Anterior Clinoid Process Pneumatization Research Articles

Optico-carotid recess and anterior clinoid process pneumatization â€" proposal for a novel classiï¬cation and uniï¬ed terminology: an anatomic and radiologic study.

The aims of this study were to propose a novel and uniï¬ed classiï¬cation system of the optico-carotid recess (OCR) and anterior clinoid process (ACP) pneumatization, determine their frequency in a Caucasian population and measure the size of the OCR. A total of 200 specimen (400 sphenoid sinuses) were evaluated in a separate anatomic cadaveric study (n=100) and radiologic study (n=100) by using sphenoidal sinus cast and computed tomography (CT) scan. OCR was divided according to its location to the optic nerve into sub-optical and latero-optical OCR grade I-III. An OCR was found in 39% of the samples (78/200) and in 19% (38/200) it occurred bilaterally. Both, sub-optical and latero-optical OCR were identiï¬ed in 14% of the sides (58/400), with a mean length and depth of 6.9 mm; 7.7 mm and 2.3 mm, 7.1 mm, respectively. We determined the pneumatized ACP frequency with 23% (46/200) and deï¬ned 3 uniï¬ed different types of pneumatization. The OCR is a reliable landmark to identify the optico-carotid region in endoscopic sphenoid sinus surgery, and can even be visualized by CT. Hence, preoperative investigation of the sphenoid region is mandatory. In our opinion, the classiï¬cation presented in this study can be useful in order to avoid surgical complications.

Is there a relationship between Onodi cell and optic canal?

We investigated the relationship between Onodi cells and optic canal by paranasal sinus computed tomography (PNSCT). In this retrospective study, 508 PNSCT (265 males and 243 females) was examined. Onodi cell presence, pneumatization types, optic canal types; and also sphenoid sinusitis and anterior clinoid process pneumatization were evaluated. The prevalence of Onodi cells was 21.2% of the patients. Onodi cells were observed 40.7% on the right side and 25.9% on the left side. In 33.4% of the patients, bilateral Onodi cells were present. Male/Female ratio was 24.5%/17.6%. Onodi cell types were detected as Type I > Type II > Type III bilaterally. There was a positive correlation between the right and left Onodi cell types (p < 0.05). Optic canal types were detected as Type IV > Type I > Type II > Type III. bilaterally. There was a positive correlation between right and left optic canal types. Onodi cell presence and ACP pneumatization were found as statistically significant (p < 0.05). In 65.5% of the patients, Onodi cells and ACP pneumatization were absent. ACP pneumatization was present in 35.4% of the cases. In nine cases, bilateral Onodi cells and ACP pneumatization were detected. Sphenoid sinusitis was detected in 11.4% of Type I and 13.8% of the Type II Onodi cells on the right side. On the left side, it was detected in 12.9% of the Type I and 19.0% of Type II Onodi cells. Identification of Onodi cell is very important clinically because of its proximity to optic nerve canal. We concluded that type IV Onodi-optic canal relationship was the most common finding in our study. Onodi cell presence and their patterns of pneumatization must be evaluated on PNSCT preoperatively to avoid optic canal damage.

The effect of frontal sinus pneumatization on anatomic variants of paranasal sinuses.

The aim of this study is to determine the effect of frontal sinus pneumatization on various variations of paranasal sinuses on maxillofacial CT. A total number of 120 patients (62 females, 58 males) were included in this study. Patients were divided into three groups regarding their frontal sinus pneumatization extent on paranasal sinus CT as Type 1 pneumatization (aplasia and hypoplasia), Type 2 pneumatization (medium) and Type 3 pneumatization (hyperplasia). The prevalence of various variations on paranasal sinus CT like pneumatization of upper and middle concha, presence of agger nasi, Haller and Onodi cell, maxillary sinus and sphenoid sinus hypoplasia, pneumatization of anterior clinoid process, pterygoid process and greater wing of sphenoid sinus, dehiscence and protrusion of internal carotid artery and optic nerve and vidian canal types were ascertained and compared within each group. The prevalence of upper and middle concha pneumatization, Haller cell, pneumatization of anterior clinoid process, pterygoid process and greater wing of sphenoid and internal carotid artery dehiscence and protrusion was higher in Type 3 group compared with other groups. Excessive pneumatization of frontal sinus has various effects on paranasal sinus variations at maxillofacial CT. Surgeons dealing with endoscopic sinus surgery, maxillofacial and skull base surgery must be vigilant of association between certain variations when analyzing CT scan preoperatively for avoiding complications.

Surgically Relevant Bony Anatomical Variations in Paraclinoid Aneurysms-Three-Dimensional Multi-Detector Row Computed Tomography-Based Study.

Objective:To evaluate the proportion of surgically relevant anatomical variations such as caroticoclinoid foramen, interclinoid osseous bridge, and anterior clinoid pneumatization in patients with paraclinoid aneurysms based on computed tomography (CT) cerebral angiography studies.Materials and Methods:Fifty-four CT cerebral angiography studies showing paraclinoid aneurysms involving the cavernous, clinoid, and supraclinoid internal carotid artery (ICA) were retrospectively evaluated. Source images were processed for three-dimensional reconstructions to evaluate the presence and type of caroticoclinoid foramen, interclinoid osseous bridge, and multiplanar reconstructions with bone algorithm to study the type of pneumatization.Results:The study included 30 female and 24 male patients with mean age of 45.61 (10.47) years. Among the 108 sides studied in 54 patients, caroticoclinoid foramen was seen in 24 cases (22.22%), interclinoid osseous bridge was seen unilaterally in 1 case (0.9%), and pneumatization of anterior clinoid process occurred in 12 cases (11.11%). Incomplete caroticoclinoid foramen (11 cases) and Type I pneumatization (7 cases) were seen to be predominant subtypes. There was no statistically significant gender difference in the occurrence of caroticoclinoid foramen and anterior clinoid pneumatization. Seventy-four aneurysms were detected in 54 patients. Based on their location, 46 aneurysms involved supraclinoid ICA, 18 aneurysms in the clinoid segment, and 10 aneurysms in the cavernous segment. Caroticoclinoid foramen was most prevalent in clinoid aneurysms with 12 cases occurring in the clinoid segment.Conclusion:Notable proportions of caroticoclinoid foramen and pneumatization occur in cases of paraclinoid aneurysm. Radiological reports should emphasize on these surgically relevant bony anatomical variations.

Optic Nerve Canal Relation to Posterior Paranasal Sinuses in Indian Ethnics: Review and Objective Classification.

Posterior paranasal sinuses consisting of posterior ethmoid and sphenoid sinuses show varying pneumatization and relationship to Optic Nerve Canal (ONC). Most commonly ONC is superolateral to sphenoid sinus, however varied protrusion of ONC into the sinuses may occur. Rarely it may pass completely through the sinus. Optic Nerve (ON) is covered by a thin bony layer or by periosteum and sinus mucosa without bone. Extensive pneumatization of sphenoid sinus and bony dehiscence predisposes to ON injury. The posterior ethmoid cell namely the Onodi cell is of great surgical importance when the ON is along its lateral wall and surrounds the nerve. These varied relations imply that a detailed knowledge of the intimate relationship of ONC with the posterior paranasal sinuses is necessary to avoid unintentional complications during the surgeries involving the ONC region. To assess relationship of ONC to the posterior paranasal sinuses in Indian Ethnic study group. Retrospective review of 100 paranasal sinus Computed Tomography (CT) scans were done using 64 row Multi Detector Computed Tomography (MDCT). Multiplanar reformation images were assessed for ONC relation to posterior ethmoid and sphenoid sinuses, wall dehiscence, and Pneumatization of Anterior Clinoid Process (PACP). 200 optic nerve canals were assessed and grouped into four types based on the modification of Delano et al., classification. The most common OCN was Type-1 (60%), followed by Type-2 (15%), Type-3 (14%) and Type-4 (11%). Dehiscence was seen in 35(17.5%) mostly in Type-3 canals. PACP was seen in 30 (15%). Knowledge of ON relationship to posterior paranasal sinuses will reduce the devastating complications during sinus surgeries. Our modified ONC classification is based on the bony canal morphology and the degree of protrusion into sinuses. As with other reported studies worldwide, Type-1 ONC is the commonest among the Indians also. Type-2 and 3 ONC with sinus wall dehiscence and PACP are the most important anatomical variations which may potentially predispose to risk of surgical injury to the optic nerves.

Prevalence of Anatomical Variants on Computed Tomography of Nose and Paranasal Sinuses

Objective: Aim of the study was to determine the prevalence of anatomical variations of nose and paranasal sinuses based on the findings seen on computed tomography. Methodology: CT SCAN of the patients with sinonasal symptoms was performed for evaluation of the anatomical variants of nose and paranasal sinuses. The sections were then analysed for anatomical variations. The data collected was subjected to statistical analysis. Results: The most commonly encountered anatomical variation was DNS, present in 86.25% (69) of patients. Pneumatised septum was present in 25% (20) of patients. Concha bullosa was present in 28.75% (23) while Concha lamella was seen in 17.5% (14) of patients. Paradoxical middle turbinate was present in 13.75% (11) while pneumatization of uncinate process in 10% (8), pneumatized superior turbinate in 5% (4), Haller cells in 8.75% (7), prominent Agger nasi cells in 15% (12), pneumatized crista gali in 8.75% (7), Onodi cells in 20% (16), pneumatization of anterior clinoid process in 17.5% (14) while pneumatization of greater wing of sphenoid/ pterygoid process was present in 11.25% (9) of patients. Conclusion: It is very important to recognize the clinical and surgical significance of these variations. Thus, prior to FESS, imaging with CT scan is mandatory to evaluate the anatomy of PNS and its variations.

Anatomical Variations of the Anterior Clinoid Process: A Study of 597 Skull Base Computerized Tomography Scans.

The anterior clinoid process (ACP) is surrounded by a complex anatomy; variations include pneumatization and the formation of bone bridges with the middle and posterior clinoid, which complicate surgery. The key to avoiding microsurgical complications is a perfect understanding of this anatomy. To explore the anatomic variations of the ACP. Between January 1, 2013, and September 6, 2014, 597 skull base computed tomography scans were performed to evaluate inner ear disease in patients with no history of paranasal sinus disease or endonasal surgery. The base width and length of the ACP, complete carotid-clinoid foramen and sella turcica bridge, and sphenoid sinus pneumatization volume were assessed. ACP pneumatization was assessed with the use of a novel classification system. The scans were derived from a population of 343 female patients (57.5%), with a mean age of 38.6 years (0.2-90 years). ACP base width and length were 7.7 ± 1.73 and 10.31 ± 2.1 mm, respectively. Anatomic variations were present in 38.7% of scans. ACP pneumatization was present in 25.5% of scans, and carotid-clinoid foramen and sella turcica bridge were present in 14.2% and 14.4% of scans, respectively. There was no pneumatization of the ACP in patients <10 years of age and no progression of the pneumatization of the sphenoid sinus in patients >10 years old. At least 1 variation in ACP anatomy was found in 38.7% of cases with this simple method. Thus, a preoperative computed tomography scan could improve surgical procedures that involve removal of the anterior clinoid process.

Presence and types of anterior clinoid process pneumatization, evaluated by Multidetector Computerized Tomography.

The types and ratio of anterior clinoid process (ACP) pneumatization in paranasal sinus Multidetector Computerized Tomography (MDCT) were investigated the importance of ACP in neurosurgical approaches discussed. Paranasal MDCT images of 499 subjects (259 male, 240 female), between 17 and 65 years of age, were included in the study. Presence and types of pneumatization of the ACP and pneumatization types (I, II or III) were evaluated. ACP pneumatization was detected in 37.5% of the males and 33.3% of the females. Right, left and bilateral ACP pneumatizations were detected in 12.7%, 9.3% and 15.4% of males and 9.2%, 8.3% and 15.8% of the females, respectively. The most commonly detected types of pneumatization were Type I (49.1%) for right pneumatizations and Type II pneumatization for left (40.9%) and bilateral (37.2%) pneumatizations. In males, Type I (37.1%) and in females, Type II (40.0%) pneumatizations were detected more frequently. Type III pneumatization was detected in 29.9% of the males and 22.5% of the females. ACP pneumatization ratios were higher in younger subjects and lower in older subjects. Sclerosis process related to aging may be responsible for the lower pneumatization ratios in older subjects. When Type III ACP pneumatization is present, clinoidectomy should not be performed: in this type of ACP pneumatization, cerebrospinal fluid fistula develops in all cases.

Anatomical variants of surgically important landmarks in the sphenoid sinus: a radiologic study in Southeast Asian patients.

Failure of a surgeon to understand the local variations of the anatomical landmarks of the sphenoid sinus is a potential risk factor to cause damage to the optic nerve (ON) or internal carotid artery (ICA) that lies on the walls of the sphenoid sinus. The aim of this study was to identify the anatomical variants of the sphenoid sinus and its related surrounding structures among the Southeast Asian (SEA) population, based on computed tomography (CT) scans. This cross-sectional study analyzed 300 CT scans of the brain, paranasal sinuses (PNS), and head and neck (H&N) at a tertiary referral centre in Malaysia utilizing the Osirix software. The images were reconstructed into 1 mm cuts on bone window. Demographic details and scan findings were documented in a standardized data collection sheet. The rates of ON dehiscence, ICA dehiscence and ICA protrusion in the SEA population were 7.0, 3.0 and 10.0 %, respectively. The rate of ON protrusion was 2.3 %. There was no statistically significant relationship (p > 0.05) noted on Chi-square test, between anterior clinoid process (ACP) pneumatization and ON protrusion. The rate of Onodi cells in our population was 14.3 %. The average vertical distance of the ostia from the roof of the posterior choanae was 1.42 cm (±0.32). The horizontal distance of the ostia from the anterior end of the superior turbinate was 1.58 cm (±0.41) and the oblique distance of the ostia from the anterior nasal spine was 5.35 cm (±0.48). Independent t tests showed that there is a statistically significant difference between the means of each of these parameters (p < 0.001) and their international averages. The rate of ON protrusion is lower in the SEA population, whereas the rates of ON dehiscence, ICA dehiscence and ICA protrusion fall within the range of international averages. In our population, ACP pneumatization is not related to ON protrusion. The distance of the ostia from given landmarks was significantly shorter than in other studies.

Anterior Clinoid Process and the Surrounding Structures

The anterior clinoid process (ACP) is located close to the optic nerve, internal carotid artery, ophthalmic artery, and can be easily injured in an ACP-related surgery. An anatomical study clearly defining the ACP is of great importance. In addition, computed tomographic (CT) images may be a new tool for the anatomical analysis of ACP compared with the use of a cadaver and skull study, and more data related to ACP can be measured by CT images. We studied the anatomical structure of ACP and the structures surrounding it to provide information to surgeons for ACP-related surgery. Computed tomography angiographic images of 102 individuals were reviewed. The measurement was performed on coronal, sagittal, and axis planes after multiplanar reformation. The length of ACP and the distance between apex of ACP and sagittal midline were measured in the axial plane; the classification of ACP and the occurrence rate of bone bridge were also viewed in axial plane. The thickness of ACP was measured in sagittal plane. In Chinese population, 12.3% of the ACP is gasified, and the pneumatization of ACP has a relationship with the pneumatization of sphenoid sinus. The length and thickness of ACP are similar to that in previous studies in cadaver. The apex of ACP is relatively stationary to the C3 and C4 segments of the internal carotid artery. The occurrence rate of anterior and middle clinoid bone bridge was 7.8%; the occurrence rate of anterior and posterior clinoid bone bridge was 9.3%. The anatomical structure of ACP can be studied effectively in CT images. Recognizing the anatomical characteristics of the ACP and optic strut is important in decreasing the incidence of surgical complications of an anterior clinoidectomy and in the proper intraoperative management to prevent these complications.

Pneumatization degree of the anterior clinoid process: a new classification

The objective of this study is to determine the incidence and degree of anterior clinoid process pneumatization, in addition highlighting to their clinical significance. Multidetector-row CT scans of the skull base were reviewed in 648 subjects between 2007 and 2008. The presence of pneumatized anterior clinoid process and its degree were studied and documented. These data were statistically analyzed. Pneumatization of the ACP was found in 62 of 648 patients (9.6%) including 32 (51.6%) men and 30 (48.4%) women. The age of these patients ranged from 21 to 82 years (mean, 41 +/- 15.7 years). Pneumatization of the ACP occurred only on the left side in 14 cases (22.6%), only on the right side in 11 cases (17.7%), and bilaterally in 37 patients (59.7%). ACP pneumatization Type I, in which less than 50% of the ACP is pneumatized, was found in 47 of 124 sides (38%), Type II, in which more than 50% but not totally pneumatized ACP, was found in 28 of 124 sides (22.6%), and Type III, in which the ACP is totally pneumatized, was found in 22 of 124 sides (17.7%). The incidence of Type I in the general population was 6.6%, Type II was 3.5%, and Type III was 2.5%. Radiologically recognizing the degree of ACP pneumatization is important in decreasing the incidence of surgical complications during anterior clinoidectomy. Proper intraoperative management can be undertaken with special attention to the new classification.

ASSESSMENT OF THE RELATION OF THE OPTIC NERVE TO THE POSTERIOR ETHMOID AND SPHENOID SINUSES BY COMPUTED TOMOGRAPHY

The aim of this study was to observe the relationship of the sphenoid sinus and posterior ethmoid cells with the optic nerve. 34 CT scans (68 sides) of paranasal sinuses of patients older than 18 years were retrospectively reviewed. Images were assessed in two planes--axial and coronal. We observed the position and relationship of the optic nerve to the posterior ethmoid and sphenoid sinuses, bony dehiscence and protrusion of the optic nerve into sinuses, and pneumatization of the anterior clinoid process. The most frequent position of optic nerve (ON) was a location close to the posterior ethmoid and sphenoid sinuses without contacting or indentation of the wall--55.9% (38 nerves). The bulging of ON to sphenoid sinus was found in 14.7% (10 nerves) and the course of the nerve through sinus in 16 nerves (23.5%). The position of ON intimately to both sinuses was observed in 5.9% (4 nerves). Protrusion of ON, dehiscence of the bony wall and pneumatization of anterior clinoid process (ACP) was seen in 12 (35.3%), 4 (11.8%) and 9 (26.5%) patients, respectively. Both the protrusion of ON and ACP pneumatization were present in 8 (23.5%) patients on the right side and in 5 (14.7%) patients on the left side. Variations of posterior ethmoid and sphenoid sinuses are numerous and may entail potential risk of injury of the ON during sinus surgery. Knowledge of individual differences and configurations in the operation area may help the surgeon to prevent complications. Computed tomography is the preferred radiographic modality for evaluation of bony variations and the pathology of this region.

Anatomic Variation of Sphenoid Sinus and Related Structures in Libyan Population: CT Scan Study

Background: Sphenoid sinus is the most inaccessible paranasal sinus, enclosed within the sphenoid bone and intimately related to numerous vital neural and vascular structures. Anatomic variation of the sphenoid sinus is well documented and may complicate surgery in such a place. Objective: To outline the surgically risky anatomic variants of the sphenoid sinus as well as the variable relationships between the sinus and related neurovascular structures, for the safe removal of intrasphenoid and pituitary lesions. Materials and Methods: We undertook a prospective review of 300 paranasal sinus CT scans of Libyan patients; coronal CT scans were obtained by special parameter techniques. We assessed pneumatization of pterygoid process (PP), anterior clinoid process (ACP), and greater wing of sphenoid (GWS); we also examined protrusion and dehiscence of internal carotid artery (ICA), optic nerve (ON), maxillary nerve (MN), and vidian nerve (VN) into the sphenoid sinus cavity. Results: Pneumatization of PP, ACP, and GWS were seen in 87 (29%), 46 (15.3%), and 60 patients (20%), respectively. Protrusion of ICA, ON, MN, and VN were noticed in 123 (41%), 107 (35.6%), 73 (24.3%), and 81 patients (27%), respectively; dehiscence of these structures was encountered in 90 (30%), 92 (30.6%), 39 (13%), and 111 patients (37%), respectively. Statistically, there was a highly significant association between ACP pneumatization and ICA protrusion, ACP pneumatization and ON protrusion, PP pneumatization and VN protrusion; and GWS pneumatization and MN protrusion (p-value < 0.001). Conclusion: The sphenoid sinus is highly variable; this variability necessitates a comprehensive understanding of the regional sphenoid sinus anatomy by a detailed CT scan sinus examination before surgery in and around the sinus. This study indicates the possibility of a racial anatomical variation of the sphenoid sinus in the Libyan population.

Anatomic Variation of Sphenoid Sinus and Related Structures in Libyan Population: CT Scan Study

BackgroundSphenoid sinus is the most inaccessible paranasal sinus, enclosed within the sphenoid bone and intimately related to numerous vital neural and vascular structures. Anatomic variation of the sphenoid sinus is well documented and may complicate surgery in such a place.ObjectiveTo outline the surgically risky anatomic variants of the sphenoid sinus as well as the variable relationships between the sinus and related neurovascular structures, for the safe removal of intrasphenoid and pituitary lesions.Materials and MethodsWe undertook a prospective review of 300 paranasal sinus CT scans of Libyan patients; coronal CT scans were obtained by special parameter techniques. We assessed pneumatization of pterygoid process (PP), anterior clinoid process (ACP), and greater wing of sphenoid (GWS); we also examined protrusion and dehiscence of internal carotid artery (ICA), optic nerve (ON), maxillary nerve (MN), and vidian nerve (VN) into the sphenoid sinus cavity.ResultsPneumatization of PP, ACP, and GWS were seen in 87 (29%), 46 (15.3%), and 60 patients (20%), respectively. Protrusion of ICA, ON, MN, and VN were noticed in 123 (41%), 107 (35.6%), 73 (24.3%), and 81 patients (27%), respectively; dehiscence of these structures was encountered in 90 (30%), 92 (30.6%), 39 (13%), and 111 patients (37%), respectively. Statistically, there was a highly significant association between ACP pneumatization and ICA protrusion, ACP pneumatization and ON protrusion, PP pneumatization and VN protrusion; and GWS pneumatization and MN protrusion (p-value < 0.001).ConclusionThe sphenoid sinus is highly variable; this variability necessitates a comprehensive understanding of the regional sphenoid sinus anatomy by a detailed CT scan sinus examination before surgery in and around the sinus. This study indicates the possibility of a racial anatomical variation of the sphenoid sinus in the Libyan population.

Safe Extradural Anterior Clinoidectomy

An extradural technique of complete anterior clinoid process (ACP) removal was described by Dolenc in 1983 as a component of safe entry into the parasellar region. Resection of the ACP is important for the exposure of aneurysms on clinoidal and supraclinoidal segments of ICA. It is a useful step during resection of inner sphenoid wing meningiomas and other tumors in this region. Safe clinoidectomy, which was described by Krisht in 2004 as a part of a pretemporal transzygomatic-transcavernous approach to basilar apex aneurysms, consists of controlled detachment of three extensions of the ACP and epidural dissection of the cavernous sinus lateral wall to make the ACP more mobile and accessible. Dissecting the temporal lobe dura propria gives an initial opportunity to control venous bleeding from the cavernous sinus by Tissucol glue between VI and V2. We have been using a safe technique to remove ACP since 2005. Our experience is limited: two aneurysms, four inner wing meningiomas, one chordoma, one invasive adenoma, one traumatic optic nerve compression, and one sphenopetrous meningioma. There was no visual deterioration and one liquorrhea was treated by sphenoid sinus packing. We noticed pneumatization of ACP once: this defect was packed with a piece of muscle.

Surgical Consideration to Optic Nerve Protrusion According to Sinus Computed Tomography

This study aimed to investigate the prevalence of optic nerve protrusion (ONP) and its clinical indicators by using sinus computed tomography (CT) scan. Sinus CT scans of 260 consecutive patients with chronic inflammatory sinus disease were reviewed. The prevalence of ONP in our study population was 28%. Nineteen percent of the optic nerves protruded into the sphenoid sinuses including indentation of the sinus wall (12%) and coursing through the sphenoid sinus (8%). In the presence of contralateral ONP and/or ipsilateral anterior clinoid process pneumatization, the chance of ONP occurrence was significantly higher (both P < 0.01). They were reliable indicators of ONP (R(2) = 0.47, P < 0.01). ONP is a common anatomic variation observed in patients with chronic inflammatory sinus disease. To reduce optic nerve damage in surgeries, the presence of ONP according to sinus CT scans and the intraoperative findings should be carefully evaluated. C-4.

Microsurgical Landmarks for Safe Removal of Anterior Clinoid Process

The microsurgical and radiological anatomy of the clinoid process were studied to give surgeons more details about the anterior clinoid process and its relations to the vascular and nervous neighbourhood during intradural and extradural clinoidectomy, thus making the operative procedures safer. Seven formalin-fixed (14 sides) and two fresh cadavers (four sides) were studied to reveal the surgical anatomy of the anterior clinoid process and related landmarks during intradural and extradural drilling techniques of clinoid process. Furthermore, aeration of the anterior clinoid process was investigated in 100 paranasal tomography (200 sides) scans. Careful drilling of the anterior clinoid process is mandatory to avoid damage to the extremely important adjacent structures. The anterior clinoid process must not be removed in one piece. Clinoid folds and the frontotemporal fold should be exposed adequately. The falciform ligament must be cut to visualize the optic nerve and ophthalmic artery clearly. Preoperative radiological assessment of clinoid process variations should be done. In computerized tomography scans, pneumatization of the right anterior clinoid process was found in 12%, of the left anterior clinoid process in 7% and bilaterally pneumatization was present in 9%. Removal of the ACP is one of the most critical procedures to the successful and safe management of ophthalmic segment aneurysms and tumors located in the paraclinoid region and cavernous sinus. Special attention should be paid to the anatomic landmarks indicating the relationship between the anterior clinoid process and adjacent structures. Beside that, pneumatization of the anterior clinoid process should be evaluated preoperatively with computed tomography to avoid complications such as rhinorrhea and pneumocephalus.

Quantitative Computer-Aided Computed Tomography Analysis of Sphenoid Sinus Anatomical Relationships

This study describes a novel computer-generated anatomic symmetry plane as a framework for the quantitative description of sphenoid sinus anatomy. The aim of this study was to (1) determine relationships and distances between a midline sphenoid reference point (called the central sphenoid point [CSP]) and lateral sphenoid wall structures and (2) assess the incidence of anterior clinoid process (ACP) pneumatization and pterygoid recess (PR) pneumatization. Axial computed tomography (CT) scans (1-mm slice thickness) were obtained on a VolumeZoom CT scanner (Siemens Medical, Erlangen, Germany). Mathematically derived anatomic symmetry planes were created using custom postprocessing software. A standardized review of each CT scan using surgical planning software (CBYON Suite version 2.6; CBYON, Mountain View, CA) was performed. The CSP was defined as a reference point in the midline sagittal plane at the intersection of the vertical sellar face and the horizontal sellar floor. A total of 128 sides in 64 cadaveric specimens were available for review. The incidences of ACP pneumatization and PR pneumatization were 23.4 and 37.5%. The mean distances from the CSP to the left optic canal midpoint, the left ACP entrance point, and the left PR lateral wall were 17.2, 15.6, and 27.6 mm, respectively. The corresponding distances from the CSP on the right side were 17.3, 15.8, and 28.0 mm, respectively. Measurements from the maxillary spine to the optic canal midpoint, ACP entrance point, and PR lateral wall on each side were performed also. This approach provides both quantitative and qualitative understanding of sphenoid osteology and may be coupled with intraoperative surgical navigation to reduce the risks of sphenoid surgery. Both PR and ACP pneumatization are surprisingly common. Because the CSP-derived relationships may be referenced during endoscopic surgical navigation, they may provide greater clinical utility than traditional alternatives. This paradigm may facilitate a greater understanding of sphenoid anatomy and enhance surgical safety and precision.

Variations of sphenoid and related structures.

The aim of this study was to delineate the precise relationship between the sphenoid sinus and internal carotid artery and the optic nerve, as well as to assess incidence of the anatomic variations of these structures. A review of 92 paranasal sinus tomographic scans was made for anatomic variations of the sphenoid sinus and related bony and neurovascular structures. Coronal and axial tomographic sections were obtained with 2.5-mm section thickness. We assessed the protrusion of the internal carotid artery (ICA) and the optic nerve (ON) into the sphenoid sinus, bone dehiscence of these structures, and pneumatization of the anterior clinoid process (ACP) and pterygoid recess (PR), as well as the variations of the sphenoid sinus septum. The protrusion of the ICA into the sphenoid sinus was found in 24 (26.1%) patients. An ON protrusion was present in 29 (31.5%) patients. Pneumatization of the PR was encountered in 27 (29.3%) patients. There was not a statistically significant relationship between the pneumatization of the PR and ICA protrusion into the sphenoid sinus (chi2 = 0.258, p = 0.168). A significant relationship between the ACP pneumatization and protrusion of the ON into the sphenoid sinus was found (chi2= 0.481,p = 0.007). Preoperative recognition of the anatomic variations by the radiologist is beneficial for identification of the limits of dissection. This is particularly important in the sphenoid sinus area where extensive pneumatization of the skull base bones may distort the anatomic configuration. Therefore, axial and coronal CT sections should always be obtained prior to any surgery in the sphenoid sinus area.