The part of the
olfactory cortex that is on the temporal lobe covers the area of the uncus, which leads into the two significant clinical aspects: herniations and seizures •
Herniations of the brain can occur if increased intracranial pressure due to a
tumor,
hemorrhage, or
edema pushes the uncus over the
tentorial notch against the brainstem and related
cranial nerves. This can
compress the
oculomotor nerve (CN III). This causes problems associated with a non-functional or problematic CN III - the pupil on the
ipsilateral side fails to constrict to light and absence of medial/superior movement of the orbit, resulting in a fixed, dilated pupil and an eye with a characteristic "down and out" position due to dominance of the abducens and trochlear nerves. Further pressure on the midbrain results in progressive lethargy, coma and death due to compression of the mesencephalic
reticular activating system. Brainstem damage is typically
ipsilateral to the herniation, although the contralateral
cerebral peduncle may be pushed against the tentorial notch, resulting in a characteristic indentation known as
Kernohan's notch and ipsilateral
hemiparesis, since fibers running in the cerebral peduncle
decussate (cross over) in the lower medulla to control muscle groups on the opposite side of the body. The landmark indicates the
amygdala. •
Seizures that originate in the uncus are known as
uncinate fits which are characterized by hallucinations of taste or smell. ==Function==