Introduction
The piriform aperture (PA) and nasal bones (NBs) are important structures that contribute to the formation of facial structures. Morphological features of the PA and NBs are widely used in different areas, such as nasal reconstruction, rhinoplasty, and for surgical or aesthetic purposes. Further, they can be used in forensic facial reconstruction, which is a method used to identify the dead and determine sex for anthropological purposes.[1] Furthermore, the structure of the NB and the PA for physiological respiration is as important as the morphological structure of the choana and the length of the airway.[2]
The NB is an important structure in the center of the face. It is surrounded by the frontal bone on the superior. The superior margin of the NB is narrow, thick, and wavy, and articulated with the nasal notch of the frontal bone. The inferior margin of the NB is thin. This inferior margin clings to the lateral cartilages of the nose. The lateral margin of the NB is redented for articulation with the frontal process of the maxilla. The medial margin articulates with NB on the other side and superior this margin is thicker. The vertical part of the medial margin extending posteriorly is articulated with the spine of the frontal, the perpendicular plate of the ethmoid bone, and the septal cartilage of the nose.[234] The nose has three vaults, including the bony, upper cartilaginous, and lower cartilaginous vaults. The shape of the bony vault (comprising of paired NBs and the frontal process of the maxilla) is usually pyramidal and forms one-third of the external nose.[3456]
The PA is located at the most anterior side of the bony nasal airway[7] and it is generally pear-shaped and surrounded by the NBs on the top, the frontal process of the maxilla on the left and right sides, and the palatine process of the maxilla below.[1] The region of the PA is the narrowest portion of the bony nasal airway, and this region constitutes 2/3 of the total nasal resistance in the bony cavum.[8]
All surgical procedures in this region should be performed on the basis of NBs and PA differences. Rhinoplasty is a surgical procedure that should have as little margin of error as possible. Anatomical structural differences should be taken into account in surgeries performed in this area. Similarly, osteotomies are widely used for narrowing or widening the nasal base, improving bone deformities, and repairing open-roof deformities. NB osteotomies (especially lateral osteotomy) may be performed safely at the transition zone that exists along the frontal process of the maxilla from the PA to the radix, along the lateral nasal wall. Because of the fragmentation risk, osteotomies may be more difficult in patients who have short NBs.[3456] A detailed understanding of the structure and function of the nasal region is critical for providing proper treatment. Besides knowing where the anatomical differences are, it is important to know how they contribute to clinical procedures. Thus, we aimed to determine if there is any difference in the NB, PA, and choana that may affect structurally the nasal respiration.
Material and Methods
Our study was performed with 83 Turkish dried skulls obtained from the bone collection at Necmettin Erbakan University and Karatay University. Permissions were obtained from Karatay University's, Pharmaceuticals, and Non-Medical Devices Research Ethics Board (2016/012). A digital caliper was used for skull measurements including the height of the NBs at the midpoint (HNB), the lateral edge height of the right NB (HNB-R), the lateral edge height of the left NB (HNB-L), the width of the NB at the top (WNBT), the width of the NB at the bottom (WNBB), the width of the right NB (RNB) and left NB (LNB) at the midpoint (WRNB and WLNB, respectively), the apex width of the PA (AWPA), the width of the PA at the level of the lower ends of the NBs (WPAT), the width of the PA at the bottom (WPAB), the height of the PA (HPA), the distance between the nasion and anterior nasal spine (N-ANS), the width of the right and left choana (CW1, CW2) at the level of the midpoint of the posterior bony aperture of the choana and the height of the right and left choana (CH1, CH2). The shape of the NBs and PA were classified.
A new classification derived from the Lang and Baumeister[9] classification was used for NB typing. NBs were classified into eight subtypes.
- Type 1 and Type 3: There is an angulation which becomes narrower from the edges toward the midline at the bottom. If the transverse thickness of the bone on the midline is greater than 4 mm, it is called type 1. If the thickness is lower than 4 mm, it is called type 3
- Type 2 and Type 6: There is an angulation which becomes narrower from the edges toward the midline on the top of the NB. If the transverse thickness of the bone is greater than 4 mm, it is called type 2. If the thickness is lower than 4 mm, it is called type 6
- Type 4 and Type 8: There is no angulation. Nasomaxillary sutures are parallel to each other on the midline. If the transverse thickness of the bone is greater than 8 mm, it is called type 8. If the thickness is lower than 4 mm, it is called type 4
- Type 5: There was an angulation at the midpoint of the NB
- Type 7: There was no angulation. The NB is wider at the bottom and narrower on the top [Figure 123].
;)
Figure 1: Schmeatic drawing of nasal bone types (Lang and Baumeister[
9] classification was revised, a: midline transverse thickness)
(a) Type 1 NB, (b) Type 2 and 3 NB, (c) Type 5 NB (NB: Nasal bone, RNB: Right nasal bone, LNB: Left nasal bone, yellow arrows show angulation level in nasal bones, angulation is in the lower part of the nasal bone in type 1 and type 3, in the upper part of type 2, and in the middle part in type 5)
Figure 3: (a) Type 6 NB, (b) Type 7 NB, (c) Type 4 and 8 NB (NB: Nasal bone, RNB: Right nasal bone, LNB: Left nasal bone, yellow arrows show angulation level in nasal bones, *angulation is in the upper part of type 6)
The PA was classified into seven types, including 1-Pear shape, 2-Reverse heart shape, 3-Rhomboid shape, 4-Drop shape, 5-Ellipsoid shape, 6-Trapezoid shape, and 7-Round shape [Figure 4 and Figure 5].
Figure 4: The most common type of piriform aperture (Type 5-Ellipsoid shape)
Figure 5: Other types of piriform aperture (pear shape, drop shape, reverse heart shape, trapezoid shape, rhomboid and round shape of piriform aperture)
Statistical analysis
All data were evaluated using SPSS 21.0 (Statistical Package for the Social Science; IBM, Chicago, IL, USA). The mean values, standard deviations, maximum and minimum values, and percentages were determined for descriptive analyses. Furthermore, the relationship between RNB and LNB shape and PA shape was analyzed with multiple corresponding analyses.
Results
This study was conducted on 83 dried skulls (unknown gender). The mean values and standard deviations of the parameters of the NBs, PA, and choana were identified and are shown in Table 1. NB forms were categorized into eight subtypes by revising the classification of Lang and Baumeister [Figures 123].[9] Type 1 (narrowing from the edges to the midline, angulation at the lower part of the bone, bone mid thickness greater than 4 mm) was the most commonly observed shape of NB [Table 2 and Figures 1Figure 2a]. Type 3 was the least common type of NB [Table 2, Figures 1 and 2b]. The most common type of PA was Type 5 (ellipsoid shape, 20%–24.1%) and the least common type of PA was Type 7 (round shape, 4%–4.8%) [Table 3, Figures 4 and 5].
Table 1: Maximum, minimum, mean values and standard deviations of the nasal bone, piriform aperture, and choana parameters (n: skull number, mm)
Table 2: Nasal bone types (%)
Table 3: Piriform aperture types (%)
The association between shapes of the NB and PA was evaluated through multiple corresponding analyses (SPSS 21.0). The statistical analysis revealed that the shape of the PA tended to be in the form of a reverse heart, ellipsoid, or drop if the left NB was Types 2 or 7. The shape of the PA tended to be in the form of a trapezoid if the left NB was Type 3 or 6. Similarly, it was found that the shape of the PA tended to be in the form of a pear, round, or rhomboid if the left NB was Type 1, 4, or 8. Besides, it was observed that NBs that had an angulation at the midpoint, namely Type 5, did not contribute to the formation of the PA shape [Figure 6].
Figure 6: The multiple corresponding analysis graphic of the left nasal bone and piriform aperture
When the relationship between the RNB and the PA was examined, it was seen that pear and round shaped PA were present with Type 4 and 7 RNBs. If the RNBs were Type 1 or 8 the PA tended to be in the form of a reverse heart, ellipsoid, or rhomboid. Similarly, if the RNB was in the form of Type 2, the PA tended to be in the form of a drop. In addition, Type 5 and 6 did not contribute to the formation of PA shapes [Figure 7].
Figure 7: The multiple corresponding analysis graphic of the right nasal bone and piriform aperture
Discussion
The NB, PA and choana were evaluated on 83 dried skulls of Turkish origin in this study. The size and morphology of the NB, PA, and choana are variables between different races, ethnic groups, genders, and ages.[671011121314] The differences in these parameters revealed the importance of measurements of NB, PA, and choana in a wide range of fields from forensic medicine to maxillofacial surgery. There are studies that present the bone structure of the nasal through computed tomography (CT) and bone studies in the literature.[141015161718192021] Although recent CT studies have gained momentum due to clear gender determination and high resolution, the shapes of the NB due to the angulation with the maxillary bone may be detected.[1]
The nose is located in the central part of the face and is physiologically and esthetically important. Esthetic and functional nasal surgeries are performed in plastic surgery procedures worldwide.[4] Two-thirds of the nose isstructurallyimmobile and is comprised two separate anatomic parts, including the bony (upper) vault and the cartilaginous (middle) vault. The anatomical structure of the nasal region may be deformed after rhinoplasty procedures. Surgeons should be aware of the anatomical structure of the nasal region and the possible conditions of the nasal region to avoid potential risks (nasal valve obstructions-middle vault collapse). The incidence of collapse on the middle vault was higher in patients with shorter NBs, longer, weaker or upper lateral cartilages, and thinner skin compared to patients with longer NBs. The knowledge of the morphometric measures in the nasal region is of relevance for surgical procedures such as rhinoplasty, osteotomies, and aesthetic reconstructions.[22]
The most remarkable findings in NB measurements of this study that the mean NB width was 12.65 mm at the proximal location and the lateral side edges of the NBs stretched down, becoming concave at the midpoint (approximately 7.66 mm) [Table 1]. In comparison to other studies conducted on Turkish populations, it was observed that the NB height in our study was higher in the data obtained from the studies of Kaplanoglu et al.[15] and Yuzbasioglu et al.,[1] but lower than the data obtained from Karadag et al.[20] Our findings were consisted with the data of Uygur et al.[24] In this study, the NB height has been found lower than German, Austrian, Black American, Korean, and Iranian populations. Especially, this height was found to be higher than the Indian population [Table 4]. The NB width on the midpoint was lower than German, Korean, Indian population and also than in the Turkish population in the study of Yuzbasioglu et al.[1] [Table 4]. This finding confirms that the NB has a more concave structure toward the midline in our population.
Table 4: The comparison of the nasal bone and piriform aperture measurements according to the researchers (mm)
The NB shape was categorized into eight types in the German population (79 dried skulls) by Lang and Baumeister.[9] Although the Lang and Baumeister[9]'s classification is quite wide, it is considered complex by some authors. Thus, other researchers have revised the classification into five types.[4161718] Type B and Type A were most common (52.3% and 43.2%, respectively-88 dried skulls from Korean adults) according to Hwang et al.[4] Similarly, Prado et al.[16] found that the most common type of NB was A (28.6% for female, 20.6% for male), while D (1% for female, 1% for male) was the least common type in both genders. They also emphasized that there was a significant difference between sexes. Asghar et al.[17] stated that the most common types of NB were Type A (45%) and Type C (20%), followed by Type B (15%), Type E (15%), and Type D (5%), without any significant sexual variation (P = 0.1443). It was emphasized that the Type A and Type B were the most common types of NBs in the most comprehensive studies about Turkish NB classifications which were performed by Yuzbasioglu et al.[1] and Kaplanoglu et al.[15] According to this classification, the most common NB types were Types A (39.76%), B (27.11%), and E (24.7%), respectively. Unlike other researchers, type E has a significant value with a percentage of 24.7 [Table 5] [The types corresponding to type A, B, C, D, and E are given as an explanation at the bottom of [Table 5]. When compared with other studies conducted on Turkish populations, type A was higher in this study than the data obtained by Kaplanoglu et al.[15] and Yuzbasioglu et al.,[1] but lower than the data obtained by Uygur et al.[24]
Table 5: Nasal bone types according to some researchers (%)
Anthropological studies have emphasized that nasal structures of individuals belonging to races living in different geographies are adapted for warming and moistening of inspired air. The length of the nasal airway is increased and the base is narrowed in colder and drier climates. Depending on the increase on the surface area, the period for warming and moistening of the inspired air is longer.[19] Hwang et al.[4] has been reported that the shape and size of the PA may be affected by environmental conditions.[41516] Furthermore, morphological differences and dimensions of the PA have been reported as an important sex indicator. PA size and shape may be used as an anatomical landmark for determination of ethnic differentiation.[116] PA is a variant opening in terms of shape. These differences also affect the width and height of the opening. Therefore, the width measurement was performed on three different regions, including the apex, upper and lower part in this study.
Our study showed that the width of the PA ranged from 20–32 mm (the mean PA width was 24.27 mm) [Table 1 and Table 4]. When compared with other studies conducted on the Turkish populations, it was observed that the PA width in our study was found consistent with the data of Aksu et al.,[2] Yuzbasioglu et al.[1] and Uygur et al.,[24] but also higher than the data obtained by Karadag et al.[20] In addition, the PA width data was similar to other races; however, it was found significantly larger than the study of Lopez et al.[25] [Table 4]. The mean PA height was found 28.63 mm in our study.
This data were lower than the findings of other researchers. This finding supports the ellipsoid shape, which was the most common PA shape observed in our study [Table 4].
Ofodile[19] emphasized that the PA was oval in the Ashanti population, triangular in White and Indian populations, and varied from oval to triangular in American individuals. Prescher et al.[30] evaluated 84 human skulls anthropologically. They declared that the PA area was larger in males and the shape of the PA was pear-shaped in both genders. Yuzbasioglu et al.[1] found the most common type of PA was Type 1 (pear-shape). Asghar et al.[17] and Durga et al.[18] classified the PA into four types (1-long and narrow, 2-triangular, 3-triangular to oval, and 4-tending to roundness), based on the shape and the PA index. Asghar et al.[17] and Durga et al.[18] found the most common PA type to be Type 3 (83.5% for Asghare et al.[17] and 45.09% for Durga et al.[18]). De Araújo et al.[21] stated that the most common PA shape was pear-shape (39.1%). Yuzbasioglu et al.[1] classification system was used in our study and the ellipsoid-shape (Type 5, 24.1%) was the most common PA aperture type [Table 3 and Figure 4].
Moreover, choana is the convex structure where the airflow passes from the posterior cavum to the nasopharynx. Therefore, choana width and length measurements are important parameters for NB and PA to warm and moisten the inspired air. The choana width at the level of the midpoint of the posterior bony aperture of the choana and choana height was found to be 13.21 ± 1.4 mm, 13.89 ± 1.81 mm, and 25.56 ± 3.06 mm, 26.1 ± 2.5 mm for the right and left side, respectively [Table 1]. Aksu et al.[2] determined this rate 13.09 ± 1.56 mm, 13.33 ± 1.36 mm and 24.45 ± 2.61 mm, 23.77 ± 2.42 mm, respectively.
Conclusion
This study provided information about the morphological structures of the NB, choana, and PA in the Turkish population. The anatomic data presented in this study on the width of the PA correlated with other studies. Compared to other investigators, we observed significant changes in the form of NBs. The data obtained from this study show a data series belonging to the Turkish population. Anatomical structures of races should be well-known to reduce postoperative complications and plan appropriate surgical techniques. We believe that results obtained from this study may provide information for selection of osteotomes in adequate sizes, procedures of corrective rhinoplasty, PA augmentation and resection.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
Acknowledgment
This study conformed to the Helsinki Declaration. Permissions were obtained from Karatay University's, Pharmaceuticals and Non-Medical Devices Research Ethics Board (2016/012).
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