Imaging findings

CT scan of the brain would reveal 

• Changes of the primary injury (Figure 1), like intracranial hemorrhage, trauma etc with secondary changes of global hypoxia. 
• There will be diffuse cerebral edema with effacement of sulcal spaces, cisterns and the ventricles (Figure 2). 
• Gray white matter differentiation would be lost. 
• White cerebellar sign may be appreciated due to diffuse hypodensity of cerebral parenchyma (Figure 3). 
• Pseudo subarachnoid hemorrhage may be seen due to presence of static blood which appears hyperdense in veins present in sulcal spaces (Figure 4). 
• When mass effect increases there will be transcompartmental herniations, like tonsillar herniation with sagging brainstem (Figure 5). 

In CT angiography, volume acquisition of the brain is done immediately following contrast injection followed by a venous phase after 60 seconds. 

• There will be no contrast opacification of bilateral internal carotid arteries (Figure 6).
• Cerebral CT silence i.e., absence of visualization of internal cerebral veins, cortical segments of the middle cerebral arteries (MCA) and pericallosal segments of anterior cerebral arteries (ACA); though stasis filling of more proximal parts of MCA and ACA can be seen (Figure 7).

Many studies have proven the efficacy of CT angiography in diagnosis of BD, first by Dupas et al. They found high sensitivity and specificity of 100%. Later studies however did not get such high accuracy of CT in BD. Major advantage of CT Angiography is that it is non-invasive, quick and demonstrates the primary cause leading to coma. However it can give fallacious results in case of slow flow.

MRI findings of these patients will depict

• changes of primary insult 
• Diffuse gyral swelling with effacement of sulcal and cisternal spaces (Figure 8)
• diffuse T2W hypointensity of the cerebral white matter (Figure 9)
• T2W hyperintensity of the cerebral cortex with bilateral loss of vascular flow voids (Figure 10). 
• On DWI, there is reduction of ADC values in entire brain (ADC values typically <50% of normal values); subependymal diffusion restriction may be seen (Figure 11). 
• In SWI bilateral transcerebral vein sign and bilateral cortical vein sign, may be appreciated (Figure 12). 
• In TOF MRA: Absence of flow in the supraclinoid internal carotid arteries (ICA) with preserved flow in the external carotid arteries (ECA) is seen (Figure 14). 
• Intense enhancement around the nose and scalp may be seen, called the hot nose sign.