What are the anatomical relationships of the sphenoid sinus?

Anatomical Relations of the Sphenoid Sinus

The sphenoid sinus is critically related to the optic nerve, internal carotid artery, cavernous sinus (containing cranial nerves III, IV, V1, V2, and VI), and pituitary gland—relationships that make sphenoid pathology uniquely dangerous for intracranial complications and require meticulous preoperative imaging to identify bony dehiscences. 1, 2

Superior Relations

• Pituitary gland (sella turcica): The sphenoid sinus lies directly inferior to the pituitary fossa, making transsphenoidal approaches to pituitary tumors anatomically feasible 2
• Optic chiasm and optic nerves: The optic canals course along the superolateral walls of the sphenoid sinus, and bony dehiscence over the optic canal occurs as an anatomical variant that must be identified preoperatively 1, 2

Lateral Relations

• Cavernous sinuses: These venous structures flank the sella laterally and contain cranial nerves III (oculomotor), IV (trochlear), V1 (ophthalmic division of trigeminal), V2 (maxillary division of trigeminal), and VI (abducens), along with the internal carotid artery 2
• Internal carotid arteries: These vessels course through the lateral walls of the sphenoid sinus, and bony dehiscence overlying the internal carotid arteries occurs as an anatomical variant in a significant proportion of patients 1, 2, 3
• Foramen rotundum: This canal transmits the maxillary nerve (V2) and is positioned in close relationship to the lateral sphenoid sinus wall 4
• Vidian canal: Contains the vidian nerve and courses along the floor of the sphenoid sinus 3, 4

Anterior Relations

• Posterior ethmoid sinuses: The sphenoid sinus is separated from the posterior ethmoid air cells by a thin bony partition 1
• Sphenoethmoidal recess: The sphenoid sinus ostium opens into this recess, positioned superior to the superior turbinate, allowing endoscopic visualization and cannulation 1, 2

Inferior Relations

• Nasopharynx and choana: The anterior wall of the sphenoid sinus forms part of the posterior nasal cavity 1

Clinical Implications and Pitfalls

High-Risk Complications

• Intracranial spread: Because of its location adjacent to the frontal and sphenoid sinuses, infection in the sphenoid sinus has a greater propensity to cause intracranial complications compared to other sinuses 1, 2
• Cavernous sinus thrombosis: Sphenoid sinusitis can spread directly into venous channels draining into the cavernous sinuses, potentially causing cranial nerve deficits and internal carotid artery thrombosis 2
• Cerebrospinal fluid leak: Inadvertent dural violation during sphenoid surgery can lead to CSF leak 2
• Vascular injury: Internal carotid artery injury or pseudoaneurysm formation is a potentially fatal complication 2
• Visual loss: Optic nerve injury during surgery can cause permanent visual impairment 2
• Meningitis: Contamination during surgery or direct infectious spread can cause meningitis 2

Essential Preoperative Imaging

• Always obtain thin-section CT with multiplanar reformatting and MRI to identify variant anatomy, bony dehiscence over the internal carotid artery and optic canal, and septum insertion patterns before any sphenoid surgery 2
• Bony dehiscence overlying critical neurovascular structures occurs frequently enough that preoperative identification is mandatory to prevent catastrophic intraoperative injury 2, 5

Anatomical Variants

• The sphenoid sinus demonstrates highly variable pneumatization patterns, ranging from minimal to extensive, which affects surgical approach 2, 5, 6
• In pediatric patients with incompletely pneumatized sinuses, transsphenoidal surgery remains feasible with appropriate image guidance 2, 7