Table 1:

Classic SDH stages in CT and MRI (at 1.5T)^{^a}

Characteristics	Stage
Characteristics	Hyperacute	Acute	Early Subacute	Late Subacute	Chronic
Assumed time range^{^b}	Min: 0 hr	Min: 1 day	Min: 2 days	Min: 1 wk	Min: 2 wk
Assumed time range^{^b}	Max: 24 hr	Max: 3 days	Max: 2 wk	Max: 3 wk	Min: 2 wk
NECT^{^c}	↓/↔	↑	↑	↔	↓
MRI^{^c} (T1)	↔	↔	↑	↑	↓
MRI^{^c} (T2)	↑	↓	↔/↑	↑	↑
Hb state	Oxy-Hb	Desoxy-Hb	Met-Hb	Met-Hb	Ferritin/hemosiderin
Hb localization	Intracellular	Intracellular	Intracellular	Extracellular	Extracellular
Fe oxidation state	Fe²⁺	Fe²⁺	Fe³⁺	Fe³⁺	Fe³⁺
Pathophysiology	Unclotted blood	Clotted blood, clot retraction	Max clot retraction, erythrocytes predominantly (still) intact, oxidative denaturation of the desoxy-Hb into met-Hb	Lysis of erythrocytes, thereby increase of extracellular met-Hb, start of disintegration to heme and globin, Fe³⁺ is stored within the macromolecule ferritin and the phagocytic product hemosiderin, respectively	In contrast to intraparenchymal hematomas, removal of ferritin and hemosiderin within the extra-axial space is accelerated due to the missing blood-brain barrier (therefore ↑ in T2)

Note:—NECT indicates nonenhanced CT; Hb, hemoglobin; ↑, hyperdense/hyperintense; ↓, hypodense/hypointense; ↔, isodense/isointense; Min, minimum; Max, maximum; Desoxy-Hb, Desoxy-Hemoglobin; Oxy-Hb, Oxy-Hemoglobin; Met-Hb, Met-Hemoglobin.
↵a According to Hedlund,22 Vezina,28 Lee et al,61 Duhem et al,62 Tung,63 Cramer et al,64 Bradley,65 and Bergström et al.66
↵b Due to insufficient data base, the time intervals stated do not represent absolute borders—that is, the ranges may be exceeded or undercut in single cases.
↵c Density/signal intensity compared with cortical brain tissue.