21st Jun 2021

ICRI CASE OF THE WEEK

Contributed by : Dr. G. Ananta Ram, Dr. Vivek Thakkar
Department of Radio-diagnosis
Krishna Institute of Medical Sciences
Secunderabad, Telangana

Copyright of the Case belongs to : Dr G. Ananta Ram

Clinical Details

• A 21 year old male, with no e/o any co-morbidities, was brought to the
Emergency department with history of RTA with multiple bilateral lower
limb fractures (proximal shaft of right femur, left acetabulum, right pubic
bone, left medial malleolus and left humerus).

• This was followed by two episodes of GTCS on the next day morning, and
then loss of consciousness. Following this, the patient was intubated.
On examination in ICU, the patient had GCS E1 VT M4.

Starfield pattern on DWI
T2 and FLAIR hyperintensities in areas corresponding to Diffusion restriction

Punctate foci of blooming on SWI images

Imaging Findings

• MRI Brain showed innumberable tiny foci of diffusion restriction
involving bilateral cerebellar hemispheres, brainstem, basal ganglia,
thalami, deep watershed territories, periventricular white matter and
grey white matter junction of bilateral cerebral hemispheres
(Starfield pattern).

• Corresponding areas show hyperintense signal on T2 and FLAIR
sequences.

• Involved areas show multiple punctate foci of blooming on SWI
sequence.

Discussion

• Fat Embolism Syndrome (FES) is emergency condition that occurs most
commonly due to the long bone fractures and less commonly due to non-
traumatic conditions. It occurs 12 to 72 hours after the trauma. The incidence
of cerebral fat embolism (CFE) has been reported to be 0.9%–2.2%.

What is the pathophysiology ?
It is thought to occur due to two mechanisms –
• an initial mechanical obstruction of arterial circulation by neutral fat,

followed by
• delayed extensive biochemical toxic injury from free fatty acids. Long bone

fracture occurs in the lower limbs, fat globules from the bone marrow of long
bones are disseminated into pulmonary circulation, and can pass later into
systemic circulation.

Why white matter tracts are more affected to infarcts ?
• Because myelin has a high lipid content and a slow turnover; all the

myelinated tracts are particularly vulnerable to the accumulation of
lipophilic substances and to lipid peroxidation. Therefore, cerebral white
matter may be selectively vulnerable due to its lipophilic property.

Clinical diagnosis of FES done by Gurds criteria :
Major criteria - Cerebral involvement

Respiratory insufficiency
Petechial rash
Minor criteria : Fever, thrombocytopenia, tachycardia, anaemia and high ESR

Imaging patterns on MRI :

Type 1 - Scattered Cytotoxic Edema : Most well-known pattern of CFE.
On DWI sequences, scattered foci of diffusion restriction seen. The signal
on T2WI may be iso- or hyperintense. The lesions are distributed bilaterally
in watershed zones and deep gray matter, such as the centrum semiovale,
basal ganglia, and thalami.

Type 2A - Confluent Cytotoxic Edema in White Matter : The MR imaging
feature is confluent symmetric lesions with restricted diffusion on DWI in
periventricular and subcortical white matter bilaterally. The cerebellar
peduncles, corpus callosum, and posterior internal capsule may be
involved.

• Type 2B - Vasogenic edema lesions that may enhance : It is mainly seen
in subacute stage. The difference is that these lesions usually have a small
dot or patch shape, and the signal on the DWI image shows increased
diffusion instead. The lesions lie in both gray and white matter.

• Type 2C: Petechial hemorrhage of white matter : It is common to detect
tiny petechial hemorrhages of the perivascular space in CFE. It is seen in
SWI or gradient sequences. This pattern can be seen in all the stages i.e
acute, subacute and late stages.

• Type 3: Chronic sequelae : At the late stage, most lesions resolve, while
brain atrophy begins. Most lesions are hyperintense on T2WI without
restricted diffusion on DWI. Some show a dot/nodule shape, and some
have a large amorphous shape. These may represent sequelae of
infarction, cavitation, scar formation, gliosis, or chronic demyelination.

• Early diagnosis is important for appropriate management and better
prognosis. This includes immobilization of the fracture site, maintaining
intravascular volume and ventilatory support. The case indicates
potentially good outcome even in severe cases of cerebral FES though
extended intensive care, and supportive, rehabilitative care may be needed
for this.

• Although the neurologic findings are transient and fully reversible in most
cases, the condition is often misdiagnosed and fatal if the treatment is
delayed. An early diagnosis not only prevents morbidity and mortality, but
also reduces cost burden of additional investigations for correct diagnosis.

Differential diagnosis

• Multiple embolic infarcts : Rarely produce the dozens or even hundreds
of lesions as seen with CFE. Lesions tend to involve the basal ganglia
and corticomedullary junctions more than the white matter

• Diffuse axonal injury : which presents with petechial hemorrhage. It
mainly occurs in the gray-white matter interface of the fronto-temporal
lobes and corpus callosum, while CFE petechial hemorrhage is located
predominantly in the white matter.

References

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Diagnosis of Cerebral Fat Embolism. Journal of Neuroimaging, 17(1), 78–80. doi:10.1111/j.1552-6569.2006.00068.x
2) Bardana D, Rudan J, Cervenko F et al. Fat embolism syndrome in a patient demonstrating only neurologic symptoms.
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