Postmortem CT and MRI findings of massive fat embolism

Fat embolism: a systematic review to facilitate the development of standardised procedures in pathology

Fat embolism (FE) is a historically recognised but still actively researched topic in forensic pathology. Several aspects remain not fully elucidated, such as its aetiopathogenesis, its causal role in death determination, the impact of interfering factors (e.g. cardiopulmonary resuscitation or other medical procedures) and both qualitative and quantitative diagnostic methodologies in clinical and forensic contexts. These issues are further underscored by the potential involvement of FE in the causal determination of non-traumatic deaths, which often raises questions of professional liability. The present study aims to provide a comprehensive and up-to-date overview of the most recent scientific evidence relevant to forensic pathology. Our systematic research has included 58 articles from 1990 to the present on the topic of FE and fat embolism syndrome (FES). From these articles, we identified 45 case reports, from which the authors' descriptions were extracted to provide information on individual cases and the operational methods of forensic pathologists. Additionally, 21 experimental studies were identified, and their key findings have been summarised narratively. It has emerged that both traumatic and non-traumatic cases are frequently reported in the forensic context, with orthopaedic and cosmetic surgery being among the highest-risk specialities. Experimental studies have re-evaluated the role of a patent foramen ovale in the pathogenesis of FE, as well as the impact of cardiopulmonary resuscitation in causing FE severe enough to result in death. Additionally, there are new findings regarding diagnostic techniques, including radiological and immunohistological methods; however, they have not yet fully bridged the reliability gap compared to an accurate autopsy-histological evaluation. The major critical points that emerged include the lack of complete and detailed information on premortem clinical conditions, the underutilisation of grading systems and the methodological heterogeneity applied, resulting in considerable variability regarding the organs studied histologically and the diagnostic techniques used. Despite the limitations associated with the analysis of case reports and the heterogeneity of included experimental studies, we believe that this study can provide a comprehensive overview of the FE topic. It furnishes pathologists with an updated overview useful for clinical practice and guiding future research trends, as well as facilitating the development of standardised procedures.

A diagnostic strategy for pulmonary fat embolism based on routine H&E staining using computational pathology

Pulmonary fat embolism (PFE) as a cause of death often occurs in trauma cases such as fractures and soft tissue contusions. Traditional PFE diagnosis relies on subjective methods and special stains like oil red O. This study utilizes computational pathology, combining digital pathology and deep learning algorithms, to precisely quantify fat emboli in whole slide images using conventional hematoxylin-eosin (H&E) staining. The results demonstrate deep learning's ability to identify fat droplet morphology in lung microvessels, achieving an area under the receiver operating characteristic (ROC) curve (AUC) of 0.98. The AI-quantified fat globules generally matched the Falzi scoring system with oil red O staining. The relative quantity of fat emboli against lung area was calculated by the algorithm, determining a diagnostic threshold of 8.275% for fatal PFE. A diagnostic strategy based on this threshold achieved a high AUC of 0.984, similar to manual identification with special stains but surpassing H&E staining. This demonstrates computational pathology's potential as an affordable, rapid, and precise method for fatal PFE diagnosis in forensic practice.

Pulmonary fat embolism: a potentially new fatal complication of SARS-CoV-2 infection. A case report

BACKGROUND

So far, there have been more than 761 million confirmed cases of SARS-CoV-2 worldwide, with more than 6.8 million deaths. The most common direct causes of death for COVID-19 are diffuse alveolar injury and acute respiratory distress syndrome. Autopsy results have shown that 80-100% of COVID-19 patients have microthrombi which is 9 times higher than in patients with influenza. There are reported cases of fat embolism associated with Covid-19, but relevant epidemiological investigations and fatal cases of pulmonary fat embolism are lacking. In this report, we describe the first COVID-19 patient to die from pulmonary fat embolism.

CASE PRESENTATION

A 54-year-old woman suddenly felt unwell while at work. She had difficulty breathing for 40 min and lost consciousness for 20 min before being taken to the hospital. On admission, her temperature was 36 ℃, but her respiration, heart rate, and blood pressure were undetectable. Laboratory examination revealed C-reactive protein, 26.55 mg/L; D-dimer, 11,400 µg/L; and procalcitonin, 0.21 ng/mL. She was declared clinically dead 2 h after admission due to ineffective rescue efforts. At autopsy, both lungs were highly oedematous with partial alveolar haemorrhage. The presence of microthrombi and pulmonary fat embolism in small interstitial pulmonary vessels was confirmed by phosphotungstic acid haematoxylin staining and oil red O staining. The immunohistochemical results of spike protein and nucleocapsid protein in laryngeal epithelial cells confirmed SARS-CoV-2 infection.

CONCLUSIONS

Pulmonary fat embolism may be another fatal complication of COVID-19 infection, and clinicians should pay more attention to it.

Application of postmortem MRI for identification of medulla oblongata contusion as a cause of death: a case report

Whiplash injury is common in traffic accidents, and severe whiplash is characterized by cervical spinal cord injuries with cervical dislocation or fracture, that can be diagnosed by postmortem computed tomography (PMCT), postmortem magnetic resonance (PMMR), or conventional autopsy. However, for cervical spinal cord injury without fracture and dislocation, PMMR can be more informative because it provides higher resolution of soft tissues. We report the case of a 29-year-old male who died immediately following a traffic accident, in which the vehicle hit an obstacle at a high speed, causing deformation of the bumper and severe damage of the vehicle body. PMCT indicated no significant injuries or diseases related to death, but PMMR showed patchy abnormal signals in the medulla oblongata, and the lower edge of the cerebellar tonsil was herniated out of the foramen magnum. The subsequent pathological and histological results confirmed that death was caused by medulla oblongata contusion combined with cerebellar tonsillar herniation. Our description of this case of a rare but fatal whiplash injury in which there was no fracture or dislocation provides a better understanding of the potentially fatal consequences of cervical spinal cord whiplash injury without fracture or dislocation and of the underlying lethal mechanisms. Compared with PMCT, PMMR provides important diagnostic information in forensic practice for the identification of soft tissue injuries, and is therefore an important imaging modality for diagnosis of whiplash injury when there is no fracture or dislocation.

Label-Free Diagnosis of Pulmonary Fat Embolism Using Fourier Transform Infrared (FT-IR) Spectroscopic Imaging

The diagnosis of pulmonary fat embolism (PFE) is of great significance in the field of forensic medicine because it can be considered a major cause of death or a vital reaction. Conventional histological analysis of lung tissue specimens is a widely used method for PFE diagnosis. However, variable and labor-intensive tissue staining procedures impede the validity and informativeness of histological image analysis. To obtain complete information from tissues, a method based on infrared imaging of unlabeled tissue sections was developed to identify pulmonary fat emboli in the present study. We selected 15 PFE-positive lung samples and 15 PFE-negative samples from real cases. Oil red O (ORO) staining and infrared spectral imaging collection were both performed on all lung tissue samples. And the fatty tissue of the abdominal wall and the embolized lipid droplets in the lungs were taken for comparison. The results of the blind, evaluation by pathologists, showed good agreement between the infrared spectral imaging of the lung tissue and the standard histological stained images. Fourier transform infrared (FT-IR) spectroscopic imaging significantly simplifies the typical painstakingly laborious histological staining procedure. And we found a difference between lipid droplets embolized in abdominal wall fat and lung tissue.

Fat Embolism, Fat Embolism Syndrome and the Autopsy

Fat embolism is common following trauma and is a common autopsy finding in these cases. It may also be seen in non-traumatic cases and is seen in children as well as adults. In comparison fat embolism syndrome (FES) only occurs in a small number of trauma and non-trauma cases. Clinical diagnosis is based on characteristic clinical and laboratory findings. Fat embolism exerts its effect by mechanical blockage of vessels and/or by biochemical means including breakdown of fat to free fatty acids causing an inflammatory response. Fat embolism can be identified at autopsy on microscopy of the lungs using fat stains conducted on frozen tissue, including on formalin fixed but not processed tissue. With FES fat emboli can be seen in other organs including the brain, kidney and myocardium. Fat can also be identified with post-fixation staining, typically with osmium tetroxide. Scoring systems have been developed to try and determine the severity of fat embolism in lung tissue. Fat embolism is also common following resuscitation. When no resuscitation has taken place, the presence of fat on lung histology has been used as proof of vitality. Diagnosis of fat embolism syndrome at autopsy requires analysis of the history, clinical and laboratory findings along with autopsy investigations to determine its relevance, but is an important diagnosis to make which is not always identified clinically. This paper reviews the history, clinical and laboratory findings and diagnosis of fat embolism and fat embolism syndrome at autopsy.