FIGURE 36–1. Endoscopic image of a cadaveric dissection of the anterior skull base region after complete exposure of the anterior ventral skull base via a modified Lothrop procedure anteriorly, total ethmoidectomies laterally, and extended sphenoid sinusotomy posteriorly. Note: Right frontal sinus (RFS); left frontal sinus (LFS); right anterior ethmoid canal (RAE); left anterior ethmoid canal (LAE); right posterior ethmoid canal (RPE); left posterior ethmoid canal (LPE); right fovea ethmoidalis (RFE); left fovea ethmoidalis (LFE); planum sphenoidale (PS); right lamina papyracea (RLP); left lamina papyracea (LLP); right lamina cribrosa (RLC).
• Lies laterally
• Divided by basal lamella of middle turbinate into two portions
1. Anterior ethmoid complex (bullar and suprabullar recesses)
2. Posterior ethmoid complex
• Recommended to isolate anterior and posterior ethmoidal arteries during surgical approach
Anterior Ethmoidal Artery (branch of ophthalmic artery)
• Runs medial to optic nerve, between superior and medial rectus muscles, and enters anterior ethmoidal foramen of the lamina papyracea
• Twists posteriorly and then anteriorly in the anterior ethmoidal canal toward lamina cribrosa
• Variable in position, but often found between the second and third ethmoidal lamellae
• Useful to identify frontal recess because of its close relationship with anterior ethmoidal canals
Posterior Ethmoidal Artery
• Runs between superior rectus and superior oblique muscles to enter the posterior ethmoidal canal
• Defines posterior rim of olfactory groove
• Crosses the ethmoidal roof horizontally, anterior to the opticocarotid recess
• Lies a few millimeters anterior to planum sphenoidale
• Figure 36–2 illustrates the sphenoid sinus and parasellar region with the mucosa of the sphenoid sinus removed.
• Figure 36–3 illustrates the sphenoid sinus and parasellar region with the bone of the lateral sphenoid and suprasellar skull base removed.
• Extends from planum sphenoidale to sellar floor inside the sphenoid sinus cavity
• Defined by superior, posterior, and lateral walls of the sphenoid sinus
• For exposure: remove superior/supreme turbinates and posterior ethmoid cells
• Care must be taken to avoid injuring posterior ethmoidal artery and the lamina cribrosa anteriorly
• Sella turcica lies midline/center
• Accessed via: endoscopic endonasal transplanum transtuberculum for pituitary lesions with suprasellar extension, craniopharyngiomas, and tuberculum sellae meningiomas
FIGURE 36–2. Endoscopic view of cadaveric dissection image of the sphenoid sinus and parasellar region. The mucosa of the sphenoid sinus has been removed. The intersinus septum (ISS) and posterior septum have been resected. Note: Planum sphenoidale (PS); tubuculum sellae (TS); right and left optic canal (R. OC and L. OC); left opticocarotid recess (L. OCR); sellar floor (SF); right cavernous carotid canal (R CCC); clival recess (CR).
Planum Sphenoidale and Tuberculum Sellae
• Lies anterior/superior
• Tuberculum sella represents angle formed by sphenoid planum and sellar floor
1. Removal limited to 2 cm in anterior-posterior direction
2. Limited by optic nerves laterally
3. Intercavernous sinus lies at this level
• Lies posterior/inferior
• Lies lateral
• Inferior protuberance: paraclival segment
• Superior protuberance: parasellar segment
FIGURE 36–3. Endoscopic view of cadaveric dissection image of the sphenoid sinus and parasellar region. The bone of the lateral sphenoid and suprasellar skull base has been removed. Note: Right optic nerve (R. ON); ophthalmic artery (Oph A.); optic chiasm (OC); cavernous carotid artery (CCA); paraclival carotid artery (PCA); oculomotor nerve (CN III); trochlear nerve (CN IV); abducens nerve (CN VI); ophthalmic division of the trigeminal nerve (V1); maxillary division of the trigeminal nerve (V2); pituitary gland (PG); pituitary stalk (PS); resected intersinus septum (ISS).
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