Abstract
Fat embolism syndrome describes a constellation of symptoms that follow an insult and that results in a triad of respiratory distress, neurologic symptoms, and petechia. The antecedent insult usually entails trauma or orthopedic procedure, most frequently involving long bone (especially the femur) and pelvic fractures. The underlying mechanism of injury remains unknown but entails biphasic vascular injury with vascular obstruction from fat emboli followed by an inflammatory response. We present an unusual case of a pediatric patient with acute onset of altered mental status, respiratory distress, hypoxemia, and subsequent retinal vascular occlusions after knee arthroscopy and lysis of adhesions. Diagnostic findings most supportive of the fat embolism syndrome included anemia, thrombocytopenia, pulmonary parenchymal, and cerebral pathologic findings on imaging studies. This case highlights the importance of fat embolism syndrome as a diagnostic consideration after an orthopedic procedure, even absent major trauma or long bone fracture.
Key Words: fat emboli, fat embolism syndrome
Fat embolism syndrome (FES) entails a triad of respiratory, neurologic, and dermatologic symptoms after an identifiable insult. Most antecedent events involve trauma and long bone or pelvic fractures.1, 2, 3, 4 Mortality rates range between 5% and 20%.1,4,5, 6, 7 We present a previously well 16-year-old boy with altered mental status, respiratory distress, with laboratory results and imaging consistent with FES after left patellar arthroscopy that did not include any bone fractures or major bone manipulation.
Case Report
Patient CC is a 16-year-old boy (BMI, 17.7 kg/m2) who presented with altered mental status, respiratory distress, and hypoxemia after left knee arthroscopy with lysis of adhesions and debridement for treatment of decreased range of motion. Scarring was removed in the suprapatellar pouch and medial and lateral gutters. Patient was given ropivacaine nerve block, sedated with propofol and versed, and pain managed with fentanyl without hemodynamic instability. In the initial 18 postoperative hours, CC received 1.5 tablets of hydrocodone-acetaminophen (10 to 325 mg). On postoperative day 1, the patient was confused and febrile (38.3ºC). Emergency medical services were called; oxygen saturation was 60% with initial Glasgow coma scale of 3 that did not change after naloxone (1 mg). At an outside hospital, CC was treated with naloxone (1.6 mg), high flow nasal cannula, and IV fluids. CT head scan was normal, and CT scan angiography of the chest showed diffuse patchy nodular infiltrates and dense consolidation in posterior, lower lung fields bilaterally (Fig 1) and no pulmonary embolism. Ampicillin/sulbactam was started for presumed aspiration pneumonia. CC was amnestic of the prior 20 hours. He was weaned from high to low flow oxygen via nasal cannula. On postoperative day 3 (Glasgow coma scale, 15), the patient was transferred to a quaternary care children’s hospital. CC was somnolent, but arousable with mildly increased work of breathing, and had diminished breath sounds in the dependent lung fields bilaterally with bibasilar crackles. Laboratory studies revealed pancytopenia (WBC count, 3.8 K/μL; hemoglobin, 10 g/dL; platelet, 105 K/μL), erythrocyte sedimentation rate 11 mm/hr (elevated to 16 mm/hr the next day), and c-reactive protein 3.1 mg/dL. Diagnostic considerations included obtundation secondary to slow metabolism of opiate with subsequent aspiration pneumonia, viral encephalitis, diffuse vasculitis, and FES. Chest CT scan was concerning for FES, given the bilateral parenchymal involvement and peripheral nodularity (Fig 1). EEG and transthoracic ECG results were normal. Because of persistent blurry vision, a fundoscopic examination was performed that revealed bilateral cotton wool spots along superior and inferior arcades and perifoveal region. MRI/MRA brain scan revealed numerous foci of T2 susceptibility throughout the brain, concerning for multiple emboli (Fig 2). Further infectious (serum and cerebrospinal fluid) and autoimmune workup was unremarkable. On postoperative day 6, CC was transiently febrile to 39.5°C but remained afebrile thereafter. Supplemental oxygen was continued through postoperative day 6. Patient returned to neurologic baseline on postoperative day 9.
Figure 1.
CT scan imaging from postoperative day 1 shows bilateral ground glass opacities, patchy interlobular septal thickening, and nodular airspace opacities, with predominant involvement of the posterior, lower lobes.
Figure 2.
MRI brain T2/FLAIR performed on postoperative day 6 shows scattered subcortical and periventricular T2/FLAIR hyperintensities.
Discussion
In contrast to prior reports, this case highlights an antecedent procedure that did not include fractures or manipulation of long bones. This patient met criteria for FES (Table 1) based on two major criteria and five minor criteria.8, 9, 12, 13 Chest CT scan findings that were consistent with FES include patchy ground-glass opacities, consolidations, and small centrilobular nodules.9,12 Brain MRI imaging can show “starfield pattern” with multiple, small, nonconfluent, hyperintense lesions on T2-weighted images.13 CC’s brain MRI revealed bilateral subcortical microhemorrhages characteristic of FES (Fig 2). The multiple cotton wool spots noted on fundoscopic examination, which persisted through postoperative day 18 (Fig 3), are consistent with a diagnosis of FES.14
Table 1.
Gurd, Schonfeld, and Lindeque List of Clinical Criteria for Diagnosis of Fat Embolism Syndrome
| Criteria | Findings | Points |
|---|---|---|
| Gurd8,a | ||
| Major | Respiratory insufficiency | … |
| Cerebral involvement | … | |
| Petechial rash | … | |
| Minor | Fever | … |
| Tachycardia | … | |
| Retinal changes | … | |
| Jaundice | … | |
| Renal changes | … | |
| Anemia | … | |
| Thrombocytopenia | … | |
| Elevated erythrocyte sedimentation rate | … | |
| Fat macroglobulinemia | … | |
| Schonfeld10,b | Petechia | 5 |
| Chest radiograph changes | 4 | |
| Hypoxemia (PaO2 < 9.3 kPa) | 3 | |
| Fever (> 38C) | 1 | |
| Tachycardia (> 120 beats/min) | 1 | |
| Tachypnea (> 30 beats/min) | 1 | |
| Lindeque11,c | Sustained PaO2 (< 8 kPa) | … |
| Sustained Pco2 (> 7.3 kPa or pH < 7.3) | … | |
| Sustained respiratory rate (> 35 beats/min) | … | |
| Increased work of breathing (dyspnea, accessory muscles, tachycardia, anxiety) | … |
At least one major feature and four minor features needed for diagnosis.
Cumulative score > 5 required for diagnosis.
One of the criteria indicates a diagnosis of fat embolism syndrome.
Figure 3.
A and B, Fundus of A, left and B, right eye show cotton wool spots bilaterally below the optic disc and microhemorrhage below the left optic disc. Fundus photography was performed on postoperative day 18.
FES pathogenesis has been described with the use of a mechanical (vascular obstruction) and biochemical (inflammatory response) paradigm. Although the mechanical and biochemical theories are considered distinct, a construct wherein the fat embolism result in diffuse vascular injury may be more precise. After an inciting event, fat cells from the bone marrow or adipose tissue entered venous sinusoids leading to platelet aggregation.15 Fat cells can enter the arterial circulation via a patent foramen ovale or pulmonary capillaries.16 Lipase activity frees charged fatty acid molecules that injure endothelial cells, compromising barrier function, matching of ventilation and perfusion, and pulmonary compliance.15 Subsequently, inflammation can occur with the release of cytokines.15 Thus, a fat embolism entering the circulation can cause obstruction, diffuse vascular injury, and inflammation, which results in multiorgan involvement.17, 18, 19 Although FES treatment is mainly supportive, timely diagnosis facilitates identification and management of pulmonary and neurologic sequelae. In contrast to the present case that involved only arthroscopy, FES classically results from trauma or orthopedic surgery that involves long bone fractures.2 FES can also occur in the context of IV administration of mineral oil,20 hemoglobinopathies,21 and fatty liver disease.22 Given the high potential for morbidity and death in FES, even despite the low incidence, FES merits diagnostic consideration in children.
Funding/Support
This work was supported by National Institutes of Health grant HD092316 (DNC), the Stanford Center for Excellence in Pulmonary Biology (DNC), the Chan Zuckerberg Biohub (DNC) and Chan Zuckerberg Biohub Physician Scientist Fellowship Program (NS), Stanford Maternal and Child Health Research Institute, Ernest and Amelia Gallo Endowed Postdoctoral Fellowship.
Financial/Nonfinancial Disclosures
The authors have reported to CHEST the following: The authors receive financial support from National Institutes of Health grant HD092316 (D. N. C.), the Stanford Center for Excellence in Pulmonary Biology (D. N. C.), the Chan Zuckerberg Biohub (D. N. C.) and Chan Zuckerberg Biohub Physician Scientist Fellowship Program (N. E. S.), Stanford Maternal and Child Health Research Institute, and Ernest and Amelia Gallo Endowed Postdoctoral Fellowship.
Acknowledgments
Author contributions: J. B.-H. contributed to the concept and design of the case report, performed chart review, analyzed clinical data, outlined the manuscript, drafted the manuscript, coordinated the reviews among the authors, and revised and reviewed the manuscript. N.E.S. aided in image selection and analysis, interpretation of clinical data, and utilization of specialty specific clinical expertise to critically review and revise the manuscript. D. M. assisted in the development of the concept and design of the case report and the initial drafting. M. V. H., A. C., and D. P. performed chart review, aided in interpretation of clinical data with known available literature to revise and review the manuscript accurately. D. N. C. critically reviewed and revised the manuscript for important intellectual content, aided with clinical expertise to help discuss novel conceptualization of diagnosis. All authors approved the final manuscript as submitted and agree to be accountable for all aspects of the work.
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