Herniations & Hemorrhages
Herniations & Hemorrhages
Compartments
Supratentorial Compartment
- Contains the Cerebral hemispheres (telencephalon and diencephalon).
Infratentorial Compartment
- Contains the brainstem and cerebellum.
Intracranial hemorrhages
Clinical Correlation - The different heme products have different imaging characteristics on MRI, which can help age the blood and determine the time-course of the disease.
key forms of herniation
- Subfalcine
- Central
- Uncal
- Upward cerebellar
- Tonsillar herniation (commonly seen in Chiari Malformation)
Hemorrhages
Epidural hematoma
- Biconvex lens-shaped: pushes aside the spongy brain parenchyma because of its high-pressure blood, which collects between the dura and skull: hence its name, epi-dural).
- The middle meningeal artery is the most common source of epidural hematoma within the cranium.
- The venous plexus is the most common source in the spinal canal.
- Crescent-shaped: layers beneath the dura from low-pressure blood (technically the doral border cell layer).
- Bridging veins are the most common cause of subdural hematoma.
Distinguishing Epidural vs Subdural Hematomas:
- Epidural hematoma shape is that of a biconvex lens vs. Subdural hematoma shape is crescent.
- Epidural hematoma is blocked by cranial sutures (the attachments at the adjoining skull bones); they lie above the dura so they don't affect subdural hematomas vs. Subdural hematoma is blocked by dural reflections (inward dural deviations into the cranium (such as the falx cerebri)); they lie beneath epidural hematomas and don't affect them.
- Although subarachnoid hemorrhage can occur anywhere within the subarachnoid space, we highlight this area because it is particularly life threatening.
- Arterial aneurysm rupture is the most common cause of subarachnoid hemorrhage.
- Obliteration of the CSF basal cistern spaces due to subarachnoid hemorrhage is a potential finding – and one that is especially worrisome.
BG is the most common site. Cerebral lobe (lobar) is also a common site.
- Arterial rupture from hypertension (high blood pressure) is the most common cause of intraparenchymal hematoma.
Herniation
Supratentorial compartment:
- In subfalcine herniation, one cerebral hemisphere herniates underneath the falx cerebri.
- In central herniation (aka transtentorial herniation), the diencephalon herniates directly down through the tentorium cerebelli.
- In uncal herniation, the medial temporal lobe (the uncus) herniates over the tentorium cerebelli.
Infratentorial compartment:
- In upward cerebellar herniation, the cerebellum herniates upward into the supratentorial cavity.
- In tonsillar herniation, the cerebellar tonsils undergo downward herniation through the foramen magnum.