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Radiology
Case of the Month
| Case No. : | 12 |
| Month : | December |
| Year : | 1999 |
| Contributor : | Dr. Shekar Datar |
A routine obstetric ultrasound examination was performed on a 22 year old primiparous woman.
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| Fig 1a | Fig 1b |
The bony Calvarium is not identifiable and the orbits appear to be protruding. A "soft tissue mass" is seen in the supra orbital region. Poly hydramnios is evident.
These features are classical for anencephaly.
Anencephaly is a universally fatal congenital malformation .
The literal meaning of anencephaly is absence of brain. This is the most common anomaly affecting the central nervous system and the most common of the open neural tube defects [1].
It has a clear female preponderence of 4:1.
Though anencephaly means absence of brain, functioning brain tissue is always present. The amount of eviscerated brain seen with anencephaly is variable [2] The telencephalon is usually absent in this condition.
The mechanism of anencephaly is the failure of the neural tube to close at its cephalic
end [3]. The defect is never covered by the normal bone or skin and is usually covered by the thick membrane of angiomatous stroma.
Sonographically, it is most commonly detected in the second trimester of the pregnancy, at the time of measurement of the biparietal diameter. The symmetric absence of cranial bones makes the specific diagnosis of anencephaly. Identification of head is not sufficient to exclude the diagnosis of anencephaly. The bony skull base and the orbits are usually present and may give an impression of a cranial structures, if viewed hurriedly. Failure to identify normal bony structure and brain tissue cephalad to bony orbits is the most reliable feature of this anomaly.
Polyhydramnios and spinal and non CNS abnormalities are common with anencephaly [4].
The common associations are the spinal defects (40-50% of cases) which include spina bifida with or without myelomeningocele, and polyhydramnios (40-50% of cases).
The differential diagnosis of this condition include microcephaly. The absence of cranial vault differentiates anencephaly from microcephaly. Amniotic band syndrome can also present a confusing picture, as this entity may destroy most of the brain and the cranial vault [5] and but the destruction of the cranium is asymmetrical .
Termination of pregnancy can be offered to the patient at any time once the diagnosis of anencephaly is made.
Anencephalic patients are a potential source of organ of transplantation. [6]
The recurrence of anencephaly can be up to 25%. Widespread alfa feto protein testing can detect almost all the cases of this fatal anomaly and should be used to detect this fatal congenital anomaly.
- Main DM ,Mennuti MT: neural tube defects: issues in prenatal diagnosis and counselling. Obstet Gynecol 67:1,1986.
- Goldstein RB, Filly RA: prenatal diagnosis of anencephaly: spectrum of sonographic appearances and distinction from amniotic band syndrome, AJR 1988;151:547-550.
- Moore KL : the nervous system in the developing human, third edition, pp 375-412. Philadelphia, WB Saunders,1982.
- Goldstein RB, Filly RA, Callen PW. Sonography of anencephaly: pitfalls in early diagnosis. J clinical ultrasound 1989;17:397-402.
- Mahony BS, Filly RA, Callen PW, Golbus MS: The amniotic band syndrome: antenatal sonographic diagnosis and potential pitfalls. American Journal of Obstet. and Gynecol.152:63,1985
- Holzgreve W , Beller FK, Buchholz B et al. Kidney transplantation from anencephalic donors. N Engl J Med 316: 1069,1987.