Current issues in postmortem imaging of perinatal and forensic childhood deaths

Abstract

Perinatal autopsy practice is undergoing a state of change with the introduction of evidence-based cross-sectional imaging, driven primarily by parental choice. In particular, the introduction of post mortem magnetic resonance imaging (PMMR) has helped to advance less-invasive perinatal autopsy in the United Kingdom (UK) and Europe. However, there are limitations to PMMR and other imaging techniques which need to be overcome, particularly with regard to imaging very small fetuses. Imaging is also now increasingly used to investigate particular deaths in childhood, such as suspected non-accidental injury (NAI) and sudden unexpected death in infancy (SUDI). Here we focus on current topical developments the field, with particular emphasis on the application of imaging to perinatal autopsy, and pediatric forensic deaths. Different imaging modalities and their relative advantages and disadvantages are discussed, together with other benefits of more advanced cross-sectional imaging which currently lie in the research domain. Whilst variations in local imaging service provision and need may determine different practice patterns, and access to machines and professionals with appropriate expertise and experience to correctly interpret the findings may limit current practices, we propose that gold standard perinatal and pediatric autopsy services would include complete PMMR imaging prior to autopsy, with PMCT in suspicious childhood deaths. This approach would provide maximal diagnostic yield to the pathologist, forensic investigator and most importantly, the parents.

Keywords: Autopsy; Forensic; Imaging; MRI; Pediatric; Perinatal.

Fig. 1

Normal appearances on PMMR. Coronal T₂-weighted PMMR in a late gestation stillbirth, demonstrating normal physiological post mortem imaging appearances. There is intracardiac gas, pleural and pericardial effusions in the chest (black arrows), bowel dilatation and widespread subcutaneous edema (white arrows), all of which can be misinterpreted as pathological to radiologists unfamiliar with autopsy imaging

Fig. 2

PMMR of congenital abnormalities. PMMR is particularly good for congenital anatomical abnormalities, such as intracranial hemorrhage, brain malformations, renal anomalies, congenital heart disease and skeletal dysplasias. This example shows bilateral enlarged high signal kidneys at coronal T₂-weighted PMMR in a 27 week gestation fetus, which are classical features of autosomal recessive polycystic kidney disease (a), confirmed at microscopy (b)

Fig. 3

PMMR to document injuries. Post mortem imaging is useful to document the extent of intracranial injury prior to autopsy. In this case, axial T2-weighted PMMR demonstrates a large left parietooccipital subdural hemorrhage, which is causing mass effect on the brain. There is a small amount of intraventricular hemorrhage in addition

Fig. 4

Fracture detection on PMMR. Long bone fractures are still probably best imaged using conventional radiographs, as these demonstrate long bone fractures adequately and some subtle fractures may be missed on PMMR, such as this corner metaphyseal fracture of the left distal humerus in a 5 month old child. It was identified on conventional radiography (a) but deemed too subtle to be identified on PMMR (b). Reproduced with permission from [16]

Fig. 5

Example of non diagnostic PMCT. PMCT has several disadvantages, including reduced soft tissue contrast due to reduced abdominal and subcutaneous fat. In an 18 week fetuses, an abdominal wall defect was clearly diagnosed on PMMR (b), with liver and small bowel loops herniated outside of the normal abdominal cavity in gastroschisis (white arrow), but the PMCT in the same patient was non-diagnostic. Gastroschisis was clearly identified at autopsy (c; white arrow). Reproduced with permission from [22]

Fig. 6

PMCT for fractures. PMCT is becoming particularly useful at detecting rib fractures. An example is given of a 4 month old girl with a rib fracture on the right, difficult to identify on the frontal chest radiograph (a), easier to see on the oblique view of the left sided ribs (b), and very easy to identify on axial 3D reconstructed PMCT (c). PMCT confirms that there are bilateral anterolateral fractures, in a typical location resuscitation related injuries, and there were no other signs of injuries in this child. Fresh anterolateral fractures are highly likely to be related to resuscitation if there are no other associated injuries

Fig. 7

3D prototype printing. 3D model of a fracture skull and underlying brain hemorrhage in an infant brain. The PMCT dataset (to provide the 3D skull structure) was co-registered with the PMMR image (to identify the bleed volume and position) to give a composite image (d). This was printed into a skull (b), to demonstrate the fracture (black arrow head, a) and internal hemorrhage (black arrows, c). These findings were confirmed at autopsy. Reproduced with permission from [50]

Fig. 8

PMMR for lung aeration. Signal intensity differences in the lungs on PMMR may be used to differentiate between a baby who has breathed (dark airways and lungs on coronal T2-weighted PMMR image in a 2 week old baby; a) versus one that has not (light lungs in a 30 week gestation fetus with no signs of life at delivery; b). Reproduced with permission from [54] under Open Access agreement

Fig. 9

PMMR of hypoxic brain changes. Axial T2-weighted PMMR image through a fetal post mortem brain, showing an example of typical low signal change in the basal ganglia which may be associated with hypoxia. Conventional PMMR cannot currently distinguish antemortem from postmortem hypoxic change

Fig. 10

Limits of body PMMR imaging. 3D reconstruction from high resolution CISS PMMR image of a 14 week gestation (b). Skeletal radiography (a) at this gestation is often better than the highest resolution imaging at 1.5 T PMMR (b), which at low body weights is often non-diagnostic [58]

Fig. 11

Micro CT of fetal heart. Normal fetal heart from an unexplained intrauterine fetal death at 23 weeks gestation (heart weight 5.3 g) at autopsy (a) with the corresponding micro-CT volume rendering at approximately 20 μm spatial resolution, following immersion in iodine (b). Adapted with permission from [62]