Increased Intracranial Pressure (ICP)

1. Definition:

Increased intracranial pressure (ICP) is a condition where the pressure inside the skull rises above normal levels, typically exceeding 20 mmHg/ cmH2O. Normal intracranial pressure ranges from 5 to 15 mmHg.

2. Mechanism of Increased Intracranial Pressure:

The skull is a closed cavity containing the brain, blood, and cerebrospinal fluid (CSF). Intracranial pressure is maintained by a delicate balance between the volumes of these three components. When the volume of one or more components increases, intracranial pressure rises accordingly.

Mechanisms of Increased Intracranial Pressure:

• Increased Brain Tissue Volume:
  • Space-occupying lesions: Brain tumors, severe cerebral infarction (stroke), cerebral hemorrhage, brain contusion (bruising), and brain abscesses. These lesions displace the brain, leading to increased pressure.
  • Cerebral edema (swelling): Caused by changes in blood vessel permeability, cell membrane permeability, or osmotic pressure. Common causes of cerebral edema include hypoxia (oxygen deprivation), acute liver failure, encephalitis (brain inflammation), and traumatic brain injury.
• Increased Blood Volume: Heart failure, obstruction of the superior vena cava (the major vein in the chest), or jugular vein thrombosis (blood clot in a neck vein) can slow blood flow and increase the volume of blood in the skull.
• Increased Cerebrospinal Fluid (CSF) Volume: Obstruction of CSF flow pathways, such as from a brain tumor, meningitis (inflammation of the brain and spinal cord membranes), or congenital malformations (birth defects), can lead to CSF buildup. Hydrocephalus (excess CSF in the brain) can also occur due to excessive CSF production or impaired CSF absorption.

3. Mechanisms of Intracranial Pressure Regulation:

The body has natural mechanisms to regulate intracranial pressure. When ICP rises, the body responds by:

• Decreasing Blood Volume: Blood vessels constrict, reducing the amount of blood in the brain.
• Decreasing Cerebrospinal Fluid Volume: Increased CSF absorption and decreased CSF production occur.

However, these mechanisms are effective only within a limited range. If ICP rises excessively, these regulatory mechanisms become overwhelmed, resulting in persistent ICP.

4. Causes of Increased Intracranial Pressure:

a. Brain Tissue:

• Space-occupying Lesions:
  • Intracranial: Brain tumors, severe cerebral infarction (stroke), cerebral hemorrhage, brain contusion, brain abscess.
  • Extracranial: Meningiomas (tumors of the brain membranes), metastatic tumors to the brain.
• Cerebral Edema:
  • Generalized: Due to hypoxia, acute liver failure, encephalitis.
  • Localized: Due to focal injuries like cerebral infarction or cerebral hemorrhage.
• Increased Blood Volume: Heart failure, obstruction of the superior vena cava, or jugular vein thrombosis.

b. Cerebrospinal Fluid (CSF):

• Obstructed CSF Flow: Due to brain tumors, meningitis, congenital malformations.
• Hydrocephalus: Due to excessive CSF production or impaired CSF absorption.

c. Other Causes:

• Traumatic Brain Injury: Epidural hematoma (blood collection between the skull and dura mater), subdural hematoma (blood collection between the dura mater and the brain), and brain contusion.
• Malignant Hypertension (Hypertension Crisis): Causes cerebral edema.
• Meningitis (Brain and Spinal Cord Membrane Inflammation): Causes cerebral edema and obstruction of CSF flow.
• Cerebrovascular Disease (Brain Blood Vessel Disorders): Cerebral infarction (stroke) and cerebral hemorrhage.
• Rare Causes: Endocrine disorders, metabolic disorders, medications.

5. Consequences of Increased Intracranial Pressure:

• Reduced Cerebral Blood Flow: Leads to brain hypoxia (oxygen deprivation) and brain damage.
• Hydrocephalus: CSF accumulation, causing increased ICP.
• Brain Herniation: Brain displacement from its normal position, resulting in brain damage.
• Compression of the Optic Nerve: Causes visual impairment and blindness.

6. Clinical Presentation:

Classic Triad:

• Headache: Severe, progressively worsening headache, often bilateral, worse at night, during exertion, coughing, or straining.
• Vomiting: Easy, projectile vomiting, without nausea beforehand, with temporary headache relief after vomiting.
• Papilledema: Swelling of the optic nerve head, visible upon funduscopic examination (examination of the back of the eye).

Visual Abnormalities:

• Double Vision: Caused by damage to the sixth cranial nerve.
• Vision Loss: Occurs later, when ICP is severe.
• Visual Field Defects: Narrowing of the visual field.

7. Diagnostic Studies:

• Computed Tomography (CT) Scan of the Brain: Detects tumors, hemorrhages, infarctions, and cerebral edema.
• Magnetic Resonance Imaging (MRI): Provides more detailed images than CT, aiding in accurate diagnosis of brain pathologies.
• Electroencephalography (EEG): Detects abnormal brain electrical activity.
• Cerebrospinal Fluid Analysis: Detects infections and brain inflammation.

8. Common Causes of Increased Intracranial Pressure:

• Space-occupying Lesions:
  • Supratentorial (above the tentorium cerebelli, which separates the cerebrum from the cerebellum): Brain tumors, meningiomas, metastatic brain tumors, brain abscesses, cerebral hematomas (blood clots in the brain).
  • Infratentorial (below the tentorium cerebelli): Brain tumors, cerebral hematomas.
• Cerebrovascular Disease: Malignant hypertension (hypertension crisis), subarachnoid hemorrhage (bleeding into the space between the brain and its membranes), large cerebral infarction (stroke).
• Inflammatory and Infectious Diseases: Meningitis, encephalitis.
• Traumatic Brain Injury: Epidural hematoma, subdural hematoma, brain contusion.
• Non-tumoral Hydrocephalus: Due to congenital malformations, meningitis, obstruction of CSF flow.
• Other Causes: Acute liver failure, acute kidney failure, respiratory failure, poisoning.

9. Complications:

• Brain Herniation: Brain displacement from its normal position, causing brain damage.
• Coma: Due to brain hypoxia and brain damage.
• Death: Caused by severe brain damage and respiratory failure.

10. Types of Brain Herniation:

• Subfalcine Herniation: The medial portion of the cerebral hemisphere is displaced across the midline through the falx cerebri (a fold of dura mater that separates the two cerebral hemispheres).
• Transtentorial Herniation (Uncal Herniation): The temporal lobe or deep brain structures are pushed downward through the tentorial notch.
• Transtentorial Herniation (Upward): Posterior fossa space-occupying lesions push the brainstem and lower cerebellum through the foramen magnum (the opening at the base of the skull).
• Tonsillar Herniation: Posterior fossa space-occupying lesions displace the cerebellar tonsils through the foramen magnum, compressing the brainstem.
• Herniation Through a Craniotomy (Surgical Opening in the Skull): Brain tissue is pushed out through a craniotomy opening.

11. Treatment:

Treatment Principles:

• Treatment of the Underlying Cause: Removing the cause of increased ICP.
• Treatment of Cerebral Edema: Reducing cerebral edema and decreasing ICP.
• Treatment of Hydrocephalus: Reducing CSF volume and decreasing ICP.

12. Cerebral Edema Treatment:

• Corticosteroids: Indicated for brain tumors and brain abscesses.
• Hypertonic Solutions (Mannitol): Indicated for stroke and traumatic brain injury.
• Diuretics: Help eliminate water, reducing cerebral edema.
• Hyperventilation: Increases blood oxygen levels, reducing cerebral edema.
• Barbiturates: Reduce brain activity, decreasing cerebral edema.
• Induced Hypothermia (Lowering Body Temperature): Reduces the brain’s oxygen requirement, decreasing cerebral edema.

13. Hydrocephalus Treatment:

• Cerebrospinal Fluid Shunting:
  • External Shunting: Draining CSF externally from the body.
  • Internal Shunting: Draining CSF from the ventricles to the cisterna magna (a CSF reservoir at the base of the brain).
• Ventriculoperitoneal Shunt: Creating a connection between the ventricles and the peritoneal cavity (the space within the abdomen), allowing CSF to drain into the abdomen.

Note:

• Increased intracranial pressure is a serious condition that can be fatal.
• Prompt diagnosis and treatment by a neurologist or neurosurgeon are crucial.
• Self-medication or home treatment is not recommended.
• Regular health checkups are important for early detection of conditions that could lead to increased ICP.

This information is for educational purposes only and should not be considered medical advice. If you have concerns about increased ICP or any other medical condition, please consult with a qualified healthcare professional.

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