Encephalocele Cranium bifidum occultum 2008-03-18T09:37:00Z SNOMEDCT_US:718099006 Cranium bifidum occultum, also known as Catlin mark, is a congenital midline skull defect presenting as an enlarged posterior fontanelle in the upper posterior angle of the parietal bone close to the intersection of the sagittal and lambdoid sutures. Cranium bifidum occultum occurs due to a defect in intramembranous ossification, a process through which skull bones (frontal, parietal, squamous temporal and occipital bones superior to the mendosal suture) ossify under a vascularized membrane toward the midline to cover the brain. Unlike cranium bifidum cysticum, cranium bifidum occultum does not have herniation of intracranial contents. As the skull grows, the midline cranium bifidum occultum defect is separated into bilateral enlarged parietal foramina (EPF) by a midline osseous bridge. Cranium bifidum tends to resolve into distinct enlarged parietal foramina over the first few years of life through the midline ossification of a central bridge of bone bisecting the defect. HP:0004423 UMLS:C1868598