Classification by localization and mechanisms
Depending on the location of excess cerebrospinal fluid (CSF), the following forms are distinguished:
- Internal form: dilatation affects only the ventricular system.
- External form: fluid accumulates over the hemispheres and in the cisterns.
- Mixed form: simultaneous expansion of all CSF spaces.
Depending on the cause of CSF accumulation, hydrocephalus is divided into the following types:
- Obstructive (occlusive). Develops when a block occurs in the outflow pathway of CSF from the lateral ventricles to the base of the brain. Fluid accumulates inside the ventricles, dilates them, and compresses adjacent structures.
- Aresorptive. Occurs when fluid reabsorption is impaired (e.g., due to arachnoid granulation dysfunction or cistern adhesion). Primarily external hydrocephalus is formed, as high external pressure prevents the ventricles from expanding.
- Normal pressure. Characterized by the enlargement of CSF spaces without prominent intracranial hypertension. A frequent cause is previous meningitis or subarachnoid hemorrhage (SAH), in which arachnoid villi are blocked by blood breakdown products.
- Hydrocephalus ex vacuo. A secondary process accompanying neural tissue loss in neurodegenerative pathologies (vascular dementia, Alzheimer's disease).
Causes of intracranial hypertension
Hydrocephalus is often accompanied by an increase in intracranial pressure (ICP). This occurs due to one of four reasons:
- Increase in intracranial volume (hemorrhage, tumor, extensive infarction).
- Obstruction to CSF circulation or absorption (meningitis, SAH).
- Excessive CSF production (choroid plexus papilloma).
- Elevated pressure in the venous system (sagittal sinus thrombosis, superior vena cava obstruction).
In newborns, hydrocephalus is frequently congenital. It can be triggered by intrauterine infections, brain hemorrhages (especially in premature infants), or anatomical anomalies such as aqueductal stenosis.
Clinical manifestations and complications
Disease manifestation depends on the patient's age and the form of the pathology. In infants under two years of age, the cranial sutures are still pliable, so the leading sign is rapid head circumference growth.
Acute hypertensive hydrocephalus (against the background of SAH or cerebellar hemorrhage) manifests as rapid depression of consciousness. If ICP reaches 40–50 mm Hg, blood supply to the nervous tissue drops critically, and the patient falls into a coma. Meanwhile, venous congestion is registered in the fundus, and extraocular nerve function is also impaired.
The most formidable complication is herniation (dislocation) — the displacement of brain tissue into other intracranial compartments. This poses a fatal risk due to respiratory and circulatory arrest:
- Upper (transtentorial) herniation: a space-occupying lesion in the hemisphere displaces the temporal lobe beneath the tentorium cerebelli. The upper brainstem is compressed, resulting in external eye muscle paresis and pupillary dilation.
- Lower (tonsillar) herniation: in pathologies of the posterior cranial fossa, the cerebellar tonsils descend into the vertebral canal through the foramen magnum, disrupting the functions of the caudal brainstem.
Diagnostics and treatment
The gold standard for confirming the diagnosis is neuroimaging — CT or MRI. The images clearly determine the degree of ventricular or external space dilatation.
Patient management tactics:
- Etiotropic therapy: eliminate the underlying cause whenever possible (e.g., resect the mass lesion).
- Temporary treatment: lumbar puncture with CSF evacuation is used for rapid pressure reduction. Caution: the procedure is strictly contraindicated in intraventricular occlusion.
- Surgical intervention: bypass pathways for fluid outflow are created for a sustained effect. Shunting is performed: ventriculoperitoneal (fluid is diverted from the ventricles to the peritoneal cavity) or lumboperitoneal (from the spinal canal to the peritoneal cavity).
When meningeal syndrome develops (against the background of SAH, trauma, or infections), the patient requires immediate hospitalization to identify the cause and initiate emergency therapy.
Briefly: answers to topical questions
Which structures are displaced and compressed during transtentorial (upper) herniation?
During transtentorial (upper) herniation, the cingulate gyrus is displaced beneath the falx, and the mediobasal part of the temporal lobe and uncus (uncus) are displaced medially and downward beneath the tentorium cerebelli (tentorium cerebelli).
The following structures are compressed:
- Upper regions of the brainstem — compression and deformation of the midbrain occur.
- Oculomotor nerve — compression leads to pupillary dilation and external eye muscle paresis.
- Basal cisterns — suprasellar, ambient, and quadrigeminal cisterns.
- Posterior cerebral artery (PCA) — compression causes infarction in its vascular territory.
What types of shunt operations are used for the surgical treatment of hydrocephalus?
Operations to create bypass pathways for cerebrospinal fluid outflow are used for the surgical treatment of hydrocephalus.
The following types of interventions are distinguished:
- Ventriculoperitoneal shunting — placement of a shunt between the ventricular system of the brain and the peritoneal cavity.
- Lumboperitoneal shunting — connection of the subarachnoid space of the spinal canal with the peritoneal cavity.
- Ventriculoatrial shunting — diversion of CSF into the atrium of the heart.
- Third ventriculostomy (endoscopic third ventriculostomy) — creation of an opening in the floor of the third ventricle for CSF outflow into the suprasellar cistern.
- External ventricular drainage — placement of an external ventricular drain.
What anatomical anomalies and syndromes cause congenital hydrocephalus in newborns?
Congenital hydrocephalus in newborns may be associated with developmental malformations and conditions that disrupt CSF circulation:
- Aqueductal stenosis or atresia.
- Chiari II malformation (Arnold-Chiari), which is frequently combined with hydrocephalus.
- Dandy-Walker malformation, frequently combined with hydrocephalus; characterized by cystic dilatation of the fourth ventricle and hypoplasia or aplasia of the cerebellar vermis.
- Neural tube defects, including spina bifida, meningocele, and myelomeningocele, associated with Chiari II malformation and hydrocephalus.
- Colloid cyst of the third ventricle, causing obstruction of CSF pathways.
- Arachnoid cysts of the posterior cranial fossa, which can enlarge and cause obstructive hydrocephalus.
What are the normal values of intracranial pressure in adults in the supine position?
Normal intracranial pressure values range from 90 to 150 mm H2O, which is equivalent to 6–11 mm Hg.
The provided materials do not specify normal pressure values exclusively for the supine position, but general physiological parameters are indicated. Intracranial hypertension is diagnosed when cerebrospinal fluid pressure increases above 200 mm H2O (14 mm Hg).
What changes are detected in the fundus oculi in severe intracranial hypertension?
In severe intracranial hypertension, specific pathological changes are detected in the fundus oculi.
These include:
- Venous congestion — occurs due to impaired venous outflow from the optic nerves.
- Optic disc edema (choked disc) — the most important objective sign of increased intracranial pressure.
- Optic disc hyperemia — accompanies the development of edema.
- Optic disc atrophy — forms as a consequence of prolonged edema and leads to irreversible damage to fibers up to complete blindness.
Which parts of the brain are damaged during downward (tonsillar) herniation?
During downward (tonsillar) herniation, the cerebellar tonsils are displaced downward through the foramen magnum into the spinal canal.
As a result of this process, the following parts of the brain are damaged:
- Brainstem — direct compression occurs.
- Caudal part of the brainstem — undergoes compression, leading to severe impairment of its functions (including vital respiratory and circulatory functions).
- Cerebellar tonsils — directly herniate and become entrapped in the foramen magnum.
Where is cerebrospinal fluid normally produced and through which structures is it absorbed?
Normally, cerebrospinal fluid is produced in the choroid plexuses of the four cerebral ventricles: the right and left lateral ventricles (the main production site), the third, and the fourth.
Absorption (resorption) of CSF into the venous bed is carried out through the following structures:
- Arachnoid granulations (Pacchionian granulations) — located near the superior sagittal sinus.
- Perineural spaces (perineural sheaths) of the spinal cord.
To memorize the causes of ICP elevation, use the "4 volumes" rule: the volume of Tissue increases (tumor), CSF volume (hypersecretion), Blood volume (venous congestion), or a Circulation block appears (occlusion).
Class and exam questions
Why do the ventricles not dilate significantly in aresorptive hydrocephalus?
When CSF resorption is impaired, CSF pressure rises on the outside of the brain. This "external" hypertension mechanically prevents excessive ventricular dilation from within.
Can lumbar puncture be performed in any type of hydrocephalus?
No. If there is an intraventricular occlusion (blockade of the cerebrospinal fluid pathways), lumbar puncture is strictly contraindicated, as it may provoke a fatal brainstem herniation.
What explains the development of hydrocephalus ex vacuo?
It occurs as a consequence of the death and atrophy of neural tissue during neurodegenerative processes. The CSF simply passively fills the space freed up in the cranium, so no significant pressure increase occurs.
What else to study on this topic
- Meningeal syndrome: clinical presentation and management algorithm
- Anatomy of cerebrospinal fluid pathways and arachnoid granulations
- Subarachnoid hemorrhage: etiology and pathogenesis
- Technique and complications of ventriculoperitoneal shunting
- Topical diagnosis of oculomotor nerve lesions in brain herniation
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