INTRODUCTION

A thorough knowledge of neurovascular exit points from orbit to supraorbital region is essential in determining the technique used by the surgeon in maxillofacial, ophthalmologic and plastic surgery (^{Janis et al., 2008}; ^{Fallucco et al., 2012}; Janis et al., 2013). Various forms of exiting points to supraorbital region have been reported in the literature. They may be foramen or notch separately or two foramina or sometimes foramen and notch together or sometimes absence of foramen and notch, proceeding in the upper wall of orbit (^{Andersen et al., 2001}; ^{Cheng et al., 2006}; ^{Woo et al., 2013}; ^{Tubbs et al., 2016}; ^{Filipovic et al., 2017}).

With the increased supraorbital area nerve decompression surgeries in last 10 years such as migraine and endoscopic forehead lift surgeries in addition to increased Botox and local anesthetic injections, determining

whether these nerves come from notch or foramen exit points is important during pre-op period (Fallucco et al.; ^{Janis et al., 2013}; Anderson et al.). A preoperative computed tomography (CT) scan might be useful in clearing this situation for the surgeon and it also helps in other ways such as choosing the surgical technique used on patient and planning the surgical approach. However, there is a limited number of studies in the literature that deal with preoperative CT scans on this subject (Turhan-Haktanır et al.; Woo et al.; ^{Bjelakovic et al., 2016}).

The aim of this study was to provide the radiological data by multi-detector CT for estimating exiting points of the neurovascular bundles of the supraorbital region (SON/F) whether through foramen or notch in living subjects related to side (right/left), sex and age.

MATERIAL AND METHOD

Study population. CT examinations of the maxillofacial region, performed between June-December 2015 in the Radiology Department of the Mersin University, were evaluated retrospectively. Consecutive 214 (102 male and 112 female) adult patients, aged between 18 and 80 years old (average 44.2 ± 14 years), were included in the study. Patients who had a surgery, fracture or congenital abnormality in the supraorbital region were excluded from the study. This study was approved by institutional ethics committee and performed according to the 1964 Helsinki Declaration.

CT scan technique. CT examinations were performed with a 64-row multi-detector CT scanner (Aquillon 64, Toshiba Medical, Tokyo, Japan). CT parameters for this protocol included slice thickness of 0.5 mm, peak tube voltage of 120 kV and tube current of 50 mA. Reformatted three-dimensional CT images were obtained from source images on a workstation. Evaluation and measurements were performed on three-dimensional computed tomography images by two experienced radiologists in consensus.

Evaluation. Presence or absence, number and nature (foramen/notch) of exiting points of neurovascular bundles were noted in each side regarding sex and age groups. Age groups consisted of 112 cases aged between 18-45 years and 102 cases aged between 46-80 years. The distance of foramen/notch to the midline was measured (Fig. 1) and recorded. Nasion was accepted as the midline reference point for measurements.

Statistical analysis. To summarize the data obtained, notch, foramen, sex, age groups and side categories were expressed as number (n) and percentage (%) values. Continuous variables such as age and distance from midline were also shown with mean and standard deviation values. Student-t test was used to compare intergroup parameter differences in age and gender groups. Chi-square test was used to assess the relationship between categorical variables such as age and foramen. Significance level was set as p<0.05 in all comparisons.

Fig. 1 The photo showing the distances from the notch to midline (d1) and from the foramen to midline (d2). n: nasion, the midline of the face. 

RESULTS

The assessment of 214 cases’ CT scans in terms of presence/absence status of SON/F and their percentages and spread according to sex, side and age groups was shown in Table I. The various forms of absence and presence of SON/F were demonstrated in Figure 2. If present, single notch was seen on the right in 123 and in 134 on the left, single foramen was seen in 62 on the right and in 56 on the left side and finally, double foramen was seen in 13 on the right and in 6 on the left. The absence of SON/F, i.e. the neurovascular structures exiting from their own passage to supraorbital region, was seen in 16 on the right and 18 on the left side. No significant difference was seen when presence frequency was compared between the sexes and age groups (p>0.05).

Fig. 2 The photos showing the various forms of exiting points of supraorbital neurovascular bundles: a) absence of foramen and notch on both sides, b) bilateral foramen, c) bilateral notch, d) foramen on the left and notch on the right side. 

The unilateral/bilateral status of SON/F were summarized as 58 (30 female, 28 male) unilateral foramina and 39 (17 female, 22 male) bilateral foramina. Notch was unilateral in 75 (35 female, 40 male) and bilateral in 95 (52 female, 43 male) sides.

The assessment of foramen/notch midline distance according to sex and side was presented in Table II and the assessment of those according to age groups and side were shown in Table III. In comparison with females, it was shown that males had a wider distance between right side foramen and left side notch to midline (p<0.001 and p=0.010). Age groups did not show a significant difference in terms of side (p>0.05).

DISCUSSION

In the study, 3D images obtained by axial and coronal slices with CT were used to assess the orbital exit points of nerve structures on supraorbital region (foramen/notch or absence), their differences in terms of side, sex and age groups and their distance to midline. In the literature, although there were studies on anatomical structure of this area using dry skull (^{Webster et al., 1986}; ^{Gümüsburun et al., 2002}), cadaver (^{Miller et al., 2000}; ^{Janis et al., 2008}, ^{Jeong et al., 2010}; Fallucco et al.; ^{Konofaos et al., 2013}), skull and cadaver (^{Saylam et al., 2003}) and clinical (Filipovic et al.) models, as suggested by Bjelakovic et al., we also thought that the most correct discussion method should be performed using a similar subject and methodology and therefore, we discussed our study results on previous studies that used CT scans and living samples for assessment.

The most common type was found to be single-notch (57.5 % in the right / 62.6 % in the left) and single foramen (29 % in the right / 26.2 % in the left) in our study. Another study by ^{Turhan-Haktanir et al. (2008}), also found similar results with single notch (69.4 % in the right / 68.2 % in the left) and single foramen (12.4 % in the right /14.5 % in the left) as the most common types. Woo et al.’s study reported the presence status on the right-side notch (39.5 %) and foramen (37 %), yet it was the opposite on the left side (notch 35.4 %, foramen 42.3 %). The study of Bjelakovic et al., which included 105 subjects reported the most common presentation of supraorbital passage as single SON (73.33 %). In our study, we found out that foramen/notch presence was statistically unaffected by the sex and age factors in 214 cases.

The absence of foramen and notch structures, i.e. neurovascular bundle exits from own passage was found to be 7.4 % on the right and 8.4 % on the left side. Woo et al.’s (9.9 % in the right / 11.7 % in the left) and Turhan-Haktanir et al.’s (11.5 % in the right / 12.5 % in the left) study results showed similarity to our own results. However, Bjelakovic et al.’s study showed a very high rate of SON/F absence with 56.19 %.

Males had relatively longer distances between left notch and midline (24.9±2.9 mm) and right-side foramenmidline (29.9±3.8) compared to females in our study. TurhanHaktanir et al.’s study reported bilateral supraorbital foramina and left supraorbital notches to be more laterally located in men. Notches were significantly closer to the midline than foramina on both sides. Distances from SON/ F to midline were 32.3 and 25.8 mm in the right, and 29.1 and 24.6 mm in left sides, in male and female cases respectively. Woo et al.’s study reported the distances from the nasion to the foramen/notch were significantly greater in males. Finally, Bjelakovic et al., reported the distance of the SON/F to the facial midline was 22.52 ±3.2 in males and 21.25 ±2.87 in females.

Unilateral/bilateral presence rates of SON/F were more frequent in notch (17.5 % unilateral, 22.5 % bilateral) and foramen was relatively rare (13.6 % unilateral / 9.1 % bilateral) in the present study. Bjelakovic et al.‘s study also reported more frequent unilateral (39.01 %) and bilateral (34.29 %) SON presence. SOF presence rates were reported as 2.86 % unilateral and 3.81 % bilateral. Moreover, no significant difference was found between the sides or the sexes.

Different from previous studies, we divided the parameters into 2 separate groups for age factor but it was statistically shown that age had no effect on those structures at all. Turhan-Haktanır et al.’s study reported a single positive correlation between the age factor and left supraorbital foramina, and no other relations with other findings.

In terms of surgery, notch can be palpated during physical examination of supraorbital region for preoperative assessment but foramen cannot be felt. In addition, in condition of absence also cannot be detected by palpation alone. In our study, absence and foramen presence made up about 30-40 % of all cases. This tells us that in almost in every 3 patients, neurovascular bundle damage can be seen during sub-periosteal interventions. Especially in endoscopic face lifts and migraine surgeries, preoperative assessment of orbital exit points of that SON/F is essential for the surgeon in avoiding damage to trigeminal branch endings by increased awareness when getting close to the neurovascular bundle while working on sub-periosteal plane.