Type:
Educational Exhibit
Keywords:
Forensic / Necropsy studies, CT, Education, Forensics
Authors:
D. Stephens, M. Nasreddine
DOI:
10.26044/ranzcr2022/R-0097
Imaging findings OR Procedure details
Fluid in paranasal sinuses
- Fluid in the paranasal sinuses is a very common, and highly sensitive finding. Sensitivity approaches 100% in multiple studies.3 If absent, one should strongly consider other causes of death apart from drowning.5
- However, this is not a specific finding, and can also be seen in non-drowning cases. 6,7 This finding may also be explained by ante-mortem conditions causing sinusitis, regurgitation and post-mortem effusion. Passive post-mortem passage of fluid due to prolonged submersion, is also a theoretical consideration.
- PMCT easily demonstrates fluid in the paranasal sinuses, compared to classical autopsy where this may be more difficult.
Sediment in airways, lungs and stomach
- The presence of high attenuation sediment in airways, lungs and stomach has excellent specificity and is also highly suggestive of drowning. It has been suggested by some authors that this can be the key to the diagnosis of drowning.3,6
- The sensitivity of presence of sediment however is low. The presence of sediment is dependent on the nature of the water.3 In freshwater drownings, the presence of high attenuation sediment discernable on CT is thought to represent sediment from silt-laden fresh water, and in the case of salt water the high attenuation is attributable to sand.6
Froth in nose, mouth and airways
- External inspection of a fresh-drowned body commonly demonstrates frothy fluid exuding from the mouth and nostrils, representing surfactant and proteinaceous exudate mixed with the drowning media.8
- Frothy fluid is sensitive, but not a specific finding.3 It may also be found in the upper airways of cases due to pulmonary oedema,8 and asphyxiation from causes other than drowning.9
Fluid in the subglottic trachea and bronchi
- Fluid in the subglottic trachea and bronchi has a sensitivity of 93%3 and is supportive of drowning, but not specific. It can also be seen in perimortem inhalation and in advanced putrefactive states.3
- The absence of fluid in the airways however does not exclude drowning as consideration should also be given to the rarer so-called “dry drowning” – in which there is laryngospasm as a response to fluid inhalation.3 However, controversy exists in the literature as to the existence of this phenomenon.6
- PMCT is an excellent tool to visualize fluid in the trachea and bronchi, compared to autopsy where the fluid can move during handling of thoracic contents.
Lungs and pleural spaces
- The cascade of drowning is complex and is thought to commence with the aspiration of small amounts of fresh water,10 diluting the pulmonary surfactant and leading to instability of the alveoli with atelectasis.7 Loss of pulmonary surfactant reduces lung compliance and contributes to air trapping. Atelectasis leads to intrapulmonary shunting with pulmonary venous admixture and hypoxaemia. Aspirated fluid is an irritant and causes bronchospasm resulting in expiratory obstruction and hyperinflation. At autopsy, emphysema aquosum is described, with hyperinflated lungs, and a cut surface wet with foamy fluid.11 The fluid aspiration followed by bronchospasm is more multifocally scattered throughout the lung than diffusely, which results in a mosaic pattern of dry, hypoperfused and wet, hyperperfused areas.7
- Aspiration of freshwater also leads to peribronchial cuffing,10 reflecting an attempt to remove excessive fluid from the airways into the circulation. Aspiration of hypertonic saltwater can pull fluid into the alveoli from the plasma, resulting in pulmonary oedema.7,11
- The following PMCT features have been described in the literature:
- Ground glass opacity – the most described pattern is a mosaic appearance associated with freshwater drowning
- Emphysema
- Pulmonary oedema
- Bronchospasm
- Pleural effusions
- All the PMCT features of drowning however are non-specific and are seen in other pathological processes. It is also important to be aware of post-mortem changes and decomposition, which may mimic or mask the lung changes in drowning.10 For example, dependent areas of increased attenuation are seen in the lung as part of normal postmortem change, known as livor mortis. Aspiration is a not infrequent occurrence around the time of agony and may result in ground glass opacities and consolidation, mimicking or obscuring lung parenchymal changes.
Stomach
- The presence of high attenuation sediment in the stomach appears to be a specific sign of drowning, but similar to sediment within the paranasal sinuses and airways, is not sensitive.3
- Gastric distension from swallowing water has good diagnostic sensitivity but it is not specific. There are many other causes of gastric distension including resuscitation attempts and drinking before death.3 Putrefaction can also lead to gastro-intestinal distension with fluid.
- Similarly, dilution of stomach contents secondary to swallowing water during active drowning, has also been described in the literature.3,7
Haemodilution
- The pathophysiology of drowning is different for fresh water and salt water. In freshwater aspiration, the hypotonic fresh water in the alveoli is rapidly absorbed into the circulation with dilution of blood and hypervolaemia. Aspiration of sea water however results in a hypertonic solution within the alveoli, which pulls additional fluid from the plasma. This leads to pulmonary oedema and haemoconcentration.7,11
- Haemodilution in freshwater drowning has been described in several PMCT studies,3,7,9 manifested as a reduction in Hounsfield density and confirmed by placement of a large region of interest (ROI) over the cardiac chambers. A blood density below 55 HU is considered indicative of haemodilution.3 However, a more recent study by Leth et al11 which compared 24 saltwater drownings, 16 freshwater drownings and 80 controls did not find any significant difference between the groups.
- Haemodilution is not specific and may be secondary to resuscitation attempts or antemortem anaemia.3 The phenomenon of intra-cavity blood sedimentation seen as a normal finding after death may also affect assessment of haemodilution by ROI measurement,3,11 whereby a layering effect is seen in the cardiac chambers and great vessels due to normal separation of blood into serum and erythrocytic components postmortem.