Spontaneous Intracranial Hypotension (SIH) is a neurological condition caused by reduced pressure within the skull and spinal column. This low-pressure state results from an abnormal loss of the cerebrospinal fluid (CSF) that surrounds the brain and spinal cord. Although rare, with an estimated annual incidence of five per 100,000 people, SIH is often underdiagnosed. It carries specific, potentially severe risks that necessitate timely recognition and intervention.
The Mechanism Behind Spontaneous Intracranial Hypotension
Cerebrospinal Fluid (CSF) is a clear, protective liquid that bathes the brain and spinal cord, providing buoyancy and cushioning. It circulates within the dura mater, a tough membrane encasing the central nervous system, where its volume and pressure are precisely regulated.
SIH occurs when this system is breached, typically by a tear or defect in the dura mater along the spine. This dural defect allows CSF to leak into surrounding tissues, reducing fluid volume and pressure. The cause of the dural tear is often unclear, hence the term “spontaneous,” though connective tissue disorders may predispose individuals to this weakness.
According to the Monro-Kellie doctrine, the total volume of brain tissue, blood, and CSF within the skull must remain constant. When CSF is lost, the body attempts to compensate by increasing intracranial blood volume. This mechanism is often insufficient to restore normal pressure, resulting in the low-pressure state defined by the condition.
Recognizing the Primary Symptoms
The most frequent and characteristic symptom of Spontaneous Intracranial Hypotension is the orthostatic headache. This pain intensifies significantly when the patient is upright (standing or sitting) and resolves completely when lying flat. This positional nature results directly from low CSF pressure, which causes a downward pull on pain-sensitive structures when gravity takes effect.
The headache onset is often abrupt and can become persistent if the leak is not sealed. Severe pain may lead to associated symptoms such as nausea and vomiting. Patients often report neck stiffness or pain, thought to be caused by the downward pull on the brainstem and supporting structures.
Other common symptoms include auditory and vestibular disturbances. These manifest as tinnitus (ringing in the ears), changes in hearing acuity, dizziness, vertigo, and photophobia (sensitivity to light). In some cases, the classic orthostatic pattern diminishes over time, resulting in a persistent daily headache that complicates diagnosis.
Serious Risks and Neurological Complications
The persistent loss of CSF and resulting low intracranial pressure can lead to serious neurological complications. The primary mechanism is “brain sag,” which occurs when the CSF buoyancy is lost. As the brain descends, it places traction and stress on surrounding blood vessels and nerves.
A major risk is the development of a subdural hematoma (SDH), a collection of blood between the brain’s outer layer and the dura mater. Brain descent stretches and tears the small bridging veins, causing bleeding and hematoma formation. SDH can cause severe symptoms or be life-threatening, often requiring emergency neurosurgical intervention.
Chronic low pressure can also lead to superficial siderosis, a complication caused by the recurrent leakage of blood products into the CSF and their deposit onto the brain’s surface. These iron deposits cause progressive neurological deficits, including bilateral hearing loss and ataxia (poor coordination and unsteady gait). The pressure imbalance also increases the risk of dural venous sinus thrombosis (CVT), a blood clot in the brain’s venous drainage system.
In severe, untreated cases, profound brain descent can lead to brainstem compression and disorders of consciousness. SIH can result in stupor or coma, associated with temporal lobe herniation. This progression highlights the potential for chronic disability or a fatal outcome if the CSF leak is not promptly repaired.
Medical Interventions to Stabilize CSF Pressure
The goal of treatment for Spontaneous Intracranial Hypotension is to seal the CSF leak and restore normal intracranial pressure. The initial approach involves conservative measures for mild symptoms, including strict bed rest to reduce hydrostatic pressure. Increased hydration and the use of caffeine, which increases CSF production and constricts cerebral blood vessels, are also recommended as first-line therapies.
When conservative management fails, the primary intervention is the Epidural Blood Patch (EBP). This procedure involves injecting the patient’s own blood (autologous blood) into the spinal epidural space, where it clots and forms a temporary seal over the dural defect. An EBP can be non-targeted, performed at a general lumbar level, or targeted, guided by imaging directly to the confirmed leak site.
Targeted EBP and variations, such as using larger blood volumes or injecting fibrin glue, are often necessary for leaks that do not respond to the initial approach. Fibrin glue patching uses a concentrated sealant to repair the dural tear, offering a robust closure in specific cases. These percutaneous interventions are effective, with most patients experiencing symptomatic relief after one or two procedures.
If repeated patching is unsuccessful, or if the leak involves a complex defect like a CSF-venous fistula or a bony spur, surgical intervention may be required. Surgery involves directly accessing the spine to repair the dura mater with sutures or patches, providing definitive closure. Successful sealing of the CSF leak resolves the underlying low pressure, leading to symptom resolution and elimination of neurological risks.