A Patient With Mild Trigonocephaly and Concomitant Horizontal Constricting Ring of the Skull

Metopic craniosynostosis causes characteristic cranial deformities such as a keel-shaped forehead, known as trigonocephaly. Mild trigonocephaly refers to cases of metopic craniosynostosis in which the cranial deformity is generally mild. The authors report a case of mild trigonocephaly accompanied by an atypical horizontal constricting ring of the skull that was successfully treated surgically. The patient was a 3-month-old boy with no notable medical history who presented to a pediatric clinic with frontal prominence. Computed tomography (CT) revealed premature fusion of the metopic suture, and he was referred to the authors' department for surgical treatment. A midline frontal ridge was observed but the keel-shaped forehead was not prominent, and the patient was diagnosed with mild trigonocephaly. Mild depression was observed in the temporal regions, and CT demonstrated a horizontal constricting ring of the skull (circumferential depression) extending approximately three-quarters of the way from the frontal region to both temporal areas. At 11 months of age, 1-stage cranial reconstruction was performed for mild trigonocephaly, along with correction of the constricting deformity. Through a coronal incision, the supraorbital bar and frontal bone flap were removed and reshaped. The parietal and temporal bones posterior to the frontal bone flap were barrel-staved, and the depressed bone fragments were elevated to reconstruct the constricted region. Postoperatively, the frontal contour improved, and the constricting ring observed before surgery resolved, resulting in an overall satisfactory cranial shape. One year after surgery, no signs of developmental delay or neurological impairment were observed. The authors experienced a rare case of mild trigonocephaly accompanied by an atypical horizontal constricting ring of the skull. Cases of nonsyndromic craniosynostosis with a horizontal constricting ring are extremely rare, and to our knowledge, none have been previously reported. Possible etiologies include an amniotic constriction band, a constricting ring caused by squamosal suture fusion as seen in cloverleaf skull, or compensatory deformation associated with restricted cranial growth; however, the exact mechanism remains unclear. In the present case, cranial reconstruction successfully improved the deformity, though long-term follow-up is necessary.