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1ANATOMICAL VARIATIONS OF THE MASTOID FORAMEN: MORPHOMETRIC
ANALYSIS USING EXIT HOLE MAPPING Muhammad Kalim Raza
Assistant professor, Samarkand State Medical University, Samarkand, Uzbekistan
Alkov Ruslan Alimjonovich Student, Samarkand State Medical University, Samarkand, Uzbekistan Lutfullaev Xafizullo Zaynullaevich Student, Samarkand State Medical University, Samarkand, Uzbekistan https://doi.org/10.5281/zenodo.14201889 Abstract: The mastoid foramen is an anatomical structure critical for neurosurgical interventions due to its role in venous drainage via the mastoid emissary vein, which connects the sigmoid sinus to the external veins of the skull. This study aimed to investigate the morphometric parameters of the mastoid foramen by analyzing 28 dried human skulls from the Anatomy Department at Samarkand State Medical University. Measurements focused on the foramen's length, width, and shape, revealing that the average diameters for the right and left mastoid foramina were 0.13 cm and 0.1 cm, respectively. The predominant shapes identified were star-shaped and round, underscoring significant variability in anatomical features. Additionally, the exit shapes of the foramina were assessed, which further elucidated the potential anatomical variations that can influence surgical approaches. These findings are crucial for enhancing the understanding of the anatomical characteristics of the mastoid foramen and its clinical implications, particularly in reducing operative risks associated with neurosurgery. Future research could expand on these findings to clarify the anatomical variations and improve surgical strategies involving the mastoid region.
Keywords: Mastoid foramen, emissary vein, craniometry, anatomical variations, neurosurgery, exit shape
АНАТОМИЧЕСКИЕ ВАРИАЦИИ СОСЦЕВИДНОГО ОТВЕРСТИЯ: МОРФОМЕТРИЧЕСКИЙ АНАЛИЗ С ИСПОЛЬЗОВАНИЕМ КАРТИРОВАНИЯ
ВЫХОДНОГО ОТВЕРСТИЯ Аннотация: Сосцевидное отверстие является анатомической структурой, критически важной для нейрохирургических вмешательств из-за его роли в венозном дренаже через сосцевидную эмиссарную вену, которая соединяет сигмовидный синус с наружными венами черепа. Целью данного исследования было изучение морфометрических параметров сосцевидного отверстия путем анализа 28 высушенных человеческих черепов с кафедры анатомии Самаркандского государственного медицинского университета. Измерения были сосредоточены на длине, ширине и форме отверстия, что показало, что средние диаметры правого и левого сосцевидных отверстий составляли 0,13 см и 0,1 см соответственно. Преобладающими формами были звездообразная и круглая, что подчеркивает значительную изменчивость анатомических особенностей. Кроме того, были оценены формы выходных отверстий, что дополнительно прояснило потенциальные анатомические вариации, которые могут влиять на хирургические подходы. Эти результаты имеют решающее значение для улучшения понимания анатомических характеристик сосцевидного отверстия и его клинических последствий, особенно для снижения операционных рисков, связанных с нейрохирургией. Будущие исследования могут расширить эти результаты для уточнения анатомических
вариаций и улучшения хирургических стратегий, затрагивающих область сосцевидного отростка.
Ключевые слова: сосцевидное отверстие, эмиссарная вена, краниометрия, анатомические вариации, нейрохирургия, форма выхода
INTRODUCTION
The mastoid foramen plays a critical role in neurosurgical interventions in its vicinity. Given that this foramen accommodates a key component of venous drainage—the mastoid emissary vein, which connects the sigmoid sinus (a cranial venous sinus) to the external veins of the skull—knowledge of its position and variability significantly reduces operative risks. While existing studies have presented diverse craniometric data, including shape, diameter, and prevalence of the foramen, an essential aspect for understanding the nature of this structure lies in approximately predicting the vein's course from the foramen. Our initial goal was to define the morphometric parameters of the mastoid foramen and to create a model simulating the vein's approximate path, to enhance the understanding of its anatomical characteristics and potential clinical risks, accounting for variations in its location.
MATERIALS AND METHODS
The craniometric method was employed to measure the mastoid foramina, with evaluations of the foramen shape, exit shape, length, and width. Additionally, the vein's course was estimated based on the exit shape.
The study material comprised 29 dried, intact human skulls without selection for sex or age, obtained from the Anatomy Department Laboratory at Samarkand State Medical University.
For craniometric measurement of foramen shape and diameter, a calibrated metal caliper was used—Set 3-D of drawing tools, manufactured by MINPRIBOR USSR, Rylsk, Model U-9, GOST 6100-68.
To compare measurements and convert them to centimeters, an electronic caliper was utilized—Matrix Digital Caliper, 150 mm, MTX, 316119.
For statistical analysis of the data, Microsoft Excel 2010 and appropriate calculation formulas were used.
RESULTS AND DISCUSSION
The average length-width of the right foramen is 0.29-0.24 cm, and for the left foramen, it is 0.22-0.19 cm. Applying the ellipse average diameter formula D=2*a*b/a+b (where «a» is an approximate length, and «b» is approximate width) we obtain the mean diameter of the foramina. The mean diameter of the right foramen is 0.13 cm, and for the left, it is 0.1 cm. Средний диаметр обоих отверстий 0.12 cm
No Right foramina Right foramina Left foramina Left foramina
length width length width
1 0,22 0,22 0,18 0,19
2 0,09 0,06 0,08 0,08
3 0,46 0,26 0,23 0,25
4 Absent Absent Absent Absent
5 0,16 0,21 0,2 0,2
6 Absent Absent 0,25 0,2
7 0,4 0,37 0,23 0,27
8 0,2 0,27 0,2 0,25
9 0,24 0,22 0,24 0,17
10 0,21 0,19 0,31 0,25
11 Absent Absent 0,33 0,26
12 0,22 0,2 0,25 0,24
13 Absent Absent 0,19 0,14
14 0,22 0,22 0,21 0,22
15 0,21 0,18 0,26 0,21
16 0,18 0,14 0,25 0,16
17 Absent Absent 0,27 0,19
18 0,18 0,17 0,19 0,13
19 Absent Absent 0,12 0,1
20 0,33 0,32 0,19 0,18
21 0,11 0,9 0,14 0,14
22 0,21 0,13 0,18 0,16
23 0,14 0,17 0,31 0,3
24 0,28 0,38 Absent Absent
25 0,22 0,21 0,16 0,17
26 0,26 0,25 0,33 0,3
27 0,24 0,14 0,26 0,15
28 0,24 0,16 0,24 0,15
29 Absent Absent Absent Absent
Table 1. Measurement Results of Length and Width for the Right and Left Foramen
The most common shape of the mastoid foramen on the right side was star-shaped (9 cases or 32.1%) and round (5 cases or 17.8%). Similarly, on the left side, the most frequently observed shape of the mastoid foramen was also star-shaped (11 cases or 37.8%) and round (7 cases or 24.1%). The overall measurement data is presented in Table 2.
No Right foramina shape Left foramina shape
1 Ellipse Stellate
2 Stellate Round
3 Stellate Stellate
4 Absent Absent
5 Ovale Round
6 Absent Round
7 Round Stellate
8 Stellate Ovale
9 Ovale Stellate
10 Stellate Ovale
11 Absent Ellipse
12 Round Stellate
13 Absent Ellipse
14 Triangle Round
15 Stellate Ellipse
16 Ellipse Stellate
17 Absent Stellate
18 Round Ellipse
19 Absent Stellate
20 Round Stellate
21 Stellate Stellate
22 Stellate Round
23 Ellipse Ellipse
24 Ellipse Absent
25 Triangle Ellipse
26 Round Round
27 Stellate Stellate
28 Stellate Round
29 Absent Absent
Table 2. Results of Shape Measurement of the Foramen on the Right and Left Sides As an additional aspect in measuring the mastoid foramina of the skull, the "shape of the exit from the foramen" was also highlighted, indicating the presence of small grooves from the foramen both externally along the path and internally, thinning medially or, in rare cases, laterally (1 case, as indicated in Table 3). Graphic illustrations showing the variation of different exit shapes of the foramina are provided below in Figures 1-5
The following graphical representations illustrate the exit shapes of the foramina, highlighting the presence of grooves.:
• Gray-filled oval — Represents the foramen itself.
• Light-colored area — Indicates the groove around the foramen and its direction.
• Blue color — Symbolizes a schematic representation of the vessel, specifically the mastoid emissary vein, and its course through the foramen.
Fig. 1. Medially directed upward cou^ Fig. 2. Medially directed posterior course
Fig. 3 Medially directed ventral course
Fig. 4 Medially directed inferior course
Fig. 5 Medially directed superior ventral course
Fig.6 Medially directed superior posterior course
Fig.6
Figure 7,8. Main characteristics of the mastoid foramina, which served as the material for the study, along with some anatomical structures to facilitate navigation.
a - Circle/oval - diameter and length of the foramina at the defined borders, with an arrow indicating the exit of the foramen, predicted as the path of the emissary mastoid vein exiting from the foramen; the dashed line marks the edges of the groove forming the exit from the foramen.
b - Mastoid process, its posterior border. c - Mastoid notch.
After measuring the exit from the mastoid foramen, we obtained the following results:
• Exit from the right foramen: The most common orientation is medially-superiorly-posteriorly (10 cases, 34.5%), followed by medially-superiorly (6 cases, 20.69%) and medially-posteriorly (5 cases, 17.24%). Complete absence of the foramen was observed in 7 cases (24.14%). Only a single case of medially-superiorly-ventrally oriented foramen exit was identified, suggesting this may be an anomaly.
• Exit from the left foramen: The most common orientations are medially-superiorly-posteriorly and medially-posteriorly (9 cases each, 31.03%), followed by medially-superiorly (4 cases, 13.79%) and medially-inferiorly (3 cases, 10.34%). Absence of the foramen was noted in 3 cases (10.34%). Only a single strictly medial case was identified, indicating a complete lack of groove formation.
The total presence of foramina on the right and left sides is 82.7% (48 cases), a significant indicator highlighting the prevalence of this emissary foramen.
No Right foramina exit shape Left foramina exit shape
1 Medially - Superiorly - Posteriorly Medially - Superiorly - Posteriorly
2 Medially - Superiorly - Posteriorly Medially - Superiorly - Posteriorly
3 Medially - Superiorly - Ventrally Medially - Superiorly - Posteriorly
4 Absent* Absent*
5 Medially - Superiorly - Posteriorly Medially - Superiorly
6 Absent* Medially - Inferiorly
7 Medially - Superiorly - Posteriorly Medially - Inferiorly
8 Medially - Posteriorly Medially - Superiorly
9 Medially - Superiorly - Posteriorly Medially - Superiorly
10 Medially - Superiorly - Posteriorly Medially - Posteriorly
11 Absent* Medially - Posteriorly
12 Medially - Superiorly Medially - Superiorly - Posteriorly
13 Absent* Medially - Superiorly - Posteriorly
14 Medially - Posteriorly Medially - Posteriorly
15 Medially - Superiorly - Posteriorly Medially - Posteriorly
16 Medially - Superiorly - Posteriorly Medially - Posteriorly
17 Absent* Medially - Posteriorly
18 Medially - Superiorly - Posteriorly Medially - Posteriorly
19 Absent* Medially - Posteriorly
20 Medially - Superiorly Medially
21 Medially - Superiorly Medially - Superiorly - Posteriorly
22 Medially - Posteriorly Medially - Inferiorly
23 Medially - Superiorly Medially - Superiorly - Posteriorly
24 Medially - Superiorly Absent*
25 Medially - Superiorly Medially - Superiorly - Posteriorly
26 Medially - Superiorly - Posteriorly Medially - Superiorly
27 Medially - Posteriorly Medially - Superiorly - Posteriorly
28 Medially - Posteriorly Medially - Posteriorly
29 Absent* Absent*
Table 3. Results of the Measurement of Foramina Exit
CONCLUSION
The study aimed to investigate the anatomical variations of the mastoid foramen through morphometric analysis, emphasizing its clinical significance in neurosurgery. Key findings were obtained from the analysis of 28 dried human skulls: foramina were present in 48 out of 58 cases (considering both the right and left sides of one skull), which accounts for 82.7%, indicating that it is a relatively common opening among skulls. The most frequently observed shape of the foramina on both sides was star-shaped, suggesting the passage of veins and adjacent structures such as small nerves and arteries. The average diameter measured 0.12 cm, which aligns with standard measurements reported in previous studies.
The results of the study on the exits from the mastoid foramen highlight significant anatomical variability, which is critical for neurosurgery. On the right side, the most common orientation observed was medially-superiorly-posteriorly (34.5%), followed by medially-superiorly (20.69%) and medially-posteriorly (17.24%). Complete absence of the mastoid foramen was noted in 24.14% of cases. On the left side, the most frequently encountered exits were medially-superiorly-posteriorly and medially-posteriorly (both at 31.03%), followed by medially-superiorly (13.79%) and medially-inferiorly (10.34%). Absence of the foramen was noted in 10.34% of cases.
These anatomical variations can significantly affect access to vital structures, increasing the risk of complications. Awareness of such differences allows neurosurgeons to tailor their approaches to the individual anatomical characteristics of patients, thereby enhancing the safety and success of surgical interventions.
Understanding these variations contributes to recognizing potential anatomical challenges, ultimately leading to safer neurosurgical practices and improved treatment outcomes. Future research may further clarify these variations, refining surgical strategies in the region of the mastoid process.
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