Author B Jason Brotherton, MD, MS1,2; Robert Kivindu, MBChB1; Kristina E. Rudd, MD, MPH3
1Department of Internal Medicine, Kijabe Hospital, Kijabe, Kenya 2Department of Critical Care, Kijabe Hospital, Kijabe, Kenya 3Department of Critical Care Medicine, University of Pittsburgh School of Medicine, Pittsburgh, PA, USA
Case
A previously healthy 22-year-old woman was transferred to our
hospital in rural Kenya from an outside facility for a higher level of
surgical care. One day prior to transfer she was involved in a road
traffic accident, where she was a passenger on the back of a motorcycle.
She sustained fractures of her right ischium, midshaft of the right
femur, and distal right tibia and fibula. No other injuries were
reported.
Shortly after arrival to our hospital she was noted to become newly
tachypneic and hypoxemic. Vital signs at that time were the following:
blood pressure 107/51 mm Hg, pulse 112 beats/min, respiratory rate 28
breaths/min, peripheral capillary oxygen saturation breathing ambient
air 84%, and Glasgow Coma Scale 15. A computed tomography (CT) scan with
intravenous contrast of the chest was obtained (Figures 1a, 1b) and a
diagnosis was made.
Question
Based on the history and CT findings, what is the most likely diagnosis?
A. Pulmonary embolism B. Aspiration pneumonia C. Fat embolism D. Pulmonary contusion
Answer
C. Fat embolism
Discussion
CT images of this patient revealed bilateral ground glass opacities
(*) and patchy nodular infiltrates (red arrow). The pulmonary arteries
showed no filling defect.
This patient was diagnosed with fat embolism, defined as the presence
of fat globules in the pulmonary circulation. Fat embolism occurs in as
many as 80% of patients with traumatic skeletal injuries, and long bone
fractures are the most common associated injury.1 The underlying pathophysiology is not well understood, but there are two proposed mechanisms.2 The mechanical theory
suggests that long bone injury forces fat globules out of the venous
sinusoids into the circulation that then travel to the lungs and
systemic circulation, causing occlusive injury. The biochemical theory
posits that mobilized fat globules initiate a proinflammatory state.
These inflammatory molecules are then hydrolyzed, releasing free fatty
acids while simultaneously stimulating further cytokine release. This
results in more peripheral tissue damage by generating vasogenic and
cytotoxic edema.2
Symptoms from a fat embolism occur 12-72 hours after the initial
insult. While fat embolism syndrome (FES) is classically described as a
triad of respiratory distress, altered mental status, and petechial
rash, none of these three signs are pathognomonic for the condition.
Pulmonary manifestations of dyspnea, tachypnea, and hypoxia are the most
common, occurring in 96% of cases of FES.1 Neurologic
findings, including altered mental status, seizures, and focal
neurologic deficits, are next most common, but are only present in 59%
of patients with FES. Petechial rash occurs in non-dependent areas of
the head, thorax and axilla. It is last to appear and least common,
emerging in only 20% of cases.1
Historically diagnosis has been made clinically but there have been
three different sets of criteria to devised to aid in diagnosing FES:
Gurd’s, Schonfeld’s, and Lindeque’s criteria.1,2,3 These criteria were based upon separate, small clinical studies and have not been prospectively validated.1,2,3 Gurd’s criteria have been the most frequently used, and require 1 major and 4 minor criteria for diagnosis of FES (Table 1).2 There are no specific laboratory tests for FES, but frequently patients also
present with anemia, thrombocytopenia, elevated ESR and CRP, or
hypoalbuminemia.2 Our patient was diagnosed with fat
embolism based upon her clinical presentation and radiographic imaging.
She did not meet for the full criteria for FES.
Chest imaging can be beneficial in the correct clinical setting.
Chest radiographs often have bilateral, diffuse patchy infiltrates
resembling Acute Respiratory Distress Syndrome. CT scan of the chest, as
in our patient, often shows bilateral ground glass opacities and
consolidation with clear demarcation between areas of normal lung and
areas of affected lung. Other CT findings can include “crazy paving”
which is characterized by a reticular pattern superimposed on
ground-glass opacities.4 The term is used because it
resembles the appearance of paths made with broken pieces of stone. The
extent of findings seen on CT scan have been correlated with severity of
clinical disease.5 The bilateral, well demarcated ground
glass opacities (*) , patchy nodular infiltrates (red arrow), and
interlobular septal thickening (not depicted in our images) are
characteristic of fat embolism.
Regarding the other options listed, the history, presentation, and CT
findings made fat embolism most likely. The pre-test probability for
pulmonary embolism was low given her lack of recent surgery, immobility
for less than three days, likelihood of current symptoms being due to a
diagnosis other than PE, and no prior history of deep vein thrombosis or
PE. The pulmonary and segmental vessels were patent, which an
occlusion to these vessels is the primary radiologic finding.
Radiographic findings of aspiration pneumonias are often in gravity
dependent areas.6 The diffuse location of the ground glass
opacities and lack of history of loss of consciousness made aspiration
pneumonia less likely. Pulmonary contusions are common in trauma
patients, and often have similar symptom onset and appearance on
radiography as patients with fat embolism. The key distinguishing factor
on CT scan is that in pulmonary contusions, there is often 1-2 mm of
sub-pleural sparing of the lung parenchyma adjacent to the thoracic wall
injury not seen in fat embolism.7
There is no disease-specific, evidence-based management for fat
embolism, but addressing the underlying etiology is imperative.
Therapies such as heparin, intravenous fluids, corticosteroids, and
aspirin have been tried previously, but none have proven to be of
benefit. Despite the severity of initial presentation of these
patients, the outcome is generally favorable, with mortality being less
than 10% in the setting of early fixation of the fracture(s) and
aggressive supportive care.1 Our patient had fixation of her
multiple fractures, and experienced complete recovery from her
respiratory distress over the following three days. She was discharged
home in good condition one week later.
References
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Lee CH. The Crazy Paving Sign. 2007; 243: 905-906.
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