Anencephaly

Screening OB Ultrasound • Xray of the Week 2016 • Week #39

This 28 year old had a routine OB ultrasound. What is the abnormality? What is the significance of this finding?

Fig 1A: Prenatal ultrasound. Coronal head. Absence of the calvarium and brain with associated bulging orbits giving the "frog eye" appearance.

Fig 1B: Prenatal ultrasound. Sagittal head and neck. Absence of the calvarium and brain.

Anencephaly is the most severe neural tube defect (NTD) with complete absence of most of the cranium, meninges, and calvarium due to failure of closure of the rostral neural tube. All women of child-bearing age should consume 0.4 mg of folic acid daily, especially those attempting to conceive or who may possibly conceive, as this can reduce the risk of anencephaly from 0.1 % to 0.03%.

Genetics may play a role in the cause of anencephaly as women with a prior pregnancy with NTD have a 3% risk of having another child with a NTD. Other possible factors include insulin-dependent diabetes, exposure to anticonvulsants, and toxins such as lead, chromium, mercury, and nickel.

Antenatal screening for NTD’s with ultrasound and maternal serum alpha-fetoprotein is essentially 100% effective. With ultrasound, no brain parenchymal tissue is seen above the orbits and the calvarium is largely absent. As in this case, coronal ultrasound of the head demonstrates absence of the calvarium and brain with associated bulging orbits giving the "frog eye" appearance. [Fig.1A] Associated findings on ultrasound may include: other neural tube defects such as spina bifida, congenital heart defects, cleft lip/palate, diaphragmatic hernia, spinal dysraphism, clubfoot, omphalocele, and urinary tract anomalies such as hydronephrosis. Prognosis is dismal with 100% fatality, most within the first few hours after delivery.

References:

1. Cameron M, Moran P. Prenatal screening and diagnosis of neural tube defects. Prenat Diagn. 2009 Apr;29(4):402-11

2. Goldstein RB, Filly RA. Prenatal diagnosis of anencephaly: spectrum of sonographic appearances and distinction from the amniotic band syndrome. AJR Am J Roentgenol. 1988;151 (3): 547-50.

3. Morbidity and Mortality Weekly Report (MMWR). Effectiveness in Disease and Injury Prevention Use of Folic Acid for Prevention of Spina Bifida and Other Neural Tube Defects -- 1983-1991 http://www.cdc.gov/mmwr/preview/mmwrhtml/00014915.htm

4. Timor-tritsch IE, Greenebaum E, Monteagudo A et-al. Exencephaly-anencephaly sequence: proof by ultrasound imaging and amniotic fluid cytology. J Matern Fetal Med. 5 (4): 182-5.

Kevin Rice, MD serves as the Medical Director of the Radiology Department of Valley Presbyterian Hospital in Los Angeles, California and is a Member of Renaissance Imaging Medical Associates. Dr. Rice has made several media appearances as part of his ongoing commitment to public education. Dr. Rice's passion for state of the art radiology and teaching includes acting as a guest lecturer at UCLA. In 2015 Dr. Rice launched Global Radiology CME to provide innovative radiology education at exciting international destinations, with the world's foremost authorities in their field.

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