Premature closure of a cranial suture is termed synostosis. This condition involves the early fusion of one or more sutures in the skull, which can lead to abnormal skull shape and potentially increased intracranial pressure if untreated. Clinically, recognizing cranial synostosis is critical for timely surgical intervention to allow normal brain growth and to correct deformities. Surgical correction often involves releasing the fused suture to restore the skull’s flexibility. Ankylosis refers specifically to joint stiffness, syndesmosis is a type of fibrous joint, and diastasis refers to the separation of normally joined bones, making these terms incorrect for suture fusion.

Reference: Gray's Anatomy, 42nd Edition.