Two Cases of Secondary Intracranial Hypotension

The unique symptom of intracranial hypotension (IH) is an orthostatic headache caused by low cerebrospinal fluid (CSF) pressure and is not so rare. IH results from loss of CSF caused by a dural defect in the spine, cranial vault, or skull base. The classic orthostatic headache commences within 15 minutes, but occasionally symptoms last up to several hours, after standing or upright sitting position. The criteria of the International Classification of Headache Disorders are widely used to diagnose this type of headache. These criteria require at least one of the following to confirm the diagnosis of IH; low CSF pressure; diffuse pachymeningeal enhancement of brain MR imaging; or evidence of CSF leakage on conventional myelography, CT myelography, or radionuclide cisternography (RNC). However, low CSF pressure is not always present in IH. A broad spectrum of neuroimaging features has also been recognized in patients with IH, particularly diffuse dural enhancement and sagging of the brain on MR imaging. However, such diagnostic abnormalities are not always detected. RNC and CT myelography are the spinal imaging studies which have been used for identification of the actual site of a CSF leakage. However, in general, neurologists or neurosurgeons do not routinely perform these studies because these invasive modalities required a dural puncture, so that it may worsen the patient’s condition; also there are some debates regarding appropriate timing of study. At our institution, RNC is routinely performed for patients suspected of having IH. In this case series, we report two patients in whom IH was suspected. One case showed a false localizing CSF leakage, while the other case showed progressive subdural hematoma (SDH) after epidural blood patch (EBP). The purpose of this case series is to describe the clinical and imaging features of patients with IH.