CT measurement of the frontal sinus – Gender differences and implications for frontal cranioplasty

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Summary

Objective

To describe frontal sinus anatomy and explore gender variations that may have significance for cranioplasty and sinus surgery.

Methods

150 subjects who underwent maxillofacial computed tomography (CT) between 1/1/2008 and 6/11/2008 were enrolled. Frontal sinus dimensions and forehead measurements were taken at midline and at 10, 20, and 30 mm to the left and right of midline using sagittal, coronal, and axial images. The data was analyzed for significant differences between measurements made at the selected points in the frontal sinus, for left to right variations, and for gender variations.

Results

Mean anterior table thickness ranged from 2.6 to 4.1 mm and was thinnest at 10 mm left and right of midline (2.9 and 2.6 mm). Mean anteroposterior depth of the frontal sinus ranged from 8.0 to 9.3 mm and did not vary significantly at any distance from midline. Frontal sinus height was greatest at midline (mean = 24.5 mm) and progressively lessened at lateral distances. Mean total width at the level of the supraorbital ridge was 52.2 mm. For all measurements, no significant left to right variation was noted. Comparing the sexes, males were found to have greater dimensions in most frontal sinus measurements, though these differences were only found to be significant at or close to midline. The male forehead was marked by more acute nasofrontal angle (119.9° versus 133.5°) and a steeper posterior forehead inclination (−7.2° versus −3.5°). The glabella was wider in males (44.4 versus 33.9 mm) and more frequently protruded beyond the ideal forehead slope line (51% versus 30%).

Conclusions

Using CT imaging, forehead and frontal sinus dimensions have been described. Generally, males had larger overall frontal sinus dimensions, and this was most pronounced in the medial area of the supraorbital ridge known as the glabella.

Introduction

Surgery in and around the frontal sinus is utilized for a variety of indications including trauma, neoplasm, and sinusitis (Kuhn, 2006, Tadros and Costantino, 2008). Due to its position embedded within the frontal bone, it may also be necessary to open the frontal sinus as part of access to the anterior cranial fossa and skull base. The resulting involvement/penetration of the frontal sinus may potentially lead to adverse post-operative sequelae including cerebrospinal fluid (CSF) fistula formation, bone-flap infections, meningitis, and brain abscesses (Zöller et al., 2001, Pondé et al., 2003, Kinnunen and Aitasalo, 2006). As such, knowledge of frontal sinus anatomy is crucial to the success of these and other related procedures.

Another important indication for forehead/frontal sinus surgery is for aesthetic purposes. As an example, pneumosinus dilatans, a rare craniofacial malformation marked by enlargement of the paranasal sinuses, often presents with primarily cosmetic complaints (Dempf et al., 2005). In such patients, selective reduction of the frontal sinus may be desirable in order to address the exaggerating frontal bossing which accompanies this condition. In addition, alteration in the appearance of the frontal bone/anterior skull may be sought by patients seeking to reduce undesired facial masculinity. Transsexualism, a condition marked by a strong and persistent cross-gender identification, is commonly and understandably accompanied by the desire to have one's physical appearance congruous with their experienced gender-identity (Becking et al., 1996, Sohn and Bosinski, 2007). Frontal cranioplasty may be extremely useful in the care of the transsexual patient as an important element of gender confirming surgery as one of many procedures encompassed in facial feminization surgery (FFS). FFS is the general term for a group of specific procedures utilized to alter the perceived gender of an individual's face (Spiegel, 2008).

Regardless of the indication for bony surgery of the frontal bones/anterior skull, knowledge of the anatomy of the frontal sinus is essential in best preparing the surgeon to achieve the desired goal without precipitating untoward events (Caroli et al., 2004). Until recently, our understanding of gender variations in craniofacial anatomy has been chiefly built upon anthropometric studies, which typically employ facial surface measurements or plain film radiography (Farkas and Kolar, 1987, Hurst et al., 2007). However, a common limitation to these studies is the inability to describe in detail the three dimensional anatomy of the frontal sinus and its anatomical relationship to the forehead.

With modern technological advances in computed tomography (CT) imaging, studies have utilized this imaging modality with increasing frequency to describe forehead and frontal sinus anatomy. A number of studies have reported data of frontal sinus dimensions using measurements obtained from axial CT images (Spaeth et al., 1997, Pondé et al., 2003). Sánchez Fernández et al. (2000) and more recently, Tatlisumak et al. (2008) have conducted similar studies, but reported measurements obtained from CT images in both the axial and coronal planes. The results of these and other relevant anatomical studies are summarized in Table 1.

The goal of this study was to confirm and to expand upon the existing base of knowledge. Using CT imaging, this study reports upon the measurements of the forehead and frontal sinus in the axial, coronal, and sagittal planes, at discrete points throughout the sinus. The data compiled in this study allows for the creation of a comprehensive “map” of frontal sinus dimensions, as well as provide measurements relevant to forehead/frontal sinus surgery which have, to these authors' knowledge, not been reported in the current body of literature. Importantly, we evaluated the thickness of the frontal sinus anterior table bone. This data may be useful in predicting fracture patterns, area of dehiscence in inflammatory disorders, and is valuable in predicting areas of thin bone when contouring the frontal sinus, such as for feminizing cranioplasty.

Section snippets

Patient selection

This is a computer-assisted anatomical measurement study utilizing existing maxillofacial CT studies performed at our institution. Consecutive one hundred male and fifty female (a total of 150 patients) who underwent maxillofacial CT between the dates of 1/1/2008 and 6/11/2008 were enrolled in this study. The exclusion criteria included bilateral absence of the frontal sinus, a history of prior frontal sinus surgery, current or prior facial skeletal fracture, and congenital or acquired

Total sample population

The average age for the total sample population was 40.1 years (range 18–90 years). There was no statistically significant left to right asymmetry noted for any of the measurements made. Mean anterior table thickness ranged from 2.6 to 4.1 mm and was found to be thinnest at 10 mm to left and right of midline (2.9 and 2.6 mm). This difference was statistically significant when compared to both midline and to measurements made 20 and 30 mm to the left and right of midline. AP depth measurements were

Discussion

The frontal sinuses are a pair of triangularly shaped, air-filled chambers lined by mucoperiosteum and located between the inner and outer tables of the frontal bone. Typically asymmetrical and irregularly shaped with numerous incomplete septae, the frontal sinuses are marked by an intricate anatomical architecture. In point of fact, the frontal sinuses possess such complex and variable anatomy that they have been utilized for the purposes of forensic identification of unknown deceased persons (

Conclusion

Using maxillofacial CT images in the axial, coronal, and sagittal planes, we report on anatomical measurements made at discrete points throughout the forehead and frontal sinus. Our measurements of forehead and frontal sinus dimensions may serve as a normative map of the surgical anatomy in this area. Specifically, this can be useful when the physician wishes to avoid opening of the sinus during surgical procedures involving the frontal bone. Additionally, gender variations in facial anatomy

Conflict of interest

None.

Acknowledgements

None.

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