![]() Type 2 are from leaking nerve root diverticula with extradural fluid collection (42.3%). 10 Type 1 are caused by a dural tear, often from a calcified ventral osteophyte leading to an extradural CSF collection (26.6%). 9 Potential causes of CSF leak were classified in a study of 568 cases (Figure 1). Although a CSF leak may be spontaneous, as the name suggests, it can also be traumatic, masquerading as a posttraumatic headache and leading to misdiagnosis. 8 EtiologiesĮtiology of CSF leaks is variable. Cranial CSF leaks, however, are not associated with orthostatic headache of SIH. ![]() Owing to the hydrostatic indifference point, cranial CSF leaks, unlike spinal leaks, may be associated with headache, rhinorrhea, otorrhea, and even recurrent meningitis. The pressure difference equalizes in the supine position with less CSF leak and headache. This change in the hydrostatic indifference point leads to increased CSF expulsion in the upright position with possible venous dilation causing orthostatic headache. In people with SIH, the zero-pressure point moves downward leading to negative intracranial pressure relative to the lower spine. 6,7 Therefore, if CSF pressure is measured at this point, it will be the same in the upright and supine positions. 5 According to the hydrostatic indifference point mechanism, there is a zero-pressure point, usually located in the upper cervical spine, where CSF pressure changes from positive to negative relative to the atmospheric pressure. The second proposed mechanism is the hydrostatic indifference point, which highlights the change in lumbar compliance in the presence of SIH. 5 Therefore, when CSF is lost, as seen in SIH, a resultant decrease in intracranial pressure causes intracranial venous structures to dilate. Dating back 2 centuries, the Monro-Kellie doctrine applied the understanding of physics to the skull, stating that the following volumes must remain constant or intracranial pressure will change: brain, CSF, and intracranial blood. 2,3 Awareness of this diagnosis has been increasing, but because of atypical symptoms, often normal initial findings, and refractory symptoms, SIH diagnosis is often missed or delayed. 1 Although we believe there is a female predominance and an average age of onset at 40 to 45 years, SIH can be seen at any age. Commonly underdiagnosed, SIH has an estimated incidence of 5 per 100,000. Symptoms may mimic a postdural puncture headache, but presentation and prognosis for SIH can be quite variable. Spontaneous intracranial hypotension (SIH) is a secondary headache etiology attributed to a cerebrospinal fluid (CSF) leak or CSF-venous fistula involving the nerve root sheath.
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