Exencephaly

SavageGlow · #1 ● 06-12-2024, 03:44 PM

Exencephaly is a rare malformation of the neural tube with a large amount of protruding brain tissue and absence of calvarium. It is considered to be an embryological precursor of anencephaly where the facial structures and the base of brain are always present. Most cases are stillborn. We report a case of Exencephaly in a live full term fetus which succumbed after 3 hours.

A 21 yr old gravid, primipara was admitted with a history of post maturity. Ultrasound of the abdomen revealed a single live fetus with breech presentation and a suspicion of anencephaly. She was given a trial labour with no response. Hence an elective caesarean section was performed. Intra-operatively minimal liquor was detected and the presentation was complete breech. The female infant was 3kgs in weight and had an APGAR score of 6 to 8. The infant expired after 3 hours.

At autopsy the fetal skull vault was absent and the brain was covered by a thick membrane with visible tortuous blood vessels [Figure 1]. Three other swellings were noted in the occipital region, one extending up to the cervical vertebrae [Figure 2]. The fetus had a normal forehead and the eyes were protruding. The ears, oral cavity and nasal cavity were normal. No other external anomalies were seen [Figure 3].

Internal autopsy showed the brain and overlying tissue being covered by a highly vascular layer below which was a layer of loose connective tissue 2 to 4 cms thick [Figure 1]. When this layer was removed, two roughly symmetrical cerebral hemispheres were seen. In the cerebral cortex the gyri were flattened, sulci were shallower and all surfaces were highly vascular. Cut sections of the cerebrum showed a single large ventricular chamber lined by numerous multi lobular soft tissue masses with a vague corpus callosum like white area. The average cortical thickness of the cerebrum was 2cms. The occipital nodules also showed similar findings. All thoracic and abdominal organs were normal and well formed. Lungs floatation test was positive.

On microscopic examination, the layer between the cortical surface and meninges was composed of loose connective tissue containing numerous tortuous vascular channels and focal nodules of dysplastic neural elements. The cerebral tissue contained scattered neurons, neuroblasts and glial elements with a thinned out layer of cortical tissue. The nodules in the occipital region showed cerebellar tissue composed of nodules of dysplastic neural elements and was also covered by a highly vascular layer. Spinal subarachnoid space also showed foci of dysplastic neural tissue.

Exencephaly is characterized by the absence of cranial cavity and scalp with a large amount of protruding brain tissue covered by a membrane, and with prominent bulging eyeballs. Exencephaly is considered to lie somewhere on the spectrum between anencephaly and encephalocoele.[1,2] It is much less common than anencephaly but it has the same etiology and recurrence risk as other neural tube defects.[3] Exencephaly is an uncommon malformation of the cranium that characteristically involves a large disorganized mass of brain tissue. The flat bones of calvaria are absent and the brain mass is left uncovered. It is a clinical entity which is incompatible with life.1

Neural tube defects account for most CNS malformations. Failure of a portion of neural tube to close or reopening of a region of the tube after successful closure, may lead to one of the several deformities. In our case the primary diagnosis of anencephaly was ruled out on the basis that the flat bones of calvarium were absent. The marked dysplasia and disorganized development of cerebrum were atypical of meningoencephalocoele.[3] Exencephaly is rarely reported in human embryos. Anencephaly occurs in 1 in 5 per 1000 live births, more commonly in females.[4] It is thought to develop at 28 wks of gestation. As with anencephaly, exencephaly is also incompatible with life.[1,2] Forebrain development is disrupted and all that remains is the area cerebrovasculosa with a flattened remnant of disorganized brain tissue admixed with ependymal, choroid plexus and meningothelial cells.[4]

Exencephaly is a rare precursor of anencephaly in which a large amount of brain tissue is present despite the absence of the calvaria. The brain in these cases consist of a disorganized, anarchic outgrowth of nervous tissue with polymicrogyria and nodules of heterotopias. In our case all the macroscopic and microscopic findings were as described in literature, although we could not explain the persistence of exencephaly late in pregnancy and survival of the fetus for 3 hours.