Intracranial Hypotension and Intracranial Hypertension

Intracranial pressure

Intracranial pressure (ICP) is the pressure within the intracranial space. In the steady state, pressure within the brain parenchyma and intracranial extra-axial spaces are equal. Normal values of ICP are 5 to 15 mm Hg (6–20 cm H₂O) in adults and older children (ages 8 years and older) in the supine position, 1 to 7 mm Hg (1–10 cm H₂O) in younger children, and up to 18 mm Hg (25 cm H₂O) in obese patients.1, 2 ICP increases with Valsalva maneuver, and falls below atmospheric pressure in the

Intracranial hypotension

In intracranial hypotension, low CSF volume results in orthostatic headache, and, less commonly, nausea, vomiting, photophobia, and, rarely, decreased level of consciousness. Intracranial hypotension results from loss of CSF through a dural defect in the spine, cranial vault, or skull base. SIH refers loosely to cases of intracranial hypotension in which a dural defect is identified and cannot be attributed to a prior procedure or to trauma. Causes of secondary intracranial hypotension include

Pathophysiology

Most CSF is formed in the ventricular system through active secretion by the choroid plexus. The average CSF volume in adults is approximately 150 mL, and the rate of CSF formation in adults is approximately 500 mL/d.18, 19 The arachnoid granulations (projections of the arachnoid membrane into the venous sinuses) are the major site of CSF absorption.

Post–lumbar puncture headache was described as early as 1899 by Dr August Bier, a pioneer of spinal anesthesia, who stated after undergoing such a

Diagnosis

The diagnosis of SIH is based on a combination of clinical signs and symptoms, head and spine imaging, and intrathecal pressure measurements.

Treatment

Although recognition of SIH has increased in the past decade because of the increased sensitivity of MR imaging, SIH continues to be frequently misdiagnosed. Suboccipital craniotomies for Chiari 1 malformation, catheter angiography for unexplained headache, and craniotomies for meningeal biopsy or subdural hematoma evacuation have been performed in cases of undiagnosed SIH (Fig. 7). A 2003 study reported that 17 of 18 consecutive patients referred to a surgical practice for treatment of SIH

Intracranial hypertension

Intracranial hypertension can occur in chronic or acute forms in a large variety of neurologic and systemic disorders, including intracranial mass lesions such as tumor or abscess, traumatic brain injury, ischemic or hemorrhagic stroke, dural venous sinus thrombosis, dural arteriovenous fistula, hydrocephalus, or diffuse cerebral edema such as in liver failure. A diagnosis of IIH is made in the setting of chronic elevated ICP when a specific cause cannot be defined. Normal values of ICP in

Clinical presentation

Acute, abnormal increase of ICP results in headache, nausea and vomiting, blurred vision, and, in severe cases, reflex bradycardia and altered level of consciousness or death caused by cerebral hypoperfusion and/or brain herniation.

In IIH, characterized by mild to intermediate chronic increase of ICP, the most common presenting symptom is chronic daily headache.62, 63 Other common presenting symptoms in IIH are pulsatile tinnitus (60%) and transient visual obscurations (75%),⁶⁴ the latter