<prompt> Acute SDH is seen on CT scan as:Lentiform-shaped hyperdense lesionCrescent-shaped hypodense lesionCrescent-shaped hyperdense lesionLentiform-shaped hypodense lesion  <response>: Ans. c Crescent-shaped hyperdense lesion. Ref. Annie Osborns Diagnostic Neuroradiology, 205.A Crescent-shaped or concavoconvex collection is SDH. Hyperdense on CT are fresh bleeds.Extradural hematoma verse subdural hematomaFeaturesEDHSDHIncidence1-4 overall10-20 overallAsso fractureAssociated in 85-95 cases.Underlying may not be presentEtiologyLacerated middle meningeal artery dural sinusStretching, tearing of bridging in 70 to 85 cases and venous OOZE or MMA cortical veins tear without in 15 cases onlyLocationBetween skull and dura.Between dura and arachnoid.Crosses dural attachments but not sutures.ImagingCT: Biconvex LentiformAcute are hyperdense on CT.Chronic are hypodense on CT.CT: . Concavo-convex Crescentic.Acute are hyperdense on CT. Chronic are hypodense on CT. 