastic flap, or defining the extent of nasofrontal beak exposure before Draf III sinusotomy. Some procedures, such as an image-guided external biopsy of lateral frontal sinus disease, depend entirely on the IGS technology.
Image-guidance systems typically used in ESS can be either optically based or electromagnetic-based, and consist of a computer workstation, tracking system, and specially designed navigation instruments ( Fig. 1 ). The patient’s image-guidance compatible computed tomography (CT) scan, usually an axial noncontrast CT with 1 mm or thinner cuts, is loaded into the system either by CD-ROM or over a broadband network preoperatively. Once the image guidance is registered to the patient, intraoperative localization of a given navigation instrument is displayed in real time on the patient’s preoperative CT in axial, coronal, and sagittal planes ( Fig. 2 ). Image-guidance accuracy has been shown to be within 2 mm and a variety of frontal sinus navigation instruments have been developed to make it well suited for this type of surgery. Although excellent for general localization or reorienting the surgeon, they are not accurate enough to help with submillimeter decision-making around critical skull base anatomy.
Utility of image guidance in endoscopic sinus surgery
Several studies directed at IGS use in ESS have been performed to analyze its associated complication rate, revision rate, patient quality of life outcomes, cost, and medicolegal role.
Complications
In an evidence-based review with recommendations (EBRR) by Ramakrishnan and colleagues, 6 studies reported complication rates in IGS compared with non-IGS groups. Four of the 6 studies showed no statistically significant difference in complication rates with IGS, whereas 2 studies did show a significant difference in major complications with IGS use. One of these studies showed fewer major complications with IGS use (intracranial injury, orbital injury, major hemorrhage, and aborted procedure) but no difference in minor complications (not specifically defined), whereas the other actually showed an increased rate of orbital injuries with the use of IGS but no other significant differences. There was determined to be a preponderance of benefit versus harm based on C-level quality of evidence, making the use of IGS for the reduction of complications an option. In a meta-analysis of 13 relevant studies, including 5 of the 6 studies in the previously mentioned EBRR, Dalgorf and colleagues reported that the rate of major complications and total complications did favor the use of IGS with statistical significance when the data was pooled.
Revision Rate
In a retrospective review of 120 subjects who underwent ESS with use of IGS, 16.5% of subjects went on to require revision surgery, although there was no comparison group in this study. Fried and colleagues retrospectively reviewed 160 subjects and did report a significantly higher need for revision surgery in the non-IGS patient group than in the IGS group. However, a similarly designed study with 203 subjects had contradicting findings. More recently, 2 separate meta-analyses found no significant difference in subsequent revision rates with or without the initial use of IGS.
Quality of Life Outcomes
Three studies compared subject quality of life outcomes after ESS with or without the use of IGS. One retrospective chart review found no difference in Sino-Nasal Outcome Test (SNOT)-20 scores at least 6 months after surgery. Two prospective, nonrandomized studies found conflicting results, 1 with improved Rhinosinusitis Outcome Measure (RSOM)-31 scores 6 months after IGS and the other with no difference in visual analog scale (VAS) scores 12 months after IGS. Although these studies show varied results individually, when their data were pooled by Dalgorf and colleagues there was no evidence of a significant difference in quality of life outcomes whether or not IGS was used.
Cost and Medicolegal Concerns
The cost of IGS is an accumulation of the navigation system, disposable supplies or equipment costs, and any added operative time. One study reported that in otherwise similar subject groups, IGS was 6.7% more expensive than non-IGS. They noted, however, that significant intangible benefits of this surgical adjunct may justify its use despite the increased cost but be too difficult to illustrate.
With respect to medicolegal situations, whether or not IGS was used did not play a role in ESS litigation initiation or outcomes from 2004 to 2013. Case-specific factors and expert opinion from the operating surgeon should determine whether or not the cost and extra setup time is justified, instead of a habitual practice of defensive medicine.
The literature illustrating advantages or disadvantages of IGS is very limited. For example, to show a statistical difference in complication rate with IGS, power analyses have indicated that thousands of subjects would need to be enrolled in a prospective study. That image guidance is currently widely accepted as being indicated in certain scenarios based on expert opinion makes future randomized studies (in which some subjects will be randomized away from IGS use even if the surgeon feels it is necessary) ethically impossible. The American Academy of Otolaryngology–Head and Neck Surgery endorses the use of IGS during ESS in select cases guided by expert opinion, surgeon preference, and patient-specific factors. These indications are at the discretion of the surgeon and include revision surgery, distorted anatomy, extensive sinonasal polyposis, frontal or posterior sinus disease, disease-abutting vital structures, skull base defects, and neoplasms.
Endoscopic uses of image guidance
Maximizing the Frontal Sinusotomy
The frontal sinus and its outflow tract are known for variable anatomy, surrounding vital structures, and a narrow ostium predisposed to scarring and obstruction following surgical manipulation. The frontal recess is bordered medially by the middle turbinate, laterally by the lamina papyracea, anteriorly by the agger nasi cell, and posteriorly by the superior aspect of the ethmoid bulla along with the anterior ethmoid artery. In addition to the agger nasi cell anteriorly, there can be 1 or numerous frontal cells that sit above the agger nasi and pneumatize into the frontal recess, into the frontal sinus, or be isolated within the frontal sinus ( Fig. 3 A ). Posteriorly and laterally to the frontal recess, patients can have frontal bullar cells or supraorbital cells that similarly encroach on the outflow space ( Fig. 3 B).
