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2Brain

mogeneous, swirling appearance due to a mixture of clotted and unclotted blood.

Venous epidural hematomas, which ac-count for approximately 10% of EDHs, arethe consequence of dural venous sinus dis-ruption or, rarely, diploic vein or arachnoidgranulation rupture. They are low-pressurehemorrhages that typically do not enlargeover time and rarely require evacuation. Incontrast to arterial hematomas, traumaticvenous EDHs often occur in children andare not necessarily associated with skullfractures. They are most commonly seenin the middle cranial fossa adjacent to thegreater wing of the sphenoid bone, wherevenous EDHs are due to disruption of thesphenoparietal venous sinus. They also mayfollow injury to the sagittal or transverse si-nuses and can traverse the tentorium at theocciput or the falx at the vertex (Fig. 2.6).

◆Epidural Hematoma

Most epidural hematomas (EDH) are of arterial origin and result from calvarial fractures that cross branches of the middle meningeal artery. Hemorrhage under arte-rial pressure separates the outer layer of the dura from the skull, creating an extraparen-chymal intracranial mass that compresses the adjacent brain, leading to ischemia and potential compartmental herniation. Epi-dural hematomas can enlarge rapidly and, if not treated, are often rapidly fatal. With early evacuation, however, the prognosis is good; the skull absorbs most of the energy of impact as it fractures, sparing the under-lying brain parenchyma from direct injury.

An acute EDH is a smooth, hyperdense biconvex extraparenchymal blood col-lection, limited by the coronal sutures, to which the dura is especially adherent. Hyperacute, active bleeding has an inho-

Fig. 2.6a–f a–d Arterial epidural hematoma. Hyperdense, right parietal, lenticular, extraparenchymal hematoma with maximal thickness 2.7 cm. Ipsilateral cortical sulcal and lateral ventricular compression with minimal subfalcine shift. Contralateral anterior temporal lobe hemorrhagic contusion. Right parietal vertex scalp hematoma and laceration.

e,f Venous epidural hematoma. Lenticular (1-cm) extraparenchymal mixed-density hemorrhage adja-cent to the right sphenotemporal buttress with mild compression of the anterior temporal lobe. Right preseptal periorbital and temporal scalp hematoma. The underlying brain parenchyma is normal, and the perimesencephalic cisterns are patent.