Intracranial hypotension (IH) is a condition characterized by abnormally low pressure of cerebrospinal fluid (CSF), the fluid that surrounds the brain and spinal cord. This reduction in pressure is nearly always a direct result of a CSF leak, allowing the fluid to escape the closed system protecting the central nervous system. When CSF volume decreases, the brain loses buoyancy, causing it to sag within the skull. Intracranial hypotension, particularly when spontaneous (SIH), is often an underdiagnosed cause of severe headaches.
The Role of Cerebrospinal Fluid Leaks
Cerebrospinal fluid provides a cushion for the brain and spinal cord, protecting these structures from injury and delivering nutrients. The fluid is continuously produced within the brain’s ventricles and circulates around the central nervous system, contained by the dura mater. A spinal CSF leak occurs when there is a tear or defect in the dura mater, allowing the fluid to escape into surrounding tissues.
When CSF escapes, the overall volume and pressure within the skull and spinal canal decrease, causing intracranial hypotension. Leaks can be iatrogenic, caused by medical procedures like a lumbar puncture or epidural injection. Many cases are spontaneous, occurring without a clear inciting event, often due to structural weakness in the dura or an underlying connective tissue disorder. Spontaneous leaks can also be caused by a CSF-venous fistula, where the fluid drains directly into a nearby vein.
Key Symptoms and Characteristics
The defining characteristic of intracranial hypotension is the orthostatic headache, severe pain that is dramatically worse when upright and improves significantly when lying down. This positional dependency occurs because the loss of CSF volume causes the brain to sag downward when standing, pulling on pain-sensitive structures like blood vessels and nerves. The headache is often described as a throbbing or dull ache, typically localizing to the back of the head or neck.
Associated symptoms frequently accompany the headache. Individuals often experience neck stiffness or pain, nausea, and vomiting. Neurological symptoms may include changes in hearing, such as muffled hearing or tinnitus (ringing in the ears), and visual disturbances like blurred or double vision. Dizziness, imbalance, and a reduced ability to concentrate, sometimes called “brain fog,” also commonly occur.
Confirming the Diagnosis
The diagnosis of intracranial hypotension is initially suspected based on the unique, positional pattern of the headache and associated symptoms. Medical confirmation relies on specialized imaging techniques to look for indirect signs of low pressure and to locate the site of the CSF leak. A brain Magnetic Resonance Imaging (MRI) with contrast is often the first step, as it can reveal signs of reduced CSF volume.
Doctors look for signs such as pachymeningeal enhancement, where the dura mater appears thickened and brightly enhanced after contrast injection, and a visible descent or “sagging” of the brain structures within the skull. To pinpoint the exact location of the leak, specialized spinal imaging is required, such as Computed Tomography (CT) myelography or Digital Subtraction Myelography (DSM). These procedures involve injecting a contrast agent into the spinal canal, allowing it to escape through the defect and highlight the leak site on scans.
Repairing the Spinal Fluid Leak
Initial management for spinal CSF leaks begins with conservative measures, which may include extended bed rest, increased hydration, and sometimes caffeine intake. Caffeine constricts the cerebral blood vessels, which can temporarily help increase intracranial pressure and provide short-term relief. If symptoms persist despite these efforts, a more definitive intervention is necessary.
The most common and effective invasive treatment is the Epidural Blood Patch (EBP). This procedure involves injecting a small volume of the patient’s own blood into the epidural space near the suspected leak site. The blood forms a clot that seals the dural tear and immediately restores pressure. If an EBP is unsuccessful or the leak is precisely located, a targeted patch using fibrin glue or surgical repair may be performed to close the defect. Surgical repair is typically reserved for complex leaks, such as large dural tears or CSF-venous fistulas, that do not respond to less invasive patching techniques.