Endoscopic Endonasal Transsphenoidal Surgery: Route and Causes of Anosmia
The endoscopic endonasal transsphenoidal approach involves accessing the pituitary gland through the nasal cavity and sphenoid sinus, with the standard surgical route proceeding from the nostril through the nasal cavity to the sphenoethmoid recess, then through the anterior wall of the sphenoid sinus to reach the sella turcica.
Surgical Route
The procedure begins with the nasal phase, where the endoscope is introduced through the chosen nostril and advanced to the sphenoethmoid recess 1.
The sphenoid phase follows with detachment of the nasal septum from the sphenoid rostrum, anterior sphenoidotomy, removal of sphenoid septa, and identification of landmarks inside the sphenoid sinus 1.
The final sellar phase involves opening the sellar floor to access and remove the lesion, with angled scopes providing wide visualization of the sellar environment 1.
Two main approaches exist within the endonasal route:
The endoscopic approach differs from microscopic techniques by using the endoscope as the primary optical device and eliminating the need for a transsphenoidal retractor 1.
Causes of Anosmia
Anosmia (loss of smell) following endoscopic endonasal transsphenoidal surgery can occur due to several mechanisms:
Damage to the septal olfactory strip (SOS) - The surgical corridor often jeopardizes the olfactory mucosa located in the superior nasal cavity 3.
Mucosal trauma - Significant disturbances in olfactory performance occur after transnasal surgery due to trauma to the nasal mucosa during the approach 4.
Long-term olfactory dysfunction - Studies show that 67.1% of patients experience hyposmia or anosmia after surgery, with 14.9% developing long-term olfactory dysfunction 4.
Risk factors for persistent anosmia include:
Techniques to Minimize Anosmia Risk
Bilateral "rescue flap" technique - Preserves the mucosa containing the nasal-septal vascular pedicles and the septal olfactory strip, reducing the risk of postoperative anosmia 3.
Endoscopic modified transseptal transsphenoidal approach (EMTS-TSA) - By bypassing the nasal mucosa and approaching through the septum bilaterally, this technique better preserves early postoperative olfactory function 5.
Studies show that modified approaches can maintain preoperative olfaction in up to 97% of patients 3.
The EMTS-TSA approach shows no significant difference between preoperative and 3-month olfactory function (VAS scores from 90.6 to 88.8; P = 0.403), while traditional approaches show significant decline (from 92.5 to 81.3; P = 0.002) 5.
Clinical Recommendations
For most pituitary adenomas, transsphenoidal surgery is the technique of choice, even in patients with incompletely pneumatized sphenoid sinuses 6.
Consider endoscopic rather than microscopic transsphenoidal surgery for potentially superior efficacy in preserving pituitary function 6.
Endoscopic approaches are recommended for better visualization of residual tumor after standard microsurgery 6.
Physicians should assess olfactory function preoperatively and discuss the risk of postoperative anosmia with patients, particularly those with preexisting nasal conditions or smoking history 4.