Dorsal clinoidal space

General

• Dorsal clinoidal space (DCS)

• Located dorsally (posteriorly) to the internal carotid artery (ICA) at the level of the clinoidal segment

• Bounded by the proximal and distal dural rings.

• Abbreviations
• A. = artery; ACA = anterior cerebral artery; ACP = anterior clinoid process; Ant. = anterior; Bas. = basilar; Call = callosum; Car. = carotid; Cav. = cavernous; CCL = caroticoclinoid ligament; Cer. = cerebral; Clin. = clinoid; CN = cranial nerve; COM = carotid-oculomotor membrane; Comm. = communicating; Corp. = corpus; CS = cavernous sinus; DCS = dorsal clinoidal space; Diaph. = diaphragm; Falc. = falciform; Fr. = frontal; Hyp. = hypophyseal; ICA = internal carotid artery; ICL = interclinoidal ligament; Inf. = inferior; Inn. = inner; Int. = interior; IPL = inferior parasellar ligament; Lig. = ligament; LOCR = lateral opticocarotid recess; LTC = lateral tubercular crest; MCP = middle clinoid process; Med. = medial; Memb. = membrane; Mid. = middle; N. = nerve; Oculo. = oculomotor; Ophth. = ophthalmic; Orb. = orbital; Out. = outer; Paraclin. = paraclinoid; Petrosphen. = petrosphenoidal; Pit. = pituitary; P.C.A. = posterior cerebellar artery; Post. = posterior; S.C.A. = superior cerebellar artery; See Fig. 1 legend for additional abbreviations; SHA = superior hypophyseal artery; Str. = straight; Sulc. = sulcus; Sup. = superior; Symp. = sympathetic; Tent. = tentorial; Tuberc. = tuberculum sellae; V = vein; VCS = ventral clinoidal space.

Clinical relevance

• This space is challenging to access using traditional transcranial approaches but has become more accessible with the advancement of endoscopic endonasal techniques.

• Understanding its anatomy is crucial in surgical planning and safe tumor resection, as it allows for:
• Maximizing the extent of tumor removal (especially for tumors with parasellar extension).
• Precise knowledge of the DCS facilitates safer exposure of the ICA during anterior clinoidectomy, reducing the risk of vascular injury.
• Mastery of the DCS enables improved total resection rates for tumors and minimizes surgical complications related to the neurovascular structures traversing or neighboring this zone.
• Minimizing the risk of injuring the ICA and adjacent cranial nerves.
• The space is an important surgical corridor for tackling lesions that invade or encase the ICA in this region, such as meningiomas, pituitary adenomas, and aneurysms.
• Clarifying the boundaries of the extradural and intradural compartments relevant to aneurysm clipping and vascular interventions.
• The DCS is separated from the cavernous sinus by a connective tissue layer, so bleeding is usually limited unless this layer is violated.

DCS: Endoscopic endonasal view

• Endoscopic anteroinferior view of a half-dissected sellar floor exhibiting the DCS with medial retraction of the pituitary.

• The CCL serves as the floor, anchored to the medial wall of the CS.

 

• Further dissection provides a better anterior view of the DCS, which is delimited superiorly by the distal dural ring as its roof (green dotted line), inferiorly by the CCL as its floor (yellow dotted line), medially by the extension of the medial wall of the CS (blue dotted line), and laterally by the ICA (red dotted line).

 

• Medial mobilization of the ICA revealed the VCS, delimited by extension of the distal (green dotted line) and proximal (yellow dotted line) dural rings from the ICA to the optic strut.

• Corresponding endoscopic endonasal anatomy of the DCS. The image was obtained after the anterior wall of the sellar floor and CS had been removed and the pituitary mobilized medially to provide a better view of the DCS.

 

• Enlarged view of panel E shows the DCS presenting an irregular contour given the transverse trajectory of the paraclinoidal ICA.

• It is defined superiorly by the distal dural ring as the roof (green dotted line), inferiorly by the CCL as the floor (yellow dotted line), medially by the medial wall (blue dotted line), and laterally by the paraclinoidal ICA (red dotted line).

• The SHAs run superolaterally in the DCS.

Endoscopic endonasal stepwise dissection of the right DCS.

• The landmark for the anterior wall of the DCS in the endoscopic endonasal approach includes the
• LOCR
• Lateral tubercular recess,
• Medial opticocarotid recess (MOCR; white asterisks).

• The DCS (green shading) is closely inferior to the MOCR, with some overlap in the lateral tubercular recess.

 

• Superior view of the skull base reveals the corresponding location of the DCS (green shading), which sits on a narrow junctional region between the carotid sulcus and the pituitary fossa.

• Borders
• Superiorly by the LTC,
• Inferiorly by the MCP, laterally by the carotid sulcus and optic strut,
• Medially by the tuberculum sellae and pituitary fossa.

• Further half-dissection of the sellar floor revealed the paraclinoidal ICA, the CS, and the dural cover of the pituitary fossa.

• The double-layered nature of the sellar floor is exhibited;

• The CS and inter-CS run between the inner and outer layers, which are in continuity with the medial and anterior walls of the CS, respectively.

• Medial retraction of the pituitary exposed the contents of the CS, and the inferior hypophyseal artery originating from the posterior genu of the ICA is seen crossing the CS just anterior to the posterior clinoid and reaches the pituitary gland.

• Medial retraction of the pituitary exposed the DCS.

• In this specimen, it is a narrow triangular pyramidal shape, delimited superolaterally by the paraclinoidal ICA (red dotted line), inferiorly by the CCL (yellow dotted line), and medially by the medial wall (blue dotted line).

• Illustration of the DCS from the endoscopic endonasal view.

• In most cases, the DCS is a narrow rectangular pyramidal shape, which is delimited superiorly by the distal dural ring as its roof (green shadow), inferiorly by the CCL as its floor (yellow shadow), medially by the extension of the medial wall of the CS (blue shadow), and laterally by the ICA (red shadow).

 

DCS: Microsurgical view

• The clinoidal space, which is limited by the distal dural ring superiorly (green dotted line) and the proximal dural ring inferiorly (yellow dotted line), can be divided into 2 regions:
• The VCS, located at the anterolateral aspect of the clinoidal ICA
• Defined as the upward extension of the CS through the lower dural ring and inside the carotid collar.
• Borders
• Superiorly by the distal dural ring (green dotted line),
• Inferiorly by the proximal dural ring (yellow dotted line)
• Laterally by the medial margin of the ACP (green dotted line).
• The DCS, located at the posteromedial aspect of the clinoidal ICA.
• Borders
• Superiorly by the distal dural ring as its roof (green dotted line), inferiorly by the proximal dural ring as its floor (yellow dotted line)
• Medially by the extension of the medial wall of the CS (blue dotted line)
• Laterally by the ICA (red dotted line).

 

• Lateral mobilization of the ICA exposed the carotid cave, which sits superolaterally to the DCS.

• The distal ring and diaphragm, which serve as the roof of the DCS, were cut to expose this space from a superior view.

• The distal ring is removed totally, and a fenestrated CCL can be seen, which means that venous connections and a potential tumor-invasion channel exist between the clinoidal space and the CS.

• Corresponding endoscopic endonasal dissection of the DCS.

• The DCS was opened after resection of the anterior wall of the CS.

• It is delimited superiorly by the distal dural ring as its roof (green dotted line), inferiorly by the proximal dural ring as its floor (yellow dotted line), medially by the extension of the medial wall of the CS (blue dotted line), and laterally by the ICA (red dotted line).

• Removal of the ICA exposed the medial wall of the CS, which forms the lateral boundary of the hypophyseal fossa and separates the pituitary gland from the cavernous segment of the ICA and the venous channels.

• The distal ring, which forms the roof of the DCS (green dotted line), is identified as a periosteal layer and is attached at the level of the upper part of the carotid sulcus, which is the roof of the clinoidal space.

• The proximal ring, which forms the floor of the DCS (yellow dotted line), lines the lower margin of the ACP.

• In the posterolateral part, the COM folds as a dural band called the “ICL,” extending from the ACP to the posterior clinoid process.

• In the anteromedial part, the COM forms several strong fibrous bundles, anchored to the medial wall of the CS or MCP, called the “CCL.”

• Further dissection revealed the osseous relationships in the DCS.

• It is bounded superiorly by the LTC and inferiorly by the MCP, which provide an attachment for the distal ring (green dotted line) and the CCL (yellow dotted line), respectively.

• The posterior half-resection of the medial wall revealed the pituitary gland.

Microsurgical stepwise dissection of the VCS and DCS.

• The carotid artery passes upward, and the optic nerve enters the optic canal on the medial side of the ACP.

• The SHA in this specimen arises from the ophthalmic segment of the ICA and runs to the pituitary stalk and infundibulum.

• The oculomotor nerve enters the roof of the CS and passes through the lower margin of the ACP.

• Hollowing the ACP and separating the double-layered dura revealed the relationship between the VCS and the DCS.

• The VCS, located at the anterolateral aspect of the clinoidal ICA, serves as the superior tributary of the CS and can be seen through the carotid collar.

• The DCS, located at the posteromedial aspect of the clinoidal ICA, was limited by the distal and proximal dural layer.

• Green dotted line indicates the distal ring

• yellow dotted line, the proximal ring.

• Further peeling off the distal dural layer in the clinoid area revealed the proximal dural layer, which is also regarded as the COM because it separates the lower surface of the clinoid from the oculomotor nerve.

• It forms the floor of the clinoidal triangle and the roof of the CS. In the posterolateral part, the COM folds into a dural band called the “ICL,” which extends from the ACP to the posterior clinoid process.

• In the anteromedial part, the COM forms several strong fibrous bundles, anchored to the medial wall of the CS or MCP, called the “CCL.”

• In this specimen, the CCL presented as the pattern of an intact broad ligamentous band without fenestration.

• Medial retraction of the pituitary gland revealed the medial wall of the CS, which serves as an anchor for the CCL.

• The doublelayered dura encircled the paraclinoidal ICA, and the distal ring has been lifted to expose the VCS, located at the anterolateral aspect of the clinoidal ICA.

• Green dotted line indicates the distal ring;

• yellow dotted line, the proximal ring.

 

• A close-up view of the DCS, located at the posteromedial aspect of the clinoidal ICA.

• The distal ring forms the roof of the DCS (green dotted line), whereas the proximal ring forms the floor of the DCS (yellow dotted line).

• Lateral perspective of a stepwise dissection of the VCS and DCS in another specimen.

• The ACP has been removed, and the optic nerve has been lifted to expose the left clinoidal space.

• The lateral wall of the CS has been removed to show the trigeminal, oculomotor, and trochlear nerves.

• Close-up view of the clinoidal space located between the distal and proximal rings.

• The carotid cave, enclosed in the dural sheath, is uncovered.

• The blue veins in the CS and DCS have been removed to get a better view.

• The clinoidal space can be divided into 2 region
• The VCS, located at the anterolateral aspect of the clinoidal ICA,
• The DCS, located at the posteromedial aspect of the clinoidal ICA.

• Green dotted line indicates the distal ring; yellow dotted line, the proximal ring.