TRANSTENTORIAL OR UNCINATE HERNIATION:

 

 

The tentorium cerebelli is an inward fold of the dura matter that separates the cerebrum with the cerebellum from the lateral sides.

Increased cranial pressure in the supra-tentorium (above the tentorium cerebelli) puts pressure on the the insula (between the frontal and temporal lobe) and the insula moves downwards in the notch between the midbrain and tentoriom cerebelli. In the midbrain it damages the following structures from lateral to medial.

The posterior cerebellar artery, the optic tract causing contralateral homonymous hemianopia and the parasympathetic fibers, overstimulates the 3^rd nerve nucleus causing pupillo-constriction. It also pushes the midbrain towards the opposite side, damaging the cortico-spinal fibers of the other side resulting in hemiplegia (paralysis of muscles of the limbs and trunk of one side of the body). The hemiplegia is on the same side as the herniation, although the opposite cortico-spinal tracts are affected because the cortico-spinal tracts of one side innervate the other side of the body. In severe cases the third nerve nucleus may get damaged and there is no innervation to the medial rectus muscle. Thus! The eyeball of the eye on the side of the herniation can not move on the side of herniation.

Kernohans notch is a notch formed in the continuous cerebral peduncle due to damage to some fibers of the peduncle.

In the midline region and paramedian regions of the midbrain arteries and veins rupture causing DURET HEMORAGES.

PAPILLEDEMA:

It is edema in the optic disc in which the optic disc shows a blurred circumference. Due to high intracranial pressure in the subarachnoid space both retinal arteries and veins {that enter across the optic nerve penetrating the dura, arachnoid and pia matter to enter the inside of the eye via the optic disc.} get compressed. When arteries get compressed blood is pushed faster (since blood is moving under high pressure) while when veins are compressed, blood is not allowed to pass through it (since blood is moving under low pressure). Since blood moves faster into the eye through the arteries and cannot be drained by the veins edema or accumulation of fluid takes place in the optic disc. Papilledema may also be caused due to infection.

PTOSIS:
Of the extraoccular muscles of the eye, the superior rectus & superior oblique (collectively called superior tarsal muscles) and the levator palpebrae superioris control the opening and closing of the eyelids.

These muscles are innervated by axons from the 3^rd nerve nuclei and the sympathetic fibers. If these muscles get paralysed due to various reasons, drooping of the eyelids take place, a condition called ptosis.

Disruption of the sympathetic fibers (HORNERS SYNDROME) leads to occulo-sympathetic ptosis.

Disruption of the 3^rd nerve nucleus fibers leads to occulo-sympathetic ptosis.

Neuro-muscular junction disorders such as myasthenia gravis {auto-immune antibodies are produced against the ACH receptors on the post synaptic membrane, blocking them} can also paralyze these muscles leading to occulo-myasthemic ptosis.