FAT embolism syndrome (FES) is a known complication of long bone trauma and orthopedic surgery with in tramedullary manipulation. The syndrome typically occurs 8 to 72 h after trauma or surgery and is characterized by respiratory failure, neurologic dysfunction, and thrombocytopenia with petechial rash. 1The clinical pre-sentation of FES varies greatly, however, so that diagnosis may be difficult, particularly in the postoperative period. The authors describe a patient with atypical manifestations of FES in the perioperative period, in relation to fat embolism through a patent foramen ovale.
A 16-yr-old boy (height: 150 cm; weight: 50 kg) underwent bilateral femoral lengthening surgery for constitutional short stature. After premedication (prazepam and glycopyrrolate), anesthesia was induced with propofol, sufentanil, clonidine, and cisatracurium. The lungs were ventilated with oxygen and nitrous oxide (2l/2l). Anesthesia was maintained with propofol (total dose: 2320 mg) and small boluses of sufentanil (total dose: 36 μg). During the 9-h operation, heart rate, mean arterial blood pressure, oxygen saturation, end tidal carbon dioxide and core temperature remained within physiologic ranges. Hemoglobin decreased from 10.1 to 9.1 g/dl. Before the end of surgery, the patient received proparacetamol 2 g, tramadol 100 mg, and ketorolac 20 mg.
Ten minutes after withdrawal of anesthetic agents, the patient opened his eyes but did not follow commands consistently. Since cough and swallow reflexes were present, the patient was extubated and transferred to the recovery room where he was noted to have a roving gaze, and mumbled vague sounds after auditory stimuli. His pupils were equal and reactive and he moved both arms spontaneously. His respiratory rate was 16/min, blood pressure 170/68 mmHg, heart rate 68/min, and oxygen saturation 97% under 2 l/min oxygen by face mask.
Over the next few hours, the patient sank progressively into a deeper coma. No analgesics or sedatives were administered after surgery. Cardiorespiratory parameters were stable. On neurologic examination 8 h postoperatively, the Glasgow coma score was 6 (eyes opening only to painful stimuli; absence of verbal response to any stimulus; motor response characterized by a withdrawal of upper extremities to pain). A positive Babinski reflex was noted bilaterally. Brain contrast computed tomography scan was normal.
The patient was transferred to the intensive care unit. Laboratory data (electrolytes, glucose, ammonium, arterial blood gases, toxicological screening), chest x-ray, electroencephalogram, funduscopic examination, and contrast transthoracic echocardiography were unremarkable.
In view of the neurologic deterioration, the patient was reintubated to protect his airway and magnetic resonance imaging (MRI) was performed. Small hyperintense foci were demonstrated on conventional sequences (proton density and T2-weighted turbo spin-echo sequences and FLAIR sequence) in the basal nuclei (Fig. 1). The high signal intensity of the lesions appeared more conspicuous on the diffusion sequences (Fig. 1). These findings suggested the existence of focal acute ischemic lesions of embolic origin.
On the basis of these findings, a repeat echocardiographic examination was performed (contrast transesophageal echocardiography [TEE], under pressure support ventilatory mode), demonstrating the presence of a patent foramen ovale with right to left shunt. There were no signs of pulmonary hypertension and the right ventricle was not dilated.
The next day, a petechial rash was noticed on the trunk, and the platelet count decreased to 149,000 mm−3, from 265,000 mm−3preoperatively.
By the third postoperative day, the patient showed some neurologic improvement, opening his eyes to verbal stimuli, and performing handgrip on command. The patient exhibited no clinical or radiologic signs of lung involvement throughout his postoperative course. He was extubated on day 4, and transferred to the orthopedic ward on day 7, recovering cognitive functions completely within the next 10 days. Limb elongation (ratcheting of the prosthetic devices for gradual lengthening) was achieved by physiotherapy, and the patient was discharged 4 weeks after surgery. Magnetic resonance imaging at 2 months showed complete regression of the hyperintensities in the basal nuclei.
The patient failed to wake after surgery. No hypotension or hypoxia had been observed during surgery and searches for a metabolic or toxic origin were negative. Fat embolism was finally diagnosed although respiratory manifestations were totally absent.
Although neurologic manifestations of FES were originally thought to be a consequence of arterial hypoxemia, recent observations suggest that they are related to cerebral fat embolism. Cerebral fat emboli have indeed been found at autopsy in patients who died from FES, 2and MR findings in patients with acute FES are characteristic of ischemic lesions of embolic origin. 3–6Cerebral fat embolization is thought to result from the passage of fat emboli to the systemic circulation either directly through the pulmonary vasculature, or via intracardiac shunts. 7
A diagnosis of FES in this patient was made on the basis of the close temporal association between medullary manipulation and the occurrence of symptoms, the development of cerebral symptoms with the exclusion of other causes of coma, the presence of hyperintense lesions located bilaterally in the basal nuclei on MRI, and the late occurrence of petechiae over the chest wall. Moreover, the demonstration of a patent foramen ovale with right-to-left shunting on contrast TEE provides an explanation of the mechanism of cerebral embolization of fat particles in the patient.
This case is remarkable because of its unusual presentation; lung involvement was absent, and interestingly, the patient had a prolonged period of unconsciousness after elective surgery.
Rare incidents of isolated cerebral fat embolism without pulmonary involvement have been reported. 5,8–9The reason for the absence of pulmonary manifestations in these cases is unclear. In contrast to our patient, in whom persistent unconsciousness after surgery misled diagnosis, these individuals presented more typically with a sudden deterioration several hours after trauma or surgery. In FES, the delay that is normally present before the appearance of neurologic signs has been suggested to be related to the time required for transpulmonary passage of emboli. 10In our patient, this delay may have been masked because of the long duration of surgery and because of the intracardiac (rather than transpulmonary) passage of the fat emboli.