Hello dear, I shall try to give an easy explanation for this shadow thing,you want to know about.This shadow is a vaguely used term with respect to a brain imaging modality like magnetic resonance imaging(MRI) or computerised tomography scans(CT scan).Let me try to explain it with respect to a brain MRI.Whenever a patient undergoes a brain MRI, magnetic rays pass through the brain and our brain tissue creates an image,which we see as MRI film.In this various tissues in brain,have their distinct atomic properties and interact with the external magnetic field differently,resulting into different signal intensities on a MRI film.Like cerebrospinal fluid appear white,grey matter whiter than the white matter.. on a specific kind of MRI film,a T2 weighted image.Now if there is an abnormality in brain tissue ,say for example,there is a pus filled cavity called abscess or there is a particular tuberculosis lesion called tuberculous granuloma,in that case this abnormal tissue interact differently with the external magnetic field and creates a different signal intensity image on the film,usually called as a shadow . Your friend most probably had focal seizures for which likely cause can be a structural lesion in brain,causing a shadow appearance on brain imaging.Induced coma is usually given for refractory seizures,not responding to antiepileptic medicines,and probably that was the case with your friend.Hope it helps.Please get in touch,if you need any further explanation.