Fat embolism syndrome pathophysiology

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Feham Tariq, MD [2]

Overview

Two major theories have been described to explain the pathophysiology of fat embolism syndrome(FES):^[1]^[2]

Mechanical theory:

The theory proposes that there is mechanical obstruction by fat cells from the bone marrow in the end-capillaries after trauma.

Post traumatic insult, the fat cells travel via venous sinusoids to the capillaries.
These cells have potent prothrombotic and proinflammatory potential.
They trigger rapid aggregation of platelets and accelerated fibrin generation as they travel through the venous system, eventually lodging in the pulmonary arterial circulation.
Pulmonary capillary obstruction leads to interstitial hemorrhage and edema, alveolar collapse, and reactive hypoxemic vasoconstriction.
Massive fat emboli may also lead to macrovascular obstruction and shock.
Fat cells may also enter the arterial circulation via a patent foramen ovale or directly through the pulmonary capillary bed, causing the characteristic neurological and dermatologic findings of FES

Biochemical theory:

This theory attributes the clinical manifestations of FES to the pro inflammatory effect of fat emboli.^[3]^[4]^[5]

Tissue lipases break down the fat in the bone marrow, forming high levels of glycerol and toxic free fatty acids.
These intermediate products lead to end-organ dysfunction.
In the lung, toxic injury to pneumocytes and pulmonary endothelial cells causes vasogenic and cytotoxic edema as well as hemorrhage.
Acute lung injury or acute respiratory distress syndrome. results from damaged pulmonary endothelium that triggers a proinflammatory cytokine cascade.

Hematoxylin and eosin staining shows the following changes in the lungs, kidneys and brain: Lung:

Immunohistochemical staining shows the following changes:

Kidney:

Brain:

↑ Parisi DM, Koval K, Egol K (2002). "Fat embolism syndrome". Am J Orthop (Belle Mead NJ). 31 (9): 507–12. PMID 12650535.
↑ Robert JH, Hoffmeyer P, Broquet PE, Cerutti P, Vasey H (1993). "Fat embolism syndrome". Orthop Rev. 22 (5): 567–71. PMID 8316420.
↑ Husebye EE, Lyberg T, Røise O (2006). "Bone marrow fat in the circulation: clinical entities and pathophysiological mechanisms". Injury. 37 Suppl 4: S8–18. doi:10.1016/j.injury.2006.08.036. PMID 16990064.
↑ Estèbe JP (1997). "[From fat emboli to fat embolism syndrome]". Ann Fr Anesth Reanim. 16 (2): 138–51. PMID 9686075.
↑ Hofmann S, Huemer G, Kratochwill C, Koller-Strametz J, Hopf R, Schlag G; et al. (1995). "[Pathophysiology of fat embolisms in orthopedics and traumatology]". Orthopade. 24 (2): 84–93. PMID 7753543.