Endoscopic windows for increased visualization in endoscopic skull base surgery

Theodore Schuman, MD1, Katherine Adams, BS1, Cristine Klatt-Cromwell, MD1, Brian Thorp, MD1, Charles Ebert, MD1, Deanna Sasaki-Adams, MD2, Matthew Ewend, MD2, and Adam Zanation, MD1

1Division of Rhinology & Skull Base Surgery, Department of Otolaryngology – Head & Neck Surgery, 2Department of Neurosurgery University of North Carolina at Chapel Hill, Chapel Hill, NC

Theodore A. Schuman, MDDept. of Otolaryngology – Head & Neck SurgeryUniversity of North Carolina at Chapel HillEmail: tschuman@med.unc.eduWebsite: www.med.unc.edu/entPhone: 984-974-6484

Contact1. Castelnuovo P, Dallan I, Battaglia P, Bignami M. Endoscopic endonasal skull base surgery: Past, present and future. Eur Arch Oto-Rhino-

Laryngology. 2010;267(5):649-663. 2. Jho HD, Carrau RL. Endoscopic endonasal transsphenoidal surgery: experience with 50 patients. J Neurosurg. 1997;87(1):44-51. 3. Zwagerman NT, Zenonos G, Lieber S, et al. Endoscopic transnasal skull base surgery: pushing the boundaries. J Neurooncol. 2016;130(2):319-330. 4. Upadhyay S, Dolci RLL, Buohliqah L, et al. Effect of Incremental Endoscopic Maxillectomy on Surgical Exposure of the Pterygopalatine and

Infratemporal Fossae. J Neurol Surgery, Part B Skull Base. 2015;77(1):66-74. 5. Garcia H, Otten M, Pyfer M, et al. Minimizing Septectomy for Endoscopic Transsphenoidal Approaches to the Sellar and Suprasellar Regions: A

Cadaveric Morphometric Study. J Neurol Surg Part B Skull Base. 2016;77(6):479-484. 6. Cho HJ, Kang JW, Min HJ, et al. Robotic nasopharyngectomy via combined endonasal and transantral port: A preliminary cadaveric study.

Laryngoscope. 2015;125(8):1839-1843.

References

Objectives: To quantify progressive nasopharyngeal and posterior maxillary wall exposure using a 0-degree endoscope through the addition of a posterior septal window and Denker’s procedure in endoscopic skull base surgery.Design: Anatomic cadaver study.Setting: Anatomy laboratory.Participants: Eight dissections in latex injected human cadaver specimens.Main Outcome Measures: After complete endoscopic sinus surgery including medial maxillectomy, nasopharyngeal and maxillary sinus mucosal exposure were measured with a 0-degree endoscope inserted to the head of the inferior (IT) or middle turbinate (MT). Measurements were repeated after a 1x2xm posterior septectomy and Denker’s procedure.Results: Initial exposure of nasopharyngeal mucosa was 2.0 +/- 0.9 cm2 from the IT and 2.6 +/- 0.9 cm2 from the MT. The posterior septal window led to a statistically significant increase in nasopharyngeal exposure to 4.3 +/- 2.2 cm2 from the IT and 7.5 +/- 4.7 cm2 from the MT (two-tailed t-test, p<0.05). Initial lateral exposure of the posterior maxillary sinus was 1.6 +/- 0.5 cm at the IT and 2.5 +/- 0.5 cm at the MT. The Denker’s procedure resulted in a significant increase in lateral exposure to 3.3 +/- 0.4 cm and 4.0 +/- 0.1 at the IT and MT, respectively (two-tailed t-test, p<0.05). Conclusions: The posterior septal window results in a significant increase in nasopharyngeal exposure, and Denker’s procedure a significant increase in lateral exposure of the posterior maxillary wall in skull base surgery with a 0-degree endoscope. When working with a two-surgeon, four-handed technique, 0-degree visualization gives the team the most direct operating corridor and facilitates use of instruments that are optimized for 0-degree exposure. These endoscopic “windows” provide important tools to the endoscopic skull base surgeon for maximizing targeted exposure to the skull base while minimizing surgical morbidity.

Abstract

Visible nasopharyngeal mucosal area after FESS and medial maxillectomy was 2.0 +/- 0.9 cm2 from the IT and 2.6 +/- 0.9 cm2 from the MT. The septal window led to a significant increase in exposed mucosa, 4.3 +/- 2.2 cm2 from the IT and 7.5 +/- 4.7 cm2 from the MT (two-tailed t-test, p<0.05) (See Table 1). Lateral exposure of the posterior maxillary sinus wall after endoscopic medial maxillectomy was 1.6 +/- 0.5 cm at the IT and 2.5 +/- 0.5 cm at the MT. Addition of Denker’s procedure resulted in a significant increase in lateral exposure to 3.3 +/- 0.4 cm and 4.0 +/- 0.1 at the IT and MT, respectively (two-tailed t-test, p<0.05).

Introduction

Eight dissections were performed in latex-injected human cadaver specimens using a 0-degree endoscope for endonasal visualization. The procedure commenced with complete bilateral functional endoscopic sinus surgery (FESS) including sphenoethmoidectomy, frontal sinusotomy, and endoscopic medial maxillectomy. With the tip of the endoscope inserted to the head of IT or MT, visible nasopharyngeal (See Table 1) and posterior maxillary wall mucosa were measured. Through-cutting instruments were then used to remove a 1cm tall x2 cm deep full-thickness window of the posterior nasal septum just above the maxillary crest. An endoscopic Denker’s procedure was performed by isolated the caudal margin of the piriform aperture and removing bone and soft tissue laterally to the level of the infraorbital foramen. Measurements of visible mucosa within the nasopharynx and posterior maxillary sinus were then repeated in order to quantify changes in surgical exposure.

Methods and Materials

Discussion

The posterior septal window resulted in a significant increase in area of nasopharyngeal exposure, and Denker’s procedure a significant increase in lateral exposure of the posterior maxillary wall in skull base surgery with a 0-degree endoscope. When working with a two-surgeon four-handed technique, 0-degree visualization gives the team the most direct operating corridor, and facilitates the use of instruments optimized for 0-degree exposure. These endoscopic “windows” provide important tools to the endoscopic skull base surgeon for maximizing targeted exposure to the skull base while minimizing surgical morbidity.

Conclusions

Endoscopic endonasal surgery (EES) has advanced rapidly since Hopkins modified the endoscope in the 1950s, paving the way for early pioneers to address inflammatory paranasal sinus disease in a minimally-invasive fashion.1 As experience accumulated and endoscopic instrumentation became more sophisticated, EES techniques expanded to address the skull base. Jho and Carrau reported the first series of endoscopic transnasal resection of pituitary neoplasms in 19972, and since that time ongoing refinement has allowed purely endoscopic resection of benign and malignant neoplasms in both the sagittal and coronal planes.3

Given the proximity of critical neurovascular structures within the skull base, safe and effective surgery demands a thorough, real-time appreciation of complex three-dimensional anatomic relationships. While advances in digital imaging, optics, instrumentation, and image-guidance technology may facilitate smaller surgical ports, safe and effective access often still requires purposeful resection of normal intranasal structures in order to create “windows” for a two-surgeon, four-handed technique. Prior authors have described the use of extended maxillectomy techniques, including the Denker’s procedure, to increase exposure of the posterior maxillary sinus and facilitate dissection into the pterygopalatine and infratemporal fossae.4 Similarly, posterior septectomy has been reported to expand access to sellar5 and nasopharyngeal6 regions. The current study is designed to quantify increased exposure of nasopharyngeal and posterior maxillary wall mucosa through the creation of a posterior septal window and Denker’s procedure, respectively.

Results

Table 1. Nasopharyngeal mucosa visible with 0-degree endoscope before and after posterior septectomy. * denotes p < 0.01.

Figure 1. Measurement of visible nasopharynx mucosa (A) from the head of IT before posterior septectomyand (B) from the MT after septectomy.

Figure 2. Lateral visualization of posterior maxillary wall using 0-degree endoscope placed at head of IT after (A) endoscopic medial maxillectomy and (B) Endoscopic Denker’s procedure.

Endoscope positionHorizontal

NasopharynxVertical

NasopharynxNasopharyngeal

Area Visible

IT 0.9 +/- 0.3 cm 2.1 +/- 0.6 cm 2.0 +/- 0.9 cm2

MT 1.2 +/- 0.1 cm 2.2 +/- 0.7 cm *2.6 +/- 0.9 cm2

IT with septal window 1.8 +/- 0.7 cm 2.1 +/- 0.6 cm 4.3 +/- 2.2 cm2

MT with septal window 2.9 +/- 1.3 cm 2.1 +/- 0.6 cm *7.5 +/- 4.7 cm2

Creation of endoscopic “windows” via a limited posterior septectomy and Denker’s procedure significantly increased nasopharyngeal and posterior maxillary wall exposure in this series of endoscopic cadaver dissections. In live-patient surgery this may translate into improved endoscopic visualization and freedom of mobility, especially when employing a two-surgeon, four-handed technique. Ostensibly, improved visualization would allow a better appreciation of nearby critical neurovascular structures, although further research is necessary to determine whether increased exposure would lead to more complete tumor resection or reduced rate of complications.

The current study findings are echoed in the literature. Garcia et al investigated the effect of posterior septectomy size on surgical exposure, reporting improvement with progressive enlargement of the septal window until 20mm width, which is the size utilized in the current study.5 Posterior septectomy is associated with minimal morbidity, although epistaxis is possible with disruption of the posterior septal artery and requires vigilant intraoperative control of any bleeding from the sphenoid face. Upadhyay et al assessed endoscopic access to the pterygopalatine and infratemporal fossae with incremental maxillectomy, finding that the endoscopic Denker approach resulted in superior exposure and surgical freedom when compared with endoscopic medial maxillectomy with or without anterior extension, transseptal, and sublabial approaches.4 Denker’s procedure does, however, carry a risk of epiphora due to disruption of the lacrimal duct.