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Fetal Cephalocele

Occipital Cephalocele
Encephalocele at 14 weeks
Frontal Encephalocele

Findings:

A predominantly cystic mass is seen protruding from the occipital region. In the adjacent case a predominantly solid mass (arrow) is seen herniating from the occiput in this 14 week fetus. In the case on the far right, a frontal solid encephalocele (arrow) is seen.

Discussion:

Cephaloceles are complex neural axis malformations which manifest as herniation of the meninges and often cerebral tissue through a defect in the fetal calvarium. The commonly used term encephalocele describes the condition in which there is herniation of brain as well as the meninges. Herniation of the meninges alone, cranial meningocele, may occur in isolation. The incidence varies geographically from 1.2 in 10,000 in the U.S. to 0.3-0.6 / 1000 births in England. In one center, cephaloceles accounted for nearly 10% of fetal neural axis abnormalities malformations detected with prenatal ultrasound over a 4 year period. In one pathologic study, encephalocele was the most common neural axis abnormality in fetuses spontaneously aborted at less than 20 weeks. The site of involvement in the fetal calvarium varies geographically although most occur in the midline. In the Western part of the world occipital cephaloceles are most common occuring in 75% of cases. Anterior, frontal lesions occur in 15-20% of cases but are more common in the Eastern part of the world. They may also occur in parietal or nasopharyngeal locations. The etiology is controversial. Most investigators believe it is due to failure of closure of the rostral end of the neuropore resulting from either overgrowth of neural tissue in the line of closure or a failure of induction by adjacent mesodermal tissues which in turn interfere with normal closure of the skull.

Other cranial or neural axis abnormalities may occur in association with cephaloceles. Microcephaly is seen in 20% of cases of cephaloceles, spina bifida is seen in 7-15% of cases and hydrocephalus occurs in 80% of occipital meningoceles, 65% of occipital encephaloceles and 15% of frontal cephaloceles. In addition, cerebellar abnormalities, callosal agenesis and migrational abnormalities may be seen. Cephaloceles may be associated with other medical conditions such as maternal diabetes or rubella or with genetic syndromes most notably Meckel-Gruber sydnrome, an autosomal recessive disorder in which dysplastic kidneys and polydactyly are seen in addtion to an encephalocele. Cephaloceles occuring from amniotic-band disorder do not recur and can be recognized by their assymetrical appearance.

Syndromes Associated with Cephaloceles*

Syndrome
Inheritance
Sonography

Occipital

Chemke

Autosomal Recessive

Hydrocephalus

Cryptopthalmos

Autosomal Recessive

Dyssegmental dwarfism

Autosomal Recessive

Short bowed tubular bones, small thorax, cleft palate, vertebral abnl

Knoblock

Autosomal Recessive

None

Meckel

Autosomal Recessive

Dyspastic kidneys, polydactyly, hydrocephalus, cleft palate, heart defects, liver cysts

Roberts

Autosomal Recessive

Short or absent limbs, facial cleft, hypertelorism, heart and kidney defects

Fetal warfarin

None

Short limbs, hydrocephalus

Frontal

Frontonasal Dyplasia

Sporadic, some familial

Hyperteleorism

Variable Location

Early amnion rupture sequence

Sporadic

Limb amputations, facial clefts, thoraco-abdominal wall defects,malfomed skull, amniotic bands

*Adapted from: Chervenak FA, Issacson G, Mahoney MJ, Berkowitz RL, Tortora M, Hobbns JC. Diagnosis and management of cephalocele. Obstet Gynecol 64:89, 1984

Sonographically, these lesions may appear either as 1) a cyst protruding from the fetal calvarium representing a meningocele or cyst within cyst appearance, seen in 20% in one series; 2) a solid mass protruding from the calvarium representing a herniated brain - encephalocele and 3) either or both of the above associated with a defect in the calvarium. A false positive diagnosis of a cephalocele may be made if: a cloverleaf skull is misinterpreted as a cephalocele (here the "protrusion" is bone covered) or if a "critical angle dropout" is misinterpreted as a gap in the calvarium. In addition, the following diagnostic entities should be considered as part of the differential diagnosis for a "calvarial mass": cystic hygroma, scalp edema, teratomas, hemangiomas and branchial cleft cysts and iniencephaly. Iniencephaly is a abnormality of the occipital bone in addition to a spina bifida deformity of the cervical and upper thoracic spine. Cerebral tissue and spinal cord lie adjacent to the occipital area and upper thoracic spine. The head is often hyperextended. While many neural axis abnormalities are first detected due to abnormal levels of maternal serum AFP, fetal cephaloceles may escape detection, as they may be covered by normal or modified skin. The prognosis is dependent upon the presence and amount of herniated brain, the presence of hydrocephalus, the presence of microcephaly and associated abnormalities. In the presence of brain herniation the mortality is 44%. Among survivors 74% may be retarded.

References:

Graham D, Johnson TRB, Winn K, Sanders RC. The role of sonography in the prenatal diagnosis and management of encephalocele. J Ultrasound Med 1:111-115, 1982

Bronshtein M, Zimmer EZ. Transvaginal songraphic follow-up on the formation of fetal cephalocele at 13-19 weeks gestation. Obstet Gynecol 78:528, 1991

Chervenak FA, Issacson G, Mahoney MJ, Berkowitz RL, Tortora M, Hobbns JC. Diagnosis and management of cephalocele. Obstet Gynecol 64:86, 1984

Schulman K. Encephalocele, Birth Defects Compendium. Second edition. Edited by D Bergsma. New York, Alan R. Liss, Inc., 1979, pp 390-391

Ingraham FD, Swah H. Spina bifida and cranium bifidum I. A survey of five hundred and forty six cases. N Engl J Med 228:559,1943

Leong AS, Shaw CM. The pathology of occipital encephalocele and a discussion of the pathogenesis. Pathology 11:223, 1979

Cohen MM, Lemire RJ. Syndrome with cephaloceles. Tertology 25:161,1982

Goldstein RB, LaPidus A, Filly RA. Fetal cephaloceles: diagnosis with US. Radiology 180:803-808, 1991

Creasy MR, Albeman ED. Congenital malformations of the central nervous system in spontaneous abortions. J Med Genet 13:9-16, 1976

Lorber J, Schofield JK. The prognosis of occipital encephalocele. Z Kinderchir 28:347-35,1979

Fleming AD, Vintzileos AM, Scorza WE. Prenatal diagnosis of occipital encephalocele with transvaginal sonography. 10:285-286, 1991

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Peter W. Callen, M.D.
Professor of Radiology, Obstetrics, Gynecology and Reproductive Science
University of California Medical Center, San Francisco, California