Address correspondence to: Ana Monte­agudo, MD, Columbia Presbyterian Medical Center, 622 West 168th Street, New York, NY 10032-3784, Ph: 212-305-2169, Fax: 212-305-3869.

Synonyms: Cranium bifidum, encephalocele, meningocele, meningoencephalocele, encephalocystocele, ventriculocele, ence­phalocysto­meningocele, hydranen­ce­pha­locele, frontonasal en­ce­pha­locele, sincipital ence­phalocele.

Definition: Midline frontonasal herniation of brain and/or meninges through a skull defect.

Prevalence: 0.5:10.000 live births.

Etiology: Sporadic, familial or associated with other malformations.

Pathogenesis: Unclear.

Associated anomalies: Ocular hypertelorism, nasal widening, complex facial malformations such as cleft palate, lip and median nasal fissure, spina bifida, agenesis of the corpus callosum, ocular malformations and ventriculomegaly, deformity of the frontal bones known as the lemon sign in ultrasonography and microcephaly.

Differential diagnosis: Teratoma and gliomas, both of which have similar embryologic development. Also included are: dermal sinus cyst, facial hemangioma, lacrimal duct cyst, orbital duplication and prosbosis.

Prognosis: Depending on the contents of the cephalocele sac.

Recurrence risk:  Although most of the anterior cephaloceles are sporadic, some are associated with chromosomal aberrations or with syndromes which may be familial.

Management: Prenatal: Anatomic survey to search for associated anomalies and chromosomal analysis. Termination of pregnancy before viability is an option. Cesarean section for fetal indications is not recommended. Postnatal: prevent infection and surgery.

MESH Encephalocele BDE 0343 POS 3720 ICD9 742.0 CDC 742.085

Case report

A 26-year-old black woman G₄P₁₀₂₁ was referred at 16 weeks for routine ultrasound. The ultrasound examination revealed a single live fetus with an irregularly shaped, solid appearing mass protruding from the right side of the fetal mouth (fig. 1).

Figure 1: Top left: Relationship of the mass and the face. Top right: Parasagittal section through the mass and the sonolucency over the area of the right frontal lobe. Bottom left: A slightly more lateral section than the top-left one. Bottom right: Coronal section demonstrating the relationship of the mass, the orbits and the maxilla.

On transvaginal sonography a sono­lucency was noted in the right frontal aspect of the brain. The facial mass appeared to be connected with the lower aspect of the right frontal lobe (fig. 2). No other fetal anomalies were noted. The differential diagnosis was anterior cephalocele versus facial teratoma. The patient"s past obstetrical and family histories were noncontributory.

Figure 2: Left: Axial section of the fetal head, demonstrating the unilateral sonolucency over the right anterior aspect of the brain. Middle & right: Coronal sections demonstrating the relationship of the mass and the orbit and maxilla.

After extensive counseling, the patient elected to terminate the pregnancy. An amniocentesis was performed for karyotyping, and the pregnancy was terminated using Prostin^® suppositories. A male fetus weighing 200g was delivered. Examination of the fetus revealed a dark color mass measuring 10 by 15 mm, stretching the right upper lip over the mass (fig. 3).

The nose was depressed longitudinally and the nares widely spaced. A sagittal hemisection of the entire head of the fetus demonstrated that the mass penetrated the palate and possibly the sphenoid bone (fig. 4). No other fetal malformations were noted. The karyotype revealed a normal male. The pathological diagnosis was sincipital cephalocele of the naso-ethmoidal type.

Figure 3: Sagittal hemisection. The mass perforates the palate and possibly the sphenoid bone (arrows). Note the area (open arrow) which created the sonolucency in the sonogram of the forebrain.

Figure 4: The two main types of cephaloceles: on the left, the sincipital cephaloceles; on the right, the basal cephaloceles.

Discussion

Definition

Anterior cephaloceles are mid- line frontonasal herniations of brain and/or meninges through a skull defect. Often, cephaloceles occur at the sites of the fontanelles (frontal, sphenoidal) or at the cribriform plate of the ethmoid, the foramen cecum, the foramen magnum, or through a suture line^7,8. In general, cephaloceles can be further classified into three types, depending on the contents of the herniated sac. The three types are meningocele which contains only meninges, encephalomeningocele which contains brain and/or meninges and en­ce­phalomeningocystocele which includes part of the ventricular system as well^9,10.

Prevalence

The incidence of all cephaloceles is 0.5:10,000 live births¹. The incidence of anterior cephaloceles is higher in Southwest Asia (Thailand) and Russia compared to the incidence in Western Europe and the United States. In some geographical areas the ratio of occipital cephaloceles to sincipital cephaloceles varies from 1:1 to 1:15. In the West, 80% of the cephaloceles are occipital; the other 20% are equally divided among frontal and parietal cephaloceles^2-6.

Etiology

Anterior cephaloceles may occur as a sporadic developmental defect, as part of a syndrome or occurring in association with other malformations. Syndromes or malformations which feature an anterior cephalocele include aberrant tissue band, frontonasal dysplasia, absent corpus callosum, clefting, craniostenosis, hypothalamic pituitary dysfunction, meningomyelocele and Robert"s-SC phocomelia syndrome. Cephaloceles have also been reported with several chromosomal syndromes^2,11,12.

Embryology

The pathogenesis of anterior ­ce­pha­lomeningoceles is still unclear. A paper written in 1938 summarizes some of the theories which are still valid today⁷. Already in 1827, Saint Hillaire published an interesting theory attributing this pathology to a faulty adhesion between the dura, the brain and the skin of the cranium, resulting in a maldevelopment of the bony vault and subsequent “outpouring” of the brain. Later on, hydrocephalus was implicated in its pathogenesis, raising the possibility of increased intracranial pressure purporting the lesion. In 1890, Berger was the first to call this lesion “encephalomata”. To somehow shorten the list of authors and the large number of theories on the pathogenesis of this brain pathology, one should review the embryology of the skull and brain.

At the end of the third month, the frontal end and the ethmoid bones are still apart. It has been observed that the cephalocele defects were always smooth and rounded, and clearly punched out. They were never cleft or “split”. This would suggest that the meningeal and brain protrusions existed first and the bony defect was secondary. This also would support the theory that meningeal and brain protrusions occur before the formation of the ethmoid and the nasal septum, around the sixth week of intrauterine life.

It seems that the events leading to the formation of anterior cephalocele must occur quite early in development at around 45-50 days embryonic age. This is the time when the base of the occiput and the sphenoid body develop and assume their normal appearance¹³.

Pathogenesis

Overdistension of the neural tube occurs with the closure of both the neural groove and anterior neural pore. Adhesion of the anterior neural pore to the overlying tissue and ectoderm occurs for unknown etiological factors. The defect in the mesoderm does not resolve, and the final lesion is established due to the protrusion of the primitive brain and its coverings. The site of the cephalocele depends on the pathway taken through the developing bones. It is believed that intermittent increase in intracranial pressure may further push on the brain tissue and enlarge the lesion. Many feel that cephaloceles are developmental and non-familial and are not necessarily associated with other congenital malformations. The cephaloceles are not confined to man but are found also in lower animals⁹.

It was postulated that the higher frequency in southwest Asia is due to 1) a defective germplasm which is endemic and inherent in certain races; 2) infections of the mother during the first months of pregnancy;  3) the effect of unknown medication in the first months of pregnancy; and 4) the effect of some unknown inherent dietary factor.

Types

A nasofrontal lesion protrudes through the junction of the frontal and nasal bones. The nasoethmoidal lesion would push through between the ethmoids, the nasal and the frontal process of the maxillary bones. Finally a naso-orbital lesion would emerge through a defect between the frontal and the lacrimal bones. The cephaloceles always occur in the midline sagittal axis of the cranium (fig. 4)^6-8,11. Anterior cephaloceles are divided into two main types: the sincipital and the basal defects.

The sincipital cephaloceles are always external lesions which occur near the root of the nose (glabella) and are subdivided into nasofrontal, nasoethmoid and naso-orbital types.

The basal cephalocele is an internal lesion which occurs within the nose, the pharynx, or the orbit. These are subdivided into five types: spheno-orbital, spheno­maxillary, transethmoidal, sphenoethmoidal and sphenopha­ryn­geal.

Diagnosis

The prenatal diagnosis of occipital cephaloceles in the second and third trimester of pregnancy is relatively easy and accurate. But prenatal diagnosis of atypically located lesions (eg., anterior or parietal cephaloceles) or diagnosing these lesions in the first trimester may prove challenging, especially since anterior cephaloceles are rare in the United States.

Since cephaloceles develop very early during fetal development, they will be present at the time of the earliest obtained transvaginal sonography. The earliest sonographic features which may be recognized in the late first trimester are:

·         abnormal fetal profile

·         discrepancies in the BPD and head circumference measurements

·         changes in the sagittal and coronal sections of the face.

These features may be examined and evaluated as early as 9-14 weeks²⁰. Transvaginal scanning allows the use of sagittal and coronal planes that may be difficult to obtain with abdominal scans and allows early assessment. Also, detection of hypertelorism, ocular abnormalities as well as limb defects may be identified at this time.

Prognosis

The prognosis of cephaloceles depends largely on the contents of the cephalocele sac and the presence of other associated abnormalities. Encephalomeningocele or encephalomeningocystocele, in which a large amount of brain tissue is in the herniated structure and which is usually associated with microcephaly, hydrocephaly or other abnormalities, have a poor prognosis. The child dies as a result of complications, and the rare survivors are severely mentally and physically handicapped. Surgical procedures for the repair of anterior cephaloceles have been reported but offer only very limited improvement of facial deformities^3,14-17. Yet, it appears from the literature that anterior cephaloceles have a slightly better outcome than other types of cephaloceles. The presence of an isolated malformation, when repaired, does not preclude normal mental and physical development. However, many of the children who have survived suffer cosmetic facial and eye deformities^1,3,11,18,19.

Management

Prenatal management of an anterior cephalocele depends largely upon when the lesion is diagnosed. If the lesion is diagnosed early, before 24 weeks gestation, the parents have the option to terminate the pregnancy. If the pregnancy is terminated, every effort should be made to deliver the fetus intact. A karyotype should be obtained, although the association with a karyotypic abnormality is very low. An autopsy should be performed to look for evidence of associated malformations or syndromes which may be familial and therefore affect a future pregnancy. If the parents elect to continue the pregnancy or if the lesion is diagnosed after fetal viability, a detailed ultrasound should be performed to look for associated facial malformations, cleft lip and palate, hypertelorism, as well as microcephaly, hydrocephaly, absence of the corpus callosum, holoprosencephaly, meningo­mye­lo­cele and other associated mal­formations. The parents should be counseled that the chance for a good outcome is minimal, and cesarean section for fetal indications is not recommended¹.

References

1. Chevernak FA, Isaacson G, Mahoney NJ, et al: Diagnosis and management of fetal cephalocele. Obstet Gynecol 6486-90,1984.

2. Diebler C, Dulac O: Cephaloceles: clinical and neuroradiological appearance. Neuroradiology 25:199-216,1983.

3. Suwanwela C, Hongsaprabhas C: Fronto-ethmoidal encephalomeningocele. J Neurosurg 25:172-182,1966.

4. Hughes GB, Sharpino G, Hunt W, et al: Management of the congenital midline nasal mass: A review. Head Neck Surg 2:222-233,1980.

5. Goldstein RB, LaPidus AS, Filly RA: Fetal cephaloceles: Diagnosis with US. Radiology 180:803-8,1991.

6. Warkany J, Lemire RJ, Cohen MM. Mental Retardation and Congenital Malformations of the Central Nervous System. Year Book Medical Publishers, Chicago, 1981 pp 158-175.

7. Mood GF: Congenital anterior herniations of brain. Ann Otorhinolaryngol 47:391-401,1938.

8. Whatmore WJ: Sincipital encephalomeningoceles. Br J Surg 60:261-70,1973.

9. Harley EH: Pediatric congenital nasal masses. Ear Nose Throat J 70:28-32,1991.

10. Jeanty P, Shah D, Zaleski W, et al: Prenatal diagnosis of fetal cephalocele: A sonographic spectrum. Am J Perinatol 8:144-149,1991.

11. Cohen MM, Lemire RJ: Syndromes with cephaloceles. Teratology 25:161-172,1982.

12. Jones KL: Smith"s Recognizable Patterns of Human Malformation. Fourth Edition. Philadelphia, WB Saunders, 1988, p 710.

13. Rapport RL, Dunn RC, Alhady F: Anterior encephalocele. J Neurosurg 54:213-219,1981.

14. Paller AS, Pensler JM, Tomita T: Nasal midline masses in infants and children. Arch Dermatol 127:362-366, 1991.

15. Soyer P, Dobbelaere P, Benoit S: Case report: Transalar sphenoidal encephalocele. Uncommon clinical and radiologic findings. Clin Radiol 43:65-67,1991.

16. Nyberg DA, Mahony BS, Pretorius DH: Ultrasound of fetal anomalies text and Atlas. Year Book Medical Publishers, Chicago, 1990, p 203.

17. Dodge HW, Love M, Kernohan JW: Intranasal encephalomeningoceles associated with cranium bifidum. Arch Surg 79:87-96,1959.

18. Mealey J, Dzenitis AJ, Hockey AA: The prognosis of encephaloceles. J Neurosurg 2970;32:209-218.

19. Lipschitz R, Beck JM, Froman C: An assessment of the treatment of encephalomeningoceles. East Afr Med J 43;609-619,1969.

20. Timor-Tritsch IE, Monteagudo A, Peisner DB: High frequency transvaginal sonographic examination for the potential malformation assessment of the 9-14 weeks fetus. JCU 2:20:231-23,1991.