Fetal postmortem imaging: an overview of current techniques and future perspectives.

Fetal death because of miscarriage, unexpected in utero fetal demise, or termination of pregnancy is a traumatic event for any family. Despite advances in prenatal imaging as well as genetic diagnosis, conventional autopsy remains the gold standard since in up to 40% of cases it can provide additional information that was not available during fetal life and this by itself may change the recurrence risk and hence future counseling for parents. However, conventional autopsy is negatively impacted by procedures involving long reporting times because the fetal brain is prone to the effect of autolysis, which may result in suboptimal examinations, particularly of the central nervous system. More importantly, fewer than 50-60% of parents consent to invasive autopsy, mainly due to concerns about body disfigurement. Consequently, this has led to the development of noninvasive perinatal virtual autopsy using imaging techniques. Since a significant component of a conventional autopsy involves anatomical examination of organs, imaging techniques such as magnetic resonance imaging (MRI), ultrasound (US), and computed tomography (CT) are possible alternatives. With a parental acceptance rate of nearly 100%, the use of imaging techniques as part of the post-mortem examination has in recent years and in some countries become widespread. Postmortem MRI using 1.5-T magnets is the most studied technique and offers an overall diagnostic accuracy of 77-94%. It is probably the best choice as a virtual autopsy technique for fetuses above 20 weeks of gestation. However, for fetuses <20 weeks of gestation, its performance is poor. The use of higher MRI magnetic fields such as 3.0-T may slightly improve performance. Most importantly, in cases of fetal maceration, MRI may offer diagnoses in a proportion of brain lesions where conventional autopsy fails. Postmortem US examination using a high-frequency probe offers overall sensitivity and specificity of 67-77% and 74-90%, respectively, with the advantage of easy access and affordability. The main difference between postmortem US and MRI relates to their respective abilities to obtain images of sufficient quality for a confident diagnosis. The non-diagnostic rate using postmortem US ranges from 17-30%, depending on the organ examined, whereas the non-diagnostic rate using postmortem MRI in most situations is far less than 10%. For fetuses ≤20 weeks of gestation, microfocus-CT achieves close to 100% agreement with autopsy and is likely to be the technique of the future in this subgroup. Lack of histology has always been listed as one limitation of all postmortem imaging techniques. Image-guided needle tissue biopsy coupled with any PM imaging can overcome this limitation. Besides describing the diagnostic accuracy and limitations of each imaging technology, we propose a novel, stepwise diagnostic approach and describe the possible application of these techniques in clinical practice as an alternative, an adjunct, or for triage to select cases that would specifically benefit from invasive examination, with the aim of reducing parental distress and the pathologist's workload. Widespread use of postmortem fetal imaging is inevitable, meaning that hurdles such as specialized training and dedicated financing must be overcome to improve access to these newer, well-validated techniques.