Spontaneous Intracranial Hypotension (SIH) usually presents as a postural, orthostatic headache, often with subtle and and insidious onset, and occasionally with a sudden, debilitating onset. There is often no major trauma or precipitating event, or the event is a seemingly minor trauma. The key to this type of headache is that the patient reports marked worsening or onset of the headache within 15 minutes of standing, and improvement or resolution within 30 minutes of laying down. It is exactly like a post lumbar puncture headache, without a history of lumbar puncture. Associated symptoms include a significant posterior neck pressure, neck stiffness, visual changes, vertigo, hearing loss (sometimes intermittent), extreme nausea, radicular nerve pain in the arm, and sometimes a parkinsonian like syndrome. Often the patient cannot be upright at all.
The onset of a clearly positional headache with no associated major trauma or prior spinal or neurosurgery leaves little room in the differential. To confirm the diagnosis, an epidural blood patch may be perfomed. Placing 15 to 20 ml of autologous blood in the lumbar epidural space should result in a marked improvement, if not resolution, of the patientís symptoms. However, in many cases, the patch is of temporary relief, and patients relapse, often within a few days.
Opening pressure on lumbar puncture is often low. However, normal opening pressures in an otherwise symptomatic individual does NOT rule out the syndrome.
An MRI scan can be helpful in that highlighting of the dura after gadolinium enhancement is often seen. The presence of this sign puts the patient in a better prognosis category, as patients who are symptomatic without this sign seem more refractory to interventions. Sagging of the brain and subdural fluid collections can also be seen.
Patients who do not have a permanent response to epidural blood patches should under go a CT myleogram with thin cuts. On reviewing the study, attention should be directed to evidence of leakage at the nerve roots and the presence of diverticulae of the dura of the nerve roots. Note that radionucleotide scans of the spine looking for CSF leaks have proven much less sensitive than the CT myleogram method.
In many cases, leaking of CSF (often without indentifiable stuctural changes) at their exit through the neuronal formamina, or diverticulae of the dura along the nerve root is noted. This is frequently found at the cervicothoracic spine or thoracic spine. It is assumed that CSF is leaking out of the nerve root dural covering at these points, and indeed this had been observed during operative repair of these lesions. The leaking CSF results in a low volume and/or low pressure condition, causing the brain to be displaced posteriorly and inferiorly , putting traction on the pain sensitive intracranial dura.
There is some controversy in the literature as to whether the headache is caused by a low pressure situation or a low volume situation. As noted, some patients present with a spinal type headache and yet have normal range opening pressures.
There has been no unifying underlying problem with SIH patients, although a large subset of patients (approximately 20%) seem to have evidence of connective tissue disorders such as Marfanís Syndrome, polycystic kidney disease, neurofibromatosis Type I, and Lehman Syndrome.
The epidural blood patch is the primary mode of treatment. In some cases, a high volume of blood, up to 30 cc, has yielded a better success rate than lower volumes. Higher volume patches are often associated with significant post-procedure leg and back nerve pain.
If a specific leak site is found on imaging studies, and the patient is refractory to blood patches, an experienced interventional radiologist may attempt a percutaneous placement of fibrin glue to the leak site.
Failing this, open surgery with laminectomy at the level of the leak with packing of the area with fibrin glue, gelfoam, blood and muscle has been successful. Ligation of any dural diverticulae may also be indicated.
Bed rest, theophylline therapy, and increasing fluids have not had any signficant success in treating this syndrome, but may offer palliation.
For patients with enhancement on MRI, the prognostic outlook is better than non-enhancers. Most respond to epidural blood patches, or surgical interventions. Some patients seem to relapse in spite of repair of clearly defined leaks. Some patientís headaches transition from postural to non-postural and stop responding to epidural blood patches.
Schievink,W.I.,Spontaneous Spinal Cerebrospinal Fluid Leaks: A Review,Neurosurgical Focus 9(1), 2000. Full Text Article.
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