S Addison

Post-mortem MRI as an alternative to non-forensic autopsy in foetuses and children: from research into clinical practice

Although post-mortem MRI (PMMR) was proposed as an alternative to conventional autopsy more than a decade ago, the lack of systematic validation has limited its clinical uptake. Minimally invasive autopsy (MIA) using PMMR together with ancillary investigations has now been shown to be as accurate as conventional autopsy in foetuses, newborns and infants and is particularly useful for cerebral, cardiac and genitourinary imaging. Unlike conventional autopsy, PMMR provides a permanent three-dimensional auditable record, with accurate estimation of internal organ volumes. MIA is becoming highly acceptable to parents and professionals, and there is widespread political support and public interest in its clinical implementation in the UK. In the short to medium term, it is desirable that a supraregional network of specialist centres should be established to provide this service within the current National Health Service framework.

Diagnostic accuracy of post mortem MRI for abdominal abnormalities in foetuses and children

BACKGROUND To compare the diagnostic accuracy of post-mortem magnetic resonance imaging (PMMR) specifically for abdominal pathology in foetuses and children, compared to conventional autopsy. METHODS Institutional ethics approval and parental consent was obtained. 400 unselected foetuses and children underwent PMMR using a 1.5T Siemens Avanto MR scanner before conventional autopsy. PMMR images and autopsy findings were reported blinded to the other data respectively. RESULTS Abdominal abnormalities were found in 70/400 (12%) autopsies. Overall sensitivity and specificity (95% confidence interval) of PMMR for abdominal pathology was 72.5% (61.0, 81.6) and 90.8% (87.0, 93.6), with positive (PPV) and negative predictive values (NPV) of 64.1% (53.0, 73.9) and 93.6% (90.2, 95.8) respectively. PMMR was good at detecting renal abnormalities (sensitivity 80%), particularly in foetuses, and relatively poor at detecting intestinal abnormalities (sensitivity 50%). Overall accuracy was 87.4% (83.6, 90.4). CONCLUSIONS PMMR has high overall accuracy for abdominal pathology in foetuses, newborns and children. PMMR is particularly good at detecting renal abnormalities, and relatively poor at detecting intestinal abnormalities. In clinical practice, PMMR may be a useful alternative or adjunct to conventional autopsy in foetuses and children for detecting abdominal abnormalities.

Diagnostic accuracy and limitations of post-mortem MRI for neurological abnormalities in fetuses and children.

AIM To compare the diagnostic accuracy of non-invasive cerebral post-mortem magnetic resonance imaging (PMMRI) specifically for cerebral and neurological abnormalities in a series of fetuses and children, compared to conventional autopsy. MATERIALS AND METHODS Institutional ethics approval and parental consent was obtained. Pre-autopsy cerebral PMMRI was performed in a sequential prospective cohort (n = 400) of fetuses (n = 277; 185 ≤ 24 weeks and 92 > 24 weeks gestation) and children <16 years (n = 123) of age. PMMRI and conventional autopsy findings were reported blinded and independently of each other. RESULTS Cerebral PMMRI had sensitivities and specificities (95% confidence interval) of 88.4% (75.5 to 94.9), and 95.2% (92.1 to 97.1), respectively, for cerebral malformations; 100% (83.9 to 100), and 99.1% (97.2 to 99.7) for major intracranial bleeds; and 87.5% (80.1 to 92.4) and 74.1% (68 to 79.4) for overall brain pathology. Formal neuropathological examination was non-diagnostic due to maceration/autolysis in 43/277 (16%) fetuses; of these, cerebral PMMRI imaging provided clinically important information in 23 (53%). The sensitivity of PMMRI for detecting significant ante-mortem ischaemic injury was only 68% (48.4 to 82.8) overall. CONCLUSIONS PMMRI is an accurate investigational technique for identifying significant neuropathology in fetuses and children, and may provide important information even in cases where autolysis prevents formal neuropathological examination; however, PMMRI is less sensitive at detecting hypoxic-ischaemic brain injury, and may not detect rarer disorders not encountered in this study.

Diagnostic accuracy of postmortem MRI for musculoskeletal abnormalities in fetuses and children

The aim of this study was to compare the diagnostic accuracy of postmortem magnetic resonance (PMMR) imaging specifically for musculoskeletal pathology in fetuses and children, compared with conventional autopsy, with radiographic and histopathology assessment.

High quality genomic DNA extraction from postmortem fetal tissue

Objective: We examined the yield and quality of genomic deoxyribonucleic acid (DNA) extracted from various postmortem fetal tissues. Methods: Fetal tissues were collected at the time of autopsy, and DNA was subsequently extracted. The yield and DNA quality was assessed using ultraviolet spectrometry and agarose gel electrophoresis. We used polymerase chain reaction (PCR) to assess the DNA extracted for genomic testing. Results: The median (range) gestation of the fetuses was 22 (16–41) weeks and the postmortem interval was 5.5 (2–10) days. Non-degraded genomic DNA was successfully extracted from all fetal tissues. Liver tissue had the lowest quality and muscle the highest quality. DNA yield or purity was not influenced by the postmortem interval. Conclusion: High quality genomic DNA can be extracted from fetal muscle, despite postmortem intervals of several days.

PFM.33 Estimating Maceration Severity Using Whole Body Magnetic Resonance T2 Relaxometry

Background Magnetic resonance (MR) imaging is an ideal modality to observe gross global changes in tissue structure, as is present with maceration. As tissue degrades, its MR transverse relaxation time (T2) should increase, with relaxometry methods enabling quantitative measurement of this. Objective To use T2 relaxometry to non-invasively classify maceration and compare this with the assessment of a pathologist. Design/Methods We performed post-mortem imaging in foetuses and neonates at 1.5T (Siemens Avanto). T2 relaxometry was performed using an eight-echo turbo spin echo sequence (TR = 2400 ms, TE = 44/88/132/176/220/264/308/352 ms), with even-echo images fitted to a mono-exponential decay function. Voxel-wise T2 values were generated from the model fit in each voxel to generate quantitative T2 maps, on which the lungs and liver were delineated (as shown in the figure). Mean T2 values in each region were evaluated against global pathology maceration scores (1 to 4; none to severe) based on findings of paediatric pathologists at autopsy. Abstract PFM.33 Figure Results T2 was increased in both the lungs and liver for maceration scores of 3 or 4, when compared to those with grades 1 and 2. However, T2 also correlated inversely to the gestational age at death. Conclusions Increasing maceration is associated with the prolongation of T2 values in the liver and lungs, but limitations arise due to conflation with gestational age effects, as younger foetuses were more macerated. T2 dependencies on gestational age are provided in the liver and lungs, allowing optimisation of post-mortem imaging for future studies.

Postmortem Genetic Testing for Cardiac Ion Channelopathies in Stillbirths

Background: Although stillbirth is a significant health problem worldwide, the definitive cause of death remains elusive in many cases, despite detailed autopsy. In this study of partly explained and unexplained stillbirths, we used next-generation sequencing to examine an extended panel of 35 candidate genes known to be associated with ion channel disorders and sudden cardiac death. Methods and Results: We examined tissue from 242 stillbirths (≥22 weeks), including those where no definite cause of death could be confirmed after a full autopsy. We obtained high-quality DNA from 70 cases, which were then sequenced for a custom panel of 35 genes, 12 for inherited long- and short-QT syndrome genes (LQT1-LQT12 and SQT1-3), and 23 additional candidate genes derived from genome-wide association studies. We examined the functional significance of a selected variant by patch-clamp electrophysiological recording. No predicted damaging variants were identified in KCNQ1 (LQT1) or KCNH2 (LQT2). A rare putative pathogenic variant was found in KCNJ2(LQT7) in 1 case, and several novel variants of uncertain significance were observed. The KCNJ2 variant (p. R40Q), when assessed by whole-cell patch clamp, affected the function of the channel. There was no significant evidence of enrichment of rare predicted damaging variants within any of the candidate genes. Conclusions: Although a causative link is unclear, 1 putative pathogenic and variants of uncertain significance variant resulting in cardiac channelopathies was identified in some cases of otherwise unexplained stillbirth, and these variants may have a role in fetal demise. Clinical Trial Registration: URL: https://www.clinicaltrials.gov. Unique identifier: NCT01120886.

PFM.25 Assessment of visceral maceration using post-mortem magnetic resonance imaging in fetuses

Background Post-mortem magnetic resonance imaging (PM MRI) is increasingly used as an alternative for perinatal autopsy, however the artefacts related to maceration has not been described. Objective To compare the severity of maceration assessed by PM MRI with that estimated by histopathology in fetuses. Design/Methods We performed PM MRI in 75 fetuses using a 1.5 Tesla Siemens Avanto MR scanner (Erlangen, Germany) before conventional autopsy. PM MRI images were reported blinded to the clinical history and autopsy data using a maceration scale of 0–3 for 6 different visceral organs, and then added to make a composite score (0 to 18). The extent of maceration on histopathology was categorised from 1–4 (none to severe). Results PM MRI maceration score showed a good correlation with the histopathology maceration score (Figure A), however no relation was seen with the delivery (death) to PM MRI interval. Figure B and C shows PM MRI of fetuses with minimal and extensive maceration, respectively. Abstract PFM.25 Figure Conclusions PM MRI can be used to quantify the extent of maceration in fetuses. The time from delivery to PM MRI did not affect the MRI assessment of maceration if bodies are stored in the mortuary at low temperature.

PC.45 Quantification of N-Acetylaspartate Concentration in the Neonatal Brain: Initial Results from the Multi-Centre Marble Study

Background Early cerebral proton magnetic resonance spectroscopy (MRS) predicts medium-term outcomes in neonatal encephalopathy (NE). Metabolite peak-area ratios are most commonly used for prognosis, but conflate pathological information from different metabolites. N-acetylaspartate (NAA) is predominantly neuronal and neuronal loss should result in reduced NAA absolute-concentration ([NAA]). Thus, thalamic [NAA] should offer significant prognostic value but is difficult to measure in a clinical setting. We have established a protocol for multi-centre [NAA] measurement with the aim to use it as a surrogate biomarker in phase II clinical trials. Objective To investigate the feasibility and utility of [NAA] quantitation across multiple centres. Design/Methods We recruited cooled, term neonates with NE (by Sarnat grade) with parental consent across participating sites. Using various 3T scanners, thalamic MRS was performed aged 7 ± 4d (PRESS; water-suppressed TR = 2s/TE = 288/60 ms;TR/TE = 5s/60 ms; non-water-suppressed TR = 10s, TE = 60/124/205/316/495/1000 ms, ~30min acquisition). Spectra were post-processed in jMRUI and metabolite contributions determined with LCModel. [NAA] was calculated, correcting for T2 effects and cerebrospinal fluid partial volume. Results Ten cases had sufficient data for [NAA] quantification. Sarnat grading <6h identified infants with highest [NAA] (median (IQR) 10.0(9.7–10.3) mmol/kg wet weight) as mild NE, with a lower [NAA] range for moderate NE (7.0(5.0–7.8) mmol/kg wet weight). Conclusions [NAA] quantification is achievable in a multi-centre setting, and agrees with clinical NE grading during the therapeutic window. Follow-up examinations will allow comparison of neonatal [NAA] with later neurodevelopmental outcomes. Abstract PC.45 Figure

8.8 Neonatal Encephalopathy in the Cooling Therapy era – Preliminary Cerebral Magnetic Resonance results from the Marble Consortium

Background Although cerebral metabolic changes during neonatal encephalopathy (NE) have been well characterised using magnetic resonance spectroscopy (MRS) in single-centre studies, the widespread effect of therapeutic hypothermia is less clear. Objective To describe patterns of brain injury in a prospective multi-centre cohort of infants with NE who had rescue hypothermic neuroprotection. Design After MRS harmonisation on 3T MR scanners (Phillips, GE, Siemens), at six participating sites we performed magnetic resonance imaging (MRI) and MRS (single-voxel PRESS, 15 x 15 × x 15 mm3 thalamic voxel, TR = 2s/TE = 288 ms) on infants <2 wks who had whole-body cooling for NE at any of the MARBLE centres. We used jMRUI to process MRS data and calculate metabolite peak-area ratios. Results Forty-three infants were recruited; 11(26%) had mild, 26(60%) moderate and 6(14%) had severe NE (<6h Sarnat staging). Moderate/severe basal ganglia and cortex were detected by MRI in 4(9%) and 1(2%) cases respectively, and 15(34%) had moderate/severe white matter injury. Thirteen (30%) had normal MRI. Elevations in lactate (Lac)/N-acetylaspartate (NAA) were noted in 6(13%) cases, Lac/choline (Cho) in 5(11%) and Lac/ creatine (Cr) in 8(18%). MRS was normal in 28(65%) infants. Abstract 8.8 Figure 1 Figure 1 displays metabolite peak-area ratios across clinical NE stages. Mean Lac ratios were higher and NAA ratios lower (p < 0.05) between severe and both mild and moderate NE, but not between mild and moderate groups Conclusions In this predominantly moderate NE cohort, white matter injury was most common, and the majority had normal MRS metabolite ratios. Ongoing work seeks to establish whether these brain injury patterns are characteristic in the cooling therapy era.