cephalocele – occipital
description
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 cranio-rachischisis. 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.
diagnosis
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.
differential diagnosis
the identification of an extracranial mass will prompt consideration of the following: in exencephaly, no cranium will be evident at all. scalp oedema 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.
sonographic features
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.
associated syndromes
- apert
- chromosome abnormalities
- cranio-telencephalic dysplasia
- fraser
- fronto-facio-nasal dysplasia
- frontonasal dysplasia
- knobloch-vitreoretinopathy
- oculo-cerebro-cutaneous
- roberts-sc phocomelia
- scalp defect-craniostenosis
- amniotic bands
references
- budorick ne, pretorius dh, mcgahan jp, grafe mr, james he, slivka j cephalocele detection in utero: sonographic and clinical features ultrasound obstet gynecol 5: 77-85
- wininger sj, donnenfeld ae syndromes identified in fetuses with prenatally diagnosed cephaloceles prenat diagn 14: 839-843
- becker r, novak a, rudolph k-h a case of occipital encephalocele combined with the right lung aplasia in atwin pregnancy j perinat med 21: 253-258
- sherer dm, perillo am, abramowicz js fetal hemangioma overlying the temporal occipital structure, initially diagnosed by ultrasonography as an encephal ultrasonography as an encephalocele j ultrasound med 12: 691-693
- winter tc, mack la, cyr dr prenatal sonographic diagnosis of scalp edema/cephalohematoma mimicking an encephalocele ajr 161: 1247-1248
- adetiloye va, dare fo, oyelami oa a ten-year review of encephalocele in a teaching hospital int j gynecol obstet 41: 241-249
- bronshtein m, bar-hava i, blumenfeld z early second-trimester sonographic appearance of occipital haemangioma simulating encephalocele encephalocele prenat diagn 12: 695-698
- bulas di, johnson d, fonda allen j, kapur s fetal hemangioma: sonogrphic and color flow doppler findings j ultrasound med 11: 499-501
- fernandez g, hertzberg bs prenatal sonographic detection of giant parietal foramina j ultrasound med 11: 155-157
- goldstein rb, lapidus as, filly ra fetal cephaloceles: diagnosis with us radiology 180: 803-808
- fleming ad, vintzileos am, scorza we prenatal diagnosis of occipital encephalocele with transvaginal sonography j ultrasound med 10: 285-286
- jeanty p, shah d, zaleski w, ulm j, fleischer a prenatal diagnosis of fetal cephalocele: a sonographic spectrum am j perinatol 8: 144-149
grundy h, glasmann a, burlbaw j, walton s, dannar c, doan l hemangioma presenting as a cystic mass in the fetal neck j ultrasound med 4; 147-150 - graham d, johnson tr, winn k, sanders rc the role of sonography in the prenatal diagnosis and management of encephalocele j ultrasound med 1: 111-115.