












































Forensic Anthropology  
DOI: 10.5744/fa.2023.0016

Copyright © 2023 University of Florida Press

Introduction

Accurate and reliable methods of personal identification are 
crucial in medicolegal scenarios. Correct identifications 
provide family members with closure and facilitate forensic 
investigations; thus, medical examiners and coroners strive 
to obtain a positive identification as quickly as possible. 
Incorrect identifications can have dire consequences, includ-
ing an emotional burden on families, the possible hindrance 
of investigations, and a high likelihood of legal ramifica-
tions. In lieu of or in addition to more familiar methods of 
identification (e.g., DNA, fingerprints, dental records), identi-
fications can be based on radiographic and computed 
tomographic (CT) comparisons using the frontal sinus (for 

reviews see Christensen & Hatch 2018; Pereira et al. 2021). 
The frontal sinus is an air- filled, mucus- lined space between 
the external and internal cortical layers of the frontal bone 
located just above the orbits. Typically, this structure con-
sists of paired (right/left) lobes separated by an inter- sinus 
septum. Each of the air- filled lobes expand superiorly and 
laterally as a series of septa (bony walls) and arcades (or 
scallops), which vary in size, shape, and number. While 
most individuals have some presence of the frontal sinus, 
others may exhibit bilateral aplasia. Bilateral aplasia (i.e., 
complete absence of a frontal sinus in adults) frequencies 
are reported to range between 2% and 24%, although this 
may be higher in Arctic and Oceanic populations (Aydin-
lioglu et al. 2003; Buck et al. 2019; Butaric et al. 2020; Fatu 
et al. 2006; Hansen & Owsley 1980). When the frontal 
sinus is present, there is a high degree of variation in the 
frontal sinus, with lobal presence/absence, positioning rela-
tive to the orbits, overall size, and morphology varying 
across individuals. Left and right lobal asymmetry is also 
common, further increasing possible levels of variation (Fatu 
et al. 2006); even monozygotic twins express visually dif-
ferent frontal sinuses (see Asherson 1965; Kjaer et al. 2012; 
Schuller 1943).

The individualistic nature of the frontal sinus makes this 
structure valuable in terms of personal identification. The 

RESEARCH ARTICLE

Age- Related Changes to Frontal Sinus Traits and Implications 
for Forensic Identification

Naeema Abdulrazaka ● Lauren Nicole Butarica* ● Heather Marie Garvina

ABSTRACT: Forensic studies on frontal sinus identification are often limited to adult samples or utilize static, simulated antemortem 
images, which overlook any potential temporal changes in sinus morphology. Further, studies on frontal sinus growth typically utilize 
lateral radiographs and/or are cross- sectional. The current study utilizes a longitudinal sample of frontal radiographs to determine the age 
at which forensically relevant frontal sinus traits stabilize during growth and development. The sample includes 1500 radiographs of 141 
individuals (66F/75M) ranging from three to 56 years of age (yoa). For each individual, trait age- of- stabilization was recorded by identify-
ing the year at which each coded trait became consistent across images.

Our results demonstrate that frontal sinus traits stabilize on average 10– 15yoa, with sinus presence being the first to stabilize and 
arcade counts the last. Females generally stabilized earlier (9– 14yoa) versus males (10– 15yoa). However, sex differences were generally 
not statistically significant. Further, traits displayed a high degree of variation with wide standard deviations (~3 years). However, by 21yoa 
almost all individuals displayed stabilization in all traits, suggesting that little change should be expected with later- aged postmortem 
radiographs. Still, given the amount of variation, forensic practitioners should be cautious using frontal sinus identification methods in 
subadults, especially when years may have elapsed between images. When conducting a radiographic comparison that involves a subadult 
antemortem image, the results of this study may help the practitioner interpret whether the differences between antemortem and postmor-
tem radiographs can be explained by age and time elapsed between radiographs.

KEYWORDS: Forensic anthropology; personal identification; RADid; paranasal sinuses

aDes Moines University, Anatomy, West Des Moines, IA, USA
*Correspondence to: Lauren Nicole Butaric, Des Moines University, 

Anatomy, 8025 Grand Avenue, West Des Moines, IA 50266, USA 
E- mail: lauren . butaric@dmu . edu.

Lauren Nicole Butaric (ORCid: 0000-0003-3743-2408)
Heather Marie Garvin (ORCid: 0000-0002-9787-4366)

This research was funded by National Institute of Justice, grant 
number 2020-75-CX-0013.

Received 26 June 2023; Revised 18 August 2023; Accepted 11 
September 2023

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2 Frontal Sinus Growth

FIGURE 1—Histogram illustrating number of radiographs distributed 
across age in years for males and females.

most commonly utilized and earliest proposed method for 
sinus identification is visual assessment, where investigators 
visually compare antemortem and postmortem radiographic 
images of frontal sinuses and determine whether they mor-
phologically match either with side- by- side comparisons or 
via superimposition (e.g., Atkins & Potsaid 1978; Culbert & 
Law 1927; Hashim et al. 2015; Jablonski & Shum 1989; 
Kullman et al. 1990; Marlin et al. 1991; Murphy & Gantner 
1982; Nambiar et al. 1999; Owsley 1993; Quatrehomme 
et al. 1996; Schuller 1921; Ubelaker 1984). However, due to 
increasing concerns for more statistically validated and 
rigorous techniques (Christensen 2004; National Research 
Council 2009), individuals have questioned whether visual 
assessment is too subjective (see Christensen 2005; Chris-
tensen & Hatch 2018). Because of this, more statistically 
objective and quantitative methods of radiographic frontal 
sinus comparisons have been developed utilizing metrics, 
coding of qualitative traits, and/or sinus outline analyses 
(e.g., Cameriere et al. 2005; Christensen 2004, 2005; Cox 
et al. 2009; Reichs & Dorion 1992; Riberio 2000; Soares 
et al. 2016; Tatlisumak et al. 2007; Uthman et al. 2010; also 
see Pereira et al. 2021 for a systematic review of methods). 
Regardless of method, frontal sinus identification studies are 
often limited to adult samples or compare duplicated post-
mortem radiographs thereby only simulating an antemortem- 
postmortem comparison. Although postmortem radiographs 
may be retaken in such comparisons to incorporate error 
from small deviations in radiographic orientation, if skeletal 
remains are utilized it eliminates any challenges with the 
superimposition of soft tissue structures. Additionally, these 
study methods overlook any potential temporal (i.e., age- 
related) changes in sinus morphology, particularly during 
the subadult period (see Kirk et al. 2002). Thus, one area of 
concern for the use of the frontal sinus in identification 
relates to patterns of growth and development of the frontal 
sinus, as well as stability of sinus morphology throughout 

one’s life. However, little is known regarding frontal sinus 
growth and development in general, and studies assessing 
sinus ontogeny are often contradictory.

Several studies attempt to assess ages of appearance and 
growth cessation of the frontal sinus. During fetal develop-
ment, the frontal recess (which will later become the frontal 
sinus) emerges as an outpouching from the nasal capsule 
either directly or indirectly via ethmoidal air cells (Kasper 
1961; Scheffer 1916; Weiglein 1999). However, most of the 
growth and development of the frontal sinus occurs postna-
tally. Since it is not well- developed at birth, visualizing this 
sinus radiographically is difficult at young ages. While 
reported to appear radiographically as young as the age of 
two (Davis 1914; Kirk et al. 2002; Maresh 1940; Park et al. 
2010; Quatrehomme et al. 1996; Weiglein et al. 1992; Yoshino 
et al. 1987), it is typically not radiographically visible until 
6– 8yoa (Dolan 1982; Duque & Casiano 2005; Enlow & Hans 
1996; Scuderi et al. 1993; Tatlisumak et al. 2007, 2008). 
Around this time, the frontal sinus usually expands superi-
orly above the orbital borders and is more easily distinguished 
from the ethmoidal air cells, which tend to obscure smaller 
frontal sinuses in radiographs. The linear dimensions, over-
all shape, and complexity of the frontal sinus continues to 
increase with age into early adulthood, with most sinus 
growth occurring during puberty (Brown et al.1984; Butaric 
et al. 2022a; Fatu et al. 2006; Gagliardi et al. 2004; Quatre-
homme et al. 1996; Sardi et al. 2018).

The age at which the frontal sinus reaches its adult size 
and shape is also still largely unknown. Generally, terminal 
development of the frontal sinuses has been suggested to 
occur by 18– 20yoa (Brown et al. 1984; Butaric et al. 2022a; 
Fatu et al. 2006; Schuller 1921; Marek et al. 1983; Prossinger 
2001; Rennie et al. 2017; Sardi et al. 2018; Spaeth et al. 1997; 
Yun et al. 2011). Studies on sinus size (e.g., sinus volume, area, 
or linear dimensions) indicate that while the sinuses tend 
to appear earlier in males (Brown et al. 1984; Gagliardi et al. 
2004), females tend to reach their adult state earlier (Brown 
et al. 1984; Gagliardi et al. 2004; Prossinger 2001; Sardi et al. 
2018). Finally, some studies suggest there may be additional 
changes that occur later in life, with conflicting accounts of 
sinuses either enlarging (Fatu et al. 2006; McLaughlin et al. 
2001; Tatlismuak et al. 2017) or decreasing in size during 
senescence (e.g., Akhlagi et al. 2016; Emirzeoglu et al. 2007).

One of the primary issues in establishing when the fron-
tal sinus attains adult maturity is that most ontogenetic publi-
cations are cross- sectional (e.g., Bargouth et al. 2002; Buyuk 
et al. 2017; Fatu et al. 2006; Mahmood et al. 2016; Moore & 
Ross 2017; Park et al. 2010; Patil & Revankar 2013; Prossinger 
2004; Sardi et al. 2018; Spaeth et al. 1997; Tehranchi et al. 
2017; Weiglein et al. 1992; Yun et al. 2011), limiting the 
understanding of individual growth patterns. When longitu-
dinal studies have been conducted, they are largely focused 
on lateral radiographs (e.g., Brown et al. 1984; Gagliardi et al. 
2004; Nathani et al. 2016; Ruf & Pancherz 1996a,1996b; Shah 

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Abdulrazak et al. 3

TABLE 1—Sample composition of number of radiographs and 
individuals based on collections utilized in the current study,  

not including individuals with bilateral aplasia.

AAOF Collection Radiographs (n) Individuals (n)

Bolton Brush 308 (136F/ 172M) 30 (14F / 16M)
Burlington 620 (300F / 320M) 63 (28F / 35M)
Forsyth Twins 60 (31F / 29M) 7 (3F / 4M)
Mathews 31 (24M / 7F) 4 (1F / 3M)
Oregon 481 (284F / 197M) 37 (20F / 17M)

TOTALS 1500 (775F/ 725M) 141 (66F / 75M)

et al. 2003), which do not capture the full scope of sinus visi-
ble in frontal views (e.g., arcades, septa, asymmetry). More 
recently, Butaric et al. (2022b) analyzed a longitudinal sample 
of frontal radiographs to assess frontal sinus shape based on 
outlines. Using averaged Loess trendlines, these authors 
found that on average sinus shape stabilized around 14– 16yoa 
for females, with male shape stabilizing around 18– 20yoa. 
While informative, that study was limited to closed outline 
shape and could not capture certain identifiable features, such 
as varying presentation of intra-  and inter- sinus septa or 
asymmetry in lobal presence. Thus, the age at which frontal 
sinuses reach their maximum number of arcades and septa— 
features that are arguably the most indicative for personal 
identifications— remains relatively unknown.

Purpose of current study

While visual, metric, coding, and outline identification meth-
ods vary in specific protocols and sinus traits utilized, most 
methods rely on consistent sinus traits in antemortem and 
postmortem images and any developmental changes in sinus 
morphology— particularly the number of arcades and septa 
and/or arcade/cell expansions— could affect match accuracy. 
However, as mentioned above, age- related changes to these 
traits during ontogeny and into adulthood are not well- 
documented, and there are no reported standards for mini-
mum decedent ages for frontal sinus identification nor 
acceptable time intervals between antemortem and postmor-
tem radiographs. As such, the current study aims to assess 
age- related changes in several frontal sinus traits to better 
understand potential method limitations in medicolegal fron-
tal sinus identification. Unlike previous studies, this study 
utilizes a longitudinal (versus cross- sectional) sample of fron-
tal (versus lateral) radiographs. The aim was to longitudinally 
evaluate changes in frontal sinus traits relevant to coding, 
outline, and visual assessments, to specifically investigate the 
age at which these traits stabilized during growth and devel-
opment. The overall purpose is to determine the minimum 
ages at which traits, regardless of method utilized, can be 
applied reliably for radiographic identifications.

Materials and Methods

Sample

A longitudinal sample of radiographs available online as part 
of the American Association of Orthodontists Foundation 
(AAOF) Legacy Growth Collection were used in this study 
(https:// www . aaoflegacycollection . org / aaof). The Legacy 
Collection includes a total of nine ontogenetic radiographic 
collections developed by multiple US and Canadian univer-
sities between 1930 and 1985 for growth and development 
studies (for reviews, see Al- Jewair et al. 2018; Baumrind & 

Curry 2015). Most of the growth studies attempted to collect 
radiographs either annually or semi- annually from study 
participants from around 3– 5yoa into early adulthood. To 
maximum sample sizes, our study used radiographs from the 
specific Burlington, Bolton Brush, Oregon, Mathews, and 
Forsyth collections as they had available frontal radiographs 
with widest age ranges (Table 1). Radiographs in these col-
lections of males and females were visually assessed, and 
images of poor quality (e.g., over exposed) that obscured 
sinus traits (see trait descriptions below) were excluded. Indi-
viduals who did not possess at least one image 18 years or 
older and/or those with less than four usable radiographs 
were also excluded. These inclusion parameters ensured that 
adult sinus morphology was captured for each individual and 
that age- related sinus changes could be documented over a 
series of radiographs for each individual, while maintaining 
acceptable sample sizes. These protocols resulted in 146 
available individuals; however, among this sample five indi-
viduals (2M, 3F; 3.4% of the sample) exhibited bilateral apla-
sia and, thus, were not included in further analyses. Those 
displaying unilateral presence of the sinus (i.e., aplasia of 
either the right or left lobe) were included in the study and 
represented 3.4% of the total sample (right- side unilateral 
aplasia: 2F; left- side unilateral aplasia: 1F/2M). This final 
sample, counting those with unilateral aplasia, includes 1500 
radiographs from 141 individuals (66F/75M) ranging from 
three to 56yoa (see Fig. 1 for distribution of ages). In terms of 
number of images per individual, the median number of 
radiographs per individual was 10; average number of radio-
graphs was 10.7; minimum number of radiographs was four; 
and maximum number of radiographs was 24. In terms of 
oldest radiographic age available, 31 (13F/18M) individuals 
had an oldest age at 18; 30 individuals (16F/14M) at 19yoa; 
51 individuals (20F/31M) at 20yoa; and 28 individuals 
(16F/12M) at 21yoa or older.

Trait collection

The radiographs were opened in ImageJ (Schneider et al. 
2012), enlarged to 3000 pixels, and brightness and contrast 
were manually adjusted to best visualize the frontal sinus. 
For each image, a total of nine traits (see Fig. 2 and Table 2) 
were assessed following trait definitions presented in 

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4 Frontal Sinus Growth

previously published coding methods: Cameriere et al. (2005), 
Tatlisumak et al. (2007), and Yoshino et al. (1987). Note, while 
the coding methods include metric dimensions, due to the 
potential introduction of additional error (see Cameriere 
et al. 2005; Tatlisumak et al. 2007) and the radiographs not 
possessing an accurate scale, metric dimensions were not 

included in the current study. However, a new trait, “lateral 
extension of the sinus,” was included to provide a scale- free 
measurement of relative sinus breadth (see Table 2)

The traits were collected without images being blinded; 
in other words, consecutive years of an individual could be 
viewed simultaneously to better ensure the accuracy of the 

FIGURE 2—Frontal radiograph with collected traits demarcated on the right (FSR) and left (FSL) frontal 
sinus lobes. Note arcades are defined along the outer margins of the sinus and do not include internal air 
cells. See Table 2 for additional trait definitions; SOB, supraorbital.

TABLE 2—Descriptions and coding for sinus traits utilized in this study. Also see Figure 2.

Name of trait* Description Code Recorded

Presence (L/R) Absolute “presence” or “absence” of lobe Absent/Present

Presence above supraorbital 
line (L/R)

“presence” or “absence” of lobe extension above the 
supraorbital line

Absent/Present

Taller lobe Whether the right or left lobe extends farther superiorly 
(or are equal)

Right/Left/Equal

Lateral extension (L/R) Lateral extension of lobe relative to orbit 0: does not reach orbital medial border; .5: at orbit medial 
border; 1: past medial border, but does not reach orbit 
midline; 1.5: at orbit midline; 2: past orbit midline

Lobes separated Whether right and left lobes are joined at the inter- sinus 
septum or are separated (i.e., discontinuous)

Separated/Joined

Arcades (L/R) Number of arcades or scallops on the lobe Count (e.g.,1,2,3,); if unclear a possible range was 
provided with minimum used in analyses

Intra- sinus complete (L/R) Number of intra- sinus septa that continue to the lobal 
borders, thereby splitting the sinus into separate 
compartments

Count (e.g.,1,2,3)

Intra- sinus partial (L/R) Number of partial or incomplete intra- sinus septa  
(do not reach lobe border)

Count (e.g.,1,2,3)

Supraorbital cells (L/R) Number of air cells located just above the orbits; may 
appear darker in color

Count (e.g., 0,1,2,3)

* (L/R) indicates that the trait was scored separately for the left and right lobes.

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Abdulrazak et al. 5

trait identification and age progression, as well as potential 
effects of differential orientation, given that the aim of the 
paper was to assess the anatomical stabilization of these 
traits not to test method reliability. Frontal sinus presence/
absence was collected in two ways: first considering the 
frontal sinus as any pneumatization regardless of whether it 
reached the supraorbital line, and secondly considering 
sinuses present only when they extended above the supraor-
bital line. Owing to the issue of superimposition, whereby 
ethmoidal air cells may obscure the frontal sinus, several 
studies advocate the use of the supraorbital line (Chris-
tensen, 2004, 2005; Cox et al. 2009; Hashim et al. 2015; 
Hanson & Owsley 1980). In such cases, the frontal sinus is 
only deemed present if it expands superiorly above a line 
drawn across the upper borders of the orbits. While this 
method ensures one is capturing the frontal sinus (as com-
pared to ethmoidal cells), it is not necessarily biologically 
accurate (see Butaric et al. 2020). Since a potential air space 
could be tracked through older ages, we were able to discern 
ethmoidal air cells from frontal sinus lobes. As such, we 
opted to collect sinus presence with and without the supra-
orbital line so that our sinus appearance results would be 
comparable across a wider range of studies.

Several structures were difficult to initially assess, with 
vague definitions provided in the original literature; thus, 
more precise definitions were standardized during a trial run. 
For example, the inter- sinus septum presented ambiguously 
several times, as it seemingly branched out in multiple direc-
tions. In such cases, only one inter- sinus septum path was 
selected based on being closer to the midline and/or based on 
the origin that was displayed in earlier radiographs for that 
individual. Additionally, the number of arcades was also 
sometimes difficult to discern owing to radiographic quality, 
especially when utilizing the zoom feature for closer inspec-
tion. Sometimes small, subtle indentations were visible and 
appeared to create smaller arcades. Therefore, the range of 
possible interpretations of arcade number were documented; 
for statistical analyses, the minimum counts were used. 
Arcades were counted along the outer contours (i.e., outlines) 
of the right and left lobes separately, using the inter- sinus sep-
tum to differentiate between lobes. Any arcades that did not 
extend to the outer contour of the sinus or did not extend to 
the superior margins were not counted.

Presence/absence, count, and coded data for the traits 
across the 1500 radiographs were recorded. For each indi-
vidual, the trait age- of- stabilization was recorded by identi-
fying the year at which each coded trait became consistent 
throughout the later ages. For example, if an individual’s age 
range was 10– 20 years and they presented with two arcades 
at 10yoa but then increased to five arcades at 13yoa, and this 
number remained consistent (five) until 20yoa, it was recorded 
that their arcade count stabilized at 13 years. All subsequent 
analyses were carried out on these age- of- stabilization data. 

Note that in the Legacy Collection, ages are given in year 
and months at each radiograph; for the purpose of this study, 
age was recorded as the given year regardless of month 
(both “16 years 1 month” and “16 years 11 months” were 
both recorded as 16yoa), following Butaric et al. (2022b).

For most individuals, several years had occurred 
between available radiographs. Thus, for each stabilization 
year recorded, the number of years since the previous image 
was also collected given that the trait may have stabilized at 
sometime between those two images. Continuing with the 
previous individual example, if their arcade count stabilized 
at 13yoa and their immediate previous radiograph was at 
10yoa, then three years was recorded as their “years since 
last.” For individuals who had a trait stabilize within the 
same year (example, age of stabilization was 13 years 8 
months of age, with last known radiograph 13 years 3 
months), 0.5 was used for the years since last value. Finally, 
it is important to note that for sinus traits across several indi-
viduals no previous ages were accounted for (i.e., the trait 
appeared stabilized at the first available radiograph); in such 
cases, the years since last value was recorded as “not appli-
cable” to prevent the assumption of that individual stabiliz-
ing at that particular age.

To account for discrepancies associated with these tem-
poral gaps in radiographs, analyses were conducted on two 
separate samples: (1) the complete sample (referred to as 
“Full Sample”), providing larger sample sizes and greater 
sinus variation, regardless of the temporal gaps or missing 
images, and (2) a subsample that included only those indi-
viduals in which stabilization of the trait occurred within 
the radiographic sample with no more than two “years since 
last” (referred to as “2- Year Transitional Sample”). Although 
the 2- Year Transitional Sample presents a more limited sam-
ple size depending on the sinus traits, its use should elimi-
nate potential bias from including individuals where the 
transition- year was not directly observed.

All data were collected on right and left sides separately. 
However, preliminary analyses indicated no significant differ-
ences in the timing of appearance and/or stabilization of right 
versus left sides for paired traits. Thus, to get an overall idea of 
trait stabilization, the maximum age- of- stabilization between 
the left and right sides of each individual was utilized to repre-
sent the time at which a trait fully stabilized in the overall 
sinus. For example, if an individual had left lobe presence sta-
bilize at age 10 and right lobe stabilize at age 12, the final age 
of stabilization for lobe presence was recorded as 12yoa.

Statistical analyses

Descriptive statistics were used to analyze the age- at- 
stabilization data. For each trait the average, minimum, max-
imum, standard deviation (SD), count, and approximated 
95% confidence interval (+/−  2SD) were calculated for each 

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6 Frontal Sinus Growth

trait. These data were also plotted to visually assess the 
ages of stabilization across the two samples, as well as sex 
differences. Preliminary analyses suggested that the data 
largely followed a normal distribution, and thus parametric 
statistical analyses were performed. Two- tailed student 
t- tests with Bonferroni corrections were conducted to test 
for sex differences in ages of stabilization. All statistical 
analyses were conducted in SPSS version 28.0 (IBM Corp, 
2021).

Results

Initial investigations into the data revealed similar trends 
for age- of- stabilization along all traits between the Full 
Sample and the 2- Year Transitional Sample. Owing to these 
similarities and to streamline the results, only the results of 
the Full Sample analyses are presented below. Results for 
the 2- Year Transitional Sample are provided in the supple-
mentary materials (see Fig. S1 and Table S1).

Table 3 presents the Full Sample descriptive statis-
tics for trait ages of stabilization, with sexes pooled and 
separated. Age- of- stabilization averages are illustrated in 

Figure 3. Trends for the pooled sample will be discussed 
first, followed by analyses of sex- based differences.

As expected, sinus presence/absence is the first trait to 
stabilize (pooled average: 10.03yoa), with frontal sinus pres-
ence above the supraorbital line occurring a few years later 
(pooled average: 12.04yoa). Arcade count was the last trait to 
stabilize (pooled average: 15.02yoa). For the remaining traits, 
stabilization occurred on average around 11– 15yoa. Beyond 
these average values, the large range encompassed by the 
two standard deviations and min/max values indicate a high 
degree of individual variability in ages- of- stabilization. For 
example, the two standard deviation range for arcade count 
stabilization was 9– 21 years, with a minimum of 6 years and 
maximum of 21 years.

Sex differences in ages of trait stabilization

Females reached ages of stabilization on average approxi-
mately one to two years earlier than males for most sinus 
traits. Similar to the trends discussed above, sinus presence 
among females was the first trait to stabilize with an aver-
age of 9.52 years of any presence and 11.23 years for pres-
ence above the supraorbital line. Sinus presence was also 

TABLE 3—Descriptive statistics for the ages of stabilization (in years) of frontal sinus traits for the Full Sample by pooled- sex, males, and females. 
Minimum (min), maximum (max), average (avg) ages, as well as standard deviations (SD) are provided. The p- values for the student  

t- tests of sex differences also provided. See Table 2 for definitions.

Variable Sex n Min Age Max Age Avg Age SD Neg 2SD Pos 2SD Test Stat p- value

Presence Pooled 141 4 16 10.028 3.207 3.614 16.442
F 66 4 16  9.515 3.034 3.446 15.584 − 1.797 .075
M 75 4 16 10.480 3.306 3.868 17.092

Presence above 
supraorbital line

Pooled 136 5 20 12.044 3.466 5.112 18.976

F 64 5 20 11.234 3.250 4.734 17.735 − 2.624 .010
M 72 5 20 12.764 3.515 5.735 19.793

Taller lobe Pooled 131 4 20 11.053 3.617 3.820 18.287
F 63 5 19 10.429 3.495 3.438 17.419 − 1.923 .028
M 68 4 20 11.632 3.657 4.319 18.945

Lateral extension Pooled 140 4 24 13.836 3.351 7.133 20.539
F 65 4 19 12.769 3.111 6.547 18.992 − 3.658 <.001*
M 75 6 24 14.760 3.296 8.169 21.351

Lobes separated Pooled 127 4 20 10.827 3.434 3.958 17.696
F 58 4 19 10.086 3.363 3.361 16.812 − 2.264 .025
M 69 5 20 11.449 3.394 4.662 18.236

Arcades Pooled 129 6 21 15.0155 3.0413 8.9328 21.0982
F 61 6 21 14.377 3.302 7.772 20.982 − 2.27 .025
M 68 6 20 15.588 2.684 10.221 20.955

Intra- sinus septum: 
complete

Pooled 64 4 20 12.703 3.201 6.302 19.104

F 26 4 16 11.077 3.273 4.531 17.623 − 3.682 <.001*
M 38 9 20 13.816 2.660 8.497 19.135

Intra- sinus septum: 
partial

Pooled 69 9 26 14.884 3.003 8.879 20.889

F 30 9 21 13.933 2.900 8.134 19.733 − 2.385 .020
M 39 9 26 15.615 2.908 9.800 21.430
Pooled 57 5 19 11.561 2.994 5.573 17.550

Supraorbital cells F 26 5 16 10.692 2.768 5.156 16.228 − 2.065 .044
M 31 5 19 12.290 3.024 6.242 18.339

Bold p- values indicate significance at .05; * indicates significance for Bonferroni- corrected p- values at .005.

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Abdulrazak et al. 7

the first to stabilize in males, at an average of 10.48 years 
and 12.76 years above the supraorbital line. Among males 
and females, the minimum age of appearance for the frontal 
sinus was the same: 4yoa without the supraorbital line, and 
5yoa when considering the supraorbital line.

Similar to the pooled sample, arcade count was also the 
last sinus trait to stabilize for each sex. On average, female 
arcades stabilized around 14.38 years, with males around 
15.59 years. Both sexes displayed minimum ages of stabi-
lization as low as 6 years, with maximum ages of arcade 
stabilization being 20 and 21 for males and females, respec-
tively. Student t- tests revealed significant differences between 
the sexes in the age of stabilization when considering unad-
justed p- values (i.e., p < .05). However, when considering 
Bonferroni corrections (p < .005), significant sex- based 

differences were only found for two traits: complete intra- 
sinus septa count (p < .001) and lateral extension of the 
sinus relative to the orbit (p < .001).

Discussion

Overall, our results demonstrate that frontal sinus traits sta-
bilize on average between 10 and 15yoa (among pooled 
sexes), with sinus presence being the first to stabilize and 
arcade counts the last to stabilize (regardless of sex). 
Although not directly measured in the current study, this 
finding may suggest that frontal sinus growth in size is 
closely integrated with arcade count; in effect, as the frontal 
sinus grows, arcade numbers increase as well. This trend 

FIGURE 3—Distributions of the ages of stabilization of frontal sinus traits from the full sample for  
averages and +/− two standard deviations among the male (blue triangles), female (red circles), and  
pooled (grey squares) sub- samples. Traits organized by age of appearance. See Table 2 for trait definitions. 
SOB, supraorbital.

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8 Frontal Sinus Growth

can be visualized in the exemplar individuals provided in 
Figures 4 and 5, which showcase an individual with large/
complex sinuses and small/simpler sinuses, respectively. The 
later timing of arcade count stabilization could potentially 
suggest a correlation with sinus size, where larger sinuses 
are more likely to be more complex compared to smaller 
sinuses (also see Smith et al. 2010). Size traits, however, 
were unable to be included in the present study and thus the 
relationship was not directly tested. With the lack of sinus 
size data, it is also important to highlight that the stabiliza-
tion of the sinus traits included in this study does not mean 
that sinus size stabilized at those times. An individual may 
have stabilized in all the traits tested, but then still have 
sinus expansion without altering number of arcades and 
septa (also see Butaric et al. 2022a).

Overall, the finding of sinus stabilization occurring 
between 10 and 15yoa, on average, aligns well with previous 
studies reporting full maturation of the frontal sinus being 
attained by mid- to- late teenage years (Brown et al. 1984; 
Butaric et al. 2022a; Gagliardi et al. 2004; Sardi et al. 2018; 
Spaeth et al. 1997). This age of stabilization for traits also 
corresponds with the general age of puberty, during which 
many other skeletal elements reach maturity (Buyuk et al. 
2018; Mahmood et al. 2016). Similarly, 95% of cranial growth 
and development is reported to cease around 14– 18yoa (Björk 
2007; Farkas et al. 1992; Humphrey 1998). Along these lines, 

previous studies also suggest pneumatization of the frontal 
sinus may correlate with cranial growth and development, 
particularly with anterior brain expansion (Enlow 1975:120; 
Shapiro & Chorr 1980; Takahashi 1984; but see Sardi et al. 
2018).

The current study also found sex differences in stabiliza-
tion trends, with females generally stabilizing approximately 
one- to- two years prior to males for individual sinus traits (see 
Table 3, Fig. 3). Overall, female traits stabilized at 9– 14yoa on 
average compared to 10– 15yoa for males. The earlier presence 
of female sinuses contradicts two previous studies (Brown 
et al.1984; Gagliardi et al. 2004), which, while also longitudi-
nal, utilized lateral radiographs. Theoretically, the difference 
in orientation should not affect sinus presence; however, lat-
eral radiographs would capture the first appearance of either 
the left or right lobe (with an inability to distinguish which one 
or the age at which both lobes became present). Our study 
assessed sinus presence age- of- stabilization across both lobes, 
which would be of more forensic relevance as it represents the 
final, stabilized state of sinus presence for that individual (i.e., 
the age at which you would not expect any further changes 
in sinus presence). If we were to instead look at the first 
appearance of either sinus lobe, we still see that females (on 
average) first present any indication of a sinus at 8.77yoa, again 
earlier than males at 9.48yoa. However, the sex differences in 
the stabilization of sinus presence did not maintain statistical 

FIGURE 4—Visual representation of sinus growth of a relatively large and complex sinus (Burlington 152M).

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Abdulrazak et al. 9

significance once a Bonferroni correction was applied; thus, 
these literature discrepancies in sinus presence between males 
and females may be a consequence of random sampling and/or 
the specific individuals included within each study. Each study 
also utilized different population groups, and it is unclear 
whether there would be population differences in sinus trait 
stabilization.

The remaining sinus traits captured in the current study 
follow similar patterns presented in previous studies focus-
ing on linear dimensions and overall size/shape. Brown 
et al. (1984) found vertical height of adult sinus was obtained 
at 14.95yoa for females and 17.51yoa for males (on average). 
When examining linear dimensions, Spaeth et al. (1997) 
reported that sinus growth ceases at 15– 16yoa for females 
and 18yoa for males. Sardi et al. (2018) identified sinus 
stabilization for volumetric and linear data at 14.6yoa for 
females and 20yoa for males. Most recently, Butaric et al. 
(2022b) indicated frontal sinus shape (as determined by out-
lines) established around 14– 16yoa for females versus 18– 
20yoa in males. Thus, the results of the current study and 
previous studies follow well- established trends in skeletal 
maturity throughout the skeleton, with females tending to 
reach maturity (in this case frontal sinus stabilization) earlier 
than males (Bulygina et al. 2006; Eveleth & Tanner 1990; 
Roche 1968; Nikitovic & Bogin 2014; Wells 2007). Despite 
these observable trends, Bonferroni adjusted p- values, how-
ever, did not find statistical sex- based differences in ages- of- 
stabilization for most traits.

The lack of statistical significance may in part be due to 
the high degree of individual variation observed in ages of 
stabilization throughout the sample. This was true for all 
traits as demonstrated by the large min/max ranges and 
95% confidence intervals. The minimum- to- maximum range 
spanned most of the sample age range for many of the traits 
(e.g., stabilization of lateral sinus extension ranged from 4 to 
24 years in the pooled- sex sample; see Table 3). It is unclear 
what individual- specific traits may influence the ages of sta-
bilization. Future studies could assess relationships with 
cranial size, sinus size, and sinus complexity or direct rela-
tionships with other skeletal maturation traits. Overall, 
however, the results of this study do suggest that most sinus 
traits stabilize by the age of 21 years, with the two outliers 
being male partial intra- sinus septa (26 years maximum) 
and male sinus lateral extension (24 years maximum). 
Although the 95% confidence intervals indicate that sinus 
traits stabilize by 21yoa, it should be noted that the study 
sample only had 28 individuals with radiographs at 21yoa or 
older. Future studies could confirm this age limit with older 
individuals.

Forensic Implications

Given the amount of variation observed in frontal sinus trait 
stabilization and overall growth and development of the 
sinus, forensic practitioners should be cautious using frontal 
sinus identification in subadults, especially when years may 

FIGURE 5—Visual representation of sinus growth of smaller, simpler sinus (Burlington 865M).

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10 Frontal Sinus Growth

have elapsed between images. Although the average ages of 
stabilization spanned 9– 15yoa depending on the sinus trait 
that is being observed, the two standard deviation ranges 
extended to 21yoa for some traits. Based on these results and 
previous literature, medicolegal practitioners can expect 
sinus traits to likely remain constant after 21yoa. If a sinus 
radiographic comparison involves an antemortem radio-
graph from an individual’s late teens, it is possible that some 
traits may not have reached final stabilization and these 
explainable differences must be considered. With an ante-
mortem radiographic image from an individual 15yoa or 
earlier, changes in trait presence and counts should almost 
be expected, with the amount of change likely related to the 
time between that antemortem radiograph and postmortem 
radiograph. The data presented in this paper may be used as 
a guide to assess which specific traits would be expected to 
be stabilized at a given age range.

With this in mind, caution is particularly warranted for 
arcade counts, as well as complete and partial intra- sinus 
septa. During data collection, while only a few instances 
were noted, these structures did exhibit reversals (i.e., 
decreases in counts). For example, in six individuals arcade 
count was noted to increase during growth and development, 
and then decrease before increasing again as the sinus con-
tinued to pneumatize into the frontal bone. It is likely that 
most of these reversals are not biologically accurate, but 
instead are artifacts of poor radiographic quality or varying 
radiographic orientation. While individuals with true rever-
sals were few, they were observed (e.g., number of septa may 
have decreased as the sinus enlarged and arcades became 
joined). Forensic practitioners should be aware of this possi-
bility when working with subadult radiographs and also 
understand that radiographic quality and/or orientation could 
also cause “false” reversals or differences in lobe, septa, and 
arcade presence (see further discussion below).

Along with radiographic quality, scoring subjectivity 
can also introduce artificial variation. Sinus traits, such as 
supraorbital cells, are not well- defined in the literature and 
little guidance is given for scoring ambiguous traits. Previ-
ous literature suggests that arcades are defined when one 
arc changes direction (i.e., creates an indent in the sinus out-
line; Besana & Rogers 2010), which seems straight forward 
in theory. However, while some arcades exhibited visible 
indentations, there were multiple occurrences where only 
faint indentations were observed, and it was unclear whether 
it should be counted as a separate arcade. Lower radio-
graphic quality and/or presence of soft tissue structures can 
further exacerbate this issue by obscuring clear borders/
septa. For example, difficulty in assessing arcade counts 
could have biased results and possibly contribute to the later 
ages of stabilization of arcades. A post hoc assessment of 
radiographic images with late arcade count stabilization, 
however, supports a biological basis to the older timeline in 

arcade count stabilization. Thus, while subjectivity may play a 
role, the variation in ages of stabilization observed is likely not 
the result of a few outliers. This is further supported by the 
similarity between minimum/maximum ages and two stan-
dard deviations.

Some traits are also interrelated; a misinterpretation of 
a complete septum as a partial septum affects both the par-
tial and complete septa counts. There were also multiple 
instances where the inter- sinus septum would branch off in 
several directions, questioning what constituted an inter- 
sinus septum versus a complete septum within a lobe. A mis-
identification of a complete septum as the inter- sinus septum 
would affect left and right lobe traits.

While many of these issues were mitigated in the present 
study by assessing consecutive ages to confirm traits, they 
could have an impact on forensic radiographic comparisons 
that have limited number of images. The greatest impact 
would be on sinus coding methods (e.g., Cameriere et al. 
2005; Tatlisumak et al. 2007; Yoshino et al. 1987). These 
methods score the various traits and then concatenate them 
into a chain code. A single difference in arcade counts or 
complete/partial septa results in a completely different chain 
code, which theoretically could result in either a misidentifi-
cation or more likely erroneous exclusion of an identity if 
there was strict use of the coding method. Likewise, age- 
related changes would result in different chain codes and 
identification issues.

Outline- based frontal sinus identification methods 
(e.g., Christensen 2004, 2005; Cox et al. 2009) may be more 
protected against quality-  and subjectivity- related trait 
identification issues; although, interpretations of arcades 
and indentations could result in slight differences in outline 
tracings between antemortem and postmortem images. Age- 
related changes in arcade numbers, lateral and vertical sinus 
extensions, however, would also impact sinus outlines. Thus, 
outline methods have to be cognizant of potential growth 
and development changes in these traits. Furthermore, given 
that outline methods typically use a supraorbital line, place-
ment of that line along with head orientation during radiog-
raphy, could potentially include/exclude features near the 
line, thereby changing the outline contours (see Butaric et al. 
2022b). Indeed, slight differences in orientation are not nec-
essarily limited to outline- based methods. Slight variations 
in orientation may affect whether more inferiorly located 
sinus traits fall above or below the supraorbital line place-
ment, and consequently whether they are included in counts. 
The ability to view consecutive radiographs of an individual 
allowed informed decisions about whether presence/absence 
of traits was an anatomical change or due to cranial orienta-
tions. Furthermore, only those radiographs in which cranial 
position appeared consistent were included in this study and 
the supraorbital boundary was only utilized for trait presence/ 
absence, not for counts or other variables. Still, forensic 

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Abdulrazak et al. 11

practitioners should be aware that slight variations in orien-
tations may be another source of discrepancy when consider-
ing a potential match or non- match— particularly among 
smaller sinuses or arcades nearer the supraorbital borders 
(also see Butaric et al. 2022b).

None of the more objective frontal sinus coding or out-
line methods can adequately account for or interpret poten-
tial age- related changes (or ambiguous trait scores), as these 
methods provide binary results (match or no match). Given 
these concerns, visual assessment of frontal sinus radio-
graphic comparisons may be the most accurate, particularly 
when subadult antemortem radiographs are involved. The 
subjectivity of the visual assessment, a characteristic typi-
cally avoided in methods, can be a major benefit when radio-
graphic assessments require interpretations of whether the 
observed differences in the antemortem and postmortem 
radiographs may be explained by age or radiographic qual-
ity. The frontal sinus age- related results presented in this 
study will be a useful tool in these interpretations, assisting 
practitioners in differentiating what changes should and 
should not be expected during growth and development.

Limitations inherent to the current study

While the present study is the first to assess the growth and 
development of specific forensically- relevant frontal sinus 
traits in longitudinal frontal radiographs, and thus contrib-
utes novel information, the study does have several limita-
tions. First, radiographs were not available at every age for 
every individual in this study, causing temporal gaps in the 
data. Thus, ages of stabilization recorded may not be pre-
cise. However, this was partially accounted for by generat-
ing a 2- Year Transitional Sample, which returned results 
similar to the Full Sample data set (see supplementary mate-
rials). Further, as discussed above, this study had a limited 
sample of radiographs beyond 21yoa. Owing to this, we have 
limited insight into potential age- related changes past this 
age. Additional longitudinal sinus studies are necessary to 
assess any changes in adult sinus morphology. However, 
given modern- day radiation and ethical concerns, obtaining 
longitudinal samples may be challenging.

The current study was also limited in terms of popula-
tion diversity. Individuals part of the AAOF Legacy Collec-
tion are overwhelming of European ancestry (Al- Jewair 
et al. 2018). As global variation in frontal sinus size and 
shape is widely reported (Balzeau et al. 2022; Buck et al. 
2019; Hanson & Owsley 1980; Noback et al. 2016; Rennie 
et al. 2017; Yoshino et al. 1987), the results of this study 
may not be directly applicable to other populations. How-
ever, it is encouraging that the current results align with 
previous subadult studies from diverse regions, including 
Aboriginal Australian (First National Australians) measured 
by Gagliardi et al. (2004) and Argentinians measured by 

Sardi et al. (2018). Still, future studies should strive to fea-
ture diverse groups to understand population differences in 
frontal sinus development. Although, larger and more diverse 
samples are always beneficial, for similar reasons discussed 
above, longitudinal radiographic samples, particularly those 
including subadults without pathological conditions or 
trauma, will be difficult to obtain.

Conclusion

Despite the limitations discussed above, the current study 
is one of the first to investigate frontal sinus trait ages of 
stabilization utilizing a longitudinal sample of subadult 
frontal (i.e., AP/PA) radiographs. Our results indicate that, 
on average, the ages of stabilization for frontal sinus traits 
occur between the ages of 10 and 15 years, with frontal 
sinus presence being the earliest (around 10 years) and 
arcade count being the latest at 15yoa. While females gen-
erally reached stabilization ages one to two years earlier 
than males, sex differences were generally not statistically 
significant. Age- of- stabilization standard deviations were 
around three years, indicating that that there is an approx-
imate 12- year range during which trait stabilization occurs, 
depending on the individual. This high degree of variation 
in trait stabilization makes predicting age- related changes 
difficult. By 21yoa, however, most individuals displayed 
stabilization in sinus traits, suggesting that little develop-
mental change should be expected with later- aged post-
mortem radiographs. Given that the age- of- stabilization 
95% confidence intervals extend to 19, 20, or 21yoa for 
various sinus variables, it appears that some individuals 
may continue to undergo slight sinus changes during this 
timeframe. The majority of these changes were limited to 
visually minor changes, such as addition of a small arcade, 
appearance of a full septum to replace a partial septum, 
extension of one sinus to just above the supraorbital line, 
etc. Although minor, such changes still need to be consid-
ered during radiographic identifications and could propose 
problems for coding methods. When conducting a radio-
graphic comparison that involves a subadult antemor-
tem image (e.g., <18yoa), the practitioner must interpret 
whether the differences between antemortem and post-
mortem radiographs can be explained by age and time 
between radiographs. This article presents the data to sup-
port such interpretations. Care must be taken in such cases 
to not use age to erroneously explain inter- individual dif-
ferences in sinus morphology. False positive or false nega-
tive identifications can have dire consequences to the family 
of the deceased, as well as potentially severe legal implica-
tions. Owing to these consequences, visual identification 
methods are recommended over more objective sinus com-
parison methods, as even the slightest variation in a single 

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12 Frontal Sinus Growth

trait (such as that due to growth/development, poor quality 
radiographs, varying orientations, and/or placement of a 
supraorbital line) could affect match versus no- match results 
reached by outline and coding methods. The practitioner, on 
the other hand, can critically assess possible explanations 
for discrepancies.

Acknowledgements

The authors would like to thank the AAOF Legacy collec-
tion’s curators and supporters for providing collections 
online, as well as the reviewers whose comments greatly 
enhanced this manuscript. This research was supported in 
part by Award No. 2020- 75- CX- 0013 granted by the National 
Institute of Justice, Office of Justice Programs, U.S. Depart-
ment of Justice. The opinions, findings, and conclusions or 
recommendations expressed in this publication/program/
exhibition are those of the author(s) and do not necessarily 
reflect those of the Department of Justice.

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Supplemental materials

TABLE S1—Descriptive statistics for the ages of stabilization (in years) of frontal sinus traits for the Full Sample by pooled- sex, males, and females. 
Minimum (min), maximum (max), average (avg) ages, as well as standard deviations (SD) are provided. The p- values for the student  

t- tests of sex differences also provided. See Table 2 for definitions.

Variable Sex n Min Age Max Age Avg Age SD Neg 2SD Pos 2SD Test Stat P- value

Presence Pooled 48 4 16 10.958 3.175 4.608 17.309
F 19 5 14 10.211 2.551 5.108 15.313 − 1.42 0.163
M 29 4 16 11.448 3.480 4.487 18.409

Presence above 
supraorbital line

Pooled 89 5 20 12.236 3.195 5.847 18.625

F 42 6 20 11.571 2.923 5.726 17.417 − 1.882 0.032
M 47 5 19 12.830 3.338 6.153 19.506

Taller lobe Pooled 50 5 18 12.420 3.375 5.670 19.170
F 23 5 18 11.739 3.414 4.911 18.567 − 1.327 0.191
M 27 6 18 13.000 3.293 6.413 19.587

Lateral extension Pooled 99 6 20 14.131 2.867 8.398 19.865
F 45 6 19 13.333 2.884 7.565 19.102 − 2.602 0.011
M 54 9 20 14.796 2.701 9.394 20.199

Lobes separated Pooled 54 5 19 11.574 3.172 5.230 17.918
F 23 5 16 11.000 2.939 5.123 16.878 − 1.149 0.256
M 31 6 19 12.000 3.317 5.367 18.633

Arcades Pooled 86 6 20 14.837 2.934 8.969 20.705
F 45 6 20 14.022 3.258 7.507 20.538 − 2.853 0.006
M 41 8 20 15.732 2.248 11.237 20.227

Intra- sinus septum: 
complete

Pooled 40 8 19 13.325 2.325 8.676 17.975

F 18 8 16 12.611 2.227 8.158 17.064 − 1.807 0.039
M 22 10 19 13.909 2.287 9.336 18.483

Intra- sinus septum: 
partial

Pooled 53 9 20 14.528 2.350 9.828 19.229

F 26 9 20 13.846 2.634 8.579 19.113 − 2.144 0.037
M 27 11 18 15.185 1.861 11.463 18.908

Supraorbital cells Pooled 30 7 19 12.533 2.649 7.236 17.831
F 13 8 16 12.077 2.565 6.948 17.206 − 0.821 0.419
M 17 7 19 12.882 2.736 7.411 18.354

Bold p- values indicate significance at .05; * indicates significance for Bonferroni corrected p- values at .005.

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16 Frontal Sinus Growth

FIGURE S1—Distributions of the ages of stabilization of frontal sinus traits from the full sample for 
averages and +/−  two standard deviations among the male (blue triangles), female (red circles), and pooled 
(grey squares) sub- samples. Traits organized by age of appearance. See Table 2 for trait definitions. SOB, 
supraorbital.

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