Appropriate Use of Preoperative Imaging in Feminization Cranioplasty

Abstract

Study Design: Retrospective chart review. Objective: The objective of this study was to determine if proceeding with feminization frontal cranioplasty without preoperative imaging adversely affected patient outcomes. Methods: This study retrospectively reviewed all patients undergoing frontal cranioplasty for facial feminization at a single tertiary care center between 2013 and 2019. All procedures were performed by a single surgeon (JS), who operated at multiple sites. The site selected is where the majority of these procedures were performed during this time. Type of cranioplasty (I vs III) was recorded. Primary outcomes included postoperative cerebrospinal fluid (CSF) leak, entering the cranium, or dural exposure or injury. Results: 422 subjects underwent cranioplasty for facial feminization between 2013 and 2019. No preoperative imaging was performed. Zero patients had CSF leak. 334 subjects (79%) had type III cranioplasty, while the remaining 88 subjects (21%) had type I cranioplasty. No subjects had documented episodes of dural injury, or postoperative brain or cranial concerns. Conclusions: This study demonstrates that frontal cranioplasty for facial feminization does not require routine preoperative imaging. The authors recommend preoperative imaging for patients with a history of congenital cranial abnormality, prior significant head trauma affecting the frontal bone, and in some cases where the patient has had prior surgery or a history of sinus disease or extensive polyposis. Routine preoperative computed tomography is therefore not indicated for patients undergoing feminizing cranioplasty.

Introduction

Frontal cranioplasty, or forehead contouring, is an essential part of feminizing the face. The male cranial skeleton is notable for a frontal prominence of varying degrees. Often this is the most important factor in how a patient’s gender is perceived by others. Gender affirmation surgery of the face, or facial feminization surgery (FFS), is a growing field, and cranioplasty is one of the most popular procedures performed within this set of surgeries [1,2,3,4,5].

Bony contouring of the frontal bone requires intimate knowledge of the anatomy. The surgeon must be mindful of a host of crucial structures in the operative field during cranioplasty: the frontal sinus, the supraorbital neurovascular bundles, the temporal branch of the facial nerve, the orbital contents, the dura, and the anterior cranial fossa. There can be significant variation in the anatomy of the frontal bone. Often, though not exclusively, a larger frontal prominence indicates a well-pneumatized frontal sinus, while a lesser brow ridge may indicate a poorly pneumatized or absent frontal sinus [4].

Ousterhout created a classification for 4 types of frontal bone morphology [1]. Based on this classification system, 2 main types of cranioplasty (type I and III) are used for feminization of the forehead. Type I cranioplasty consists of thinning of the thickened anterior table of the frontal sinus. In type I cranioplasty, the frontal sinus is not entered. In the case of a well-pneumatized, prominent frontal brow bridge, it is recommended practice to remove the anterior table of the frontal bone, recontour it, and set it back into place in a more recessed position. This is held in place with plates and screws, or wire. This is a type III cranioplasty.

Some surgeons routinely obtain preoperative computed tomography (CT) scans prior to performing forehead contouring. The stated value of this is to prepare for which type of cranioplasty will be done (type I or III), illustrate to the patient the expected changes, or use this imaging for virtual surgical planning (VSP) to create cutting guides by which the surgery can be conducted. The senior author does not routinely order preoperative CT scans. We sought out to examine whether proceeding with cranioplasty without preoperative imaging resulted in an increased rate of complications.

Methods

This study was approved by the Boston Medical Center and Boston University Medical Campus Institutional Review Board (H-37592.) A retrospective chart review was conducted of the senior author’s patients who underwent cranioplasty over the 7-year period between August 2012 and August 2019 at a single institution. The senior author operates at multiple locations. For convenience, these patients were exclusively those selected from one of the electronic medical record databases at a single site. Data included whether the patient underwent a Type I cranioplasty, which is defined as frontal sinus contouring without the use of plating, vs Type III cranioplasty, which is defined as removing the anterior table and resetting with mini plates.

Descriptive statistics were generated for surgical characteristics.

Surgical Technique

It is the senior author’s (JS) practice to first perform a coronal incision in the standard fashion. Dissection is carried out in the subperiosteal plane centrally, and deep to the temporalis fascia laterally [6]. Using periosteal elevators, the flap is raised to the nasofrontal suture line, the inferior border of the supraorbital rim, and laterally to the zygomaticofrontal suture line. This dissection allows excellent visualization of the entire bony forehead. Next, a cutting burr is used to contour from lateral to medial to take down the frontal prominence. In most patients, the lateral edge of the frontal sinus will be encountered and is “blue-lined.” This maneuver is carried out until the edges of the frontal sinus are easily visualized. Next, a 2 mm straight osteotome is used to make the final osteotomies along the edges of the frontal sinus and through the intersinus septum. This allows the anterior table to be lifted and separated en bloc, without any damage to the underlying sinus mucosa. The intersinus septum, if present, is drilled down with the diamond burr to accommodate the soon-to-be recessed anterior table. The frontal sinus outflow tract is easily viewed and its integrity inspected. The bone flap is then contoured using a diamond burr to allow it to be set back into the frontal sinus. This is then secured with low profile titanium plates. Any gaps are filled in with bone pâté collected from the prior drilling. Typically a brow lift is then achieved, as well as scalp advancement as indicated. The incision is closed in layers.

For patients where the frontal sinus is not encountered, the anterior table is thinned with a diamond burr until the appropriate contour is achieved. A layer of bone pâté is placed over the now thinned anterior table to correct any slight contour abnormalities. Occasionally a very small island of prominent frontal sinus is prominent even after thinning. A mallet can be used to displace the island to be inline with the rest of the forehead as described by the senior author previously [5]. This is again covered in bone pâté.

Results

422 of patients who underwent cranioplasty for the purpose of facial feminization by the senior author between 2012 and 2019 were reviewed. The average age of subjects was 34.7 years old. 334 (79%) of the procedures involved drilling into the frontal sinus and resecuring the anterior table using titanium plates and screws. The remaining 88 (21%) cranioplasties did not require entering the frontal sinus (

Table 1. Patient Data.

).

There were no instances of CSF leak. Similarly, there were no inadvertent dural injuries intraoperatively. To date, there have been no instances of postoperative mucocele formation nor of sinus complications from this surgery [7]. Finally, there have been no patients that developed subsequent frontal sinus fractures.

Discussion

Radiographic imaging prior to cranioplasty for facial feminization is not a necessary tool to ensure safety of the procedure. We provide evidence of 422 patients who underwent type I or type III cranioplasty without preoperative imaging—none of these patients developed CSF leak, and there were no instances of inadvertent entrance into the anterior cranial fossa. There were no instances of mucocele formation or frontal sinus fracture postoperatively.

The senior author’s technique for forehead contouring is described above. This methodology is safe, effective, and efficient. When using this technique, the surgeon evaluates the boundaries of the frontal sinus in real-time. With intimate knowledge of the anatomy and understanding of the various sub-types of frontal sinuses, the surgeon can anticipate what type of cranioplasty is required based on the intraoperative surgical findings. If the frontal sinus is indeed encountered, the anterior table is carefully removed, made smaller, and set back in a more recessed position. If the frontal sinus is not encountered, the anterior table is simply thinned and contoured to the appropriate position.

It should also be noted that the senior author’s technique consistently achieves the aesthetic goals of feminization cranioplasty: the forehead curvature is rendered less angled and more continuous, with a less prominent supraorbital ridge and less bossing of the forehead. The nasofrontal angle is therefore more obtuse, reflecting the feminine profile as delineated by anthropometric studies [1,4]. The senior author’s prior studies have examined how impartial observers viewed the femininity of pre- and post-FFS patient photographs, with specific focus on the forehead. Observers’ ratings of post-FFS proportions were more inline with a prototypical female [5,8]. These studies help confirm that feminizing cranioplasty (performed without preoperative CT scan) successfully results in an overall more feminine appearance. Additional studies have demonstrated extremely high patient satisfaction and profound improvement in quality of life after facial feminization surgery including feminizing cranioplasty [9,10,11,12].

Others have argued the benefits of preoperative CT scanning and virtual surgical planning [13,14,15]. Gray et al. compared virtual surgical planning vs none when cranioplasty was performed on cadaveric heads. Outcomes measured included efficiency (operative time), safety (dural or nerve injury), and accuracy, and all 3 were claimed to be improved in the virtual surgical planning group. However, their study reported a significant incidence of intracranial complications in the VSP group [14].

While indeed a learning curve exists for the aforementioned technique of the senior author, it can be argued that in experienced hands, all 3 measures are greatly improved upon. The use of VSP requires a considerable additional expense. It also requires an added step by the patient in order to have the imaging performed, and exposes them to unnecessary radiation. Use of third party technologists to develop the cutting guides suggests an opportunity for delay or complication in the preoperative process. In the worst situation, surgeons could have a financial incentive to obtaining preoperative imaging, or obtain the imaging primarily for advertising or self differentiation.

While it is not our practice to obtain CT scans prior to cranioplasty, there are situations when it can be beneficial.

Patients with history of prior surgery, congenital defect, significant sinus disease, or trauma to the area of the frontal bone may require imaging preoperatively. While this information is useful, it rarely changes the operative plan significantly [16].

Conclusion

While many surgeons who perform cranioplasty for facial feminization routinely obtain preoperative CT scans, this imaging provides limited value to the experienced surgeon. Our data demonstrates the safety and efficacy of performing feminizing cranioplasty without a preoperative CT scan. The senior author has performed hundreds of facial feminization surgeries and had no instances of severe outcomes such as CSF leak or inadvertent dural injury. In a culture of mounting healthcare costs, we caution against ordering unnecessary tests that provide no benefit to the surgical outcomes.