A forensic case of hydranencephaly in a preterm neonate fully documented by postmortem imaging techniques

Abstract   The authors present a medico-legal autopsy case of hydranencephaly in a male preterm newborn, fully documented by postmortem unenhanced and enhanced imaging techniques (postmortem computed tomography and postmortem magnetic resonance imaging). Hydranencephaly is a congenital anomaly of the central nervous system, consisting in almost complete absence of the cerebral hemispheres and replacement of the cerebral parenchyma by cerebrospinal fluid, rarely encountered in forensic medical practice. A premature baby was born during the supposed 22nd and 24th week of pregnancy in the context of a denial of pregnancy without any follow-up. The newborn died a few hours after birth and medico-legal investigations were requested to determine the cause of death and exclude the intervention of a third person in the lethal process. The external examination revealed neither traumatic nor malformative lesions. Postmortem imaging investigations were typical of hydranencephaly, and conventional medico-legal autopsy, neuropathological examination, and histological examination confirmed a massive necrotic-haemorrhagic hydranencephaly. This case represents in itself an association of out-of-the-ordinary elements making it worthy of interest. Key Points Postmortem unenhanced and enhanced imaging techniques (computed tomography and magnetic resonance imaging) were performed as complementary examination to conventional medico-legal investigations. Postmortem angiography of a preterm newborn is possible with catheterization of the umbilical blood vessels. Hydranencephaly is a congenital anomaly of the central nervous system, consisting in almost complete absence of the cerebral hemispheres and replacement of the brain by cerebrospinal fluid, for which several aetiologies have been postulated.


Case history
A 21-year-old woman with a denial of pregnancy, delivered at the hospital a male preterm newborn by vaginal birth, during the supposed 22nd and 24th week of pregnancy. There was never any follow-up of this pregnancy and the mother was admitted at the hospital for abdominal pain prior to delivery. The newborn died 4 h after birth and the prosecutor requested medico-legal investigations to determine the cause of death and exclude the intervention of a third person in the death.
One day after death, the body of the newborn underwent an external examination that revealed neither traumatic nor malformative lesions. He weighed 735 g and was 32 cm in length. The anatomy of the umbilical vessels was normal and consisted of two arteries and one vein.
Postmortem imaging investigations prior to medico-legal autopsy consisted of CT and MRI, without and with contrast agent. Unenhanced postmortem CT (PMCT) scans were performed with a LightSpeed VCT 64 from General Electric (Memphis, TN, USA). The scan was performed in four sets: the first set included the brain parenchyma, the second set included the head and neck, the third set included the thorax, the abdomen and the four limbs, and the fourth set included the total body. The first set used the following technical parameters: scan type, helical; detector configuration, 32 × 1.25 mm; tube voltage, 120 kV and 140 mA; rotation time, 1 s; scan field of view (SFOV), ped head, reconstruction algorithms in standard and bone plus. The second set used the following technical parameters: scan type, helical; slice thickness, 0.625 mm; interval, 0.3 mm; tube voltage, 120 kV and 121 mA; rotation time, 1 s; SFOV, ped head; pitch, 0.984:1; adaptive statistical iterative reconstruction (ASIR), 50%; reconstruction algorithms, standard, lung and bone plus. The third set used the following parameters: scan type, helical; slice thickness, 0.625 mm; interval, 0.3 mm; tube voltage, 120 kV and 121 mA; rotation time, 1 s; SFOV, large body; pitch, 0.984:1; ASIR, 40%; reconstruction algorithms, standard, lung and bone plus. The fourth set used the following parameters: scan type, helical; slice thickness, 0.625 mm; interval, 0.4 mm; tube voltage, 120 kV and 121 mA; rotation time, 1 s; SFOV, large body; pitch, 0984:1; ASIR, 60%; reconstruction algorithms, standard.
Unenhanced postmortem magnetic resonance (PMMR) images were performed with an Ingenia 1.5 T from Philips (Amsterdam, Netherlands). Three-dimensional (3D) T1W (weighted) and T2W axial acquisitions were performed on the brain, and the rest of the body was explored through 3D T1W and T2W coronal DIXON.
Postmortem unenhanced imaging investigations were typical of hydranencephaly. Indeed, PMCT revealed an absence of cerebral hemispheres replaced by fluid, and a hyperdense central mass in the supra-chiasmatic region ( Figure 1). Instead of the posterior part of the left brain parenchyma, an ovoid dense mass was visible, surrounded by a hyperdense fluid-fluid level. The brainstem seemed normal. The cerebellar hemispheres presented cystic lesions. No skeletal malformation was noticed on the PMCT. The cerebral PMMR confirmed absence of the cerebral hemispheres replaced by fluid (Figures 2 and 3). The central mass was hyperintense on T1W and corresponded to a thalamic mass. The posterior fluid-fluid level was hyperintense on T1W, as the left posterior mass.
Then, angiography was performed according to an adaptation of the protocol described by Woźniak et al. [10]. After catheterization of the umbilical vein ( Figure 4) and of one of the two umbilical arteries with a radiological sheath (5 French, Radiofocus Introducer II; Terumo Europe, Leuven, Belgium), the oily contrast agent Angiofil ® (Fumedica AG, Muri, Switzerland) mixed with paraffin oil (6% dilution) was manually injected in the umbilical vessels (20 mL in the umbilical artery and 20 mL in the umbilical vein) in order to be able to visualize the vascular system of the newborn. A first acquisition was performed after filling of the umbilical artery, and afterwards, we filled one umbilical vein and performed a second acquisition. The two acquisitions used the following technical parameters: scan type, helical; slice thickness, 0.625 mm; interval, 0.3 mm; tube voltage, 120 kV and 121 mA; rotation time, 1 s; SFOV, large body; pitch, 0984:1; ASIR 40%; reconstruction algorithms, standard, lung and bone plus.
PMMR imaging angiography (PMMRA) was performed with a 3D T1W total body acquisition.
PMCT angiography (PMCTA) showed absence of opacification of intracerebral veins. Vertebral arteries and basilar trunk were fully opacified (Figures 5 and 6). The posterior cerebral arteries were proximally visible. Internal carotids, in their cavernous portions were visible, opacified through   not opacified (Figure 7). Concerning the arterial and venous vascular system of the rest of the body, no other malformation was revealed by the contrast medium. Finally, a medico-legal autopsy was performed by two board-certified forensic pathologists, and the macroscopic and microscopic examination of the central nervous system was performed by a board-certified neuropathologist. The results of the autopsy, including extensive histological examination of the organs, and of the neuropathological examination (macroscopic and microscopic) confirmed the macroscopic aspect of foetal brain (Figure 8), with parenchymal destruction due to hypoxo-ischemic changes, all corresponding to the histological diagnosis of a massive necrotic-haemorrhagic hydranencephaly. Given the natural cause of death of the foetus and the fact that the intervention or abstention of a third person in the death was excluded, the prosecutor closed the file.

Discussion
Hydranencephaly is a typical prenatal ultrasound finding, though foetal MRI enables a more precise diagnosis [1,6,11]. Characteristic imaging features of classical hydranencephaly are a near-complete absence of the cerebrum supplied by anterior and middle cerebral arteries, hypoplasia of the supra-clinoid internal carotid arteries with normal external carotid arteries, a preserved appearance of basal portions of the temporal and occipital lobes, thalamus, cerebellum, brainstem, and falx, and a typically normal-sized or mildly enlarged cranial vault [1,2,7]. The differential diagnosis must be made with hydrocephalus and alobar holoprosencephaly [1,2].