AUTHOR AND EDITOR INFORMATION

Section 1 of 12  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT Scan
• MRI
• Ultrasound
• Nuclear Medicine
• Angiography
• Intervention
• Multimedia
• References

INTRODUCTION

Section 2 of 12  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT Scan
• MRI
• Ultrasound
• Nuclear Medicine
• Angiography
• Intervention
• Multimedia
• References

Background

Encephalocele represents one end of the spectrum of open neural tube diagnoses.¹ With ultrasonography (US) scanning, the diagnosis is based on the herniation of a spherical, fluid-filled structure, more correctly diagnosed as a meningocele or brain parenchyma (encephalocele) beyond the calvarial confines.^{2, 3, 4, 5, 6, 7, 8} The herniation occurs through a calvarial defect. The earliest reported ultrasonographic diagnosis was made at 13 weeks' gestation. Once an encephalocele is diagnosed, a thorough search for associated abnormalities should be performed.^{9, 10}

An encephalocele results from failure of the surface ectoderm to separate from the neuroectoderm. This leads to a bony defect in the skull table, which allows herniation of the meninges (cranial meningocele) or of brain tissue. The occiput is the most common site of this type of neural tube defect (75%) in the United States and Western Europe. Approximately 90% of cases involve the midline.

Other malformations and/or chromosomal anomalies are noted in at least 60% of patients with encephalocele.^{9, 10, 11} Currently, most cases are diagnosed prenatally.^{2, 3, 4, 5, 6, 7, 8, 12, 13} Maternal serum alpha-fetoprotein levels are elevated in only 3% of patients, because most encephaloceles are covered with skin. Postnatally, infants may have associated cerebrospinal fluid (CSF) rhinorrhea and recurrent meningitis.¹⁴

See also the following related eMedicine topics:
Neural Tube Defects
Neural Tube Defects in the Neonatal Period

See also the following related Medscape topic:
Resource Center Spinal Disorders

Pathophysiology

The primary abnormality in the development of an encephalocele is a mesodermal defect resulting in a defect in the calvarium and dura that is associated with herniation of CSF, brain tissue, and meninges through the defect. The root cause of an encephalocele is the failure of surface ectoderm to separate from the neuroectoderm early in embryonic development. In the calvarium, induction of bone formation may be defective, or pressure erosion from an intracranial mass may occur. Defects at the skull base may be related to faulty closure of the neural tube or to failure of basilar ossification. Encephaloceles may be occipital (75%), fronto-ethmoidal (13-15%), parietal (10-12%), or sphenoidal. Fronto-ethmoidal encephaloceles are most common in Asia.^{15, 16}   

In terms of patient survival, the absence of brain tissue in the herniated sac is the single most favorable prognostic feature.¹⁷ Brain tissue in the herniated sac is usually apparent. However, it may be difficult to confidently exclude incorporated brain tissue in sacs that appear to be filled with CSF alone. Diagnosis is thought to be impossible before skull ossification, which starts at 10 weeks' gestation.

The earliest reported diagnosis was made at 13 weeks' gestation. The ultrasonographic appearance of an encephalocele is variable in the first trimester. Once an encephalocele is diagnosed, a search for associated anomalies, including intracranial and extracranial abnormalities (60-80%), should be performed.^{9, 10, 15} The risk of chromosomal abnormalities is 13-44%; therefore, karyotyping should be offered to the mother.¹¹

Associated anomalies include findings associated with various genetic syndromes, such as Meckel-Gruber, von Voss, Chemke, Roberts, and Knobloch syndromes.^{9, 10} In addition, findings may be related to nongenetic anomalies, such as cryptophthalmos syndrome, the presence of an amniotic band, warfarin use, maternal rubella, and diabetes. Other associated brain abnormalities that may occur in isolation or as part of genetic or nongenetic syndromes include spina bifida, agenesis of the corpus callosum, Arnold-Chiari II malformation, Dandy-Walker malformation, and brain migrational anomalies. The most common associated chromosomal anomaly is trisomy 18.

Occipital encephalocele is the most common form of encephalocele in the Western Hemisphere (71% in the United States). It is often associated with Dandy-Walker malformation and Arnold-Chiari II malformation. An occipital encephalocele may be high, above the foramen magnum, or it may involve the upper cervical spine and occipital bone. (The Chiari III malformation is a cervico-occipital encephalocele that contains most of the cerebellum.)

The frontoparietal encephalocele is the most common type of encephalocele in Southeast Asia. It is associated with midline craniofacial dysraphism.^{9, 10, 18} Sphenoidal encephaloceles are often clinically occult and usually become apparent at the end of the first decade of life.

See also the following related eMedicine topics:
Chiari I Malformation
Chiari II Malformation
Dandy-Walker Malformation
Meckel-Gruber Syndrome
Spinal Dysraphism/Myelomeningocele

Frequency

United States

There are 1-4 cases of encephalocele per 10,000 live births. In fetuses that have been spontaneously aborted before 20 weeks' gestational age, it is the predominant neural axis anomaly.^{5, 15, 19}

International

The worldwide incidence of encephalocele is not known.²⁰

Mortality/Morbidity

The development of an encephalocele reduces the chance of live birth to 21%, and only half of these live births survive. Approximately 75% of survivors have a mental deficit. Encephalocele recurs in 3% of patients after surgical repair, whereas the recurrence rate is higher in Meckel-Gruber syndrome (25%). The absence of brain tissue in the herniated sac is the single most favorable prognostic feature for survival.^{15, 17}

The prognosis for and treatment of a patient with an encephalocele depend on the site, size, and contents of the encephalocele.²¹ The ultimate outcome depends on the patient's karyotype and on his/her associated syndromes, as well as on the ease of surgical correction. A good prognosis is indicated for a patient who has an anterior encephalocele containing no brain tissue and who has no associated anomalies. Poor prognostic indicators include a large or posterior encephalocele and systemic anomalies. Patients with an anterior encephalocele have a 100% survival rate, but the survival rate decreases to 55% in persons with a posterior encephalocele. A nasal meningo-encephalocele is a rare cause of recurrent meningitis.

A prenatal diagnosis of an encephalocele should prompt a thorough search for other abnormalities.^{9, 10} An accurate diagnosis is critical in determining the prognosis and in providing appropriate genetic counseling.

Race

Encephaloceles have a multifactorial etiology, and genetic and geographic factors have been implicated. Frontal encephaloceles are far more common in the Far East, particularly in the Chinese population, and are associated with a more favorable prognosis.

Sex

Encephaloceles occur more commonly in females than in males.

Age

Currently, most encephaloceles are diagnosed prenatally and present at birth.^{2, 3, 4, 5, 6, 7, 8, 12, 13} Some, particularly sphenoidal encephaloceles, may become apparent later in childhood.

Anatomy

An encephalocele results from a defective closure of the embryologic neural tube. The defect is believed to occur because of a failed closure of the rostral end of the neural tube during the fourth week of gestation. The defect causes an abnormality of the skull and underlying meninges. A spectrum of anomalies is seen, with the most mild being cranium bifidum occultum; this is analogous to spina bifida occulta.

A dermal defect is frequently present. An example is a dermal sinus leading from the cranial defect, which may also be associated with an intracranial dermoid cyst. Herniation of the meninges through the cranial defect is called a meningocele, whereas herniation of brain tissue and meninges through the bony defect is called an encephalocele.

Clinical Details

Most encephaloceles are diagnosed through routine prenatal US scanning.^{2, 3, 4, 5, 6, 7, 8} Maternal serum alpha-fetoprotein levels are elevated in only 3% of patients, because most encephaloceles are covered with skin. Postnatally, infants may present with CSF rhinorrhea and recurrent meningitis. Postnatal presentation also depends on the associated malformations and the size and contents of the defect. As previously stated, approximately 75% of survivors have a mental deficit.

Preferred Examination

US scanning remains the mainstay of fetal imaging; there is evidence, however, that fetal magnetic resonance imaging (MRI) may provide superior detail of central nervous system (CNS) anomalies.

DIFFERENTIALS

Section 3 of 12  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT Scan
• MRI
• Ultrasound
• Nuclear Medicine
• Angiography
• Intervention
• Multimedia
• References

Other Problems to Be Considered

Normal fetal hair
Scalp edema
Iniencephaly
Epidermal scalp cyst²²
Cloverleaf skull
Iniencephaly
Teratoma (In a newborn, a mature cystic teratoma in the pineal region may mimic a parietal encephalocele.)²³

In addition, a pituitary adenoma in association with a sphenoidal meningoencephalocele, although extremely rare, should be considered whenever a sellar tumor with cystic extension is encountered.  

Of these, encephalocele is the only condition associated with a calvarial defect. In most encephaloceles, other associated intracranial anomalies are present.

RADIOGRAPH

Section 4 of 12  

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• Differentials
• Radiograph
• CT Scan
• MRI
• Ultrasound
• Nuclear Medicine
• Angiography
• Intervention
• Multimedia
• References

Findings

Cranial defects that are associated with encephaloceles usually occur in the midline of the skull and appear anywhere from the base of the nose to the base of the occipital bone.^{9, 10, 24} The skull defect is smooth and well circumscribed, with no associated increased opacity at the margin of the bone defect.

Degree of Confidence

Cranial defects occurring in association with encephaloceles have a nonspecific appearance. Moreover, plain radiographs rarely provide diagnostic information regarding the contents of an encephalocele.

False Positives/Negatives

Epidermoid and dermoid cysts, craniolacunia, parietal foramina, frontal fenestrae, fibrous dysplasia, wide sutures, cranial dysostosis (including cleidocranial dysostosis), and hypophosphatasia can mimic encephalocele-related cranial defects.

CT SCAN

Section 5 of 12  

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• Introduction
• Differentials
• Radiograph
• CT Scan
• MRI
• Ultrasound
• Nuclear Medicine
• Angiography
• Intervention
• Multimedia
• References

Findings

Although prenatal diagnosis of fetal encephalocele and its associated anomalies has been achieved by using computed tomography (CT) scans, the use of radiation for diagnosis in fetuses is discouraged, particularly in the first 2 trimesters.

• Postnatally, CT scans provide an excellent depiction of the bony defect, particularly with coronal, sagittal, or 3-dimensional (3D) reconstruction. However, CT scanning is less capable than magnetic resonance imaging (MRI) in depicting soft-tissue components in an encephalocele.
• Water-soluble contrast material that is placed in the theca and that flows into the encephalocele may allow better evaluation of the contents.
• CT cisternography scanning often demonstrates a communication of the herniated sac with the intracranial subarachnoid space.
• Attenuation measurements may be used to differentiate brain tissue from CSF in the herniated sac.
• CT scans may be useful in the demonstration of associated intracranial anomalies, such as Chiari malformations, holoprosencephaly, Dandy-Walker complex, aqueduct stenosis, agenesis of the corpus callosum, and other midline abnormalities. MRI is considered superior to CT scanning in the analysis of these conditions.

Degree of Confidence

CT scanning is an excellent modality to use postnatally for depicting bony skull defects, particularly with 3D reconstruction. However, soft-tissue components of an encephalocele are not as well differentiated on CT scans as they are on MRI scans.

False Positives/Negatives

The differential diagnosis of an encephalocele includes an orbital apex, infection, trauma, and a nasopharyngeal, sinus, or temporal bone tumor. Infection and tumors usually show destruction of bone, and confusion is less likely to occur with the smooth, marginated cranial defect seen in an encephalocele. Benign tumors tend to cause bone erosion.

MRI

Section 6 of 12  

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• Introduction
• Differentials
• Radiograph
• CT Scan
• MRI
• Ultrasound
• Nuclear Medicine
• Angiography
• Intervention
• Multimedia
• References

Findings

Although US scanning has traditionally been the mainstay in fetal imaging, its resolution of the fine details of the brain and/or CNS is sometimes limited by the mother's body habitus, the surrounding amniotic fluid, and the position of the fetus. MRI may provide better detail in prenatal imaging. Fetal MRI requires fetal and maternal sedation. MRI appears to be an effective means of noninvasively assessing fetal CNS anomalies.^{12, 25} Its advantages include the following:

• The ability of MRI to resolve posterior fossa anatomy appears to be superior to that of US scanning.
• Fluid-filled and/or CSF-filled structures are demonstrated well on MRI scans.
• Postnatally, MRI is the examination of choice for the evaluation of an encephalocele. With the ability to depict the brain in multiple projections, MRI scans can provide exquisite detail of the cranial defect and the herniated contents.
• Contents of the herniated sac may include CSF, disorganized brain tissue, and even ventricles. These are depicted clearly on MRI scans.
• MRI can be useful in demonstrating associated intracranial anomalies, such as Chiari malformation, holoprosencephaly, Dandy-Walker complex, aqueduct stenosis, agenesis of the corpus callosum, and other midline abnormalities.

Degree of Confidence

Further experience with MRI may help to prove its true usefulness in analyzing fetal brain structures prenatally and vis-à-vis US scanning.

False Positives/Negatives

Postnatally, basal encephaloceles may be noted as masses protruding into the nasal cavity. They may mimic nasal polyps on CT and MRI scans. Because adenoids and nasal polyps are rare in infancy, the presence of a nasopharyngeal mass should alert the clinician to the possibility of a basal encephalocele.

ULTRASOUND

Section 7 of 12  

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• Differentials
• Radiograph
• CT Scan
• MRI
• Ultrasound
• Nuclear Medicine
• Angiography
• Intervention
• Multimedia
• References

Findings

• The prenatal ultrasonographic diagnosis of an encephalocele is based on the demonstration of a cranial defect with varying degrees of brain herniation.^{2, 3, 4, 5, 6, 7, 8}
• The classic ultrasonographic appearance is that of a mass in the midline of the skull, with most cases occurring in the occipital and (less commonly) frontal regions.
• The size of the bony defect can vary from a few millimeters upward, and the extruded sac can be small or can be larger than the fetal skull itself.
• The mass may be purely cystic, or it can contain echoes from brain tissue.
• Because skull ossification begins at 10 weeks' gestation, diagnosis is usually not possible before this time. The earliest reported diagnosis established by using a transvaginal scan was at 13 weeks' gestation. However, some have suggested that, starting at 9 weeks' gestation, the enlargement of the rhombencephalon cavity may indicate the presence of an encephalocele.
• Most encephaloceles are covered with skin; therefore, they are more likely to be diagnosed with screening US scanning than with maternal serum alpha-fetoprotein testing.
• The skull defect is identified in more than 80% of fetuses with an occipital encephalocele (75%). Associated findings may include a flattening of the basiocciput, an acute angle between the mass and skin line of the neck and occiput, ventriculomegaly, and a lemon sign (33%).
• A cyst-within-a-cyst appearance is occasionally seen. This results from herniation of the fourth ventricle in the encephalocele surrounded by CSF.
• A true frontal encephalocele is seen as an extrinsic mass near the dorsum of the nose, orbits, or forehead. Such encephaloceles are often associated with hypertelorism, midline craniofacial dysraphism, agenesis of the corpus callosum, interhemispheric lipoma, or heterotopias.¹⁸
• Sphenoidal encephaloceles are usually clinically occult and appear in the first decade of life, when it is more appropriate to use CT scanning and/or MRI than it is to employ other modalities.
• Frontal encephaloceles almost always contain brain tissue and involve the bridge of the nose (60%), as well as the nasal cavity (30%).
• Parietal encephaloceles are associated with hydrocephalus, aqueduct stenosis, Arnold-Chiari malformation, microcephaly, and Dandy-Walker cysts.
• US scanning may reveal a bony defect in the sphenoid bone that is associated with an overlying soft-tissue mass, but the mantle of the brain tissue in the encephalocele is often difficult to detect. In these cases, MRI is useful.

In one example of a fatal encephalocele, the encephalocele herniated through the clivus into the oropharynx. This appeared as a cystic mass that was surrounded by an echogenic rim protruding through the mouth. Ventriculomegaly and polyhydramnios were also noted. At delivery, airway intubation was not possible, and the baby did not survive.

Most parietal encephaloceles result from amniotic band syndrome, in which early disruption of skull development probably occurs. Encephaloceles that are secondary to amniotic bands are atypical, and their appearance is variable; moreover, they are usually not associated with other syndromes and/or genetic abnormalities.

Once an encephalocele is diagnosed, a search should be made for associated anomalies, such as Meckel-Gruber syndrome (which is characterized by an occipital encephalocele), microcephaly, cystic dysplastic kidneys, and polydactyly.^{9, 10} Meckel-Gruber syndrome may be more easily diagnosed in the first trimester, when the amniotic fluid volume is usually normal. In the second trimester, oligohydramnios may hamper visualization of polydactyly and the encephalocele.

Walker-Warburg syndrome, which also is associated with encephaloceles, is a lethal complex of the CNS and eyes.²⁶ The diagnosis is established by the detection of lissencephaly, hydrocephalus, and a cerebellar malformation. Recognizing these syndromes is important because they are autosomal recessive conditions. Because they can be recognized on prenatal US scans, targeted screening may be possible in the mother's subsequent pregnancies.

Degree of Confidence

US scanning remains the modality of choice for detecting prenatal CNS anomalies. To diagnose an encephalocele with certainty, a skull defect must be demonstrated. This is possible in 80% of fetuses with an encephalocele. Finding the defect may be difficult because of its small size; also, artifacts caused by shadowing may be present, and these can mimic a skull defect.

False Positives/Negatives

Occipital encephaloceles can be confused with a cystic hygroma, which has no cranial vault defect and contains no brain tissue.⁵ A high cervical meningocele also can mimic an encephalocele. A frontal encephalocele may be mistaken for a nasal teratoma; both conditions are rare, and the prognosis for each of them is poor.

The prenatal diagnosis of an epidermal scalp cyst simulating an encephalocele has been reported.²² Mimics of a parietal encephalocele include an ultrasonographic refraction artifact at the skull edge and a cloverleaf skull in which the temporal bone may be partially absent. An intra-oral salivary gland cyst can mimic a basal encephalocele.

NUCLEAR MEDICINE

Section 8 of 12  

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• Ultrasound
• Nuclear Medicine
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• Intervention
• Multimedia
• References

Findings

Radionuclide ventriculography and/or cisternography have been used postnatally to demonstrate the intracranial extension of an encephalocele. Currently, MRI can effectively demonstrate this extension. Radionuclide cisternography can be performed via lumbar puncture or ventricular injection by using technetium-99m (^99mTc) diethylenetriamine penta-acetic acid (DPTA) followed by planar imaging or single-photon emission CT (SPECT) scanning.

Tsuboi and colleagues reported on a 66-year-old man with a parietal intradiploic encephalocele that manifested as dizziness.²⁷ A lytic/destructive lesion of the right parietal bone was seen on a skull radiograph. CT scanning confirmed bone destruction associated with the right frontal lesion. A lesion in the parietal intradiploic space continuous with the right frontal lobe was observed with MRI. A biopsy was not considered because of the close proximity of the lesion to the central sulcus. SPECT scanning showed the same pattern of cerebral blood flow as that found in normal brain tissue, so diagnosis of an encephalocele was entertained.

On the basis of SPECT scanning and in the absence of symptoms and neurologic deficits, no surgical intervention was deemed necessary. The use of SPECT scanning, which proved instrumental in the diagnosis and management of this rare type of encephalocele, saved the patient from unnecessary surgery.

ANGIOGRAPHY

Section 9 of 12  

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• Differentials
• Radiograph
• CT Scan
• MRI
• Ultrasound
• Nuclear Medicine
• Angiography
• Intervention
• Multimedia
• References

Findings

Angiography may be needed to evaluate intracranial and extracranial vasculature before surgical repair is performed. Angiography is helpful if concern exists regarding the displacement of the dural venous sinus into the sac.

Degree of Confidence

Angiography remains the criterion standard for depicting vascular anomalies; however, cerebral angiography is rarely used in the evaluation of an encephalocele. MRI can usually depict the dural venous anatomy.

INTERVENTION

Section 10 of 12  

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• Introduction
• Differentials
• Radiograph
• CT Scan
• MRI
• Ultrasound
• Nuclear Medicine
• Angiography
• Intervention
• Multimedia
• References

Medical/Legal Pitfalls

• In infancy, the snaring of a nasal polyp should not be performed before an encephalocele has been excluded, because the procedure may result in the snaring of brain tissue.

Special Concerns

• The prognosis for patients with an encephalocele depends on the encephalocele's size, location, and contents, as well as on associated genetic abnormalities.¹⁷
• Twenty percent of fetuses with an encephalocele are stillborn.
• The prenatal diagnosis should be discussed with the parents, because in most pregnancies, termination is chosen.
• If the diagnosis is made later in pregnancy, cesarean delivery may be considered when neonatal surgery is planned.²⁸

MULTIMEDIA

Section 11 of 12  

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• Introduction
• Differentials
• Radiograph
• CT Scan
• MRI
• Ultrasound
• Nuclear Medicine
• Angiography
• Intervention
• Multimedia
• References

Media file 1:  Meckel-Gruber syndrome. Ultrasonograms show oligohydramnios-enlarged echogenic kidneys (left) and a fairly large occipital encephalocele containing brain tissue (right).
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Media type:  Ultrasound

Media file 2:  Sagittal ultrasonogram through the fetal skull shows a small occipital encephalocele.
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Media type:  Ultrasound

Media file 3:  Sagittal ultrasonogram through the fetal skull shows a fairly large occipital encephalocele containing brain tissue.
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Media type:  Ultrasound

Media file 4:  Sagittal ultrasonogram through the fetal skull shows a fairly massive occipital encephalocele associated with Dandy-Walker syndrome.
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Media type:  Image

Media file 5:  Coronal, T2-weighted magnetic resonance imaging (MRI) scan in a 7-year-old boy. The patient was examined by an ear, nose, and throat surgeon because of a nasal voice and a blocked nose. Images show a sphenoid encephalocele. Herniated brain tissue is seen in the right nostril through a sphenoid defect.
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Media type:  MRI

Media file 6:  Sagittal, T1-weighted magnetic resonance imaging (MRI) scan through the midline (same patient as in Image 5) shows brain herniation through the sphenoid into the nasal cavity (arrow).
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Media type:  MRI

Media file 7:  Axial, contrast-enhanced computed tomography (CT) scan through the basal cisterns in a 6-year-old child who presented with headaches and fever. Scan shows a rim-enhancing cystic mass eroding the inner skull table of the occiput (arrow). At surgery, an infected dermoid cyst was found.
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Media type:  CT

Media file 8:  Skull radiograph in a 76-year-old woman presenting with headaches and a palpable depression in the region of the parietal bones on both sides of the skull. The radiograph shows a well-defined thinning of the parietal bone (arrow).
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Media type:  X-RAY

Media file 9:  Transaxial, nonenhanced computed tomography (CT) scan through the vertex (same patient as in Image 8) shows developmental, bilateral parietal foramina.
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Media type:  CT

REFERENCES

Section 12 of 12

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT Scan
• MRI
• Ultrasound
• Nuclear Medicine
• Angiography
• Intervention
• Multimedia
• References

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Article Last Updated: Feb 21, 2008