It should be distinguished from cranial meningocele in which the lesion contains only meninges, and from extracranial brain herniation in which brain herniates through a dural and skull defect (e.g. post trauma or surgery).
Numerous classification systems exist for encephalocoeles, many which are only of subspecialty interest, and most use very similar terminology, sometimes with different meanings 7. As a result reading about this topic can be frustrating. The term nasal encephalocoele is, for example, variably used, often to encompass both frontoethmoidal and basal encephalocoeles 8.
A fairly common classification still widely used is that first described by Suwanwela and Suwanwela in 1972 which divides the encephaloceles according to location 4:
- occipital encephalocoele: ~75% of cases
- interfrontal encephalocoele
- associated with craniofacial clefts
- frontoethmoidal encephalocoele
basal encephalocoele: ~10% 9
- fronto-sphenoidal or spheno-orbital
They are thought to occur in one of every 4,000 live births. Fronto-ethmoidal encephaloceles are more common in South and Southeast Asian populations. There is no recognised gender predilection.
Fronto-ethmoidal encephaloceles manifest as a clinically visible mass along the nose. The intracranial root of most fronto-ethmoidal encephaloceles lies at the foramen caecum, a small ostium located at the bottom of a small depression anterior to the crista galli and formed by the closure of the frontal and ethmoid bones.
Basal encephaloceles are internal and are not generally externally visible, although they may manifest as a lump or bump in the oropharynx or nasopharynx.
Encephaloceles, when congenital (most common) are a form of neural tube defect and occur due to a failure of fusion during embryogenesis of the cartilaginous neurocranium, the membranous neurocranium or viscerocranium 6.
In adults, encephalocoeles are mainly due to traumatic or iatrogenic causes, but are also increasingly recognised in idiopathic intracranial hypertension.
Most cases tend to be sporadic.
Occipital encephaloceles may be associated with a number of additional abnormalities:
An encephalocoele may be seen as a purely cystic mass or may contain echoes from herniated brain tissue. If the mass appears cystic, the meningocoele component predominates, while a solid mass indicates predominantly an encephalocele. Larger encephalocoeles may show accompanying microcephaly.
MR imaging is the best imaging modality for defining the contents of an encephalocele prior to surgery. High-resolution CT may also be used to display the bone anatomy, but the intracranial connection is best defined with MR imaging. The extent of cerebral tissue in an encephalocele is also better defined with MR imaging, which aids in prognosis and surgical planning.
Treatment and prognosis
The prognosis is variable dependent on the presence of associated anomalies and presence of microcephaly (carries a much poorer prognosis). A Caesarian delivery may be considered to allow for less traumatic birth for the fetal head.
- 1. Morón FE, Morriss MC, Jones JJ et-al. Lumps and bumps on the head in children: use of CT and MR imaging in solving the clinical diagnostic dilemma. Radiographics. 24 (6): 1655-74. doi:10.1148/rg.246045034 - Pubmed citation
- 2. Entezami M, Albig M, Knoll U et-al. Ultrasound Diagnosis of Fetal Anomalies. Thieme. (2003) ISBN:1588902129. Read it at Google Books - Find it at Amazon
- 3. Sandler MA, Beute GH, Madrazo BL et-al. Ultrasound case of the day. Occipital meningoencephalocele. Radiographics. 1986;6 (6): 1096-9. Radiographics (citation) - Pubmed citation
- 4. Dhirawani RB, Gupta R, Pathak S et-al. Frontoethmoidal encephalocele: Case report and review on management. Ann Maxillofac Surg. 2014;4 (2): 195-7. doi:10.4103/2231-0746.147140 - Free text at pubmed - Pubmed citation
- 5. Diebler C, Dulac O. Cephaloceles: clinical and neuroradiological appearance. Associated cerebral malformations. Neuroradiology. 1983;25 (4): 199-216. Pubmed citation
- 6. Nadich T. P., Blaser S. I., Bauer B. S., et al. Embryology and congenital lesions of the midface. In: Som P. S., Curtin H. D., editors. Head and Neck Imaging. 4th. Vol. 1. St Louis, Miss, USA: CV Mosby; 2003. p. p. 3e86.
- 7. Textbooks of Operative Neurosurgery ( 2 Vol.). B.I. Publications. (2005) ISBN:817225217X. Read it at Google Books - Find it at Amazon
- 8. Hoving EW. Nasal encephaloceles. Childs Nerv Syst. 2000;16 (10-11): 702-6. doi:10.1007/s003810000339 - Pubmed citation
- 9. Suwanwela C, Suwanwela N. A morphological classification of sincipital encephalomeningoceles. J. Neurosurg. 1972;36 (2): 201-11. doi:10.3171/jns.1972.36.2.0201 - Pubmed citation