Histological examination in sudden unexpected death in infancy: evidence base for histological sampling
- Department of Paediatric Pathology, Great Ormond Street Hospital for Children, London, UK and UCL Institute of Child Health, London, UK
- Correspondence to Professor Neil J Sebire, Department of Paediatric Pathology, Great Ormond Street Hospital for Children, Great Ormond Street, London, WC1N 3JH, UK;
Contributors MAW was responsible for data collection, data analysis, data interpretation and writing of the manuscript. NJS was responsible for study conception and design, data collection, analysis and interpretation and writing of the article. MM was responsible for study design and data interpretation and JWP and MTA for contributing to data interpretation.
- Accepted 16 August 2011
- Published Online First 30 September 2011
Aim Pathologists currently follow the ‘Kennedy guidelines’ when performing autopsies for sudden unexpected death in infancy (SUDI); these include extensive histological sampling. This study establishes the frequency with which histological examination of visceral organs determines cause of death and examines associations between clinical, macroscopic and microscopic findings.
Methods Retrospective review of 546 SUDI autopsies performed for a 10-year period (1996–2005) at a single centre. The proportion of cases in which non-neuropathological histological examination directly determined the cause of death was identified, and clinical, macroscopic and histological findings at autopsy were compared.
Results Of 510 SUDIs included, 166 cases were explained SUDI, and of these, 54% (89/166) were identified solely on microscopic examination, based on histology of the lungs in 71 (43%), heart in 13 (8%), liver in 4 (2%) and kidneys in 1 (<1%). The proportions of macroscopically normal organs with significant histological findings were 26% lungs, 2% heart and 1% each of liver and kidneys, but none of spleen, thymus, pancreas or adrenals. Macroscopically abnormal organs were more likely to yield significant histological features. Symptoms preceding death were more common in cases with significant histological findings in lungs, heart, liver and adrenals.
Conclusion A non-neuropathological cause of death in explained SUDI can be established from histological examination of lungs, heart, liver and kidneys. Significant histological abnormalities may be detected in selected organs with macroscopically normal appearances. Routine histological sampling of other organs in the absence of specific clinical history or macroscopic abnormalities has a low yield for establishing cause of death.
- sudden unexpected death
- autopsy pathology
- paediatric pathology
- trophoblastic disease
Sudden unexpected death in infancy (SUDI) is the sudden death of an apparently healthy infant aged <1 year (usually 7–365 days). In some, the autopsy determines a cause of death (explained SUDI), whereas in most, a definite cause of death cannot be found (unexplained SUDI); following current autopsy protocols, almost two-thirds of SUDI remain unexplained,1 most being synonymous with sudden infant death syndrome (SIDS).2
Pathologists in the UK generally follow the ‘Kennedy guidelines’3 for SUDI autopsies, which includes extensive routine histology of lungs (all five lobes, H&E and Perls stains), heart (free wall of left and right ventricles, interventricular septum), thymus, pancreas, liver, spleen, lymph node, adrenal glands, kidneys, rib, muscle and any lesions. These are regarded as the minimum number of samples to be taken, but this is not evidence based.
In England and Wales, SUDI autopsies are performed on behalf of Her Majesty's Coroner (HMC); according to the Coroners Rules,4 5 the pathologist is only permitted to take material for histology “which in his opinion bears upon the cause of death or the identification of the deceased.” This statement is open to interpretation, especially in the context of unexplained SUDI/SIDS that, by definition, constitutes a diagnosis of exclusion and consequently requires demonstration of absence of disease. Although careful macroscopic examination seems to be the norm in adult coronial autopsies,6 histological examination is the single most useful ancillary investigation in the postmortem investigation of SUDI, revealing the cause of death in 45–70% of explained SUDI.1 7 However, there are few data examining the relationship between macroscopic and histological findings; moreover, after the implementation of new legislation,5 8 there is greater awareness and sensitivity from HMCs regarding what material is retained after autopsy, further highlighting the need for an evidence-based approach.
The aims of this study are to establish the frequency with which histological examination determines cause of death in SUDI and to examine the relationship between clinical, macroscopic and microscopic findings.
Great Ormond Street Hospital for Children is a tertiary referral centre, and paediatric autopsies are performed from a wide geographical area. A systematic retrospective case review was performed of all autopsies carried out at the centre for a 10-year period (1996–2005 inclusive) on behalf of HMC for the indication of SUDI in infants aged 1 week to 1 year. Research ethics committee approval was obtained.
Autopsies were performed by specialist paediatric pathologists according to a local protocol. The clinical history, macroscopic and microscopic findings and results of ancillary investigations were reviewed and entered into a specially designed database by a single paediatric pathologist (MAW). The cause of death was determined according to predefined criteria,1 and cases were classified as unexplained and explained SUDI. Cases with neuropathological causes of death were excluded from the analysis because the aim of this study was to examine visceral organ-specific findings. The proportion of explained SUDI in which histological examination directly determined the cause of death was identified and the relationship between clinical history, macroscopic and microscopic findings determined. Significant histological findings were defined as those that fully explained the cause of death and changes that in isolation were insufficient to explain the death but that were likely to have contributed to death. Non-significant histological findings included those described as normal or abnormalities interpreted as having no bearing on the death. Macroscopic findings were categorised into those diagnostic of cause of death (‘significant macroscopic findings’), those which were normal and those that were abnormal but that did not allow a definitive diagnosis to be made without histological examination (‘abnormal macroscopic findings’). Clinical, macroscopic and histological findings were compared for each organ. ‘Significant symptoms’ included fever, symptoms of upper respiratory tract infection (including ‘snuffles’/‘cold’/‘cough’/‘nasal discharge’/‘flu-like symptoms’/‘viral infection’), respiratory symptoms/signs (‘breathing difficulties’/‘fast breathing’/‘grunting’/‘intercostal recession’/‘apnoea’/‘wheezing’/‘respiratory distress’/‘chest infection’) and diarrhoea and/or vomiting in the week preceding death. Statistical analyses included modified χ2 test for comparison of proportions and calculation of ORs with CIs.
Cause of death
There were 546 SUDIs, of which 202 (37%) were explained SUDI. Excluding those with neuropathological causes of death (36), cause of death was based solely on histological examination in 89 of 166 (54% explained SUDI; 17% of all SUDI); this included histological examination of the lungs in 71 (43% explained SUDI), heart in 13 (8%), liver in 4 (2%) and kidneys in 1 (<1%). Cause of death was also apparent on histological examination of spleen in three (2%), lymph node in two (1%) and thymus in one (<1%), but in all such cases, cause of death could be established on histological examination of lungs, heart, liver or kidneys (figure 1).
Macroscopic findings in SUDI
A macroscopically detectable cause of death was present in only a minority of cases; these included the presence of structural congenital heart disease and other congenital malformations, cardiomyopathy (which required histology for definitive characterisation), empyema, osteomyelitis, adrenal hypoplasia, traumatic rupture of the liver and other traumatic lesions, volvulus, previously undiagnosed congenital mesoblastic nephroma of kidney; and perinephric and retroperitoneal abscess.
Abnormal but non-diagnostic macroscopic findings for lungs, heart, liver, kidneys, spleen and thymus are shown in figure 2; 25 (5%) showed non-diagnostic macroscopic abnormalities of the adrenal glands, including adrenal haemorrhage in 12 (3%), which was significantly more frequent in explained SUDI (9/177) versus unexplained SUDI (3/306, difference 4.1%, 95% CI 1.2 to 8.5%, p=0.006). The pancreas was macroscopically normal in all cases.
Histological findings in SUDI
Significant microscopic abnormalities of lungs, heart, liver and kidney are summarised in figure 3. Significant microscopic abnormalities of the spleen included one case each of cytomegalovirus infection, diffuse leukaemic infiltration, haemophagocytic lymphohistiocytosis and white pulp depletion with immunodeficiency. Significant microscopic abnormalities of the thymus were present in only two cases: thymic aplasia with absent parathyroid glands in association with truncus arteriosus type III (DiGeorge anomaly) and infiltration by Langerhans cell histiocytosis in which the thymus was firm and fibrotic. Significant microscopic abnormalities of the adrenals were present in six, including hypoplasia and haemorrhage. In none did the pancreas show significant histological abnormalities.
Minor histological abnormalities not relevant to the cause of death are summarised in figure 4. Splenic histological abnormalities were rarely reported (16/452, 4%) and included extramedullary haematopoiesis in four (<1%) and haemosiderin/haemosiderin-laden macrophages in four (<1%); extramedullary haematopoiesis was significantly more frequent in explained SUDI than unexplained SUDI (difference 2.4%, 95% CI 0.9 to 6.0%, p=0.009).
Significant histological findings in macroscopically normal and abnormal organs
The proportion of organs described as macroscopically normal at autopsy but which revealed significant findings on histological examination is summarised in figure 5A. These included 26% of macroscopically normal lungs, 2% of hearts and 1% each of liver and kidneys but none of spleen, thymus, pancreas or adrenals. Abnormal but non-diagnostic macroscopic lung findings were no more likely to yield significant histological features than lungs described as macroscopically normal (OR 1.3, 95% CI 0.8 to 2.1; figure 5B). Other organs demonstrated more frequent histological abnormalities if minor macroscopic abnormalities were present: heart (OR 6.4, 95% CI 2.3 to 22.4), liver (OR 31.6, 95% CI 10.6 to 104.0), kidneys (OR 20.2, 95% CI 4.1 to 127.6), spleen (OR infinity, 95% CI 6.4 to infinity) and adrenals (OR infinity, 95% CI 13.1 to infinity; figure 5B).
Histological yield and clinical history
Symptoms preceding death were present in significantly more cases with significant lung histology (68/156, 44%) than in those without (108/359, 30%; difference 13.5%, 95% CI 4.5% to 22.6%, p=0.003; OR 1.8, 95% CI 1.2 to 2.7; figure 5C) and in those with significant heart histology (16/28, 57% vs 149/457, 33%; difference 24.5%, 95% CI 5.9 to 41.5%, p=0.008; OR 2.8, 95% CI 1.2 to 6.5), significant liver histology (13/21, 62% vs 159/478, 33%; difference 28.6%, 95% CI 7.1 to 46.6%, p=0.006; OR 3.3, 95% CI 1.2 to 9.2) and significant adrenal histology (5/6, 83% vs 161/ 477; difference 50.0%, 95% CI 9.6 to 64.3%, p=0.01; OR 9.8, 95% CI 1.1 to 465.6; figure 5C). ORs for detecting any significant organ-specific findings at autopsy (macroscopic and/or histological examination) in the presence of antemortem symptoms are summarised in figure 5D.
Previous studies have reported that histological examination is the most useful ancillary investigation to establish the cause of death in SUDI.1 7 In this series, >90% of all abnormal histological findings involved lungs, heart or liver, consistent with data from previous studies7; however, the results of this study demonstrate that for diagnoses requiring histological examination, the cause of death can be established solely on histological examination of lungs, heart, liver and kidneys. Although microscopic examination of other tissues might contribute to the cause of death in occasional cases, in almost all of these, the diagnosis can be made on histological examination of lungs, heart, liver and kidney. In this series, provided these were sampled, no identifiable visceral cause of death would have been missed even if the other organs, as recommended by the current Kennedy autopsy guidelines,3 had not been sampled for microscopic examination. This notwithstanding, unexplained SUDI/SIDS remains a diagnosis of exclusion, making assessment of the importance of negative histological findings in other organs difficult.
In 25% of cases showing macroscopically normal lungs, significant abnormality was detected histologically, highlighting the need for routine lung sampling regardless of macroscopic appearances; in contrast, no significant microscopic abnormalities were present in any macroscopically normal adrenals, pancreas, thymus or spleen. Macroscopically abnormal organs, on the other hand, carry a significantly increased likelihood of demonstrating significant microscopic abnormalities, except for the lungs, supporting the recommendation that histological sampling is mandatory for all organs that are macroscopically abnormal.
Although providing evidence regarding yield to determine cause of death by organ, these data do not provide information regarding optimum sampling protocols to maximise diagnostic yield. For example, in this series, most cases had one sample from each lung lobe and three samples (right and left ventricles and interventricular septum) from the heart. In contrast, the international SIDS autopsy protocol recommends that 10 lung samples are obtained and 6–8 from the heart.9 There is no published evidence to support these guidelines, but it is recognised that some pathologies, such as myocarditis, which accounts for 5% of explained SUDI,1 7 may demonstrate patchy organ involvement.10 Further research is required to ascertain the optimal number of samples required from each organ.
Most pathologists would agree that comprehensive histological sampling could contribute to our understanding of the pathophysiology of unexplained SUDI/SIDS, a theoretical stance that is entirely valid. In practice, however, SUDI autopsies for HMC are for the purpose of establishing cause of death. Within this remit, given the current social and legal milieu,11 12 the findings indicate that extensive routine sampling of all organs has a low yield for determining cause of death other than lungs, heart, liver and kidneys and any macroscopically abnormal organs. In this series, no significant pancreatic histological abnormalities were demonstrated, but isolated case reports suggest a possible association between SIDS and pancreatic endocrine abnormalities, including congenital hyperinsulinism.13–15 Although most infants with congenital hyperinsulinism would be expected to present with clinical symptoms of hypoglycaemia,16 routine pancreatic sampling in SUDI should probably be recommended. Issues relating to apparent stress changes in the thymus or adrenals are more controversial; there was a higher prevalence of thymic stress changes in explained SUDI in our series, suggesting that such changes might alert the pathologist to possible underlying disease, but the demonstration of such changes has no direct bearing on the cause of death. Although haemophagocytosis in bone marrow has been suggested as a marker of infection,17 18 our data do not allow comment on the proposed sampling of the rib (bone marrow) or lymph node, as these were not routinely sampled across the 10-year study period in our centre.
In conclusion, the diagnosis of a visceral cause of death can be established solely on histological examination of the lungs, heart, liver and kidneys, even when these organs appear macroscopically normal. For most organs, microscopic abnormalities are more likely in macroscopically abnormal organs, and there is a positive association between antemortem clinical symptoms and likelihood of histological abnormality. Routine histological sampling of visceral organs other than lungs, heart, liver and kidneys in the absence of a relevant clinical history and abnormal macroscopic findings has a low yield for determining cause of death.
The diagnosis of a non-neuropathological cause of death in explained SUDI can be established solely on histological examination of the lungs, the heart, the liver and/or the kidneys in most cases.
Significant histological abnormalities may be detected in these organs even with macroscopically normal appearances.
Routine histological sampling of other thoraco-abdominal organs in the absence of a relevant clinical history or without macroscopic abnormalities has a low yield for establishing cause of death or detecting significant histological abnormalities.
The authors would also like to thank Professor Tony Risdon for his contribution to this study.
The sponsor had no role in the study design; collection, analysis and interpretation of data; writing of the report or the decision to submit the paper for publication.
Funding The study was supported by a project grant from the Foundation for the Study of Infant Deaths (grant number 1RTZ).
Competing interests None.
Ethics approval This study was conducted with the approval of the local research ethics committee.
Provenance and peer review Not commissioned; externally peer reviewed.