Previous research has described the anterior clinoid process (ACP) as a bony projection located near the medial end of the sphenoid bone’s lesser wing. It is anchored by two roots: the superior root, which forms the roof of the optic canal (OC), and the inferior root, which contributes to the lateral and ventral walls of the canal, as illustrated in Figure 1.[1]

FIGURE 1: ACP STRUCTURE

ACP is positioned medially to the optic nerve, inferolaterally to the oculomotor nerve, and inferomedially to the Internal Carotid Artery (ICA) and its ophthalmic branch. [1,2] The ACP constitutes a section of the anterior roof of the cavernous sinus (CS).[3] Various ways of accessing the parasellar and suprasellar areas encounter challenges due to the ACP, which obstructs direct visualization of critical neurovascular systems.[4]

A previous study has demonstrated that the morphology of the anterior clinoid process (ACP) shows considerable dimensional variability, which can be applied for classification and for determining the most appropriate surgical approach during anterior clinoidectomy (A-CLD).[5] This variation improves the visualization of structures surrounding the optic nerve (ON), allowing for safer manipulation of the internal carotid artery (ICA) and ON while reducing the need for extensive brain retraction.[6,7] Given the scarcity of research on this topic within the South Indian population, the present study was undertaken to investigate whether geographical factors contribute to new morphological variations on both sides.

AIM

To assess the length, width, height/ thickness of ACP.

MATERIALS & METHODS

An observational study was carried out on 50 adult skull specimens, including 34 dry skulls and 16 obtained from dissected cadavers, at the Department of Anatomy, Bhaarath Medical College and Hospital. The study was conducted following approval from the Institutional Ethics Committee, as depicted in Figure 2.

FIGURE 2: DIFFERENT SKULLS USED

The Carotico-Clinoid Foramen (CCF) was identified within the middle cranial fossa (MCF). Its presence or absence in the skull specimens was assessed using a pair of sliding Vernier calipers, as illustrated in Figure 3

FIGURE 3: VERNIER CALIPER FOR MEASURING ACP.

All measurements were recorded in millimeters. The length and width were determined at the base of the anterior clinoid process (ACP) tip, with the length being measured from its base. These reference points were adopted based on the methodology described by Souza et al. in 2016.[8] The thickness of the ACP was measured using an adjustable compass in combination with a ruler. Additionally, the ACP was classified into four distinct types through dimensional analysis, applying a modified version of the classification criteria proposed by Cecen et al. in 2016.[9]

 The Classification of ACP was as follows.

1. Length

• Type I: Short (≤ 8.14 mm)
• Type II: Long (> 10.5 mm) and narrow (≤ 10.5 mm)

1. Width

• Width greater than 8.14 mm

Inclusion Criteria:

1. Adult dry skulls exhibiting the carotico-clinoid foramen (CCF)
2. Dissected cadavers

Exclusion Criteria:

1. Damage to the parasellar region
2. Damage to the middle cranial fossa (MCF)

STATISTICAL ANALYSIS

The data were analysed using SPSS version 21.1 (IBM SPSS Statistics). Descriptive statistical measures, including the mean, standard deviation, and range, were computed to interpret the results.

RESULTS

The shape of the ACP was found to be variable.

Length

TABLE 1: MEAN LENGTH

As presented in Table 1, the mean length of the anterior clinoid process was 8.5 ± 1.8 mm, with a range spanning from 5.0 to 13.0 mm. A minor variation was observed between the sides, with the right ACP being slightly longer than the left.

Width

TABLE 2: WIDTH MEASUREMENT

In Table 2 of our study, it was observed that the width varied across different regions.

Height/ Thickness

TABLE 3: MEASUREMENT OF HEIGHT

In Table 3, we have found that the height/ thickness average had variations.

TABLE: SHAPE VARIATION

In Table 4, at different positions, different structures, and shape occurrences are present with varying average length.

DISCUSSION

Previous studies have reported that critical neurovascular structures are at risk of injury during anterior clinoidectomy (A-CLD).[10] Moreover, the anterior clinoid process (ACP) is connected to the middle clinoid process (MCP) via the carotico-clinoid ligament (CCL) [11,12], which may ossify and form the carotico-clinoid foramen (CCF).[13] Understanding morphological variations is therefore essential to reduce the risk of iatrogenic injury.[14]

In the present study, the mean length of the ACP was 8.5 ± 1.8 mm, ranging from 5.0 to 13.0 mm. A slight asymmetry was noted, with the right ACP being marginally longer than the left. The width differed between the base and tip, with measurements of 6.5 ± 1.2 mm and 3.2 ± 0.8 mm, respectively. The thickness also showed variation, with the mean height at 5.2 ± 1.1 mm, base thickness at 6.1 ± 1.3 mm, and tip thickness at 2.8 ± 0.7 mm across adult dry skulls and cadaveric specimens.

Comparable studies conducted in various regions have reported differing measurements. Lee et al. (1997) in Korea recorded a mean length of 9.18 ± 1.55 mm, width of 9.63 ± 1.49 mm, and thickness of 5.32 ± 1.07 mm. [15] Gupta et al. (2005) in Nepal found measurements of 10.74 ± 2.37 mm (length), 10.83 ± 1.20 mm (width), and 5.13 ± 1.03 mm (thickness).[16] Hunnargi et al. (2008) in India reported values of 10.68 ± 1.90 mm, 12.40 ± 2.58 mm, and 6.88 ± 1.09 mm,[17] respectively. Kapur and Mehic et al. (2012) in Europe found length and width values of 9.90 ± 1.60 mm and 9.40 ± 1.40 mm, [18] using dry bone specimens. In contrast, da Costa et al. (2016) in Brazil, employing CT imaging, [19] reported a length of 10.31 ± 2.10 mm and width of 7.70 ± 1.73 mm. In another study, female patients comprised 56.5% of the sample, with ages ranging from 38.6 to 90 years. The width and base length were each 7.7 ± 1.73 mm and 10.31 ± 2.1 mm, respectively.[20] Anatomical variations were present in 38.7% of the scans, with CCF and sella turcica bridging observed in 14.2% and 14.4% of cases, while ACP pneumatization appeared in 25.5%.

Further research by Dhakal et al. (2019) found the right ACP measured 9.88 ± 1.36 mm in length, 8.72 ± 1.50 mm in width, and 5.21 ± 1.83 mm in thickness, while the left side measured 10.30 ± 1.47 mm, 8.73 ± 1.71 mm, and 5.33 ± 1.60 mm, respectively, with no significant asymmetry. Similarly, Sibuor et al.[21] (2018) in Kenya reported right-sided measurements of 11.12 ± 2.83 mm (length), 10.52 ± 2.68 mm (width), and 5.38 ± 2.11 mm (thickness), and left-sided measurements of 10.72 ± 2.77 mm,10.34 ± 2.69 mm, and 5.47 ± 1.95 mm, with no significant differences between sides.

In our study, type I morphology was predominant, observed in 45–50% of cases, characterized by a sharp and triangular projection with an average length of 9.0 mm. Type II, exhibiting a blunt and rectangular shape with an average length of 7.5 mm, was seen in 30–35% of cases, while type III, showing a hook-like appearance with an average length of 8.2 mm, accounted for 15–20%.

Additionally, previous studies have emphasized the anatomical connections between the sellar, suprasellar, and parasellar regions with critical structures such as the pituitary gland, internal carotid artery (ICA),[22,23] cavernous sinus (CS) and its contents, optic nerve (ON), and ophthalmic artery. Adequate exposure of these areas is essential for performing safe surgical procedures in cases involving lesions in these regions. However, this remains challenging due to surrounding bony prominences. Safe surgical intervention requires precise visualization, especially in conditions involving tumors, aneurysms, or vascular complications. The pneumatization of the ACP is particularly relevant, as it has been associated with the formation of the CCF and should be confirmed through radiological assessment.[24]

CONCLUSION

The clinical implications of our study suggest that variations in the size of the anterior clinoid process impact factors such as the amount of bone that must be removed, the dimensions of the surgical pathway, and the accessibility of deeper anatomical structures. Furthermore, differences in shape influence surgical considerations, including drilling strategies, the potential for bone fracture, and the choice of operative techniques. Therefore, a thorough preoperative evaluation of the ACP’s anatomical characteristics is essential for neurosurgeons to ensure safe and effective surgical planning.

REFERENCES

1. Lee HW, Park HS, Yoo KS, Kim KU, Song YJ. Measurement of critical structures around paraclinoidal area: a cadaveric morphometric study. Journal of Korean Neurosurgical Society. 2013 Jul 31;54(1):14-8.
2. Sharma A, Rieth GE, Tanenbaum JE, Williams JS, Ota N, Chakravarthi S, Manjila S, Kassam A, Yapicilar B. A morphometric survey of the parasellar region in more than 2700 skulls: emphasis on the middle clinoid process variants and implications in endoscopic and microsurgical approaches. Journal of Neurosurgery. 2017 Aug 11;129(1):60-70.
3. Lee HY, Chung IH, Choi BY, Lee KS. Anterior clinoid process and optic strut in Koreans. Yonsei Medical Journal. 1997 Jun 1;38(3):151-4.
4. Akture E, Baskaya MK. Microsurgical anatomy and variations of the anterior clinoid process. Turk Neurosurg. 2014;24(4):484-93.
5. Sibuor W, Cheruiyot I, Munguti J, Kigera J, Gikenye G. Morphology of the anterior clinoid process in a select Kenyan population. Anatomy Journal of Africa. 2018 Apr 11;7(1):1132-7.
6. Cecen A, Celikoglu E, Is M, Kale AC, Eroglu BT. Pre-Operative Measurement of the Morphometry and Angles of the Anterior Clinoid Process (ACP) for Aneurysm Surgery. International Journal of Morphology. 2016 Dec 1;34(4).
7. Gupta N, Ray B, Ghosh S. A study on anterior clinoid process and optic strut with emphasis on variations of caroticoclinoid foramen. Nepal Medical College journal: NMCJ. 2005 Dec 1;7(2):141-4.
8. Souza AD, Smiderle OJ, Spinelli VM, Souza RO, Bianchi VJ. Correlation of biometrical characteristics of fruit and seed with twinning and vigor of Prunus persica rootstocks. Journal of Seed Science. 2016;38(04):322-8.
9. Cecen A, Celikoglu E, Is M, Kale AC, Eroglu BT. Pre-Operative Measurement of the Morphometry and Angles of the Anterior Clinoid Process (ACP) for Aneurysm Surgery. International Journal of Morphology. 2016 Dec 1;34(4).
10. Lee HW, Park HS, Yoo KS, Kim KU, Song YJ. Measurement of critical structures around paraclinoidal area: a cadaveric morphometric study. Journal of Korean Neurosurgical Society. 2013 Jul 31;54(1):14-8.
11. Giannotta SL. Ophthalmic segment aneurysm surgery. Neurosurgery. 2002 Mar 1;50(3):558-62.
12. Aragao J, Fontes L, de Aragao J, Reis F. Ossification of interclinoid ligaments and their clinical importance. International Journal of Anatomical Variations. 2013;6:201-2.
13. Standring S. Gray’s anatomy.(2008).
14. Sibuor W, Cheruiyot I, Munguti J, Kigera J, Gikenye G. Morphology of the anterior clinoid process in a select Kenyan population. Anatomy Journal of Africa. 2018 Apr 11;7(1):1132-7.
15. Lee HY, Chung IH, Choi BY, Lee KS. Anterior clinoid process and optic strut in Koreans. Yonsei Medical Journal. 1997 Jun 1;38(3):151-4.
16. Gupta N, Ray B, Ghosh S. A study on anterior clinoid process and optic strut with emphasis on variations of caroticoclinoid foramen. Nepal Medical College journal: NMCJ. 2005 Dec 1;7(2):141-4.
17. Hunnargi S, Ray B, Pai SR, Siddaraju KS. Metrical and non-metrical study of anterior clinoid process in South Indian adult skulls. Surgical and Radiologic Anatomy. 2008 Jul;30(5):423-8.
18. Kapur E, Mehić A. Anatomical variations and morphometric study of the optic strut and the anterior clinoid process. Bosnian Journal of Basic Medical Sciences. 2012 May;12(2):88.
19. da Costa MD, de Oliveira Santos BF, de Araujo Paz D, Rodrigues TP, Abdala N, Centeno RS, Cavalheiro S, Lawton MT, Chaddad-Neto F. Anatomical variations of the anterior clinoid process: a study of 597 skull base computerized tomography scans. Operative Neurosurgery. 2016 Sep 1;12(3):289-97.
20. Dhakal A, Mehta UK, Sah SK, Chaudhary RK. Morphological variation of anterior clinoid process in dry human skulls. Birat Journal of Health Sciences. 2019;4(3):813-7.
21. Sibuor W, Cheruiyot I, Munguti J, Kigera J, Gikenye G. Morphology of the anterior clinoid process in a select Kenyan population. Anatomy Journal of Africa. 2018 Apr 11;7(1):1132-7.
22. Hayashi N, Masuoka T, Tomita T, Sato H, Ohtani O, Endo S. Surgical anatomy and efficient modification of procedures for selective extradural anterior clinoidectomy. min-Minimally Invasive Neurosurgery. 2004 Dec;47(06):355-8.
23. angesh Lone M, Rajgopal L, Telang A. M ORPHOM ETRY OF ANTERIOR CLINOID PROCESS: A CADAVERIC STUDY. Int J Anat Res. 2016;4(4):3237-41.
24. Khatun SS, Yadav Y, Chhabra N, Kaul NV, Sarkar S. Morphometric measurements of anterior clinoid process in relation to parasellar osseous structures and their clinical significance. International journal of health sciences.;6(S6):10466-74.