Introduction
Although the metopic suture is the only calvarial suture to completely close and disappear in humans, premature closure in utero or soon after birth can lead to major cranial and facial deformities. Amongst these are trigonocephaly, hypotelorism, and a narrow face and forehead, as well as prominent and wide parietal eminences. If the suture closes after 3 or 6 months, the only significant clinical presentation is that of a prominent midline forehead ridge. The decision when to offer the patient surgery is easy when the deformity is severe and occurs in utero and present at birth ( Fig. 10.1 ). The question becomes more challenging as the deformity presents in milder forms and later in life ( Fig. 10.2 ). The standard and most accepted form of treatment comes in the form of an open vault procedure and includes bicoronal scalp incision, bifrontal craniotomies, removal of an orbital bandeau, and reshaping of the bandeau along with bilateral tongue-in-groove advancement. The goal is to reshape the triangular shaped forehead into a normal and rounded shape. Paul Tessier’s pioneering work in 1967 established surgery as the primary and acceptable method for treatment of craniosynostosis, originally consisting of a tongue-in-groove advancement of the roof of the orbits followed by attachment of a reconstructed forehead construct. This procedure became the standard surgical treatment until the present day. Hoffman and Mohr modified Tessier’s method with their own technique for advancement of the lateral canthal segments of the supraorbital region for treating metopic synostosis. Soon thereafter, Marchac and Renier introduced the “floating forehead” technique which they advocated for children under 6 months of age. However, this technique was associated with significant temporal hollowing and has been abandoned for other modifications. Other authors also introduced more modifications, such as Whitaker. In 1978, Marchac introduced the recontouring of the superolateral orbit and forehead to correct the deformities associated with metopic synostosis. Marsh described a modification to the Marchac technique by extending lateral orbital wall osteotomy into the body of the zygoma and placing a self-retaining tenon-in-mortise low lateral orbital wall calvarial graft buttress.
The need to stabilize the orbital-frontal bony complexes done with remodeling techniques has gone from using sutures and wires to permanent metal plating systems, which were in use for much of the 1980s and 1990s. Over time, these metal plating systems were found to be complicated by plate and screw migration intracranially and even into the intradural compartment. The use of absorbable plating systems was introduced to avoid the complications seen with permanent systems. However, in a review of absorbable systems, Eppley et al. have reported device failure from plate breakdown and fracture, delayed foreign body reactions, cyst formation, and need for plate removal from erythema and prominent and palpable plates. , In efforts to improve outcomes and results, a number of different procedures and approaches have been tried over the years. It has been our experience that immediately after surgery, all patients look great and the forehead does, indeed, round and correctly normalizes. Nevertheless, we have also found that as time goes on and the child gets older, a new set of deformities begin to develop. Turricephaly appears to be one of the most consistent problems that develops over time. This most likely occurs because, as the bandeau/cranial complex is secured to the surrounding skull base and temporal and parietal bones, the brain growth in the anterior-posterior direction is restricted by the anchoring hardware. The normally growing brain then takes the path of least resistance and grows superiorly leading to turricephaly ( Fig. 10.3 ). We published a detailed account of our metopic surgery endoscopic experience in 2019. Our experience has also been corroborated by others who have published their long-term results. As with other craniosynostosis, we were not satisfied with the long-term results obtained with the fronto-orbital advancement (FOA) and decided to apply the concept of early sutural craniotomy and release of the stenosed suture followed by helmet therapy. The original concept was to create a neosuture between the anterior fontanelle and the nasofrontal suture. Our first cases were done with larger osteotomies measuring between 1 and 2 cm wide. Linear osteotomies were diagonally cut on the frontal bones in order to increase expansion of the frontal bones. Several of the patients who had large osteotomies were found to take a very long time for the dura to reossify and close the bony defects. It seemed like the anterior frontal dura ossified somewhat differently than the dura over the vertex. Therefore, we decided to forego extensive bony removal and extra osteotomies and concentrated on making small osteotomies. The technique was modified to only resect a linear strip of midline bone of 4 or 5 mm. Although more challenging and difficult to do, these smaller osteotomies produced superb short- and long-term results. Because only a small amount of bone is resected and the frontal bones and orbits are left intact, there are no hardware issues to cause problems, no bumps, no indentations, and no turricephaly is seen. The hypotelorism correction is remarkable, as are the long-term results presented herein. Furthermore, aside from the inconsistent long-term results, the traditional FOA/ calvarial vault remodeling (CVR) has been associated with a much more complex intraoperative scenario which includes longer surgeries (mean surgical time = 233 minutes vs. 66 minutes for endoscopic surgery); older patient at surgery time (11.5 months for CVR vs. 3.8 months for endoscopic); higher blood losses (224 mL for open vs. 54 mL for endoscopic); longer hospitalization days; and higher transfusion rates (0.77 vs. 0.22) when an extensive review of the literature is performed. Consequently, it is our belief that short- and long-term outcomes are superior when treating metopic craniosynostosis if treatment is done with endoscopic-assisted minimally invasive procedures in very young infants. Nevertheless, we have also found that older patients (up to 8 months of age) still benefit from an endoscopic procedure followed by cranial orthosis therapy.
Positioning
The patient is placed supine in a neutral position on a cerebellar horseshoe headrest. The neck is slightly flexed and a small shoulder roll is used to support the shoulders. As with all other endoscopic craniosynostosis surgeries, a precordial doppler is placed on the left side of the upper chest and properly set to monitor for venous air emboli ( Fig. 10.4 ). This is of particular importance in metopic patients when the head needs to be raised in order to assist with bleeding from bridging dural veins with head elevation. Corneal protecting shields with ophthalmic ointment are placed in order to protect the corneas. The area around the nasion and orbits should be exposed, and thus the upper face, forehead, and orbits are carefully prepped with povidone-iodine solution. The solution should be diluted in half with normal saline for prepping the eyes and eyelids. The draping of the sterile field is done in such a way as to leave the orbits, forehead, nose, nasion, and cranial vault prepped and exposed ( Fig. 10.5 ). Draping the patient this way allows the surgeon access to the base of the anterior cranial fossa for transillumination, direct palpation, and manipulation during the development of the osteotomy.
Incision
Access should be obtained to the forehead from the fontanelle to the nasion. A transverse incision is made with the epicenter over the metopic suture. It should measure about 2.5 to 3.0 cm. Because of the hypermobility of the scalp after galeal dissection, the incision can be moved further side-to-side, thereby giving greater access to the surgical field. Although the incision can be placed directly over the anterior fontanelle, this placement increases the distance to the nasion and the curvature of the midforehead needs to be navigated. For such reasons, the incision is placed in front of the fontanelle but behind the hairline ( Fig. 10.6 ). As with other sutures, the epidermal incision is made with the needle tip monopolar unit (also a Colorado tip can be used for a bloodless scalp opening) ( Fig. 10.7 ). Given the patient’s young age and careful incision placement, minimal scarring occurs and the incisions is very well camouflaged. Using the rhinoplasty lighted retractor, the subgaleal dissection is undertaken ( Fig. 10.8 ) towards the fontanelle once the galea has been incised. A subgaleal dissection is also undertaken with the aid of the lighted retractor and endoscope towards the middle of the forehead ( Fig. 10.9 ). Because of the roundness of the forehead, a rigid endoscope will not reach all the way to the nasal area. Once the midforehead is reached, the rest of the galeal dissection is made bluntly with a coated brain ribbon. The brain ribbon is then gently but forcefully passed towards the nasion ( Fig. 10.10 ) and then to the nasofrontal suture ( Fig. 10.11 ). Palpation of the brain ribbon over the skin documents that the subgaleal plane has been fully and adequately developed between the fontanelle and the nasofrontal suture.
Osteotomy
Given the minimally invasive nature of this procedure, the location and extent of the osteotomy are of great importance. As previously stated, the osteotomy size need not be wide. However, it must reach all the way down to the nasofrontal suture ( Fig. 10.12 ) for the procedure to be successful. By reaching the nasofrontal suture, the frontal bones are separated and, with subsequent brain growth, allowed to mobilize laterally and correct the trigonocephalic deformity ( Fig. 10.13 ).
The osteotomy is begun with a single pediatric size (7-mm) burr hole directly over the metopic suture at the incision site. We have not had a single case of dural or sagittal sinus injury while using a craniotome perforator to make the burr hole. Greatest care must be used when placing the burr hole to minimize dural injury, as we have done. A combination of bone wax, cautery, and/or Surgiflo and suction/coagulation can be used for osseous hemostasis in cases when the suture is very thick and bleeds ( Fig. 10.14 ). A Woodson elevator is used to free the dura towards the fontanelle, followed by a #1 Penfield dissector ( Fig. 10.15 ). Once the fontanelle has been reached, the end of the Penfield can be easily palpated through the scalp. Either Mayo scissors or Kerrison rongeurs (5-mm) can be used to remove a strip of bone (5-mm) back from the burr hole to the fontanelle ( Figs. 10.16 and 10.17 ). Hemostasis is obtained as previously described. Similarly, a combination of Kerrison and Woodson work is done to free the dura from the overlying bone from the burr hole toward the midforehead. The amount of dissection can be measured with the Penfield dissector. Likewise, a pair of Mayo scissors or Kerrison or bone rongeurs can be used to make an osteotomy to the point of maximal dural dissection ( Fig. 10.18 ). To assure that the dura has been totally separated from the bone, a 30-degree endoscope may be inserted under the bone and advanced towards the nasion. The osteotomy is begun and extended towards the midforehead with the use of 4-mm bone cutting rongeurs that resemble pituitary forceps ( Fig. 10.19 ). Ongoing bony hemostasis is achieved with the suction electrocautery unit set at 60 watts on coagulation mode. Surgiflo can be used as needed along with saline irrigation. Upon reaching the midway point to the nasion, a number of small bridging veins extending from the dura to the overlying bone are typically encountered ( Fig. 10.20 ). When these veins are pulled from the bone, bleeding ensues. Sometimes the bleeding is relatively minor and sometimes more exuberant. As even a very small amount of blood can completely obscure endoscopic visualization, rapid control of the bleeding is extremely important. Irrigation and direct endoscopic bipolar coagulation are attempted and if successful, further epidural dissection is undertaken ( Fig. 10.21 ). If the bleeding is more prominent and visualization is poor, the anesthesiology team is advised to carefully listen to a louder precordial doppler sound. The table is lowered to the floor as much as possible and then the head of the patient is slowly elevated by increments of 10 or 15 degrees. Endoscopic view of the epidural space will alert the surgeon to the point where the bleeding has significantly decreased or stopped. Given the gradient between the head and the heart, the sagittal sinus will collapse onto itself and the bleeding will stop. The risk of venous air embolism is the highest at this point and careful attention to the doppler must be placed. If an embolism is detected, the head of the table must be immediately lowered along with copious irrigation of the surgical field. Using these techniques, we have not had any major air emboli nor problems at all with minor emboli. Once the bleeding has stopped or slowed sufficiently, the bleeding bridging vein(s) can be easily coagulated under direct endoscopic visualization ( Fig. 10.22 ). Bone cutting rongeurs are used to remove the remaining bone in a piecemeal fashion under direct endoscopic visualization ( Fig. 10.23 ). Epidural dissection is continued until the interdigitating dural fibers into the nasofrontal suture are encountered ( Fig. 10.24 ). This is the point of maximal dissection and the point to which the osteotomy is taken. The bone at this level tends to be very thick and the diploë very prominent. Bony bleeding is contained and controlled with the suction electrocautery unit set at 60 watts. Not uncommonly, multiple passes must be made to achieve hemostasis. The bone must be coagulated and bleeding contained. Surgiflo, gelfoam, pressure with cottonoids, and irrigation are used to get complete bleeding control. The assistant must be vigilant and help to retract and elevate the scalp over the midforehead so that a skin burn does not take place during bony coagulation. This dreaded complication has not occurred in our series. In order to completely make sure that both frontal bones are fully separated, an osteotome is used to fully osteotomized across the nasofrontal suture once fully released. Side-to-side movement of the osteotome in-situ will show free movement and separation of the right and left frontal bones ( Fig. 10.25 ). A similar maneuver can be made by spreading apart the osteotomy edges with a pituitary or bone cutting rongeurs. If totally freed, the bones will easily separate, indicating full release. The suction coagulator can be applied to the back end of a 7-French insulated suction so that the tip can be inserted into the osteotomy at the nasofrontal suture for complete hemostasis. The head can now be placed in the Trendelenburg position and generously irrigated with saline.
