Spontaneous Intracranial Hypotension
Schaltenbrand first described spontaneous intracranial hypotension (SIH) in 1938, originally calling it spontaneous aliquorrhea.
SIH results from leakage of cerebrospinal fluid (CSF) and may follow surgical or non-surgical trauma, any type of dural tear, CSF venous fistulas, congenital malformations, and spinal dural diverticula. When the CSF leakage outpaces CSF production, intracranial hypotension may result. Common presenting symptoms include postural headaches and nausea, but other neurologic symptoms and signs may develop depending on duration and severity.
Incidence and prevalence
According to one study, the incidence of SIH that is visible on computed tomography (CT) in the emergency department may be as high as 5 cases per 100,000. However, a higher incidence may be detected when using clinical criteria, magnetic resonance imaging (MRI), and other more specialized imaging to detect an occult CSF leak.
SIH has been associated with female sex, lower body mass index (BMI), and being in the 4th or 5th decade of life, but SIH can occur in any age, in either sex, and with any BMI. Connective tissue disorders (e.g. Marfan syndrome, Ehlers-Danlos syndrome) may predispose to SIH. The risk of iatrogenic CSF leak after lumbar puncture may be decreased with the use of a 29 gauge needle instead of 26 gauge needle, along with orienting the bevel parallel to the axis of the spine. Using a Whitacre or Sprotte atraumatic needle for lumbar punctures also may decrease the risk of CSF leak compared with standard needles. A history of minor trauma can be elicited in 1/3 of patients with SIH, but many cases have no trauma history. Treatments for idiopathic intracranial hypertension (IIH) can lead to secondary SIH. The required rate of CSF shunting varies with lifestyle and physical activity, with over half of shunt patients requiring postoperative adjustments to valve pressure. Cases have been reported of shunt over-drainage in IIH leading to secondary SIH.
The normal total CSF volume ranges from 90-150 ml and is formed by the choroid plexus at a rate of 0.3 to 0.4 ml/min. CSF resorption takes place through the walls of the CNS capillaries and at the arachnoid granulations. SIH occurs when increased CSF outflow results in a decrease in the CSF intracranial pressure (ICP). Large or irregular diverticula around the spinal nerve roots can cause leakage of CSF and are found in a number of SIH cases.12 CSF-venous fistulas increase outflow and are a newly discovered cause of SIH. Meningeal tears have also been associated with CSF leakage.
In 2008, a set of diagnostic criteria were suggested in the American Journal of Neuroradiology. A. Extrathecal CSF on spine imaging B. Cranial MR findings* of SIH along with one of the following: 1. Low opening pressure, defined as 60 mm H20 (<5 mm Hg) 2. Spinal meningeal diverticula 3. Improvement of symptoms with spinal epidural blood patch C. All of the following, or two of the following with typical orthostatic headaches: 1. Low opening pressure 2. Spinal meningeal diverticula 3. Improvement after epidural blood patch
- The cranial MR findings in the study included subdural fluid collections, enhancement of the pachymeninges, and “sagging” of the brain.
In addition to the full neurological exam, the Trendelenburg test may assist in the diagnosis of SIH. The patient is placed in 10-20 degrees of Trendelenburg for 5 minutes to monitor for resolution or significant improvement of symptoms.
Signs and symptoms
The most common symptoms are orthostatic headaches, nausea, and vomiting. Other symptoms including neck pain, facial numbness, visual blurring, and visual field defects may also be present. A non-localizing cranial nerve VI palsy may cause horizontal diplopia, while cranial nerve VIII involvement may cause tinnitus and vertigo. Cranial nerve VII involvement has been noted to affect the face. In severe cases of SIH, Parkinsonism and even coma can result.
In one study, optic neuropathy was seen in 3 out of 4 monkeys from the experiment group with no changes in the control group. The retinal nerve fiber layer thickness decreased by 12%-30%, and an increased cup to disk ratio was noted in 2 monkeys. Another monkey showed a splinter-like disk hemorrhage during the 1-year study interval. Among humans, a literature review found that 42% of SIH patients presented with ocular manifestations. The most common was a nonlocalizing abducens nerve deficit, with the second most common being trochlear nerve involvement. Rarely, the optic nerve can also be involved and can manifest a visual field loss. Visual deficits and ophthalmoplegia showed improvement with correction of CSF pressure in 97% of patients.
Dural enhancement was the most sensitive MRI finding, appearing in 56%-83% of patients with CSF pressure < 6 cm of water. Less sensitive MRI findings for SIH included brain sagging, subdural fluid collections, and venous distension. Ultrasound may be a faster and less expensive diagnostic procedure for SIH. An optic nerve sheath diameter (ONSD) decrease of 0.5 mm was noted between the supine and standing positions in patients with SIH. No decrease in ONSD change was noted in healthy controls. After SIH is diagnosed clinically, dynamic CT myelography can aid in localization of CSF leaks.
As many urgent conditions cause similar symptoms and radiographic findings, a broad differential diagnosis is warranted. The differential diagnosis for headache with intracranial pachymeningeal enhancement includes: 1. Meningitis: Bacterial, fungal, and aseptic 2. Autoimmune: Rheumatoid arthritis, systemic lupus erythematosus, mixed connective tissue disease, granulomatosis with polyangiitis 3. Inflammatory: Sarcoidosis, tuberculosis, syphilis, and Lyme disease. 4. Brain tumors: Meningioma, en plaque lymphoma, carcinoma 5. Iatrogenic: Intrathecal drug administration, craniotomy, ventricular shunting, hemodialysis, mucopolysaccharidosis. It is thus important to recognize SIH as a potential cause for meningeal enhancement in order to avoid unnecessary and potentially invasive or harmful testing (e.g. meningeal biopsy).
Conservative non-pharmacologic management includes bed rest, adequate fluid intake, and abdominal binders.
Medical management includes caffeine, theophylline, analgesics, and non-steroidal anti-inflammatory drugs (NSAIDs).
Epidural Blood Patches
1. Efficacy: Epidural blood patches (EBP) reported a resolution rate of between 50% and 100% for SIH. One study of 42 patients pretreated with acetazolamide who were placed into 30 degrees of Trendelenburg both during treatment and 24 hours afterward showed marked and rapid response to EBP. The increased treatment efficacy was hypothesized to be because of cephalad movement of the autologous blood.
2. Administration Patients are injected with 10-15 ml of autologous blood into the lumbar epidural space. If a CSF leak is noted in the cervical spine, 20-40 ml of blood is injected into the thoracolumbar epidural space and the patient is placed in Trendelenburg for 20-30 minutes. If this fails, a directed blood patch or percutaneous fibrin glue is administered.
Surgery is reserved for patients who fail non-surgical and conservative treatment methods (e.g. two or more EBP). For surgery to be conducted, the site of leakage must be clearly identified. Options include ligation of leaking meningeal diverticula, direct repair of dural tears, packing of the epidural space with fibrin glue, and reinforcing the dura with duroplasty.
Treatment of SIH occasionally produces intracranial hypertension through over-increasing CSF volume. Employing surgical methods may increase the risk of secondary intracranial hypertension more than blood patches. A case series documented 3 patients who experienced intracranial hypertension after surgery and one patient after blood paching.
The prognosis of SIH is good, with 87% of patients seeing improvement after the first administration of a targeted EBP and 52% of patients who received a blind EBP. Other studies have reported between 25%-90% after first administration depending on the patient premedication, dose, and Trendelenburg positioning. A majority of studies with a large sample size found between a 50% and 90% cure rate after the first EBP. One study with an 87% cure rate found that 25% reoccurred within 8 years but were successfully retreated with another EBP.
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