Fat Embolism Syndrome

Introduction

An embolus is an unattached mass that travels through the circulation and can create blockages. Accordingly, a fat embolus is a fat globule that enters the blood and reaches the pulmonary circulation. This results in a clinical syndrome known as FES, or fat embolism syndrome

After a long bone or pelvic fracture, fat can be released from bone marrow and enter the venous circulation. Eventually, it moves through the right side of the heart where it is ejected into the lungs through the pulmonary artery.

Consequently, these fat globules can collect and then obstruct pulmonary capillaries, causing respiratory symptoms.

Some really tiny fat microemboli are thought to be so small that they are able to pass through the pulmonary circulation into the left side of the heart. These microthombi will then be ejected through the aorta, back into the systemic circulation. This might explain the neurological symptoms and petechiae associated with FES.

The key takeaway here is that the goal of diagnostic evaluation is to exclude other diseases because most imaging findings are generally nonspecific. FES should really be considered as the diagnosis if an at-risk patient develops neurologic issues and petechiae.

Blood tests may show anaemia and thrombocytopaenia. Keep in mind that no specific biomarker has been validated for this disease though.

In terms of imaging, chest xray is usually normal, although a minority might show air space disease due to oedema or alveolar haemorrhage.

Other imaging might include CT chests but again, they usually normal but might show ground glass opacities. MRI brains might show a starfield" pattern of diffuse lesions if there are acute neurological abnormalities.

The onset of Fat embolus syndrome typically occurs 1 to 3 days after the initial fracture, although this obviously varies.

Respiratory abnormalities are the most common presenting features. They probably occur in up 97% of cases. These include hypoxemia, dyspnoea, and tachypnoea. However, like all of its features, pulmonary distress in non-specific.

Therefore consider differentials like other embolization syndromes, like thrombotic pulmonary embolism coming from a DVT, acute alveolar disease due to heart failure or pneumonia, and vascular disorders like lupus.

Neurological abnormalities are common, occurring in about 60% of cases. They usually start after respiratory distress and include features ranging from confusion and altered level of consciousness to seizures.

Finally, the petechial rash occurs in 30% of cases. It is usually the last feature to develop. Remember petechiae are non-blancheable red, purple or brown spots caused by bleeding into the skin. I think that of the phrase pinpoint petechiae, because it helps remind me that lesions are tiny and under 2mm across. In FES, this rash characteristically occurs on nondependent regions of the body including the head, chest, and conjunctiva.

Fat embolus syndrome presents with the classic triad of facial petechiae, altered level of consciousness, and tachypnoea due to hypoxaemia. 30% of patients get the rash, this occurs last. 60% get neurological issues, the occurs before. 90% of patients get the tachypnoea and this comes as the first presenting complaint.

If someone has these FAT symptoms, you have to try and be lazy, exclude other issues and provide them with supportive measures.