Continuing Education Activity

Trigonocephaly is the premature closure of the metopic suture causing the inability of the frontal bones to grow laterally, thus forming a triangular forehead with an obvious or subtle osseous ridge. The term "trigonocephaly" was coined by Welcker in 1862. The word metopic comes from the Greek word "metopon," which translates to the forehead. The premature fusion of the metopic suture, a type of craniosynostosis, produces a narrow forehead, causing the position of the eyes to be closer than usual (hypotelorism), raised or arched eyebrows, and lateral orbital retrusion with associated bilateral frontotemporal narrowing and compensatory occipital-biparietal widening. This activity reviews the evaluation and management of trigonocephaly and highlights the interprofessional team's role in evaluating, treating, and improving care for patients with this condition.

Objectives:

• Describe the etiology of trigonocephaly.
• Summarize the common physical exam findings associated with trigonocephaly.
• Identify the indications for trigonocephaly surgery.
• Review the differential diagnoses of trigonocephaly.

Introduction

Trigonocephaly is the premature closure of the metopic suture causing the inability of the frontal bones to grow laterally, thus forming a triangular forehead with an obvious or subtle osseous ridge. The term "trigonocephaly" was coined by Welcker in 1862.[1] The word metopic comes from the Greek word "metopon," which translates to the forehead.[2] The premature fusion of the metopic suture, a type of craniosynostosis, produces a narrow forehead, causing the position of the eyes to be closer than usual (hypotelorism), raised or arched eyebrows, and lateral orbital retrusion with associated bilateral frontotemporal narrowing and compensatory occipital-biparietal widening.[3][4] It should be distinguished from the benign metopic ridge, where hypotelorism and frontotemporal narrowing are absent and have no other clinical features. 3D computed tomography (CT) scans can be used to distinguish them.[5][6]

Etiology

Trigonocephaly is a post-neurulation defect that leads to premature fusion of the metopic suture, usually occurring before birth.[7] Metopic suture closure starts at 3 to 4 months of age and is completed at 8 to 9 months in most individuals.[8][9] The closure begins at the nasion, proceeding superiorly, and terminates at the anterior fontanelle.[9] Approximately 5.1% of the individuals have the suture open after one year of age. However, by two years of age, it should have closed. Using 3D CT scans, it has been demonstrated that the metopic suture's physiologic fusion occurs between the 3rd to 19th months.[10] Premature closure before the third month will cause trigonocephaly.

The specific etiology of craniosynostosis is unknown.[11] Genetic abnormalities, signaling pathways alterations, environmental factors, metabolic disorders, and intrauterine constraints have been implicated. Intrauterine constraint is defined as a condition where fetal movements are significantly reduced and can not move freely; if prolonged, it can cause craniofacial anomalies.[12] Some reports have associated maternal use of valproic acid with metopic craniosynostosis; however, no association was found in a recent meta-analysis.[13] 

Rare non-syndromic cases have been described in which there is the fusion of both the metopic and the sagittal suture producing significant behavior and cognitive and motor impairment.[14] These patients require a combined surgical approach to treat both sutures. Thyroid dysfunction in mothers can contribute to metopic synostosis in children, next only to sagittal and coronal synostosis. Folic acid deficiency before pregnancy has also been proposed as a causative factor for trigonocephaly.[13]

The most notable genetic mutations recently identified in non-syndromic metopic synostosis are FREM1 and SMAD6.[13]

Epidemiology

The number of children born worldwide with craniosynostosis in 2019 was estimated to be 84,665, which included 72,857 with nonsyndromic craniosynostosis.[15] The overall incidence of all types of craniosynostosis is approximately 0.6 per 1000 live births. Metopic craniosynostosis comprises 10% to 31% of all isolated craniosynostosis and is more commonly seen in males.[16][17][18][19] The incidence of metopic craniosynostosis is approximately 1 per 5000 to 15000 live births.[20] It has been noted that the prevalence of metopic craniosynostosis has been increasing over the years in Europe and the United States.[13][17][18][21][22][23][15] It is now the second most common type of craniosynostosis, second only to scaphocephaly.[2][11][24] About three quarts of the patients are male, with a male-to-female ratio of 3.3:1.[21][25] 

Nonsyndromic craniosynostosis accounts for approximately 85% of all craniosynostosis.[26] In more than 95% of the cases, it is sporadic. Trigonocephaly is usually nonsyndromic but, in some cases, can be associated with a syndrome. In a study evaluating the role of ethnicity in craniosynostosis, White race and African American parents were the principal ethnic groups identified; metopic craniosynostosis was significantly associated with the White population.[27] Many syndromic craniosynostosis patients have mental retardation. This is more prominent in metopic craniosynostosis than in other single-suture craniosynostoses.[28][29] About one-fourth of the patients with single-suture craniosynostosis have other organ-associated anomalies.

Pathophysiology

Approximately 6% to 10% of patients with trigonocephaly show genetic alterations.[30] Metopic craniosynostosis has been associated with several chromosomal abnormalities, including deletion of chromosome 11q24, 7p, 3q, 13q, 12pter, 22q11, deletion or trisomy of 9p, duplication of 15q25, and ERF and SMAD6 gene mutations.[13][26][31][32][33] Familial cases occur in approximately 5% of the cases, with an 8% frequency in twins.[34][35]

Due to the suture's premature fusion, there is lateral growth restriction of the frontal bone with shortening of the anterior cranial fossa.[9] The fusion of the suture produces a forehead midline bone ridge. The orbits are located closer than normal due to restricted lateral growth. Bitemporal indentations are noted. The anterior fontanelle is closed in about half of the cases.

Approximately 8% to 33% of the patients with metopic craniosynostosis have elevated intracranial pressure (ICP), which can produce neurodevelopmental delays, including speech and language retardation.[36][37][38][39][40][41] In one series, 78% of the patients had elevated ICP during surgery for trigonocephaly; however, most patients in this series were older, with a mean age of 5 years.[42] These findings suggest that uncorrected metopic craniosynostosis can seriously harm language development, motor function, and behavior. As the remaining skull sutures have increased compensatory growth, the cephalic index is maintained within normal limits.[43][44] The posterior skull has compensatory sagittal and transverse growth together with an upper face vertical and sagittal growth.[43] This compensatory growth of the non-fused sutures leads to the widened appearance of the parieto-occipital skull.[45]

History and Physical

Physical examination shows a visible midline forehead bony ridge leading to a deformity resembling a ship's keel. Hypotelorism is frequently noted. Patients have a narrow bitemporal skull dimension with a compensatory expanded biparietal dimension. Eyebrows are usually raised. The earlier the suture closure, the more severe will be the skull deformity.[45]

Cases can be classified as severe, moderate, and mild, depending on the angulation of the frontal bones.[46] Fundoscopy can be used for detecting raised intracranial pressure (ICP) in patients with craniosynostosis; however, papilledema is more commonly found in older children.[47]

Evaluation

The diagnosis is mainly clinical rather than radiological. The most obvious sign in the diagnosis is physical palpation of the anterior midsagittal bony ridge over the forehead. When viewed from the vertex or "birds-eye" view, the triangular shape of the head is characteristic in this condition.

Craniofacial anomalies like hypotelorism and temporal narrowing with parietal widening are, in most cases, sufficient to accurately diagnose craniosynostosis. These additional features differentiate craniosynostosis from the benign metopic ridge.

A head computed tomogram (CT) scan with 3D reconstruction is performed to confirm the diagnosis and plan the surgery. It will show that the frontal bones have a triangular shape, orbits are closer than normal, and there is anterior displacement of the coronal sutures. Widening of the posterior parietal regions, pterional constriction, and flattening of the supraorbital ridges with lateral orbital hypoplasia are also identified.

Prenatal head ultrasound can be used during the second and third trimesters to make the craniosynostosis diagnosis.[48][49][50] It can also be used in infants between the age of 8 to 12 months to avoid radiation exposure and the need for sedation.[51][52][53][54][55]

Radiographic Findings Associated with Metopic Synostosis

The presence of three or more specific findings is diagnostic for 96% of patients with metopic synostosis.[56] these findings are as follows:

1. Omega sign - the prematurely fused metopic suture forms an "omega"-shaped invagination intracranially
2. Interorbital narrowing - decreased distance between the medial orbital walls
3. Upper orbital narrowing - the shape of the upper orbit is narrower than usual
4. The frontal bone tangent intersects the orbital midline or more medially when viewed from above
5. Posteriorly displaced lateral frontal bone
6. Straight lateral frontal bone
7. "Pulled" anterior fontanelle - Anterior fontanelle is partially open down the metopic suture
8. Upsloping lateral orbital rim - the superior orbital rim is oriented more vertically than horizontally

Treatment / Management

Early operative treatment is recommended to provide the best possibility for the brain to expand and produce a normal configuration of the skull. Surgery goals are to remove the bony ridge of the metopic suture, advance both orbits and the frontal bones, achieve a rounder forehead contour, and prevent psychosocial impact and neurodevelopmental delay.[46] Advancing the orbits and frontal bones will improve the lateral and superior orbital rim projection, expand the lateral and superior frontal bones, and correct the pterional and frontozygomatic restriction.[11]

Endoscopic Surgery

This technique is best used before 3 to 4 months of age due to the skull's pliability. A small incision is made behind the hairline towards the metopic suture. A subgaleal plane is developed from the anterior fontanelle to the nasofrontal suture. A single bur hole is made, and a 30-degree endoscope is used to dissect the dura and the overlying stenosed suture. An osteotomy is made between the anterior fontanelle and the nasion using scissors.[57][58] A helmet is prepared and placed on the patient on the fifth postoperative day. It is used for the next 10 to 12 months to direct cranial growth by allowing cranial expansion. Endoscopic surgery significantly reduces blood loss, operative time, length of stay, and transfusion rate compared to open techniques.[13][59][60][61]

Open Surgery

Open surgery is usually performed before the age of 1 year (9 to 12 months). A less radical procedure is used for cases where the main goal is to remove the midline bony ridge, and there is no need for orbital rim advancement. Drilling of the prominent metopic suture suffices. If there is a temporalis hollow, the temporalis muscle can be partially split and moved to a more anterior position. A zigzag or wavy coronal incision is used to preserve the superficial temporal arteries to maintain a robust blood supply. Dissection of the scalp flaps is done above the periosteal plane to reduce bleeding.

Open surgery requires a larger incision and is usually associated with longer operative time and hospitalization. Blood transfusions are almost always needed. All these drawbacks increased overall healthcare costs. In those cases where cranial reconstruction is required, a bifrontal craniotomy is performed to reconstruct the anterior cranial vault, including the lateral portions of the sphenoid wings, to allow brain expansion. The bifrontal bone flap undergoes radial osteotomies to reshape the bone. The midline ridge requires shaping with the drill. To perform the fronto-orbital advancement, the periosteum above the supraorbital rim is open before the bilateral orbital rim osteotomy and advancement are performed. Orbital osteotomies are performed using a reciprocating bone saw. A free supraorbital bone is created and reshaped to a more convex configuration, especially along the superolateral orbital rim. This is done with several closed wedge osteotomies along the free supraorbital bone bar. If the hypoteloric deformity is severe, an interposition split-thickness cranial bone graft is added. The orbital rim is moved forward, and fixation plates are placed to maintain the advancement.[2][3][13][37][62]

Alternatively, absorbable sutures can be used. Using sutures and avoiding plates and screws reduces surgery costs and allows natural reshaping.[1] The temporal bone is split and advanced to correct the abnormal inward angulation after the lateral orbital rims are advanced. For those patients operated on at an early age, overcorrection by approximately 1.5 cm is recommended to compensate for the impaired bifrontal growth.[3][63] Using preoperative erythropoietin and ferrous sulfate with the addition of perioperative tranexamic acid reduces transfusions in patients with metopic craniosynostosis undergoing craniofacial reconstruction.[37][64]

An alternative approach when reconstructing the orbits is to remodel the orbital rim in situ to preserve the attachment to the zygoma and incline the cephalic portion of the supraorbital rim anteriorly. The fixation is done using resorbable fixation plates. The orbital rim will advance with brain growth. Another alternative approach is the in situ bandeau approach, where the supraorbital bandeau is not separated at its central point at the nasion to maintain its blood supply.[45] Partial osteotomies are made to facilitate the bending of the bandeau. Using bone benders, the bandeau is flattened to bring forward the supraorbital rims and the lateral bone margins. The lateral margins are bent back with greenstick fractures to align with the temporal bones, which are repositioned outward and then fixed to the bandeau with resorbable plates. In another alternative procedure, the supraorbital bandeau is left in situ at the temporal bones. It is split at the midline with a hinge technique, and an interposition bone graft is placed at the nasofrontal area.[65]

Lille’s technique: Involves resection of the metopic suture followed by the construction of a large frontal panel that is stabilized with absorbable plates. This is accompanied by fronto-orbital advancement, parietal craniectomies, and pterional resection. This technique facilitates the optimization of cranial expansion and permits future cranial growth.[66]

Di Rocco technique: This helps to control bleeding over the glabella and ophryon. It follows the principle of direct visualization of emissary metopic veins and the superior sagittal sinus, thereby having better control of hemostasis before removing the last piece of the frontal bone. This is achieved by manipulating the design of the frontal craniotomy so that a triangle of bone based above the glabella at the site of the osteotomy of the bandeau is conserved.[67]

Method of “hypercorrection” proposed by Bennett et al.: This technique helps to attain a better cosmetic result and to reduce relapse and the need for revision surgery. The method involves a fronto-orbital advancement of 2.5 to 3.5 cm and concomitant hyperexpansion of the bitemporal projection. Despite this, some patients may need additional corrections; lateral orbital recession and bitemporal constriction have rarely been reported following this procedure.[68]

Conservative Management

If the deformity is mild or there is only a bony ridge without hypotelorism, a more conservative approach can be used; however, the child should be followed for a minimum of 12 months of age to assess and corroborate adequate cranial growth. Clinical evaluations and family discussions regarding neuropsychological development are engaged during this time.[45] During the first years of life, the child's development is periodically evaluated to ascertain that no language, motor, or behavior problems develop.

Differential Diagnosis

The most common differential diagnosis of trigonocephaly is a metopic ridge, which is physiological and does not need surgery. Trigonocephaly presents at a younger age, and the appearance of the lateral frontal bone and lateral orbit can help distinguish whether the condition is pathological.[4]

The single metopic suture craniosynostosis has to be differentiated from syndromic craniosynostosis, which most commonly involves the coronal suture producing brachycephaly.[69]

• Apert syndrome
• Crouzon syndrome
• Muenke syndrome
• Pfeiffer syndrome
• Saether Chotzen syndrome
• Craniofrontonasal syndrome
• Carpenter syndrome

Secondary synostosis can be caused by several conditions but often involves multiple sutures.[70][71]

• Hyperthyroidism
• Hypercalcemia
• Hypophosphatemia
• Rickets
• Sickle cell anemia
• Thalassemia
• Polycythemia vera
• Microcephaly
• Prematurity
• Teratogens (phenytoin, valproic acid, retinoic acid, aminopterin)

Prognosis

Surgical correction provides adequate cosmetic results in the majority of patients. Comparison at two years of age of the endoscopic strip craniectomy followed by helmet use and the open skull reconstruction showed that both offer an excellent head shape outcome.[72] The majority of surgically corrected patients have academic achievement near the national mean and above-average intelligence quotient; however, neurocognitive function correlates with the severity of craniosynostosis.[73] The mortality rate for all types of craniosynostosis is well below 1%.[3][35]

Untreated patients show problems with cognitive functioning when compared to healthy controls.[74] Patients with untreated severe metopic craniosynostosis have been found to have reduced auditory processing of language stimuli in the frontal cortex, suggesting that the orbitofrontal deformity has a negative effect on the frontal cortex.[16]

Children with metopic craniosynostosis, unoperated or operated, have worse general cognition, motor functioning, attention, verbal and visuospatial abilities, and behavior than their healthy peers.[75] Despite corrective surgery, intellectual disabilities and behavioral disorders may occur or persist.[24][75] These patients can show behavioral, cognitive, and psychological problems and therefore necessitate support and ongoing monitoring.[75] Neurodevelopmental and ophthalmological follow-up in patients with complex craniosynostosis is recommended, even after successful cranial remodeling.

Complications

Surgical complications after metopic craniosynostosis correction are usually relatively few and minor.[37][57][76] These include:

• Excessive blood loss
• Dural tears
• Meningitis
• Stroke
• Pseudomeningoceles
• Hyperthermia
• Hypoactivity
• Local wound infection
• Epidural abscess
• Subcutaneous hematoma
• Epidural hematoma
• Subdural hematoma
• Air embolus
• Incomplete correction
• Temporal hollowing
• Stretched scar/keloid
• Reoperation
• Contact dermatitis from helmet use
• Scalp abrasion from helmet use

Despite the surgical correction, some patients may still present increased ICP, estimated to be 3% of the cases at an average of 57 months after the initial surgery.[37][77][78] This is corrected with a subsequent calvarial expansion surgery.[37] Some patients need another surgery to fill bone defects later in their life.[77]

Late Complications

Contour irregularities in the frontal region and temporal hollowing: This may need further treatment in the form of lipoinjection[79] (if the condition is affecting the academic performance and personality development of the child) or a recontouring procedure using hydroxyapatite onlay (after the age of 14 to 16 years).[37] For those with long-term sequelae, the use of cutting guides to facilitate scheduled complex reconstruction with autologous bone can be useful.[80]

Postoperative and Rehabilitation Care

Patients are sent overnight to the pediatric intensive care unit to closely monitor vital signs and evaluate the necessity of additional blood transfusions. The drain, if placed, is removed the next day. If stable, the patient is sent to the ward for another day. When discharged, the patient is followed at the clinic for wound inspection and suture removal. The head shape is followed at three months, six months, and then annually with photography and anthropometric measurements. The patients are also closely evaluated for behavioral, cognitive, and psychological problems.

Consultations

The following consultations are required:

• Pediatric neurosurgeon
• Plastic surgeon
• Craniofacial surgeon
• Pediatric intensivist
• Pediatric anesthesiologist
• Ophthalmologist
• Geneticist

Deterrence and Patient Education

Surgery for trigonocephaly is advocated before the age of 1 year for better cosmetic results.[81] There is still little consensus in cases of mild trigonocephaly. In a survey sent to 102 craniofacial surgeons, there is a disparity of opinion regarding the management of mild nonsyndromic metopic craniosynostosis.[82] However, all of them agreed to operate in moderate and severe cases. Most surgeons prefer open procedures, but the approach used varies. The ideal timing for orbital advancement is still debated; however, most prefer to perform it between 6-10 months of age.[82]

Screening for SMAD6 mutations is recommended in patients with nonsyndromic metopic craniosynostosis as its presence confers a high risk for recurrence in another pregnancy.[26] In those cases where the mutation is identified, genetic counseling is recommended.

Head 3D CT scans are helpful as an educational tool for families to understand the condition.

Enhancing Healthcare Team Outcomes

An interprofessional team of specialists includes a pediatric neurosurgeon, plastic surgeon, craniofacial surgeon, pediatric anesthesiologist, and a pediatric intensivist that must use an integrated care pathway combined with an evidence-based approach to evaluate and manage patients with metopic craniosynostosis can improve outcomes. Nursing staff round out the interprofessional team. Patients with suspected premature closure of the metopic suture should be closely followed to make an early diagnosis and avoid delays that may cause neurodevelopmental delay and later psychosocial impact on the child. Pediatricians should refer to these patients early for evaluation and possible therapy.

Referrals do not need to include radiographic studies, as these should be ordered by the specialist if necessary. Nurses can assist in assessment, perform patient counseling, and help coordinate activities of the various clinical specialties. Open communication lines between all care team members are crucial to a properly functioning interprofessional management approach, leading to improved patient outcomes. [Level 5]