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Neurosurgery:
doi: 10.1227/NEU.0000000000000184
Surgical Anatomy and Technique

The Recesses of the Sellar Wall of the Sphenoid Sinus and Their Intracranial Relationships

Peris-Celda, Maria MD, PhD; Kucukyuruk, Baris MD; Monroy-Sosa, Alejandro MD; Funaki, Takeshi MD; Valentine, Rowan MD; Rhoton, Albert L. Jr MD

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Department of Neurosurgery, University of Florida, Gainesville, Florida

Correspondence: Albert L. Rhoton, Jr., MD, Department of Neurosurgery, University of Florida, College of Medicine, PO Box 100265, Gainesville, FL. E-mail: rhoton@neurosurgery.ufl.edu

Received September 19, 2012

Accepted February 12, 2013

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Abstract

BACKGROUND: The sellar wall of the sphenoid sinus and its recesses have been previously studied, but their intracranial relationships to the diaphragma sellae, tuberculum, clinoid segment of the internal carotid artery, chiasmatic sulcus, and middle clinoid process need further definition.

OBJECTIVE: To describe these intra- and extracranial relationships of the recesses in the anterior sellar wall.

METHODS: The middle clinoid was studied in 132 parasellar areas of dry crania. Thirty-eight parasellar areas of formalin-fixed/silicone-colored specimens were dissected. After transsphenoidal endoscopic exposure, the optic, carotid, and sellar prominences; lateral opticocarotid and tuberculum recesses; and caroticosellar and medial opticocarotid points were identified. High-speed drills opened 1-mm perforations at these points to allow study of intracranial relationships.

RESULTS: Two recesses and 2 junction points can be recognized in the sphenoid sinus: lateral opticocarotid and tuberculum recesses and medial opticocarotid and caroticosellar points. The lateral opticocarotid recess corresponds to the optic strut base, and the clinoid segment of the internal carotid artery is located medially. The diaphragma sellae attachment is at the level of the tuberculum recess, which in 50% of cases corresponds to the tuberculum. A middle clinoid in base or height greater than 1.5 mm is present in 21.1% and a caroticoclinoid ring in 3%. The middle clinoid is 1 mm inferior and lateral to the caroticosellar point and 4.7 mm inferior to the medial opticocarotid point.

CONCLUSION: An understanding of the intra- and extracranial relationships of the recesses of the sphenoid sinus will aid in accurately directing transsphenoidal approaches.

Transsphenoidal microsurgical or endoscopic approaches have become the standard surgical route to the pituitary gland. The endoscopic endonasal route has also evolved in recent years to provide access to lesions located in the ventral cranial base from the crista galli to the odontoid with defined limits laterally.1-6 The superior wall of the sphenoid sinus is formed by the planum and the sellar wall. The sellar wall covers the sellar and parasellar areas including the surface between the superior limit of the optic prominences and the sellar floor.

Numerous studies have focused on endoscopic anatomy of the sphenoid sinus.7-12 However, the exact intracranial relationships of the recesses of the upper part of the sphenoid sinus with the diaphragma sellae, tuberculum, clinoid segment of the internal carotid artery, chiasmatic sulcus, and middle clinoid process need to be clarified. The objectives are to describe these relationships, and provide side-by-side views of the recesses of the sellar wall of the sphenoid sinus and the adjacent intracranial structures.

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PATIENTS AND METHODS

Dry Skull Measurements

Sixty-six crania with the calvarium removed provided 132 parasellar areas for measurements on the endocranial surface of the cranial base. The middle clinoid presence, dimensions, and its relationship with the opticocarotid elevation (elevation formed by the medial extension of the optic strut toward the tuberculum) and tuberculum sellae were examined.

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Anatomic Dissections

Thirty-eight parasellar areas from 20 formalin-fixed silicone-colored specimens were used for dissections.

Under 2-dimensional endoscopic 0° view (Karl-Storz, Tuttlingen, Germany), the posterior portion of the nasal septum was resected to allow room for binostril dissection. Posterior ethmoidectomy and sphenoidotomy were performed bilaterally. The septations inside the sphenoid sinus were removed. Three-dimensional (3-D) endoscopic images of the sphenoid sinus were obtained by combining pairs of 2-dimensional images. The objective of the 3-D images was to carefully study and mark several reference points in the sellar wall of the sphenoid sinus before performing perforations for measurements and examining intra- and extracranial relationships. Two pairs of high-definition pictures with the 0° endoscope were taken for each sinus. A ball probe tool with 2-mm tip (Karl-Storz, Tuttlingen, Germany) was placed in the center of the image for 1 of the picture pairs for size reference. The first picture of both sets was taken as perpendicular as possible to the posterior wall of the sinus with the posterior part of the endoscope optic resting on the inferior aspect of the nostril. The second picture was taken in exactly the same horizontal plane after rotating the endoscope approximately 5 to 10° to the right (up to 3-mm horizontal displacement on the tip) with the axis located at the nostril. The first picture corresponded to the image of the left eye and the second picture corresponded to the right eye. Both pictures were placed in parallel in a PowerPoint presentation (Microsoft, Redmond, Washington) for 3-D visualization with stereoscopic glasses (Pokescope; Graphic Media Research, Cannon Falls, Minnesota). The optic, sellar, and carotid prominences, as well as the recesses between them, were identified bilaterally if present, as follows (Figure 1A): (1) The tuberculum recess is defined as the horizontal depression in the sinus wall between the sella inferiorly and the planum superiorly. The lateral edge of the tuberculum recess has been described as corresponding to the medial opticocarotid recess13,14 located in the area medial to the carotid prominence between the optic prominence superiorly, the carotid artery prominence laterally, and the sellar prominence inferiorly. (2) The lateral opticocarotid recess is a triangle-shaped depression, lateral to the carotid prominence, between the optic prominence superiorly, and the carotid prominence medially.

Figure 1
Figure 1
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Table 1
Table 1
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Adobe Photoshop (Adobe Systems Incorporated, San Jose, California) software was used to place 1-mm colored points in the images at selected references that were carefully identified previously in the 3-D images. These 1-mm points measured approximately half the size of the ball probe tip. The following structures were marked with colored points when present (Figures 1B and 2): (1) the deepest point in midline of the tuberculum recess; (2) the 4 vertices of the optic prominences (the optic prominences form a rhomboidal shape, with their medial side shorter than the lateral side); (3) 2 points in each lateral aspect of the tuberculum recess (also called medial opticocarotid recess): the medial opticocarotid point, defined as the point where the optic prominence meets the carotid prominence medially, and the caroticosellar point, defined as the most superior point along the junction of the sellar prominence with the carotid artery prominence; (4) 3 points forming the vertices in the triangular-shaped lateral opticocarotid recess: superomedial (corresponding to the lateral opticocarotid junction), superolateral, and inferior.

Figure 2
Figure 2
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After carefully studying and marking the pictures, high-speed drills with 1-mm diamond tip ends (Midas Rex; Medtronic, Minneapolis, Minnesota) were used to perform perforations in the corresponding locations of the sellar wall of the sphenoid sinus.

After brain removal, the intracranial surface of the cavernous sinus and sellar area were dissected bilaterally to define the relationships of the attachment of the diaphragma sellae, proximal and distal dural rings, chiasmatic sulcus, tuberculum, and middle clinoid process with the perforations performed endoscopically.

After dissection of the sellar and cavernous sinus areas, measurements between the center of the different 1-mm diameter perforations were performed intracranially with a digital caliper (Figure 1B).

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RESULTS

Measurements in Dry Cranial Base

A recognizable elevation along the anteromedial border of the carotid sulcus forming a middle clinoid process was found in 31% of the parasellar areas (41 of 132). However, a base or height greater than 1.5 mm considered in this study as clinically relevant was present in only 15.2%, less than half of the elevations (20 of 41). This percentage excludes the caroticoclinoid foramina (Figure 3). Of the 11 specimens (16.7%) having a uni- or bilateral middle clinoid process rising more than 1.5 mm, 5 were present unilaterally and 6 bilaterally. Hence, if a relevant middle clinoid process is found, there is a 54.5% chance of finding another process contralaterally.

Figure 3
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Caroticoclinoid rings, osseous bridges created by the fusion of the anterior clinoid process with the middle clinoid process around the internal carotid artery, were found bilaterally in 1 specimen (1.5% of parasellar areas) and a middle clinoid process almost touching a prolongation of the anterior clinoid process (kissing clinoids) was found unilaterally in another specimen (0.75% of the parasellar areas).

The average size of the middle clinoid process, when considered clinically relevant (height or base >1.5 mm), was 2.57 mm (range, 1.5-4.0 mm) at the base in the widest diameter and 2.43 mm (range, 1.5-3 mm) height. The specimen with the kissing clinoid had a 4-mm base and a 3-mm height. The caroticoclinoid rings had a narrower base of 2 mm and 2.5 mm and a distance to the anterior clinoid of 4 mm bilaterally (Figure 3). The base of the middle clinoid process, when greater than 1.5 mm, had an oval shape with the largest base diameter of the middle clinoid constantly oriented in an oblique horizontal plane, closer to midline superiorly than inferiorly. The middle clinoid was found along the medial side of the carotid sulcus at the junction of the anterior or horizontal bend of the cavernous carotid just before it passed inferomedial to the anterior clinoid process in the clinoid segment (Figures 3-5). The middle clinoid was oriented in an axial obtuse angle of 116.25° posterior to the midsagittal plane (α angle in Figure 3E), and in a coronal plane, it was directed superiorly toward the anterior clinoid. The superior aspect of the middle clinoid process base was located 2.9 mm (range, 1.50-5.00 mm) inferior and just lateral to the lateral aspect of the tuberculum sellae. The middle clinoid process was located 3.86 mm (range, 2.00-6.00 mm) inferior to the medial aspect of the opticocarotid elevation.

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Figure 5
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Dissection of the Anatomic Specimens
Endoscopic Endonasal Dissection of the Sellar Wall of the Sphenoid Sinus

All specimens, except 1 (n = 19, 95%), showed a sellar or retrosellar pneumatization pattern so the carotid artery, optic nerve, and sellar prominences could be identified in the sellar wall of the sphenoid sinus. One specimen had a presellar pneumatization pattern in which the bone covered and hid all these structures (Figure 4A).

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Tuberculum Recess

A tuberculum recess was identified in 19 specimens superior to the sella between the sellar prominence inferiorly and the planum superiorly.

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Medial Opticocarotid Point

A medial opticocarotid point, seen in the lateral extension of the tuberculum recess between the optic prominence and the carotid prominence, was found in 35 of 38 parasellar areas (98.1%). The presellar type of sinus had no recesses. In a different specimen, a superomedial carotid artery point in the tuberculum recess could be misidentified as a medial opticocarotid point; however, the optic nerve prominence was not present. In this case, the carotid artery was situated anterior to the optic nerve in the medial aspect of the optic canal. This variation was due to a hypoplastic contralateral carotid artery and subsequent enlargement of the artery diameter and carotid prominence with no identifiable optic prominence in the sphenoid sinus (Figure 4F).

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Caroticosellar Point

This point was identified in the inferolateral limit of the tuberculum recess in all cases except in the presellar type of sinus.

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Lateral Opticocarotid Recess

Although the junction between the optic and carotid prominences lateral to the carotid artery was identified in most cases, a lateral opticocarotid indentation or recess was found in only 81% (30 of 37) of the parasellar areas. This absence was due to sphenoid sinus septations that joined the anterior sellar wall in a manner that prevented the formation of a complete recess (Figure 4B). Half of the carotid artery prominences had a sphenoid septation crossing their anterior surface. Three points at the vertices of the triangular-shaped opticocarotid recess were identified: superomedial, superolateral, and inferior. The superomedial point was equivalent to the lateral opticocarotid point, the superolateral point was equivalent to the inferolateral optic prominence vertex, and the inferior point was lateral to the carotid prominence usually located between both superior points in a vertical plane.

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Microscopic Endocranial Dissection of the Sellar and Parasellar Areas
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Caroticoclinoid Ring and Middle Clinoid Process

The dissections showed a caroticoclinoid ring at a higher rate than in the dry crania, 3 of 38 parasellar areas (7.8%), with 2 of them in the same specimen. This specimen, with a complete ring on 1 side, had a large middle clinoid process with a thin bone prolongation at the tip that joined the anterior clinoid to complete the ring on the contralateral side. The specimen with a unilateral foramen had a solid and complete bone ring around the carotid. Combining data from the dissections and the dry crania, the prevalence of the caroticoclinoid ring was 2.94% in our specimens.

Sixteen of 38 parasellar areas in the dissected specimens showed a middle clinoid larger than 1.5 mm in base or height, which, added to the result of the middle clinoid process presence in dry crania, results in a prevalence of 21.17% cases. The clinically relevant middle clinoid processes were 2.58 mm (range, 1.5-4 mm) in the major diameter of the base and 2.38 mm (range, 1.5-4 mm) height not counting the caroticoclinoid foramina.

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Tuberculum Recess and Tuberculum Sellae

The deepest part of the suprasellar recess, where the 1-mm diameter perforation was performed endoscopically, was located at the level of the tuberculum in 50% of cases, inferior to the tuberculum in 27.8% (1.5 mm; range, 1-2 mm), and superior to it in 22.2% (1.62 mm; range, 1-2.5 mm).

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Lateral Opticocarotid Recess and Optic Strut

When present, the 3 points that delimited the lateral opticocarotid recess were inside or within the limits of the optic strut in all but 5 cases (16.6%). The most frequently missed point was the inferior one, displaced 1.5 to 2 mm inferior to the optic strut inside the superior orbital fissure.

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The Chiasmatic Sulcus

The chiasmatic sulcus is a shallow depression between the optic foramina on the endocranial surface and is delimited by an anterior and a posterior limbus. The chiasmatic sulcus is related with the planum anteriorly and the tuberculum posteriorly, which is located along the posterior limbus of the chiasmatic sulcus (Figure 3A). There was no intrasphenoid prominence or recess corresponding to the chiasmatic sulcus, and the planum area in the midline apparently blended into the tuberculum recess. Its projection can be estimated as a rectangular area between the superomedial and the inferomedial vertices of the optic prominences bilaterally (Figure 6A).

Figure 6
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Medial Opticocarotid Point and Middle Clinoid Process

No middle clinoid process in our series corresponded to the medial opticocarotid point. The most superomedial aspect of the base of the middle clinoid process was always positioned inferior to the medial opticocarotid point on average 4.75 mm (range, 1-7.50 mm). It was also lateral to it on 8 sides, 3.18 mm on average (range, 2-5 mm). It was 1.50 mm medial on 1 side (Figures 4-7). The clinically relevant middle clinoid processes were mostly at the same lateral level as the medial opticocarotid point, lateral in 4 cases up to 3 mm and inferior in all cases of 4.96 mm (range, 3-7.5 mm).

Figure 7
Figure 7
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Caroticosellar Point and Middle Clinoid Process

The most superomedial aspect of the middle clinoid process base was 1.06 mm lateral (range, 0-4.5 mm) and 1.3 mm inferior (range, 0-3.50 mm) to the caroticosellar point. In 4 of 25 sides, this point was coincident with the superomedial base of the middle clinoid process intracranially with its highest point inferolateral to the caroticosellar point. The middle clinoid process was not medial to the caroticosellar point in any case (Figures 3-5). In the clinically relevant middle clinoid process group, the results did not vary significantly, with the middle clinoid process 1.2 mm lateral and 1.3 mm inferior to the caroticosellar point.

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Diaphragma Attachment and the Tuberculum Recess

Nearly half of the diaphragma attachments (52.63%) (n = 10) were located less than 1 mm inferior to the tuberculum recess, and 47.36% (n = 9) were located at the level of the tuberculum recess.

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Distal Dural Ring, Lateral Opticocarotid Recess, and Tuberculum Recess

The lateral aspect of the distal dural ring, formed by the dura extending medially from the upper surface of the anterior clinoid process around the carotid artery, was 1.15 mm superior to the tuberculum recess (range, 0-3 mm). The level of the clinoid segment of the internal carotid artery, located between the distal and proximal dural rings, was located slightly above and below the superior and inferior limits of the optic strut (Figure 6-7). The lateral aspect of the inferior dural ring was located slightly below the inferior level of the optic strut and diaphragma attachment, and in the view through the sphenoid sinus, approximately at the level of the tuberculum recess. When the middle clinoid process was either absent or present and did not form a caroticoclinoid ring, a caroticoclinoid ligament was seen in some specimens. The caroticoclinoid ligament joined the proximal dural ring at the tip of the anterior clinoid extending to the middle clinoid process when present and was directed to the medial edge of the carotid sulcus at the location of the anterior bend of the carotid artery when the middle clinoid was absent. This ligament presented variable extensions toward the carotid artery, the anterior aspect of the meningeal layer covering the pituitary gland, and blended into the medial wall of the cavernous sinus in the middle clinoid location (Figure 8). In other specimens, this ligament was indistinguishable from the cavernous sinus trabeculae. In the 2 specimens dissected in which the interclinoid ligament ossified forming a caroticoclinoid ring, the carotidoculomotor membrane, which forms the proximal dural ring, continued underneath the ring and blended into the periosteal dura mater of the medial wall of the cavernous sinus and the caroticoclinoid ring formed part of the roof of the cavernous sinus (Figure 9).

Figure 8
Figure 8
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Figure 9
Figure 9
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Measurements in the Sellar Wall of the Sphenoid Sinus

The length of the superior, inferior, lateral, and medial edges of the optic nerve prominence averaged 8.19 mm, 9.58 mm, 6.00 mm, and 4.85 mm, respectively. The distances between the paired superomedial and inferomedial vertices of the optic nerve prominences averaged 12.34 mm and 11.69 mm, respectively. The distance between both caroticosellar points was 10.99 mm, making this the narrowest distance between the cavernous carotids (Figure 1B, Table 1). The medial opticocarotid point was 3.50 mm superior (range, 1.50-6 mm) to the caroticosellar point. Other measurements are shown in Table 1.

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DISCUSSION

There is widespread agreement about the relationship of the lateral opticocarotid recess with the optic strut. In this study, the lateral opticocarotid recess was present in 81% of cases. The 3 limiting vertices of this triangular recess, when connected, corresponded with the triangle-shaped base of the optic strut. However, greater pneumatization extended the inferior point up to 2 mm inferiorly in few cases (Figure 6).

The intrasphenoid projection of the clinoid segment of the internal carotid artery was located immediately outside the craniocaudal limits of the lateral opticocarotid recess medial to it, with the lateral aspect of the distal dural ring located slightly more than 1 mm superior on average to the deepest part of the tuberculum recess. The panoramic view given by the endoscope makes the level of the lateral structures, for instance, the upper limit of the lateral opticocarotid recess/distal dural ring, appear higher than they really are. Hence, the clinoid segment is located approximately between a line passing 1 mm (range, 0-3 mm) above the deepest part of the suprasellar recess and a horizontal inferior line passing through the inferior limit of the lateral opticocarotid recess toward the tuberculum recess. The inferior dural ring does not extend medially around the carotid artery as does the superior dural ring.15 The dura mater that forms the distal dural ring is continuous with the diaphragma attachment medially. Previous studies7 found that the tuberculum recess was located at the inferior level of the tuberculum sellae, data that were confirmed in 22.2% cases in our series. The tuberculum is located at the level of the tuberculum recess in 50% of cases, with the remainder being located within a 2.5-mm range above or below the tuberculum recess. The diaphragma attaches to the anterior sellar wall at approximately the level of the tuberculum recess. This is important for procedures that require endonasal diaphragma sellae incision and pituitary mobilization or transposition.

No sinus prominence or recess corresponded to the chiasmatic sulcus, as the surface of the planum blended into the tuberculum recess. The chiasmatic sulcus can be referenced in the sphenoid sinus in the area above the tuberculum recess between both optic prominences. Of importance in surgeries of this area is the location of the chiasm; a prefixed type of chiasm, which overlies the tuberculum, has been reported in 15% cases, whereas a normal chiasm (70% cases) overlies the diaphragma sellae.16

The medial opticocarotid recess was previously described as the lateral extension of the tuberculum recess13,17 that served as a very important landmark in the transsphenoidal approach to tuberculum sellae meningiomas.13 This recess or keyhole in endoscopic endonasal approaches was referenced as the intrasinus correlate of the middle clinoid process when present.6,14 An entry at the level of the medial opticocarotid recess was described as accessing the carotid and optic canals, sella turcica, and medial cavernous sinus.6 These findings are contrary to our results, which agree with Fernandez-Miranda et al,18 and locate the middle clinoid process inferior to this recess. In our study, the tuberculum recess was found to be deepest in the midline and less pronounced laterally at the medial aspect of the internal carotid artery and optic nerve prominences. Accordingly, the lateral aspect of the tuberculum recess was not considered to be an indentation or recess but an area in which 2 different junction points were identified in 98% of the cases (except in the presellar type): the superior one or medial opticocarotid point, and the inferior one or caroticosellar point. An entry point in the medial opticocarotid point would allow access to the superomedial aspect of the clinoid segment of the internal carotid artery, supraclinoid segment of the carotid artery, and the optic canal. An entry point in the caroticosellar point would give access to the junction of the clinoid segment and the cavernous segments of the carotid artery laterally, and sellar compartment medially. The carotid cave is an intradural pouch that was found to extend below the level of the distal dural ring between the wall of the internal carotid artery, and the dural collar surrounding the carotid artery medially in 19 of 20 paraclinoid areas.19 When present, the carotid cave would be located between the medial opticocarotid and caroticosellar points.

The location of the middle clinoid process is of importance in avoiding and preventing carotid artery injuries in endonasal approaches because this process represents a bony protrusion that fixes the artery medially as does the medial aspect of the distal dural ring.18 The presence of the bony caroticoclinoid ring, the osseous bridge between the anterior clinoid, and the middle clinoid, adds an element of difficulty to both the endonasal procedure and the intracranial anterior clinoidectomy. The caroticoclinoid ring has been reported to be a complete ossification of the caroticoclinoid ligament that extends between the anterior clinoid and the middle clinoid,20 although its anatomy has not been well documented. This thin ligament presented great variability, as was clearly defined in some specimens, whereas in other cases, it was indistinguishable from a cavernous sinus trabecula, even under the surgical microscope (Figure 8). A ligament extending from the tip of the anterior clinoid to the medial border of the carotid sulcus below the tuberculum was also encountered in several specimens without a middle clinoid process. The medial attachment of this ligament was adjacent to the anterior bend of the cavernous carotid, in the theoretical site of the middle clinoid process. This fact leads to the consideration that a partial ossification of this ligament forms a middle clinoid process, whereas a complete ossification forms a caroticoclinoid ring. The clinoid segment of the internal carotid artery is defined as being located medial to the anterior clinoid process, between the proximal and distal dural rings. The carotidoculomotor membrane, the thin layer of dura mater lining at the lower margin of the anterior clinoid process, forms the proximal dural ring in the lateral and anterior parts of the carotid. The proximal dural ring usually fuses with the distal dural ring posterior to the carotid artery medial to the tip of the anterior clinoid (Figure 8A). The proximal dural ring is incomplete medially and posteriorly, and venous channels from the cavernous sinus pass upward between the inferior dural ring and the surface of the artery laterally.15,19 In the endocranial dissections, the middle clinoid process protruded inside the cavernous sinus below the level where the distal dural ring fuses with the proximal dural ring posterior to the carotid (Figures 6 and 7). Endonasally, the proximal dural ring cannot be clearly identified, and its location inside the sinus was represented as a projection medially from its level along the lateral side of the carotid artery (Figures 5 and 6A). If the thin layer of periosteal dura mater covering the middle clinoid process is damaged during its removal, venous bleeding will come from the cavernous sinus (Figures 5A and 5D). The caroticoclinoid ring forms a bridge passing around the medial and posterior aspect of the clinoid segment of the internal carotid artery from the medial aspect of the carotid sulcus to the anterior clinoid process. In the specimens with a caroticoclinoid ring, the carotidoculomotor membrane did not fuse with the distal dural ring just posterior to the carotid artery, but continued underneath the ring blending into the periosteal dura mater of the medial wall of the cavernous sinus. A complete osseous ring formed part of the roof of the cavernous sinus as described before,15,18 creating a true posteromedial clinoid segment of the carotid artery. The middle clinoid process varies greatly in size when present, and the prevalence of a complete caroticoclinoid ring was found in the study to be 2.94% of parasellar areas and 3.4% of cranial bases, similar to results around 4% to 4.3% in other anatomic series of different populations. There is variability in the middle clinoid, being less frequent in females and Asian populations.20-24 A study with computed tomography (CT) scans in specimens and patients revealed a greater incidence of the foramen, 13% of the parasellar areas, and 20% of the cranial bases in patients and specimens. The discrepancy in the prevalence compared with other series may be due to degeneration after death of some thin bony rings, as the authors stated,18 or to the specificity of the fine-cut CT scan that does not distinguish between incomplete rings such as kissing clinoids (Figure 3), where the clinoids are nearly touching each other, and complete foramina. The distance between the anterior clinoid tip and the medial carotid sulcus is approximately 4 mm in the absence of a middle clinoid, whereas in specimens with incomplete forms of caroticoclinoid ring, the anterior and middle clinoids can be less than 0.5 mm separated. These forms of incomplete and complete rings have been described in anatomic studies of different populations, and their total prevalence ranged from 6% to as high as 38%.20-24 The CT scan may reveal false positives regarding a complete osseous ring, but with this preoperative study, the surgeon can be aware and prepared for the presence of a prominent middle clinoid, kissing clinoids, or a complete ring before the surgery. Although the risks of carotid artery injury are greater in all these cases, as opposed to the absence of a middle clinoid, implications for surgery are different in the case of a complete ring and kissing clinoids. In case of intracranial approaches, if a caroticoclinoid ring is expected based on the CT scan, care must be taken to gently dissect the remnant of the anterior clinoid process once drilled to avoid fracturing the ring. In the case of a kissing clinoid, the clinoid tip can be dissected, but bleeding from the cavernous sinus can occur easily. In the case of an incision of the distal dural ring for carotid artery mobilization, in a complete caroticoclinoid ring, the posterior aspect of the incision will be placed over the osseous ring and might require additional drilling. In endonasal approaches, prominent middle clinoids can be completely removed endoscopically with careful dissection after removal of the sellar wall, whereas the complete rings need to be drilled, avoiding fracture.18 Middle clinoid removal allows better access to the parasellar region, especially for sellar tumors with cavernous sinus extension behind the anterior genu of the carotid artery.18 For these reasons, it is very important to accurately locate the middle clinoid process in the sphenoid sinus. In the sphenoid sinus, the superomedial aspect of the base of the middle clinoid process is commonly located just inferior and lateral to the caroticosellar point, which can be easily recognized. Another reference is the anterior bend of the cavernous carotid, which is sometimes fully visualized in the sphenoid sinus as a C with its convexity oriented anteriorly and laterally, with the middle clinoid process predictably located slightly superior to the center of this C just lateral to the upper middle aspect of the sellar prominence (Figures 4-7).

The accurate location of intracranial important structures related to the sellar wall of the sphenoid sinus from an endonasal view is essential to safely perform transnasal procedures involving the sellar and parasellar areas. However, some pathologies such as macroadenomas can distort normal anatomy and make some studied points misleading. In these cases, image guidance may complement knowledge of the endonasal references.

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CONCLUSION

Two recesses and 2 junction points can be recognized in the sellar wall of the sphenoid sinus in most cases: the lateral opticocarotid and tuberculum recesses and the medial opticocarotid, and caroticosellar points.

The lateral opticocarotid recess corresponds to and often extends into the optic strut and its medial projection is related to the clinoid segment of the internal carotid artery. The deepest part of the tuberculum recess corresponds in 50% of sphenoid sinuses to the tuberculum sellae. The diaphragma sellae attachment is located at the level of the tuberculum recess or slightly inferior. The chiasmatic sulcus is located between the medial aspect of the optic nerve prominences.

A clinically relevant middle clinoid process (>1.5 mm) is present in 21.1% of parasellar areas and forms a caroticoclinoid ring in 2.94%. The superomedial point of the middle clinoid process base is most frequently located approximately 1 mm inferior and lateral to the caroticosellar point, with its highest part further inferior and lateral. The middle clinoid is inferior to the medial opticocarotid point in all cases, 4.75 mm on average, being its highest point laterally.

A detailed knowledge of the intracranial relationships of the recesses in the sellar wall of the sphenoid sinus will aid in the accuracy of transsphenoidal surgeries in the sellar and parasellar areas.

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Disclosures

The authors have no personal financial or institutional interest in any of the drugs, materials, or devices described in this article. Financial support is through a University of Florida foundation.

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COMMENTS

This is a thorough and interesting anatomic study of the sellar and parasellar anatomy as seen via transnasal and transcranial views. Its main strength is the fact that it simultaneously displays both anatomic views side by side. Therefore, it can assist neurosurgeons to picture “the mirror anatomy” of the other side as they perform surgeries via the transnasal or transcranial route during microsurgery or endoscopy. Understandably, it should be kept in mind that this is a normal cadaveric anatomy and that “in vivo” anatomy has differences from the cadaver as well as in the existence of pathological processes.

Kenan Arnautovic

Memphis, Tennessee

The authors are to be congratulated for performing a detailed evaluation of the bony anatomy of the sellar wall and the relationship to intracranial anatomy. As neurosurgery continues to access pathology via this corridor, a thorough understanding of these relationships is paramount to surgical success and avoidance of complications. The authors evaluated parasellar regions from 20 specimens with 3-dimensional endoscopy. Notable osseous anatomy (tuberculum recess, optic prominences, medial and lateral opticocarotid points) was identified and marked. Measured locations and relationships to intracranial structures were calculated and presented. The authors demonstrated many salient features of the posterior sphenoid region: the high consistency of the tuberculum recess and its relation at or above the location of the diaphragm, an identifiable middle clinoid in 21%, and the lack of a bony reference for the optic chiasm. Likewise, although seen in only 1 specimen, the presence of a vascular anomaly (enlarged ipsilateral carotid due to contralateral hypoplastic carotid) was associated with the loss of an optic canal prominence. This underscores how, although useful, the information needs to be cautiously applied in cases in which the anatomy might be altered, as with pituitary adenomas. Although the described anatomy may remain largely unchanged in the resection of suprasellar pathology, an adenoma may notably alter the presence and/or distances between anatomic features. However, the first step of understanding pathological anatomy is a firm grasp of the normal anatomy, and, to that end, this article contributes greatly.

Nathan E. Simmons

Lebanon, New Hampshire

Keywords:

Caroticoclinoid ring; Clinoid segment; Endoscopic endonasal; Middle clinoid; Opticocarotid recess; Tuberculum recess

Copyright © by the Congress of Neurological Surgeons

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