대한흉부영상의학회 Korean Society of Thoracic Radiology

Discussion

Diagnosis With Brief Discussion

Diagnosis

Fat Embolism Syndrome

Radiologic Findings

Chest radiograph shows diffuse reticulonodular opacities with ground-glass attenuation extending to both lungs with predominantly distributed in both lower lungs. Thin-section CT scans shows diffuse ground-glass attenuation, focal consolidation, small ill-defined nodules and reticular opacities with predominant distributed in central peribronchovascular area with subpleural sparing. Follow up thin-section CT scan obtained 3 days after initial CT showed marked interval improvement of parenchymal opacity with residual centrilobular ground glass opacity nodules. Follow up chest radiograph after 7 days shows almost disappearance of abnormal opacities in both lungs (not shown).

Brief Review

The presence of numerous fat globules in the small pulmonary vessels results in dyspnea and hypoxemia. From the pulmonary circulation, the globules pass into the systemic circulation and embolize many organs, notably the brain and skin, where they result in a variety of neurologic manifestations and cutaneous petechiae. The combination of respiratory, neurologic and cutaneous disease constitutes the fat embolism syndrome (FES). The diagnosis of FES is based on the following major and minor clinical manifestations and laboratory findings. The major criteria included petechial rash, hypoxemia, CNS depression disproportionate to hypoxemia, and clinical or radiologic evidence of pulmonary edema. Minor criteria included tachycardia, pyrexia, retinal change (fat or petechia), fat present in the urine, sudden drop in hematocrit or platelets, increasing ESR, and fat globules in the sputum. At least one major and four minor criteria were required for the diagnosis of FES.
Whereas fat embolism is reported to occur in >90 % of patients with traumatic injury to the skeletal system, FES occurs in only 3-4% of these patients. Symptoms usually develop 1-2days after an injury in the long bones of the extremities or after intramedullary nailing or even after a minor trauma without bone fracture. Although the mechanism of FES is controversial, respiratory symptoms secondary to fat embolism syndrome result when fat emboli initiate an inflammatory cascade that cause increased capillary permeability following endothelial damage, diffuse alveolar damage and the adult respiratory distress syndrome (ARDS). Therefore, the radiologic features of fat embolism syndrome are presumed to be manifestations of increased pulmonary capillary permeability and edema or ARDS ; mainly progressive bilateral airspace consolidation.
There is generally a latent period of 12 to 24 hours between the inciting event and overt clinical manifestations, 85% of patents will develop signs and symptoms within 48 hours of injury. A time lag between injury and appearance of infiltrates often occurs in FES may be important in the differential diagnosis of respiratory insufficiency in a trauma patient, because radiographic abnormalities from pulmonary contusion or from thermal, toxic, or aspiration injuries are generally present from the onset. Chest radiographic findings are nonspecific and variable; but when fat embolism is extensive, a combination of multiple focal alveolar opacities, interstitial opacities, and nodular opacities develops with predominant distribution in the peripheral lung zones or predominate in the perihilar areas, simulating a pulmonary edema pattern. Recently, reported CT findings of pulmonary FES in 6 patients by Hiroaki et al, focal areas of consolidation or ground-glass opacity were seen in all patients, similar features with our case. Small nodules of various sizes (<10mm) were also seen in all patients. Which reflect to the pathophysiology of this syndrome presenting pulmonary edema, hemorrhage, and atelectasis. Their cases showed both upper lobes predominancy in five of the six patients, different features comparing with our case.

References

1. Hiroaki A, Yasuyuki K, Yasuo. Pulmonary fat embolism syndrome: CT findings in six patients. JCAT 2000;24:24-29
2. Heyneman L.E., Muller N.L. Pulmonary nodules in early fat embolism syndrome: a case report. Journal of Thoracic Imaging 2000;15: 71-74
3. Fraser R.S., Muller N.L., Colman N., Pare P.D. Diagnosis of diseases of the chest. 4th ed. Philadelphia: Saunders, 1845-1850

Keywords

Vascular, Lung, Vascular, embolism / Trauma related,