Obstetric Ultrasound Quiz

Figure 1. A longiwdal midline scan. Pregnancy at 16.5 weeks. Posteriorplacenta.

For the correct diagnosis and a review of thecondition, refer to page number 42.

She was referred for an ultrasound examination at18 weeks gestation. Additional history obtained atthis time indicated no prior malformed offspring, nogenetic diseases in the patient's or her hushand'sfamilies, no exposure to drugs or radiation, and afamiJy history of diabetes.

Realtime ultrasound examination was performed.Representative ultrasound pictures are shown.(Figures I and 2)

What is your diagnosis?

Reprint Requests: Hos am E. Fadel, M.D.,Director oj Perinatology,University Professional Cel/ter II,8/8 St. Sebastian Way, Suite 200Augusta, GA 3090/

From the Department of Obstetrics and Gynecology,Sectioll of Perinatology,University Hospital, Augusta, GA.

Case ReportMr . J. J. is a 25-year-old. G3P2002, white female.

Mrs. J. J. had stopped birth control pills about oneyear previously and since then had regular menstrua.lcycles. Her menstrual dates are known with certain­ty. At 16 weeks gestational age (menstrual dates). shehad a materna] serum alpha fetoprotein (MSAFP)screening test. The result was 41 ng/ml (10.8 MOM).The test was repeated the following week and theresult was 470 nglm1 (11.2 MOM).

Page 40 - JIMA: Volume 21, 1989

Hossam E. Fadel. M.D.Augusta, Georgia

DOI: http://dx.doi.org/10.5915/21-1-5521

Figure 2. A longitudal parasagittalscan showing the fetal head in thelower IHerine segment.

Figure 3. Same a Figure 1. The arrowspoint to the orbits .. The nose andmouth are intact.

Figure 4. Same as Figure 2. The arrowspoint to the top of the fetal head. Onlythe base of the skull is well formed.The. cranial vault i, absent. No cerebralhemispheres {anencephaly].

JIMA: Volume 21, 1989 - Page 41

AnencephalyThe ultrasound examination revealed a single

fetus. The mean ultrasonic gestational age was 16.5week~. The amniotic nuid volume was normal.

A cranial vault could not be identified and therewas no evidence of cerebral hemispheres. The facecould be seen and was normally developed. (Figure 3)The spine was intact as seen in the longitudianl; sagit­tal and coronal, sections as well as in the transversescans. Examination of the heart and abdoninalviscera revealed no additional abnormalities.

Diagnosis: Anencephaly

Discussion:Anencephaly is characterized by the absence of

both cerebral herni. pheres as well as the cranial vault.II is to be distinguished from acrania, a condition inwhich the cranial vault is partially or completely ab­sent while the cerebral hemispheres are present butare usually abnormally developed. Acrania is muchrarer than anencephaly.

MSAFP testing is a recommended strategy for thediagnosis of neural tube defects (NTDs) includinganencephaly and spina bifida. 1 This patient had twoelevated MSAFPs. Ultrasound examination is in­dicated in such situations to rule out other causes ofelevated MSAFP for example, a pregnancy Ihat imore advanced than suspected, unrecognized twinpregnancy, or fetal death. Sonography will also con­firm or rule out the diagnosis of anencephaly or otherNTDs.

Anencephaly is easily diagnosed by sonography(Figures 3) as early as the 12th-13th weeks, based onthe failure (0 demonstrate tile cranial vault. The or­bits are present but there is no normal bony structureor brain tissue cephalad to the orbits, the neck isshort, and the fetus has a characteristic frog like ap­pea ranee. , Polyhydramnios is represented in approx­imately 50070 of the cases but is not usually apparentuntil the 26th week. The differential diagnosis in­cludes amniotic band syndrome involving the headwith los of large portioins of the cranial vault, andsevere mirocephaly. The latter is especially importantto rule out in the third trimester, particularly at termwhen the fetal head is already engaged (or low) in thepelvis. If the fetus is not anencephalic, the next com­mon cause (for increased MSAFP) is spina bifida.The diagnosis of spina bidia (meningocele/men­ingomyelocele) can be missed unless the examiner isan experienced sonographer/sonologist (Level IIultrasound examination). Occasionally a small defectinvolving only one or two vertebrae, especially if it isin the sacral region, may still be missed. ',l Therefore,if no explanation for the elevated MSAFP is foundon sonography, amniocentesis and determination ofamniotic fluid alpha fetoprotein andacetylcholinesterase is indicated. MSAFP screening is

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successful in identifying more than 85<170 of cases ofanencephaly and 70<170 to 80070 of cases of men­ingmyelocele.'

The incidence of anencephaly ranges between0.211,000 births of U.S. blacks, 0.6/ 1,000 binhs inJapan, 1.2/1,000 U.S. whites to 3.5/1,000 births inthe British Isles. The incidence in abortion material isapproximately five times higher than at birth.' Theincidence of NTD is increased 3-4 fold in diabeticpregnancies. It is noteworthy that this patient has afamily history of diabetes but has not been testedduring this pregnanty.

Anencephaly results from failure of closure of theanterior neuropore. An alternative explanation isthat excess cerebrospinal nuid early on in embryonicdevelopment causes disrupture of the normally form­ed cerebral hemispheres.'

Anencephaly is commonly associated with otherfetal anomalies. Associated malformations included:spina bifida (17<170 of cases), cleft lip/palate (2<170 ofcases), and club feet (1.7<170 of cases).2

Only 1/3 of these fetuses are born alive and thedisease is unfortunately fatal within a few hours ordays. Termination of pregnancy should be offered tothe patient at any time the diagnosis is made.

Another option that has been considered, recently,is to cominue uch a pregnancy in the hope that a livebirth results and might be used as an organ donor.This, however, raises serious ethical questions andconcerns."!

The risks of recurrence of NTDs in a subsequentpregnancy is 2 to 3070 after one affecled pregnancyand 5 to 10<170 after two affected pregnancies. Insubsequent pregnancies, therefore, a detailed ultra­sound examination is recommended as early a 13-14weeks; MSAFP/amniocentesis at 16 weeks is recom­mended if ultrasound doe not show an abnormaltyin the fetus.

References:I. Burton BK: Elevated maternal serum alpha­

fetoprotein (MSAFP): Interpretation and followup. Clin Obstet Gynecol 1988;31 :293.

2. Romero R, Gianluigi P, Jeanty P, et al: Prenataldiagnosis of congenital anomalies. Connecticut:Appleton and Lange, 1988; DP 36-43.

3. Roberts CJ, Hibbard BM, Roberts EE, et al:Diagnostic effectiveness of ultrasound ill detectionof neutra.l tube defect. The South Wales ex­perience of 2509 scans (1977-1982) high-riskmothers. Lancet 1983;2: 1068.

4. Holzgreve W, Bel1er FK, Buchholz B, et al:Kidney transplantation from anencephalicdonors. N Engl J Med 1987:316:1069.

5. Arras JD, Shinnar S: Anencephalic newborns aorgan donors: A critique. lAMA 1988;259:2284.