Congenital/infantilehydrocephalus The cranial bones fuse by the end of the third year; for the head to enlarge, hydrocephalus must develop before this time. It may begin in utero but usually happens in the first few months of life
even of mild degree, it molds the shape of the skull in early life in radiographs the inner table is unevenly thinned, an appearance referred to as "beaten silver" or as convolutional or digital markings. The frontal regions are unusually prominent [bossing]
Face relatively small and pinched Skin over the cranial bones tight and thin Prominent distended veins.
Usual causes Intraventricular matrix hemorrhages in premature infants fetal and neonatal infections Arnold -Chiari malformation Aqueductal atresia and stenosis Dandy-Walker syndrome.
Clinical features Rapid head enlargement Tense anterior and posterior fontanelles Infant is fretful, feeds poorly, and may vomit frequently. With continued enlargement of the brain, inactivity sets in and the infant appears languid, uninterested in his surroundings, and unable to sustain activity.
Later, the upper eyelids are retracted and the eyes tend to turn down paralysis of upward gaze sclerae above the irises are visible; "setting-sun sign" caused by hydrocephalic pressure on the mesencephalic tegmentum.
Gradually the infant adopts a posture of flexed arms and flexed or extended legs. Signs of corticospinal tract damage are usually elicitable. Movements are feeble and sometimes the arms show tremors
later the optic discs become pale and vision is reduced. If the hydrocephalus becomes arrested, the infant or child is retarded but often surprisingly verbal. The head may be so large that the child cannot hold it up and must remain in bed
If the head is only moderately enlarged, the child may be able to sit but not stand or stand but not walk. If ambulatory, the child is clumsy. Acute exacerbations of hydrocephalus or a febrile illness may cause vomiting, stupor, or coma.
Intracranial pressure The intact cranium and vertebral canal, together with the relatively inelastic dura, form a rigid container, such that an increase of any of its contents—brain, blood, or CSF—will elevate the ICP.
an increase in volume of any one of these three components must be at the expense of the other two [Monro- Kellie doctrine]Compensatory measures Small increments in brain volume do not immediately raise the ICP due to displacement of CSF from the cranial cavity into the spinal canal
deformation of the brain and limited stretching of dural folds, specifically, the falx cerebri and the tentorium cerebelli Failure of compensating measures - mass within one dural compartment leads to displacement, or "herniation" from that compartment into an adjacent one
Further increment in brain volume will reduce the volume of intracranial blood contained in the veins and dural sinuses. CSF is formed more slowly As the brain, blood, or CSF volumes continue to increase, the accommodative mechanisms fail and ICP rises exponentially
Cerebral perfusion pressure(CPP). numerical difference between ICP and mean blood pressure within the cerebral vessels elevation in ICP that approaches the level of mean systemic blood pressure→ widespread reduction in cerebral blood flow/perfusion.
In its most severe form, this global ischemia produces brain death. Lesser degrees of raised ICP and reduced cerebral circulation cause correspondingly less severe, but still widespread, cerebral infarction that is similar to what arises after cardiac arrest.
Determinants of the degree of cerebral damage are the severity and the duration of reduction of CPP
CAUSES OF RAISED ICP A cerebral or extracerebral mass such as brain tumor; massive infarction with edema; extensive traumatic contusion; parenchymal, subdural, or extradural hematoma; or abscess Generalized brain swelling, as occurs in ischemic–anoxic states, acute hepatic failure, hypertensive encephalopathy, hypercarbia, and the Reye hepatocerebral syndrome
An increase in venous pressure- cerebral venous sinus thrombosis, heart failure, or obstruction of the superior mediastinal or jugular veins. Obstruction to the flow and absorption of CSF - within the ventricles or in the subarachnoid space at the base of the brain, extensive meningeal disease
Any process that expands the volume of CSF (meningitis, subarachnoid hemorrhage) or increases CSF production (choroid plexus tumor).
CLINICAL FEATURES OFRAISED ICP Headache Nausea and vomiting Drowsiness Ocular palsies Papilledema →periodic visual obscurations. Protracted papilledema →optic atrophy and blindness
The consequences of increasedintracranial pressure differ ininfants and small children, whosecranial sutures have not closed.
TRANSTENTORIAL ANDOTHER HERNIATIONS An expanding lesion in the supratentorial compartment, such as a subdural hematoma or a tumor in a cerebral hemisphere, may push the medial part of the temporal lobe (the uncus) down into the tentorial notch
UNCAL herniation presses on the ipsilateral oculomotor nerve. The first clinical sign of this event is impairment of the pupillary light reflex because the preganglionic parasympathetic fibers for constriction of the pupil are superficially located in the nerve.
Further herniation damage to descending motor fibers in one or both cerebral peduncles → weakness, spasticity, and exaggerated tendon reflexes on either side or bilaterally. midbrain displacement toward the opposite side→the pressure of the rigid edge of the tentorium on the basis pedunculi →upper motor neuron paresis on the same side of the body as the cerebral lesion.
Sometimes the downward displacement of the brain →occlusion of one or both posterior cerebral arteries by stretching these vessels over the free edge of the tentorium,
Later stages Contralateral oculomotor nerve may be affected. The pupil that dilates first is the most reliable lateralizing sign for the causative lesion.
Subfalcial herniation A space-occupying lesion pushes the cingulate gyrus of one hemisphere across the midline beneath the anterior part of the free edge of the falx cerebri.
Upward transtentorial herniation brain stem and cerebellum are displaced into the supratentorial compartment by a mass in the posterior fossa. may also cause medullary coning, when the brain stem and part of the cerebellum descend through the foramen magnum into the spinal canal.
Cerbellar tonsils compress the medulla, and the condition can be quickly fatal. Medullary coning can occur after withdrawal of CSF from the lumbar subarachnoid space in a patient with raised intracranial pressure
(1) cingulate herniation under the falx, (2) downwardtranstentorial (central) herniation, (3) uncal herniation over theedge of the tentorium, or (4) cerebellar tonsillar herniation intothe foramen magnum. Coma and ultimately death result when(2), (3), or (4) produces brainstem compression.