Spontaneous dural dehiscence of meningeal diverticula ( perineural cyst)Ī meningeal diverticulum can be simple (type 2a) or complex (type 2b)Ĭongenital focal absence of dura ( nude nerve root): rare Secondary to degenerative dural tears (typically related to calcified thoracic disc protrusions)Ī dural tear can be ventral (type 1a) or lateral (type 1b) Spontaneous intracranial hypotension is usually the result of a CSF leak in the spine. A decrease in CSF volume leads to compensatory dilatation of the vascular spaces, mostly the venous side due to its higher compliance. Intracranial hypotension most commonly results from a CSF leak somewhere along the neuraxis and leads to alterations in the equilibrium between the volumes of intracranial blood, CSF, and brain tissue ( Monro-Kellie hypothesis). Also uncommon, and potentially masking the underlying presence of hypotension is the development of cerebral venous thrombosis, said to occur in approximately 2% of cases of intracranial hypotension 23. Occasionally, presentation is more sinister, with reported cases of decreased level of consciousness and coma 3. Note that if done fluoroscopically, lumbar puncture should be performed in a lateral position to allow for accurate measurement of pressure. It is confirmed by an opening pressure on lumbar puncture of less than <6 cm H 2O 17. Such would be the case with cerebrospinal fluid (CSF) leak following sinus surgery, pituitary surgery or basal skull fractures. In cases of traumatic or iatrogenic intracranial hypotension, a history of abundant, clear rhinorrhea or otorrhea can sometimes be elicited. The condition often presents as a postural headache which is relieved by lying in a recumbent position, usually within 15-30 minutes 12. Of interest, this is a similar demographic to idiopathic intracranial hypertension, which is believed to be an unrecognised predisposing factor.Įpidemiology of secondary intracranial hypotension is variable and matches that of the underlying cause. Spontaneous intracranial hypotension is typically encountered in middle age (30-50 years of age) and has a predilection for women (F:M = 2:1).
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