What are the key anatomical considerations in transphenoidal sinus surgery?

Pertinent Basilar and Sellar Anatomy in Transsphenoidal Surgery

Understanding the critical anatomical landmarks and variations within the sphenoid sinus is essential for safe transsphenoidal access to the sella, as these structures guide surgical navigation and their inconsistency poses significant risk for neurovascular injury. 1, 2

Critical Vascular Structures

Internal Carotid Arteries

• The internal carotid arteries represent the most dangerous structure at risk, with mean intercarotid distance measuring only 15.8-16.5 mm 2
• Bony dehiscence overlying the internal carotid arteries within the sphenoid sinuses occurs as an anatomical variant and must be identified preoperatively 1
• The carotid arteries create a bony prominence along the lateral sphenoid sinus walls that serves as a critical landmark 3, 2
• Highly pneumatized sphenoid sinuses can distort normal anatomic configuration, increasing risk of accidental carotid injury when opening the sella 3

Optic Nerve

• The optic nerve courses along the superolateral aspect of the sphenoid sinus and is vulnerable to injury during lateral dissection 3
• Preoperative imaging must identify any bony dehiscence over the optic canal 1

Sphenoid Sinus Pneumatization Patterns

Classification and Surgical Impact

• Pneumatization pattern significantly affects safe access to the sella, with four recognized types: conchal (2%), presellar (21%), sellar (55%), and postsellar (22%) 3
• Conchal or minimally pneumatized sinuses require drilling through thick bone and make landmark identification extremely difficult 3, 4
• Even poorly pneumatized sphenoid sinuses can be safely approached using neuronavigation and intraoperative Doppler ultrasound 4
• In pediatric patients with incompletely pneumatized sinuses, transsphenoidal surgery remains feasible with appropriate image guidance 1, 5

Sellar Floor Landmarks

Sellar Bulge

• The sellar bulge is the single most important surgical landmark for identifying the sella floor, present in 78% of cases 3
• When present, the bulge is marked in 81% and mild in 19% of cases 3
• Absence of sellar bulge (22% of cases) significantly complicates identification of the sella floor and increases surgical difficulty 3

Intersphenoid Septum

• The intersphenoid septum is located in the true midline in only 23% of cases, making it an unreliable landmark 2
• Single septum present in 72% of patients, no septum in 11%, and accessory septa in 11% 3
• The terminal septum frequently inserts directly onto the carotid artery bony shield (28-37% of cases), requiring extreme caution during removal 3, 2
• Aggressive removal of septa without awareness of carotid insertion can cause catastrophic arterial injury 3

Dimensional Measurements

Critical Distances

• Mean sphenoid sinus diameter: 31.3-31.5 mm 2
• Mean vomer-to-clivus distance: 26.7-27.9 mm 2
• Optimal bony exposure of the sphenoid and sellar regions improves extent of tumor resection 1

Cavernous Sinus Relationships

• The cavernous sinuses flank the sella laterally and contain cranial nerves III, IV, V1, V2, and VI along with the internal carotid artery 1
• Tumor invasion into the cavernous sinus affects surgical approach and may require combined transcranial-transsphenoidal techniques 1
• Thin-section CT with multiplanar reformatting provides superior osseous detail for preoperative planning 1

Common Pitfalls and Safety Measures

Preoperative Planning

• Always obtain thin-section CT and MRI to identify variant anatomy, bony dehiscence, and septum insertion patterns before surgery 1, 3, 2
• Recognize that anatomical landmarks show wide variation and high inconsistency—handle with extreme caution 2

Intraoperative Navigation

• Use neuronavigation systems in all cases of poor pneumatization or complex anatomy to avoid misdirection and neurovascular injury 4, 5
• Intraoperative Doppler ultrasound helps identify carotid arteries when bony landmarks are absent 4
• Patient positioning is crucial to avoid superior or posterior misdirection 3

Midline Orientation

• Maintain constant awareness of the midline when opening the sella, especially in highly pneumatized sinuses where distorted anatomy increases risk 3
• The septum cannot be relied upon for midline identification in 77% of cases 2

Specific Complications to Avoid

• Cerebrospinal fluid leak from inadvertent dural violation 1
• Internal carotid artery injury or pseudoaneurysm formation (potentially fatal) 1
• Optic nerve injury causing visual loss 1
• Meningitis from contamination 1