Herniation Syndromes

Intracranial space occupying lesions

These (tumors, abscesses, edema, hemorrhages) can cause displacement of brain structures, thereby compressing and impairing function of other brain structures/regions; herniations can also compress the cerebrovasculature, resulting in ischemia and further brain injury.

Uncal

Involves herniation of the uncus of the medial temporal lobe and compression of the crus cerebri, may also cause PCA infarct. Key s/s are IL CN III palsy, CL UMN signs (CST & CNT; uncus compresses the IL crus cerebri)

Kernohan’s phenomenon

The herniating uncus can compress the CL crus against the tentorial notch, resulting in IL UMN signs.

Coma

Compression of the pontine reticular formation can result in…..

Subfalcine

Involves herniation of the cingulate gyrus under the falx cerebri, may result in ACA infarct. Key s/s are behavioral changes, CL LL UMN signs

Central (transtentorial)

Involves downward displacement of diencephalon and brainstem, may result in basilar artery infarcts. Key s/s are rostral to caudal progression of brainstem dysfunction (see Abnormal Posturing)

Tonsillar

Involves downward displacement of the cerebellar tonsils through the foramen magnum, may result in infarcts in the posterior circulation (vertebrals, basilar). Key s/s are medullary dysfunction, cardiorespiratory dysfunction

Cushings Triad

severe hypertension, bradycardia and irregular respirations; occurs with increased intracranial pressure and terminal brain herniation syndromes