- •
The sphenoid bone is at the center of the skull base and understanding its anatomy from multiple perspectives is important to understanding endonasal approaches.
- •
Within the sphenoid sinus, the lateral opticocarotid recess is a key landmark for identifying the locations of the parasellar carotid artery and optic nerve.
- •
The tuberculum sella is the anterior and superior limit of the sella. Limited removal of the tuberculum during pituitary surgery helps avoid CSF leak, while complete removal allows
Skull Base Anatomy
Section snippets
Key points
Sphenoid bone
The sphenoid bone sits at the center of the skull base, and knowing its anatomy is central to understanding endonasal approaches. The sphenoid bone has been described as resembling a bat with its wings outstretched (Fig. 1). It consists of a central body, which is cuboidal in shape and houses the sphenoid sinus at its center. The sella turcica is located superiorly and the upper clivus posteriorly. The lesser wings extend from the superolateral aspect of the body and the greater wings from the
Sphenoid sinus
The sphenoid sinus varies considerably in size, shape, pneumatization, and septation. The degree of pneumatization varies with age, with most pneumatization occurring in adolescence. There are three types of pneumatization patterns in adults: conchal, presellar, and sellar. The conchal type has little to no pneumatization. The presellar type has some pneumatization but does not extend beyond the plane of the tuberculum sella. The sellar type is the most common and the cavity extends beyond the
Pituitary gland
The human pituitary gland is composed of two embryologically, anatomically, and functionally distinct parts. There is an anterior lobe or adenohypophysis, and a smaller posterior lobe or neurohypophysis. The anterior lobe develops from an invagination of oral ectoderm known as Rathke's pouch. It is a glandular structure that is responsible for the production and release of growth hormone, prolactin, adrenocorticotropic hormone, thyroid-stimulating hormone, luteinizing hormone, and
Cavernous sinus
The cavernous sinus is a venous lake that communicates with multiple venous tributaries and spaces: basilar plexus; superior and inferior petrosal sinuses; superior and inferior ophthalmic veins; veins of foramen rotundum, foramen spinosum, foramen ovale, and the foramen of Vesalius; deep middle cerebral vein; superficial sylvian vein; and the contralateral cavernous sinus via intercavernous connections. In addition to transmitting venous blood, it contains multiple neurovascular structures.4
Suprasellar space
The suprasellar space extends from the diaphragma inferiorly to the floor of the third ventricle superiorly. Access to the suprasellar space is obtained by removing the tuberculum sella, prechiasmatic sulcus, and posterior planum sphenoidale. The suprasellar space is divided into the infrachiasmatic, suprachiasmatic, and retrochiasmatic areas.
Within the infrachiasmatic space is found the inferior surface of the optic chiasm and the infundibulum in the midline (see Fig. 3A; Fig. 6A). The
Anterior cranial base
The anterior two-thirds of the anterior cranial base is composed of the ethmoid and frontal bones, and the posterior one-third is formed by the planum sphenoidale (Fig. 7A). The ethmoid bone consists of the cribriform plate and crista galli in the midline; the ethmoid roofs (fovea ethmoidalis) superiorly; and the lamina papyracea laterally, which separates the ethmoid sinuses from the orbit. The perpendicular plate of the ethmoid joins the vomer to become the bony septum.12
Once the ethmoid roof
Clivus
The clivus can be divided into thirds (Fig. 8A). The upper third or “sellar” clivus is made up of the dorsum sella and posterior clinoids down to approximately the level of the floor of the sella. Dorello's canal is located at the transition point between upper and middle clivus, just a few millimeters below the floor of the sella. The middle third or “sphenoidal” clivus extends from the floor of the sella to the choana. The lower third or “nasopharyngeal” clivus extends from there down to
Summary
Technologic advances have greatly improved the ability to access the ventral skull base. The endonasal route has been expanded to allow access to the anterior, middle, and posterior cranial fossas. Understanding of the complex anatomy of the skull base has also greatly expanded. A detailed understanding of the various anatomic relationships provides one with the ability to determine the safest and most effective approach to lesions of the ventral skull base. It allows one to minimize morbidity,
References (13)
- et al.
The history and evolution of transsphenoidal surgery
J Neurosurg
(2001) - et al.
Brief history of endoscopic transsphenoidal surgery–from Philipp Bozzini to the First World Congress of Endoscopic Skull Base Surgery
Neurosurg Focus
(2005) Anatomy of the pituitary gland and sellar region
- et al.
Microsurgical anatomy and approaches to the cavernous sinus
Neurosurgery
(2005) - et al.
Endoscopic endonasal middle clinoidectomy: anatomic, radiological, and technical note
Neurosurgery
(2012) - et al.
Microsurgical anatomy of the diaphragma sellae and its role in directing the pattern of growth of pituitary adenomas
Neurosurgery
(2008)
Cited by (47)
Surgical anatomy of the anterior cranial fossa
2023, Cerebrospinal Fluid Rhinorrhea: Comprehensive Guide to Evaluation and ManagementPathophysiology and clinical evaluation of blunt force and penetrating trauma of the anterior cranial base
2023, Cerebrospinal Fluid Rhinorrhea: Comprehensive Guide to Evaluation and ManagementImaging Review of the Endoscopic Operative Corridor for Clivus Lesions
2023, Current Problems in Diagnostic RadiologyCitation Excerpt :Just lateral to the pituitary gland lies the carotid artery and cavernous sinus. Of note, the vidian nerve may run along the floor or within the sphenoid sinus and its canal can be identified on preoperative CT.11 (Fig 6) Once the sphenoid sinus is identified and opened to access the floor of the sella turcica, there are several important surface landmarks and the ventral surface of the clivus (Fig 7A-B).
Linking death, the paranasal sinuses, and traumatic head trauma
2022, Diagnosis and Treatment of Traumatic Brain Injury: The Neuroscience of Traumatic Brain InjuryThe “STARS–CT-MADE” Study: Advanced Rehearsal and Intraoperative Navigation for Skull Base Tumors
2021, World NeurosurgeryCitation Excerpt :Due to the complex anatomy of this region, even small lesions can result in significant visual symptoms (i.e., reduction of visual acuity or hemianopsia) because of the close relationship with the optic nerve and the possibility of tumor infiltration into the optic canal, which may further worsen any visual symptoms.4 Therefore the challenge lies in both the delicate relationships with different neurovascular structures (e.g., optic nerve with chiasma, internal carotid artery, anterior and middle cerebral artery), which require extreme care during surgical dissection,5,6 and the necessity of performing the unroofing of the optic canal to decompress the nerve in the case of possible tumor infiltration.7-10 For these reasons, the treatment of such lesions is often left in the hands of more experienced surgeons,11 restricting the training possibilities for residents.
Disclosure Statement: The authors have nothing to disclose.