P SPONTANEOUS INTRACRANIAL HYPOTENSION

SIH is described as CSF pressure less than 60 mmH2O and descent of the brain into the foramen magnum. The fall in CSF pressure is secondary to a CSF leak, likely due to a recent lumbar puncture or epidural anesthesia [3-4]. CSF leakage can result in venous engorgement resulting in pachymeningeal enhancement on MRI. Since CSF provides protective buoyancy to intracranial structures, a leak can cause the brain to descend and increased traction of pain-sensitive structures. Patients may present with postural occipital headache, nausea, vomiting, radiculopathy, tinnitus, vertigo, nuchal rigidity, photophobia and cranial nerve palsies [2,4-6]. Recognition of a prominent inferior intercavernous sinus may assist in diagnosing SIH, which presents as a rounded structure at the floor of the sellae seen in 50% of patients with SIH [6]. Difficulty in diagnosing SIH is due to overlapping findings with CM1, a congenital syndrome characterized by herniation of the cerebellar tonsils into the foramen magnum without brainstem involvement. The pathogenesis remains unclear, but herniation of the cerebellar tonsils can lead to pain, weakness, dysphagia and sensory disturbances. An occipital headache is one of the most common presenting symptoms occurring in 15%-98% of patients, commonly accentuated by postural change or exertion [3,7]. Puget, et al., however, described a pseudo-Chiari tonsillar herniation in SIH due to a CSF leak with no association to syringomyelia, but rather, pachymeningeal enhancement [4]. This highlights a key difference in the two syndromes. The overlap of symptomology between SIH and CM1 calls for the reliance on additional imaging to localize a CSF leak as seen in SIH. Computed tomography (CT) myelography is the preferred diagnostic modality to detect initial CSF leaks followed by dynamic CT myelography to differentiate high-flow from low-flow leaks [8]. CT myelography or digital subtraction myelography are specific for high-flow leaks, whereas magnetic resonance myelography with intrathecal gadolinium is preferred for low-flow leaks [8]. Treatment for SIH involves rest, caffeine, fluid supplementation, or an epidural blood patch (EBP). EBP is the current mainstay of treatment and can be targeted to the specific site of a CSF leak on imaging or delivered blindly into the lumbar region [6]. One retrospective, non-randomized series showed that 87% of patients who received a single targeted EBP experienced a benefit and 100% after receiving two EBP procedures