A RARE CASE OF EXENCEPHALY

ABSTRACT ID- IRIA -1221

20 years old G2 A1 lady Presented at 18 weeks POG for anamoly scan Antenatal period uneventful till date

USG

Obstetric USG Deficient cranial

vault above the levels of orbit

Brain tissue seen protruding out of the defect

Polyhydramnios

Provisional diagnosis - Exencepahaly

MRI Patient taken up for MRI

same day

To confirm presence of exencephaly

T2 HASTE sequences were performed

Fidings Supraorbital cranial vault

was absent Disorganised brain tissue

seen protruding out of the defect

Bilaterally prominent orbits : Frog Eye sign

FINAL DIAGNOSIS

EXENCEPHALY

DISCUSSION ACRANIA- EXENCEPHALY- ANENCEPAHALY SEQUENCE

Acrania is the absence of the calvarium; the skull base may be intact Exencephaly is acrania with protrusion of a substantial

portion of the CNS into the amniotic cavity Anencephaly is acrania with absence of most or all of the

brain tissue

Anencephaly is classified anatomically as merocrania when the defect does not involve the foramen

magnum holoacrania when the defect extends through the foramen

magnum; Holoacrania with rachischisis if spinal defects are

associatedType of Neural tube defect

DISCUSSION

Incidence is around 1:1000. There is a recognised female predilection with a F:M of ~4:1.

As with many other malformations, a number of associated abnormalities are recognised: other neural tube defects: spina bifida (especially

cervical) congenital heart defects cleft lip/palate diaphragmatic hernia(s) spinal dysraphism skeletal anomalies: e.g. clubfeet gastrointestinal abnormalities: e.g. omphalocele urinary tract abnormalities: hydronephrosis most

common

EXENCEPHALY Exencephaly is characterised by calvarial absence

and loss of fetal brain tissue to variable degrees and is considered a precursor to anencephaly  in the acrania-exencephaly-anencephaly sequence.

Absence of the cranial vault exposes the brain to contact with the amniotic fluid. Initially, an excessive growth of the encephalic structures occurs with a normal development of eyes and cranial nerves

Susequently, destructive processes of the exposed brain occur

The eventual result is anencephaly Markers : maternal serum alpha feto protein

(MSAFP) levels are highly elevated

RADIOGRAPHIC FEATURES

Imaging features have some overlap with that of anencephaly except that there is some brain tissue presence:

cranial vault is absent or poorly formed, cephalad to orbits

nasal bone may be absent in most cases brain tissue is herniating or dangling in

amniotic fluid brain tissue may be attached to the amniotic

membrane

US is an extremely accurate technique for the diagnosis of acrania, with almost 100% sensitivity.

Transvaginal US can be useful when the fetal head is low in the pelvis and not easily visible

The calcification of the bone structures of the skull can be discerned at the 10th week of gestation; therefore, it is suggested not to attempt a diagnosis before this week

The characteristic US feature is represented by absent visualization of the cranial vault above the orbits, which appear prominent; the thalami and ventricles are not detectable

In anencephaly it is difficult to recognize the cerebral tissue, while in exencephaly it is usually possible to detect a normal amount of cerebral tissue

AMNIOTIC BAND SEQUENCE WITH EXENCEPHALY

Amniotic bands are thin fibrous bands causing regional constrictions, amputations and disruption of cranial bone formation .The brain tissue is covered by only a vascular layer of epithelium, and can be slowly degraded by the amniotic fluid and degenerate into anencephaly.

MRI: Usually HASTE T2 or SSFSE sequence is

used , which is very fast and thus prevents motion artifacts

PROGNOSIS

Exencephaly is a precursor to anencephaly, and essentially a lethal condition

Advise and counselling for abortion is to be given to the parents.

REFRENCES

1. Wilkins-haug L, Freedman W. Progression of exencephaly to anencephaly in the human fetus--an ultrasound perspective. Prenat. Diagn. 1991;11 (4): 227-33

2. Bianchi DW, Crombleholme TM, D'Alton ME. Fetology, diagnosis & management of the fetal patient. McGraw-Hill Professional. (2000)

3. 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.

4. Papp Z, Csécsei K, Tóth Z et-al. Exencephaly in human fetuses. Clin. Genet. 1986;30 (5): 440-4.

5. Merz E, Bahlmann F. Ultrasound in obstetrics and gynecology. Thieme Medical Publishers. (2005)