Relevance of postmortem radiology to the diagnosis of fatal cerebral gas embolism from compressed air diving

Black box of diving accidents: Contribution of forensic underwater experts to three fatal cases

Diving is a popular activity, largely practiced worldwide. Diving fatalities are not rare events, with drowning being the most common cause of death, followed by cardiac-related natural causes, immersion pulmonary edema and arterial gas embolism. In such cases, positive signs of drowning are not specific, depending also on the time of submersion of corpses. Moreover, drowning can be the terminal event. Over the years, measures to perform appropriate post-mortem examination in cases of diving fatalities were suggested, including the execution of post-mortem CT-scan, the use of a decompression chamber and the adoption of specific autoptic techniques. Although a multidisciplinary approach in forensic investigations concerning diving fatalities is discussed, poor cases focus on how the analysis of diving computer records and equipment can contribute to determining the cause of death. The present study shows how the cooperation between a forensic underwater expert and a forensic pathologist played a crucial role in interpreting radiological findings, guiding the autopsy and confirming/denying circumstantial data emerging from the investigations. Technical analysis of dive computer records and diving equipment is a fundamental step in the definition of the cause of death in diving fatalities. All diving computer data, not only those related to maximum depth and ascent's profile, should be considered in detail, and the immersion graph carefully studied by both the forensic pathologist and the forensic underwater experts. The diving technical data can often play a crucial role in explaining any legal issue related to the circumstances of death, possibly leading the prosecutor to further investigation.

Post-mortem computer tomography in ten cases of death while diving: a retrospective evaluation

INTRODUCTION

Self-contained underwater breathing apparatus (SCUBA) diving deaths have always been a challenge for forensic pathologists. Post-mortem computer tomography (PMCT) allows intracorporeal gas visualization, contributing to identify the cases in which the cause of death is arterial gas embolism (AGE). However, in the literature, it is indicated to perform the radiological examination within 24 h after death.

MATERIALS AND METHODS

In this retrospective study, 32 cases of death who had undergone PMCT 24-48 h after death/corpse finding between January 2011 and March 2021 were analyzed, including ten cases of SCUBA divers who died of AGE. All cases' radiological images were reviewed to localize the intracorporeal gas distribution alongside other findings that are usually related to SCUBA diving death. A semi-quantitative evaluation was also performed.

RESULTS

Most of the divers showed gas within the left heart and the arteries. In addition, the semi-quantitative evaluation revealed that the divers presented a higher mean amount of intraarterial gas compared to the fresh corpses. On the other hand, the putrefied corpses presented gas within the portal system and generalized subcutaneous emphysema with higher frequency and quantity than the divers and fresh corpses.

CONCLUSION

Our cases suggested that the PMCT, even when performed 24-48 h after death, remains a valuable tool to diagnose AGE in cases of SCUBA diving deaths. In addition, with the limit of the small sample size, our data showed that at least a medium quantity of intraarterial gas, when not associated with a high amount of gas within the portal system and subcutaneous emphysema, could be considered a diagnostic criterion of AGE.

Diagnosis of arterial gas embolism in SCUBA diving: modification suggestion of autopsy techniques and experience in eight cases

The purpose of this study was to suggest modifications of autopsy techniques in order to improve post-mortem diagnosis of arterial gas embolism (AGE) based on multidisciplinary investigation of SCUBA diving fatalities. Five adult human cadavers from the voluntary donation program of the Human Anatomy Laboratory, and eight judicial autopsied bodies of SCUBA divers from the Forensic Pathology Service were assessed. Before performing any autopsies, we accessed the diving plan and the divers' profiles for each case. We then introduced a new dissection procedure that included identification, isolation, and manipulation of carotid, vertebral and thoracic arterial systems. The dissected vascular structures that allowed optimall isolation of the systemic arterial circulation were identified and ligated. In three of the eight judicial cases, we had a strongly suggestive history of arterial gas embolism following pulmonary barotrauma (PBt/AGE). In these cases, the additional arterial dissection allowed us to clearly diagnose AGE in one of them. The autopsy of the rest of the cases showed other causes of death such as asphyxia by drowning and heart attack. In all cases we were able to reject decompression sickness, and in some of them we showed the presence of artefacts secondary to decomposition and resuscitation maneuvers. These results allow us to suggest a specific autopsy technique divided into four steps, aimed at confirming or excluding some evidence of dysbaric disorders according to a re-enactment of the incident. We have demonstrated the presence of large volumes of intravascular air, which is typical of PBt/AGE.

Air embolism: diagnosis and management

Air embolism is an uncommon, but potentially life-threatening event for which prompt diagnosis and management can result in significantly improved patient outcomes. Most air emboli are iatrogenic. Arterial air emboli may occur as a complication from lung biopsy, arterial catheterization or cardiopulmonary bypass. Immediate management includes placing the patient on high-flow oxygen and in the right lateral decubitus position. Venous air emboli may occur during pressurized venous infusions, or catheter manipulation. Immediate management includes placement of the patient on high-flow oxygen and in the left lateral decubitus and/or Trendelenburg position. Hyperbaric oxygen therapy is the definitive treatment which may decrease the size of air emboli by facilitating gas reabsorption, while also improving tissue oxygenation and reducing ischemic reperfusion injury.

Sudden Death in a Diver: A Diagnostic Conundrum

We discuss the case of an experienced diver who ran out of air during his final ascent while scuba diving. He lost consciousness rapidly after surfacing and despite immediate cardiopulmonary resuscitation, could not be revived. On arrival at the emergency department he was noted to have copious amounts of blood in his upper airway and had developed extensive subcutaneous emphysema. Large amounts of air were observed in the central circulation following a postmortem computerized tomography scan as well as pneumomediastinum, a small right-sided hemothorax, and extensive subcutaneous emphysema. We discuss several potential pathophysiological mechanisms that might explain these findings. Finally, we end with a recommendation for an expedient whole-body postmortem computerized tomography scan and autopsy by a suitably qualified pathologist in the investigation of all dive-related fatalities, where possible.

Differentiation at necropsy between in vivo gas embolism and putrefaction using a gas score

Gas bubble lesions consistent with decompression sickness in marine mammals were described for the first time in beaked whales stranded in temporal and spatial association with military exercises. Putrefaction gas is a post-mortem artifact, which hinders the interpretation of gas found at necropsy. Gas analyses have been proven to help differentiating putrefaction gases from gases formed after hyperbaric exposures. Unfortunately, chemical analysis cannot always be performed. Post-mortem computed tomography is used to study gas collections, but many different logistical obstacles and obvious challenges, like the size of the animal or the transport of the animal from the stranding location to the scanner, limit its use in stranded marine mammals. In this study, we tested the diagnostic value of an index-based method for characterizing the amount and topography of gas found grossly during necropsies. For this purpose, putrefaction gases, intravenously infused atmospheric air, and gases produced by decompression were evaluated at necropsy with increased post-mortem time in New Zealand White Rabbits using a gas score index. Statistical differences (P<0.001) were found between the three experimental models immediately after death. Differences in gas score between in vivo gas embolism and putrefaction gases were found significant (P<0.05) throughout the 67h post-mortem. The gas score-index is a new and simple method that can be used by all stranding networks, which has been shown through this study to be a valid diagnostic tool to distinguish between fatal decompression, iatrogenic air embolism and putrefaction gases at autopsies.

Compositional discrimination of decompression and decomposition gas bubbles in bycaught seals and dolphins

Gas bubbles in marine mammals entangled and drowned in gillnets have been previously described by computed tomography, gross examination and histopathology. The absence of bacteria or autolytic changes in the tissues of those animals suggested that the gas was produced peri- or post-mortem by a fast decompression, probably by quickly hauling animals entangled in the net at depth to the surface. Gas composition analysis and gas scoring are two new diagnostic tools available to distinguish gas embolisms from putrefaction gases. With this goal, these methods have been successfully applied to pathological studies of marine mammals. In this study, we characterized the flux and composition of the gas bubbles from bycaught marine mammals in anchored sink gillnets and bottom otter trawls. We compared these data with marine mammals stranded on Cape Cod, MA, USA. Fresh animals or with moderate decomposition (decomposition scores of 2 and 3) were prioritized. Results showed that bycaught animals presented with significantly higher gas scores than stranded animals. Gas composition analyses indicate that gas was formed by decompression, confirming the decompression hypothesis.

Recent modifications to the investigation of diving related deaths

The investigation of deaths that involve diving using a compressed breathing gas (SCUBA diving) is a specialized area of forensic pathology. Diving related deaths occur more frequently in certain jurisdictions, but any medical examiner or coroner's office may be faced with performing this type of investigation. In order to arrive at the correct conclusion regarding the cause and manner of death, forensic pathologists and investigators need to have a basic understanding of diving physiology, and should also utilize more recently developed technology and ancillary techniques. In the majority of diving related deaths, the cause of death is drowning, but this more often represents a final common pathway due to a water environment. The chain of events leading to the death is just as important to elucidate if similar deaths are to be minimized in the future. Re-enactment of accident scenarios, interrogation of dive computers, postmortem radiographic imaging, and slight alterations in autopsy technique may allow some of these diving related deaths to the better characterized. The amount and location of gas present in the body at the time of autopsy may be very meaningful or may simply represent a postmortem artifact. Medical examiners, coroners, and forensic investigators should consider employing select ancillary techniques to more thoroughly investigate the factors contributing a death associated with SCUBA diving.

Decompression vs. Decomposition: Distribution, Amount, and Gas Composition of Bubbles in Stranded Marine Mammals

Gas embolic lesions linked to military sonar have been described in stranded cetaceans including beaked whales. These descriptions suggest that gas bubbles in marine mammal tissues may be more common than previously thought. In this study we have analyzed gas amount (by gas score) and gas composition within different decomposition codes using a standardized methodology. This broad study has allowed us to explore species-specific variability in bubble prevalence, amount, distribution, and composition, as well as masking of bubble content by putrefaction gases. Bubbles detected within the cardiovascular system and other tissues related to both pre- and port-mortem processes are a common finding on necropsy of stranded cetaceans. To minimize masking by putrefaction gases, necropsy, and gas sampling must be performed as soon as possible. Before 24 h post mortem is recommended but preferably within 12 h post mortem. At necropsy, amount of bubbles (gas score) in decomposition code 2 in stranded cetaceans was found to be more important than merely presence vs. absence of bubbles from a pathological point of view. Deep divers presented higher abundance of gas bubbles, mainly composed of 70% nitrogen and 30% CO₂, suggesting a higher predisposition of these species to suffer from decompression-related gas embolism.

Deadly diving? Physiological and behavioural management of decompression stress in diving mammals

Decompression sickness (DCS; 'the bends') is a disease associated with gas uptake at pressure. The basic pathology and cause are relatively well known to human divers. Breath-hold diving marine mammals were thought to be relatively immune to DCS owing to multiple anatomical, physiological and behavioural adaptations that reduce nitrogen gas (N(2)) loading during dives. However, recent observations have shown that gas bubbles may form and tissue injury may occur in marine mammals under certain circumstances. Gas kinetic models based on measured time-depth profiles further suggest the potential occurrence of high blood and tissue N(2) tensions. We review evidence for gas-bubble incidence in marine mammal tissues and discuss the theory behind gas loading and bubble formation. We suggest that diving mammals vary their physiological responses according to multiple stressors, and that the perspective on marine mammal diving physiology should change from simply minimizing N(2) loading to management of the N(2) load. This suggests several avenues for further study, ranging from the effects of gas bubbles at molecular, cellular and organ function levels, to comparative studies relating the presence/absence of gas bubbles to diving behaviour. Technological advances in imaging and remote instrumentation are likely to advance this field in coming years.

Appearance of gas collections after scuba diving death: a computed tomography study in a porcine model

INTRODUCTION

Postmortem computed tomography can easily demonstrate gas collections after diving accidents. Thus, it is often used to support the diagnosis of air embolism secondary to barotrauma. However, many other phenomenons (putrefaction, resuscitation maneuvers, and postmortem tissue offgassing) can also cause postmortem gas effusions and lead to a wrong diagnosis of barotrauma.

OBJECTIVES

The aim of this study is to determine topography and time of onset of postmortem gas collections respectively due to putrefaction, resuscitation maneuvers, and tissue offgassing.

MATERIALS AND METHODS

A controlled experimental study was conducted on nine pigs. Three groups of three pigs were studied postmortem by CT from H0 to H24: one control group of nonresuscitated nondivers, one group of divers exposed premortem to an absolute maximal pressure of 5 b for 16 min followed by decompression procedures, and one group of nondivers resuscitated by manual ventilation and thoracic compression for 20 min. The study of intravascular gas was conducted using CT scan and correlated with the results of the autopsy.

RESULTS

The CT scan reveals that, starting 3 h after death, a substantial amount of gas is observed in the venous and arterial systems in the group of divers. Arterial gas appears 24 h after death for the resuscitated group and is absent for the first 24 h for the control group. Concerning the putrefaction gas, this provokes intravenous and portal gas collections starting 6 h after death. Subcutaneous emphysema was observed in two of the three animals from the resuscitated group, corresponding to the thoracic compression areas.

CONCLUSION

In fatal scuba diving accidents, offgassing appears early (starting from the first hour after death) in the venous system then spreads to the arterial system after about 3 h. The presence of intra-arterial gas is therefore not specific to barotrauma. To affirm a death by barotrauma followed by a gas embolism, a postmortem scanner should be conducted very early. Subcutaneous emphysema should not be mistaken as diagnostic criteria of barotrauma because it can be caused by the resuscitation maneuvers.

Progressive gas formation in a deceased person during mortuary storage demonstrated on computed tomography

We report the case of an 82-year-old woman with a past history of diabetes mellitus who died following blunt head injury sustained in a fall resulting in an acute subdural hematoma. Serial postmortem CT scans of the chest and abdomen performed over a 3-day period demonstrated progressive intra-hepatic and intra-cardiac gas formation whilst the deceased was stored in a standard mortuary refrigerator at a nominated temperature of 4 degrees C. Measured mortuary refrigerator temperatures over a 7 day period showed statistically significant day to day variability in temperatures above 4 degrees C as well as variations in temperature depending on location within the refrigerator space. In the absence of other known factors associated with such gas formation, putrefaction seems the likely cause despite a lack of obvious external features. This phenomenon must therefore be taken into account when interpreting the presence of visceral gas on postmortem CT and relating such gas to the cause of death.

Gas bubbles in seals, dolphins, and porpoises entangled and drowned at depth in gillnets

Gas bubbles were found in 15 of 23 gillnet-drowned bycaught harp (Pagophilus groenlandicus), harbor (Phoca vitulina) and gray (Halichoerus grypus) seals, common (Delphinus delphis) and white-sided (Lagenorhyncus acutus) dolphins, and harbor porpoises (Phocaena phocaena) but in only 1 of 41 stranded marine mammals. Cases with minimal scavenging and bloating were chilled as practical and necropsied within 24 to 72 hours of collection. Bubbles were commonly visible grossly and histologically in bycaught cases. Affected tissues included lung, liver, heart, brain, skeletal muscle, gonad, lymph nodes, blood, intestine, pancreas, spleen, and eye. Computed tomography performed on 4 animals also identified gas bubbles in various tissues. Mean +/- SD net lead line depths (m) were 92 +/- 44 and ascent rates (ms(-1)) 0.3 +/- 0.2 for affected animals and 76 +/- 33 and 0.2 +/- 0.1, respectively, for unaffected animals. The relatively good carcass condition of these cases, comparable to 2 stranded cases that showed no gas formation on computed tomography (even after 3 days of refrigeration in one case), along with the histologic absence of bacteria and autolytic changes, indicate that peri- or postmortem phase change of supersaturated blood and tissues is most likely. Studies have suggested that under some circumstances, diving mammals are routinely supersaturated and that these mammals presumably manage gas exchange and decompression anatomically and behaviorally. This study provides a unique illustration of such supersaturated tissues. We suggest that greater attention be paid to the radiology and pathology of bycatch mortality as a possible model to better understand gas bubble disease in marine mammals.

Cerebral arterial air embolism in a child after intraosseous infusion

Cerebral arterial air embolism (CAAE) has been reported as a rare complication of medical intervention. There has been one reported case of CAAE after the use of an intraosseous infusion (IO) system. We report on a case of CAAE after tibial IO infusion in a 7-month-old girl during resuscitation.

Scuba-diving related deaths in Okinawa, Japan, from 1982 to 2007

We reviewed the autopsies of scuba-diving related deaths (SDRDs) that were collected from April 1982 until March 2007. In the period under consideration, a total of 40 SDRDs were registered, out of which 34 were males and 6 females. Ages ranged from 19 to 65 years, with the average of 41.5 years (SD=12.9). Divers over the age of 40 accounted for 60% of all fatalities. The major cause of death was drowning (62.5%), followed by disease (28.5%). The average age for drowning and disease-related deaths was 38.6 (SD=12.8) and 48.7 years (SD=10.1), respectively. Of the 40 fatalities, 24 were beginners who had little or no experience. In this study, we compared SDRDs in the first term, from April 1982 to March 1995, and in the second term, from April 1995 to March 2007. The average age in the first and second terms was 35.4 and 45.2 years, respectively; the average age for the second term was 10 years older than the first. Of those in the first term, 13.3%, and of those in the second term, 40.0%, died from complications arising from already existing conditions. This study revealed that the onset of diseases during diving frequently causes fatal accidents, especially for older divers.

Radiography after unexpected death in infants and children compared to autopsy

BACKGROUND

Postmortem radiography may reveal skeletal and soft-tissue abnormalities of importance for the diagnosis of cause of death.

OBJECTIVE

To review the radiographs of children under 3 years of age who had died suddenly and unexpectedly. To compare the radiological and autopsy findings evaluating possible differences in children dying of SIDS and of an explainable cause.

MATERIALS AND METHODS

A total of 110 consecutive skeletal surveys performed between 1998 and 2002 were reviewed. All but one were performed before autopsy and comprised AP views of the appendicular and axial skeleton and thorax/abdomen, lateral views of the axial skeleton and thorax, and two oblique views of the ribs. Radiography and autopsy findings were compared.

RESULTS

Causes of death were classified as SIDS/borderline SIDS (n = 52) and non-SIDS (n = 58), with one case of abuse. In 102 infants there were 150 pathological findings, 88 involving the chest, 24 skeletal, and 38 miscellaneous findings. The radiological-pathological agreement was poor concerning pulmonary findings. Skeletal findings were sometimes important for the final diagnosis.

CONCLUSIONS

Radiography revealed many skeletal and soft-tissue findings. Pulmonary pathology was most frequently found, but showed poor agreement with autopsy findings. Recognizing skeletal findings related to abuse is important, as these may escape recognition at autopsy.