encephalocele – occipital
cephalocele is the protrusion of intracranial contents through a bony defect in the skull or through one of the parietal foramina. cranial meningocele refers to herniation of meninges only, while encephalocele implies that brain tissue lies within the herniated sac. larger defects may extend caudally to involve and disrupt the cervical spine, a condition then known as craniorachischisis. the defect is thought to be a consequence of defective rostral neurulation, unlike the frontoethmoidal cephalocele. occipital cephaloceles have also been associated with rubella, diabetes, genetic syndromes, and amniotic band syndrome.
most cephaloceles are occipital; the presence of a posterior midline extracranial mass is characteristic. an underlying cranial bony defect is the rule but may be difficult to demonstrate if small. the mass is seen to derive from and move with the fetal head, and may be cystic, solid or both, representing meningocele, cephalocele, or meningoencephalocele respectively. this distinction is important as the prognosis will depend on the contents; demonstration of brain tissue in the herniated sac confers significant mortality (44%) and impaired cognitive development (91%). cranial meningoceles, in contrast, have a very low mortality, and 40% will demonstrate impaired cognitive function later. transvaginal ultrasound provides the enhanced resolution required to make an accurate diagnosis at an early stage, and is recommended in the evaluation of this condition. hydrocephalus is often evident, being present in 80% of meningoceles and 65% of encephaloceles. microcephaly is observed in 20%; agenesis of the corpus callosum, dandy-walker malformation, and spina bifida have been reported. other abnormalities include omphalocele, cleft lip and palate. the presence of occipital meningocele in combination with renal cystic dysplasia will prompt the diagnosis of the meckel-gruber syndrome. chromosomal abnormalities have been reported in 13-50% and include trisomy 13, trisomy 18, mosaic trisomy 20, triploidy, mosaic turner syndrome, balanced pericentric inversions, reciprocal and balanced translocations, and an enlarged proximal portion of the long arm of chromosome 1.
the identification of an extracranial mass will prompt consideration of the following: in exencephaly, no cranium will be evident at all. scalp edema due to fetal hydrops may be seen in association with pleural effusions and ascites. cystic hygroma is usually a bilateral cystic mass which may contain septations. tumours such as cranial teratomas and mesenchymal sarcomas are likely to have a solid or complex appearance. in iniencephaly the fetal head is held in fixed retroversion, and cervical dysraphism is evident. occipital haemangiomas have been reported, and doppler flow studies may help confirm the diagnosis. branchial cleft cysts are generally found inferior, anterior and lateral to the occipitocervical region.
cranial bony defect in occipital or parietal region which may be difficult or even impossible to find if very small.
if cystic, meningocele is likely; ascertain if solid components are present within the herniated sac, as this will alter the prognosis.
may be associated hydrocephaly or microcephaly.
polyhydramnios, neural tube defects or cystic renal dysplasia (meckel-gruber syndrome) may co-exist.
- aminopterin teratogenesis
- amniotic bands
- chromosome abnormalities
- cranium bifidum occultum
- diaphragmatic agenesis- midline defects
- dk-phocomelia- encephalocele- urogenital
- donnai-meckel like
- dyssegmental dysplasia (rolland- desbuquois)
- dyssegmental dysplasia (silverman- handmaker)
- facio-auriculo- vertebral
- fraser- cryptophthalmos
- fried: meckel-like
- froster-iskenius: radial-cardiac-renal
- keutel-humero radial synostois
- knobloch- vitreoretinopathy
- laryngeal atresia-hydrops
- maternal hyperthermia
- oculo-cerebro cutaneous
- oculo-encephalo- hepato-renal
- pectoralis major- renal anomalies
- von voss-cherstvoy: limb- thrombocytopenia
- warfarin embryopathy
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