Fat embolism syndrome

Fat embolism syndrome (FES) is an uncommon clinical manifestation of a minority of individuals who have fat emboli. It is the result of innumerable small fat emboli leading to a multisystem dysfunction, classically characterized by the triad of:

1. respiratory distress

2. cerebral abnormalities

3. petechial rash

Epidemiology

A clinical evident FES occurs in only ~2.5% (range 0.5-4%) of individuals with demonstrable fat embolism, seen relatively frequently in patients with long bone fractures and during orthopedic prosthetic procedures. FES has an incidence of 1-3% following long bone fractures and 33% in patients with bilateral long bone fractures ¹⁰.

Clinical presentation

Symptoms of FES usually develop 1-2 days after the event. Although fat emboli can essentially reach any organ in the body, the results of the embolic shower are most often evident in the lungs, brain, and skin.

Pulmonary dysfunction is present in 75% of patients and is the earliest to be manifested ⁶. The presence of numerous fat globules in the small pulmonary vessels results in dyspnea and hypoxemia.

Neurological symptoms are seen in 86% of patients and range from acute confusion to drowsiness, rigidity, convulsions, or even coma ⁶. 

The skin manifestation is characterized by a petechial rash in the chest, axilla, conjunctiva, and neck that appears within 24–36 hours and disappears within a week ⁶. 

Diagnosis 

Gurd and Wilson's criteria require the presence of at least one major and at least four minor criteria.

Major criteria

• petechial rash

• respiratory insufficiency

• cerebral involvement

Minor criteria

• tachycardia

• fever

• retinal changes

• jaundice

• renal signs

• thrombocytopenia

• anemia

• high ESR

• fat macroglobulinemia

Pathology

Fat particles, from bone marrow typically after lower extremity fracture, or introduced into vessels and heart during orthopedic surgery, are released in blood circulation, embolize and occlude the pulmonary capillaries. Some of the fat globules can pass through the pulmonary capillaries and reach intracranial capillaries.

The pathophysiology is thought to be most likely due to both mechanical obstruction as well as a secondary inflammatory response to the released free fatty acids from trapped fat particles within the small vessels.

Consumptive thrombocytopenia and anemia are common complications of fat embolism.

Radiographic features

FES remains a clinical diagnosis although imaging may be confirmatory and aid in excluding competing differential diagnoses.

Chest

Chest x-ray findings may be subtle and CT is better suited to making the diagnosis. Three patterns are most frequently observed: ground-glass change with geographic distribution, ground-glass with interlobular septal thickening, and nodular opacities. Fatty filling defects in pulmonary arteries are only rarely described. 

For more information see pulmonary fat embolism.

Brain

CT is often normal or demonstrates edema. MRI may also show foci of vasogenic edema in a random (i.e. embolic shower) distribution but classically a "starfield" pattern may be seen on DWI.

For more information see cerebral fat embolism.

History and etymology

The fat embolism syndrome was first described as a clinical entity by E Von Bergmann in 1873 ^6,7. It is thought to have been clinically described as a post-mortem finding by Zenker in 1862.