Table 5 Systematic review

 Current study

240 CT studies

UK

6–80 years

5%

10%

17.5% (includes mixed 2.5%)

–

 Archana et al. [26]

250 dry skulls

India

–

6.80%

5.20%**

12%

Neurosurgical implications.

 Boyan et al. [27]

34 dry skulls

Turkey

Adults

35.3%

Neurosurgical implications.

 Brahmbhatt et al. [28]

50 dry skulls

India

Adults

Not assessed (complete only)

2/50 skulls (4%)

–

Need for awareness amongst radiologists and neurosurgeons.

 Dagtekin et al. [29]

15 cadaveric heads + 25 dry skulls

Turkey

–

10%

15%

–

Neurosurgical implications.

 Efthymiou et al. [30]

76 dry skulls

Greece

Adults

69.3% (of ossified ligaments)—equivalent of 46% of total

30.7% (of ossified ligaments)—equivalent of 20.4% total**

74%

Neurosurgical implications.

 Erturk, Kayalioglu, and Govsa [31],

119 dry skulls + 52 cadaveric heads

Turkey

–

14.91

8.77%**

35.67%

Neurosurgical implications and relationship with cavernous sinus.

 Fernandez-Miranda et al. [6]

100 CT angiograms + 50 anatomic specimens

USA

–

–

20%

–

Importance with respect to endonasal neurosurgery.

 Gibelli et al. [32]

300 CT head scans

Italy

18–99 years

–

8.70%

–

Association between interclinoid and caroticoclinoid bridging. No association with age or sex.

 N. Gupta, Ray, and Ghosh [33]

35 dry skulls

Nepal

–

11.40%

8.60%**

20%

Neurosurgical implications.

 Keyes 1935 [12]

2187 dry skulls

USA

1 day–105 years

–

–

34.84%

Details of the anatomical features of mineralised ligament. Complete ossification present in cases as young as 21 days.

 Kapur and Mehić [34]

200 dry skulls

Bosnia and Herzegovina

19–91 years

9.75%

7%**

16.75%

Neurosurgical implications.

 Lee et al. [35]

73 dry skulls

Korea

n/s

11.60%

4.10%

15.7%

Neurosurgical implications.

 Miller, Chamoun, and Beahm [3]

150 maxillofacial CTs

USA

–

–

41.80%

–

Neurosurgical implications for expanded endoscopic approaches.

 Natsis et al. [14]

123 dry skulls

Greece

20–91 years

36.60%

23.60%

60.16%

Association between complete mineralisation and age and bilaterality.

 Ota et al. [2]

72 CT angiograms for paraclinoid aneurysms

Japan

–

–

–

16.60%

Use of preoperative CT prior to extradural anterior clinoidectomy.

 Peker et al. [8]

80 dry skulls

Turkey

–

–

–

34.2%

Neurosurgical implications.

 Sharma et al. 2018 [5]

2726 dry skulls

USA

18–105 years

42%*

31%**

–

Neurosurgical implications including risks of injury to the internal carotid artery.

 Skrzat, Mroz, and Marchewka [19]

80 dry skulls

Poland

Adults

–

16.3%

–

Neurosurgical implications and effects upon the internal carotid artery.

 Suprasanna and Kumar [36]

54 CT angiograms

India

18–70 years

–

–

22.20%

Importance of imaging in pre-operative planning in treating paraclinoid aneurysms.

 Aggarwal, Gupta, and Kumar [37]

67 dry skulls

India

–

13.4%

3.0%

16.4%

Neurosurgical implications.

 Current study

240 CT studies

UK

6–80 years

15.4%

5.4%

22.1% (includes mixed 1.3%)

–

 Archana et al. [26]

250 dry skulls

India

–

2.40%

1.60%**

4%

Neurosurgical implications.

 Boyan et al. [27]

34 dry skulls

Turkey

Adults

5.9%

5.9%

11.8%

Neurosurgical implications.

 Brahmbhatt et al. [28]

50 dry skulls

India

Adults

–

2% (1/50 skulls)

–

Need for awareness amongst radiologists and neurosurgeons.

 Cederberg et al. [23]

255 lateral cephalometric radiographs

USA

8–76 years

38.4%

8.2%

–

Weak association between advancing age and degree of mineralisation.

 Dagtekin et al. [29]

15 cadaveric heads + 25 dry skulls

Turkey

–

–

5%

–

Neurosurgical implications.

 Erturk, Kayalioglu, and Govsa [31]

119 dry skulls + 52 cadaveric heads

Turkey

–

–

8.18%

–

Neurosurgical implications and relationship with cavernous sinus.

 Gibelli et al. [32]

300 CT head scans

Italy

18–99 years

–

16.00%

–

Association between interclinoid and caroticoclinoid bridging. Potential association with interclinoid mineralisation and age.

 Gupta et al. [38]

1

India

–

–

–

–

Case report—misidentification of a mineralised interclinoid ligament as para-posterior communicating artery aneurysm.

 Keyes 1935 [12]

2187 dry skulls

USA

1 day–105 years

–

–

8.68%

Details of the anatomical features of mineralised ligament. Complete mineralisation in cases as young as 6.

 Kucia et al. [39]

322 lateral cephalograms

Poland

8–16  years

–

–

11.80%

Possible association with malocclusion.

 Leonardi et al. [40]

34 dry skulls

Italy

8–16 years

33.7% (controls); 58.8% (cases)

9.9% (controls); 17.6% (cases)

–

Higher incidence of sellar bridge formation in patients with dental anomalies.

 Marşan et al. [41]

118 lateral cephalograms

Turkey

Adult females (mean ages 27.2 and 25.8 years)

–

5% (class I and II); 18% (class III)

–

Association between sella turcica bridging and manifest skeletal class III malocclusions.

 Natsis et al. [14]

123 dry skulls

Greece

20–91 years

–

–

21.95%

Association between complete mineralisation and age and bilaterality.

 Ota et al. [2]

72 CT angiograms for paraclinoid aneurysms

Japan

–

–

–

2.8%

Preoperative computed tomography is useful to detect variations in the anatomy around the ACP. When performing extradural anterior clinoidectomy.

 Ozdogmus et al. [13]

50 autopsy specimens

Turkey

18–80 years

–

6%

–

Neurosurgical implications.

No significant association between ossification and age.

 Peker et al. [8]

80 dry skulls

Turkey

–

–

–

34.17%

Neurosurgical implications.

Scribante et al. [42]

78 lateral cephalometric radiographs

Italy

–

30% (controls)

13% (controls)

–

Higher incidence of sellar bridge formation in patients with dental anomalies.

 Skrzat, Mroz, and Marchewka [19]

80 dry skulls

Poland

Adults

–

13.8%

–

Neurosurgical implications and effects upon internal carotid artery.

 Suprasanna and Kumar [36]

54 CT angiograms

India

18–70 years

–

0.9%

–

Neurosurgical implications.

 Aggarwal, Gupta, and Kumar [37]

67 dry skulls

India

–

5.2%

1.5%

6.7%

Neurosurgical implications.

 Current study

240 CT studies

UK

6–80 years

8.3%

2.5%

10.8%

–

 Skrzat et al. [43]

1

Poland

–

–

–

–

Neurosurgical implications and possible role in abducens palsy.

 Joo et al. [44]

10 cadaveric heads

Korea

–

–

–

25%

Anatomical features that may predispose to abducens palsy.

 Inal et al. [16]

130 skull bases on CT

Turkey

20–78 years

9.8% (right); 9.8% (left)

2.3% (right); 2.9% (left)

–

Association between mineralisation and advancing age. Neurosurgical implications.

 Özgür and Esen [11]

523 CT heads

Turkey

18–100 years

3.60%

2.20%

5.80%

Anatomical features that may predispose to abducens palsy.

 Icke, Ozer, and Arda [45]

20 cadaveric heads

Turkey

–

–

–

5%

Neurosurgical implications. Variation in ligament morphology.

 Aggarwal, Gupta, and Kumar [37]

67 dry skulls

India

–

3.0%

2.2%

5.2%

Neurosurgical implications.

 Current study

240 CT studies

UK

6–80 years

16.7%

1.2%

18.3% (Includes mixed 0.4%)

–

 Cederberg et al. [23]

Lateral cephalometric radiographs of 255 subjects presenting for orthodontic evaluation

USA

8–76 years

23%

9%

32%

Very weak correlation with advancing age.

 Inal et al. [16]

130 temporal bone CTs

Turkey

20–78 years

26.6% (right); 29.5% (left)

5.2% (right), 4.6% (left)

–

Neurosurgical implications. Anatomical features that may predispose to cranial nerve palsy.

 Kimball et al. [18]

15 cadaveric head halves; 71 dry skulls

Grenada

68–93 years

13% (of cadaveric head halves)

20% (of cadaveric head halves)

9% skulls had large (> 2 mm) trigeminal protuberances

Neurosurgical implications. Potential role in trigeminal neuralgia.

 Ozdede et al. [46]

290 cone beam CTs

Turkey

24–81 years

–

–

33.4% (calcification in general)

Male preponderance.

 Patwardhan [47]

Case report

India

–

–

–

–

Anatomical features that may predispose to oculomotor palsy.

 Sedghizadeh, Nguyen, and Enciso [48]

500 cone beam CTs

USA

13–82 years

–

–

8% (calcification in general bilateral only)

Common finding on dental cone beam CTs.

 Skrzat et al. [49]

24 fixed specimens, 73 dry skulls (reviewed for ligament remnants)

Poland

–

–

–

1.4% (1 of 73 skulls)

Anatomy of non-calcified ligament and relationship with oculomotor nerve.

 Wysiadecki et al. [50]

1

Poland

76 years

–

–

–

Association with oculomotor palsy.

 Current study

240 CT studies

UK

6–80 years

12.5%

2.1%

17.1% (includes mixed 2.5%)

–

 Goyal and Jain [51]

55 dried adult skulls and 20 sphenoid bones

India

–

14.67%

2.67%

17.33%

Implications for surgery and neural compression.

 Shivanni and Yuvaraj Babu [52]

40 dry skulls

India

–

8%

–

8%

Surgical implications.

 Yadav, Kumar, and Niranjan [53]

500 skulls

India

–

6.2%

4%

10.2%

Implications for neural compression.

 Saran et al. [54]

50 dried skulls and 30 dried sphenoid bones

India

–

7.50%

1.25%

8.75%

Implications for surgery and neural compression.

 Shinde, Mallikarjun, and Patil [55]

65 skulls

India

–

3.07%

–

3.07%

Implications for surgery and neural compression.

 Tubbs et al. [56]

154 skulls

USA

–

0.645%

0.645%

1.3%

Implications for surgery.

 Antonopoulou, Piagou, and Anagnostopoulou [57]

50 skulls

Greece

30–60 years

25%

2%

27%

Implications for neural impingement.

 Nayak et al. 2007 [58]

416 dry skulls

India

–

3.84%

5.76%

9.61%

Phylogenetic origins and differences.

 Das and Paul [59]

50 sphenoid bones

India

–

1%

0%

1%

Implications for surgery and neural compression.

 von Lüdinghausen et al. [60]

100 skull bases. 54 halves of fixed cadaveric head and neck specimens

Japan and Germany

–

–

6%

–

Anatomical relationships on dissection. Phylogenetic differences.

 Peuker, Fischer, and Filler [9]

1

Germany

–

–

–

–

Neural entrapment in a dissection specimen.

 Tebo [61]

516 skulls

Skulls imported from India

–

33% (includes spines)

3.90%

–

Visibility on panoramic radiographs—can be mistaken for fracture.

 Lepp and Sandner [22]

Not specified

Venezuela

–

–

–

–

Morphology anatomical review of the ligaments and implications for access to the foramen ovale.

 Chouké [1]

n/a

USA

–

–

–

–

Technique modification for percutaneous access to the foramen ovale.

 Chouké [62]

2745 skulls (in addition to skulls examined in 1946 paper)

USA

16–93 years

28.71%

5.46%

–

Implications for access to the foramen ovale.

 Chouké [20]

1544 skulls

USA

16–101 years

–

6.28%

–

Anatomical description of the courses of the mineralised ligaments.

 Shaw [63]

454 skulls

UK

Known in 80 cases: 18-60 years

11.7% partial or complete formation of a pterygospinous bar 16.1% (complete 4.4%)

4.4%

16.1%

Potential association with trigeminal neuralgia

 Krmpotić-Nemanić et al. [7]

100 skulls; 50 isolated macerated sphenoid bones

Poland

Skulls 18–95 years; sphenoid bones 5–17 years

–

5%

–

Potential mechanisms for neural entrapment.

 Ryu et al. [21]

142 skulls

Korea

Unknown

16.6%

1.4%

18%

Implications for neural impingement and surgical access.

 Kamath and Kuberappa [64]

100 skulls

India

–

16%

1%

17%

Implications for neural impingement and surgical access.

 Rosa et al. [65]

93 skulls (radiographed using the Hirtz axial technique)

Brazil

–

19.36%

8.61%

27.97%

Implications for neural impingement and surgical access.

 Peker et al. [8]

452 skulls + mandibular nerves of 9 fixed cadavers

Turkey

–

–

5.50% (fixed); 8.8% (skulls)

–

Potential mechanism for neural entrapment.

 Aggarwal, Gupta and Kumar [37]

67 dry skulls

India

–

6.7% (9 of 134 sides)

3.0% (4 of 134 sides)

9.7% (13 of 134 sides)

Implications for neural impingement and surgical access.

 Current study

240 CT studies

UK

6–80 years

4.2%

1.3%

6.3% (includes mixed 0.8%)

–

 Tubbs et al. [56]

154 skulls

USA

–

0.645%

0.645%

1.3%

Implications for surgical access.

 Antonopoulou, Piagou, and Anagnostopoulou [57]

50 skulls

Greece

30–60 years

1%

7%

8%

Implications for neural impingement.

 Lepp and Sandner [22]

Not specified

Venezuela

–

–

–

–

Morphology of the ligaments and implications for access to the foramen ovale.

 Chouké [1]

n/a

USA

–

–

–

–

Technique modification for percutaneous access to the foramen ovale.

 Chouké [62]

2745 skulls (in addition to skulls examined in 1946 paper)

USA

16–93 years

17.76%

5.94%

–

Anatomical characteristics of ligamentous mineralisation.

No relationship with age.

 Chouké [20]

1544 skulls

USA

16–101 years

–

10.30%

–

Anatomical characteristics of ligamentous mineralisation.

 Shaw [63]

454 skulls

UK

Known in 80 cases: 18–60 years

–

0.67%

–

Relationship with trigeminal neuralgia.

 Ryu et al. [21]

142 skulls

Korea

–

5.60%

2.80%

8.40%

Implications for surgical access and neural impingement.

 Kamath and Kuberappa [64]

100 skulls

India

–

29%

1%

30%

Implications for surgical access and neural impingement.

 Rosa et al. [65]

93 skulls (radiographed using the Hirtz axial technique)

Brazil

–

49.44%

12.91%

62.35%

Implications for neural impingement. Use of dedicated radiographic projections.

 Peker et al. [8]

452 skulls + mandibular nerves of 9 fixed cadavers

Turkey

–

–

4.90% (fixed); 7.9% (skulls)

–

Potential mechanism for neural impingement.

 Natsis et al. [66]

145 skulls

Greece

18–91 years

27.60%

4.10%

31.70%

Implications for neural impingement.

 Pękala et al. [67]

Meta-analysis 25 studies

–

–

8.4% (overall pooled prevalence)

4.4% (overall pooled prevalence)

–

Meta-analysis.