Summary: A 22-year-old G2P1 precipitously delivered a 37-week male infant at
home. The infant was transferred to our tertiary care facility. The
prenatal record was not available, but the patient’s mother gave a
history of an abnormal prenatal ultrasound showing exencephaly. At diagnosis, the family was offered termination but declined.
Admission examination demonstrated microcephaly with absence of the
cranium above the orbital ridge with a large portion of neural tissue
covered by dura protruding from the top of his head (Figure 1). Although
computed tomography (CT) is not typically utilized to image this
condition, it was requested immediately upon admission to better
delineate the deformity, to determine prognosis, to guide clinical
intervention (or withhold intervention) and to eventually assist in
genetic counseling discussions (Figure 2).
Summary: After a meeting among
the family, neurosurgeons, plastic surgeons and our ethics committee,
the parents decided to provide palliative support. The patient expired
after five days secondary to cardiac arrhythmia. Chromosomal analysis
Exencephaly (differential diagnosis includes acrania, acalvaria, anencephaly, large encephalocele or amniotic band syndrome.)1,3
Disorganized brain tissue arising from the base of the cranium. The
skull bones are malformed and the posterior cranial fossa is small. The
flat bones of the skull are absent.
Exencephaly is a congenital malformation along a spectrum that includes
acrania and anencephaly (acrania-exencephaly-anencephaly sequence).2,3
In acrania, the flat bones of the skull are at least partially absent,
with complete but abnormal development of the cerebral hemispheres.
Exencephaly demonstrates a large amount of disorganized brain tissue
extending from a malformed skull base (Figure 3).3 Because
this brain tissue is covered by only a vascular layer of epithelium, it
can be slowly degraded by the amniotic fluid and degenerate into
anencephaly.5 The incidence of exencephaly is much lower than
that of anencephaly, but the etiology is the same, so the recurrence
risk is the same as for other neural tube defects.6 Although
the mineralization of the skull is not well established until after 10
weeks, there have been cases of prenatal diagnosis as early as 9 weeks, 3
days proven by postmortem endovaginal ultrasound.2,4 First
trimester ultrasound findings of exencephaly include decreased size of
the cranial pole compared with the chest, dorsally bulging cranial pole,
irregularity of the surface of the cranium2 and echogenic amniotic fluid.3 The
etiology of the sequence is not exactly clear, but failed migration of
the mesenchyme during the 4th week of development or failed
differentiation of the mesenchyme have been suggested.3 Although
a significant number of fetuses with open neural tube defects are
chromosomally abnormal, this child was chromosomally normal.
The acrania-exencephaly-anencephaly sequence is commonly diagnosed by
prenatal ultrasound between 14 and 18 weeks, but some findings may
suggest the diagnosis much earlier in gestation. Regardless of
gestational age at diagnosis, the prognosis is poor.
Prepared by Dr. Drinkwine, Lieutenant Commander, Medical Corps,
United States Navy, and Dr. Holston, Lieutenant, Medical Corps, United
Navy, while at the Naval Medical Center, Portsmouth, VA.
The views expressed in this article are those of the authors and do
not necessarily reflect the official policy or position of the
Department of the Navy, Department of Defense, or the United States
- Cincore V, Ninios AP, Pavlik J et al. Prenatal diagnosis of acrania associated with amniotic band syndrome. Obstet Gynecol. 2003;102:1176-1178.
- Becker R, Mende B, Stiemer B et al. Sonographic markers of exencephaly at 9 + 3 weeks of gestation. Ultrasound Obstet Gynecol. 2000;16:582-584.
- Bianca S, Ingegnosi C, Auditore S et al. Prenatal and postnatal findings of acrania. Arch Gynecol Obstet. 2005;271:256-258.
- Machado RA, Brizot ML, Carvalho MH et al. Sonographic markers of exencephaly below 10 weeks’ gestation. Prenat Diagn. 2005;25:31-33.
- Chen CP, Chang TY, Lin YH et al. Prenatal sonographic diagnosis of acrania associated with amniotic bands. J Clin Ultrasound. 2004;32:256-260.
- Nawale AJ, Merchant SA, Koteyar SSR et al. Exencephaly: A rare case diagnosed on antenatal ultrasound. Bombay Hospital Journal [serial online]. 2000;42. Available at: http://www.bhj.org/journal/ 2000_4203_jul00/case_520.htm. Accessed June 12, 2006.