Cerebral fat embolism – A diagnostic enigma in post-trauma ICU settings!

20-year-old male patient was brought to emergency with history of fall from height with major injury to lower limbs. After an initial lucid period of 40 hours, there was a sudden clinical worsening with loss of consciousness and multiple episodes of seizures with subsequent shift to Intensive Care Unit.

Bilateral thigh radiographs confirmed closed fractures of bilateral shaft of femur (Figure 1). Non-Contrast MRI Brain revealed punctate and confluent areas of T2W / FLAIR images hyperintensities predominantly involving the white matter of bilateral external watershed areas, in fronto-parietal and parieto-occipital lobes, centrum semiovale, splenium of corpus callosum, bilateral cerebellar hemispheres, brainstem and bilateral middle cerebellar peduncles (Figure 2). With scattered punctate areas of diffusion restriction giving starfield pattern are seen in the involved white matter on diffusion-weighted image and multiple punctate hypo-intensities without phase reversal on susceptibility-weighted (SWI) images (Figure 3).

Cerebral Fat Embolism (CFE) is an uncommonly encountered type of fat embolism syndrome (FES) seen in adults, subsequent to the embolization of fat particles to multiple organ systems, with isolated cerebral involvement. Even though it is frequently self-limiting in its course, nonetheless may be fatal in up to 10% of the cases [1]. It is seen in ~0.5–11% of cases with closed long bone fractures with ~30% incidence in multiple fractures setting, with increased incidence post intramedullary intervention [2], with a classical triad of cutaneous, respiratory and cerebral manifestations.

Clinical symptoms are often seen within 1 to 3 days of trauma, consisting of neurological deterioration following a lucid interval often preceded by respiratory distress. Henceforth, in cases with equivocal suspicion, performing MRI with DWI and SWI is important to reach a prompt diagnosis [3].

Three clinico-radiological stages of CFE[1] are:

1. Acute stage. Depicting the classical starfield pattern or walnut kernel pattern on SWI, characterized by multiple, scattered, small, and hyperintense lesions on a dark background, localized in both the white and deep grey matter, essentially along the boundary zones of major vascular territories with restricted diffusion [3,4]. These are usually reversible as sembolic fat vacuoles gradually split into smaller sizes and removed via the pulmonary circulation, subsequent reperfusion of hypoperfused areas and consequent excellent clinical outcome in comparison with thromboembolic phenomena.
2. Sub-acute stage. Two different radiological patterns can be seen, the more common pattern being the presence of symmetric confluent bilateral restricted diffusion and subtle T2WI signal in the involved areas owing to cytotoxic oedema. The less common pattern is vasogenic oedema with inconspicuous lesions in both grey and white matter.
3. Late stage. Chronic glioencephalomalacic changes with cerebral atrophy.

In conclusion, presence of multiple DWI-restricting foci with multiple micro-hemorrhages in external and internal watershed areas in an appropriate clinical setting should raise the possibility of acute CFE. The knowledge of characteristic early as well as late imaging findings of CFE, its etio-pathogenesis and reversible nature would lead to prompt diagnosis, helping the clinicians in accurate patient management with resultant favourable clinical outcomes.