"Overall, 85% of subdural haematomas are unilateral in adults. However, 75-85% are bilateral in infants. Common sites for subdural haematomas are frontoparietal convexities and the middle cranial fossa. Isolated interhemispheric/parafalcine subdural haematomas are seen more frequently in children and are common in cases of non-accidental trauma."
"The classic appearance of an acute subdural haematoma is a crescent-shaped homogeneously hyperdense extra-axial collection that spreads diffusely over the affected hemisphere. As the clot starts to retract, the density increases typically to >50-60 HU and is thus hyperdense relative to the cortex 4."
"As the clot ages and protein degradation occurs, the density of the subdural haemorrhage starts to drop. At some point between 3 and 21 days (typically 10-14 days), the density will drop to ~ 35-40 HU and become isodense to the adjacent cortex, making identification potentially tricky, especially if subdural collections are bilateral 4. Contrast-enhanced CT is often useful in this instance if MRI is unavailable. The key to identification is visualising several indirect signs, including:"
"T1: isointense to grey matter"
"T2: iso- to hyperintense"
"FLAIR: hyperintense to CSF"
"T1: iso- to hypointense to grey matter"
"T2: hypointense to grey matter"
"FLAIR: hyperintense to CSF"
"T1: typically hyperintense due to the presence of methaemoglobin"
"T2: variable appearance, usually hyperintense"
"FLAIR: hyperintense"
"T1: if the haematoma is stable, it appears isointense to CSF; it can appear hyperintense to CSF if there is a rebleed or infection"
"T2: if the haematoma is stable, it appears isointense to CSF; if there is rebleed, the haematoma appears hypointense"
"FLAIR: hyperintense to CSF"
"Some controversy, albeit of academic interest only, exists as to the exact location of a subdural haematoma. Classical teaching is that it is located in the potential space between the arachnoid layer and the inner layer of the dura; however, no such space really exists. Rather, the arachnoid-dura junction is composed of "avascular tissue with flake-like [...] cells stacked in several layers with narrow intercellular clefts" 10. Bleeding occurs within this multicellular layer, with these cells located on both sides of the haematoma 9,10. This possibly accounts for why some acute haematomas appear to have multiple compartments, usually ascribed to intermittent bleeding."
"extradural haemorrhage (see the article: EDH vs SDH)"
Expected headings
"Hyperacute"
"Acute"
"Subacute"
"Chronic"
"Acute on chronic"
"Hyperacute"
"Acute"
"Subacute"
"Chronic"
"bleeding diathesis (e.g. anticoagulation)"
"Some controversy, albeit of academic interest only, exists as to the exact location of a subdural haematoma. Classical teaching is that it is located in the potential space between the arachnoid layer and the inner layer of the dura; however, no such space really exists. Rather, the arachnoid-dura junction is composed of "avascular tissue with flake-like [...] cells stacked in several layers with narrow intercellular clefts" 10. Bleeding occurs within this multicellular layer, with these cells located on both sides of the haematoma 9,10. This possibly accounts for why some acute haematomas appear to have multiple compartments, usually ascribed to intermittent bleeding."
"Rarely, the periphery of the SDH may calcify; see calcified chronic subdural haematoma for an in-depth discussion regarding the CT appearance of this entity."
"T1: if the haematoma is stable, it appears isointense to CSF; it can appear hyperintense to CSF if there is a rebleed or infection"
"T2: if the haematoma is stable, it appears isointense to CSF; if there is rebleed, the haematoma appears hypointense"
"Rarely, the periphery of the subdural haemorrhage may calcify; see calcified chronic subdural haematoma for an in-depth discussion regarding the MRI signal characteristics of this entity."
"In most instances, patients are not imaged in the hyperacute phase (first hour or so), but on occasion, when this is performed they appear relatively isodense to the adjacent cortex, with a swirled appearance due to a mixture of the clot, serum and ongoing unclotted blood 4. There is often a degree of underlying cerebral swelling (especially in young patients where head trauma is often more severe), which accentuates the mass effect created by the collection 4."
"In most instances, patients are not imaged in the hyperacute phase (first hour or so), but on occasion, when this is performed they appear relatively isodense to the adjacent cortex, with a swirled appearance due to a mixture of the clot, serum and ongoing unclotted blood 4. There is often a degree of underlying cerebral swelling (especially in young patients where head trauma is often more severe), which accentuates the mass effect created by the collection 4."