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Hypodense artery sign in cerebral fat embolism
  1. Jose David Avila
  1. Department of Neurology, Geisinger Medical Center, Danville, Pennsylvania, USA
  1. Correspondence to Dr Jose David Avila, Department of Neurology, Geisinger Medical Center, Danville, Pennsylvania 17822-3050, USA; avila.jd83{at}gmail.com

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A female patient in her mid 70s underwent aortic valve replacement and single-vessel coronary artery bypass grafting, but after awakening from anaesthesia was found to have left-sided weakness. She had a history of severe aortic stenosis, hypertension, diabetes mellitus and hyperlipidaemia. On examination, there was right gaze deviation and a dense left hemiplegia. Non-contrasted CT scan of head and cerebral angiography showed a 1.5 cm hypodense filling defect in the distal M1 segment of the right middle cerebral artery, measuring –80 Hounsfield units, consistent with fat density (figure 1A,B). There were also early ischaemic changes in the right middle cerebral artery territory. The patient deteriorated rapidly due to cerebral oedema and herniation, requiring emergency decompressive craniectomy. MR scan of brain 1 week later confirmed the right middle cerebral artery occlusion (figure 1C). The hospital course was further complicated by fever and respiratory failure necessitating tracheostomy and gastrostomy tube placement. The patient was discharged to a nursing home, where she died of a cardiac arrest 1 month later. Autopsy identified an adipose tissue embolus occluding the right middle cerebral artery. The embolus was composed of partially devitalised fragments of mature adipose tissue rather than lipid droplets. There were no hematopoietic bone marrow elements. These findings suggested that the epicardial adipose tissue was the embolic source.

Figure 1

Non-contrasted CT scan of head (A) and cerebral angiography (B) axial planes show the hypodense artery sign in the right middle cerebral artery (arrows). There is also hypoattenuation of the brain parenchyma, loss of the grey–white matter differentiation and sulcal effacement in the right hemisphere (A). MR scan of brain non-enhanced T1-weighted image, axial plane (C), shows that the filling defect in the middle cerebral artery is hyperintense, as seen with fat (arrow). Also note the right skull defect.

Cerebral fat embolism is an uncommon cause of stroke, which may manifest in two distinct clinical forms, each with typical imaging findings. More commonly, cerebral fat embolism occurs after long bone and pelvic fractures as part of the systemic embolic condition known as fat embolism syndrome, characterised by the clinical triad of pulmonary dysfunction, neurological symptoms and petechial rash.1 Brain MRI shows a ‘star field pattern’ in the acute stage, comprising scattered punctate embolic infarcts without visible emboli.1 Rarely, cerebral fat embolism causes intracranial vessel occlusions leading to large territorial infarcts, usually after cardiac surgery. In this scenario, focal deficits predominate and brain imaging shows the ‘hypodense artery sign’, indicating the presence of a macroscopic fat embolus.2 The emboli may originate from median sternotomy, aortic atherosclerotic plaques during clamping or cannulation for cardiopulmonary bypass and dislodgement of pericardial or epicardial fat, as in our patient.2 It is important to recognise this radiological finding as a manifestation of cerebral fat embolism and distinguish it from the better-known ‘hyperdense artery sign’, typically due to an acute thrombus.

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Footnotes

  • Contributors JDA evaluated the patient, gathered the data, conceived the concept and design of the manuscript, and drafted and revised the manuscript for content.

  • Competing interests None declared.

  • Provenance and peer review Not commissioned; externally peer reviewed. This paper was reviewed by Robert Simister, London, UK.

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