Intracranial hypotension, or low cerebrospinal fluid (CSF) pressure, should be suspected in a patient with a positional headache that worsens within 15 minutes of standing and improves with recumbency. The positional component of the headache may become less prominent or absent over time if the intracranial hypotension is untreated. Patients can also experience nonspecific symptoms such as dizziness, photophobia, blurred vision, nausea, vomiting, and neck pain and stiffness. Uncommonly, spinal manifestations of intracranial hypotension may appear, including radiculopathies, myelopathy secondary to compression by an extradural fluid collection or enlarged venous plexus, or bibrachial amyotrophy from a ventral extradural fluid collection. Some patients with intracranial hypotension have nonpositional headaches or present without headache. In these patients, intracranial hypotension is suggested by findings on magnetic resonance imaging (MRI). Classic MRI findings in intracranial hypotension include diffuse dural enhancement, subdural fluid collections, pituitary enlargement, brainstem sagging (such as descent of the mammillary bodies and narrowing of the interpeduncular fossa), and tonsillar descent through the foramen magnum (pseudo-Chiari malformation). The presence of any of these findings on brain MRI should raise the possibility of intracranial hypotension; no one finding is consistently present in all cases. Diffuse dural enhancement is the most common MRI finding, but this may disappear with prolonged intracranial hypotension.
Intracranial hypotension is a common complication of lumbar puncture (LP) and can also complicate more invasive procedures that disrupt the dura, such as the administration of spinal anesthesia or spinal or sinus surgery. In cases of iatrogenic intracranial hypotension, further brain imaging is not necessarily required depending on the context.
Intracranial hypotension can occur spontaneously secondary to a dural tear or fistula between the cerebrospinal fluid and the venous system. In a patient with clinical symptoms, an MRI brain with gadolinium is the preferred imaging modality to confirm the diagnosis. However, this can be normal in up to 20% of patients with low CSF pressure. If there remains high clinical suspicion, an LP can be performed to assess the opening pressure taking care not to exacerbate symptoms. Low CSF pressure is defined as less than 6 cm H 2 O; note that opening pressure must be measured in the lateral decubitus position. A normal opening pressure does not exclude a diagnosis of intracranial hypotension.
Regardless of etiology, mild to moderate symptoms associated with intracranial hypotension should be treated with conservative measures that aim to restore CSF volume, including strict bed rest, oral or intravenous hydration, and high-dose caffeine intake.
If symptoms persist despite conservative management, a blind epidural blood patch should be performed. An epidural blood patch involves the injection of 5–10 cc of autologous blood into the epidural space. While an epidural blood patch can result in immediate clinical improvement, up to 50% of patients require more than one.
If symptoms persist despite epidural blood patches, spinal imaging should be performed to attempt to identify the site of CSF leakage. Common findings on MRI spine with gadolinium include an extradural fluid collection or engorgement of the epidural veins.
If MRI spine is normal or nondiagnostic, computed tomography (CT) or MR myelogram or radioisotope cisternography should be pursued. CT and MR myelogram are preferred as they provide better spatial resolution.
If the site of CSF leakage is known, a targeted epidural blood patch or epidural patching with fibrin glue may be performed at the corresponding level. If nonsurgical therapies are unsuccessful, surgical repair can be considered, which involves the placement of sutures or metallic clips around dural tears or leaking meningeal diverticula.