EDUCATION CORNER

Positive Pressure Myelogram: New Anesthetic Challenges in the Neuroradiology Suite

By Tasha Welch, MD
Sebastian Gatica, MD

Department of Anesthesiology and Perioperative, Mayo Clinic

Tasha Welch, MD
Tasha Welch, MD
Sebastian Gatica

Sebastian Gatica, MD

Spontaneous intracranial hypotension is a debilitating disorder with an incidence of five per 100,000 per year.1 Women are almost twice as likely as men to be affected by this disorder, with a peak incidence occurring in the fourth and fifth decades of life.2 The cause of spontaneous intracranial hypotension can be difficult to determine, but is often thought to be due to trivial trauma or weakness in the dural sac, which then causes cerebral spinal fluid leakage and low pressure of the cerebral spinal fluid. A dural venous fistula can also lead to intracranial hypotension.

This disorder is commonly characterized by orthostatic headache and low cerebral spinal fluid pressure. Other symptoms include possible neurologic deficits including cranial nerve impairments, hearing loss, tinnitus, visual impairments, dizziness, nausea, and back and neck pain.3 Diffuse meningeal enhancement on magnetic resonance imaging of the brain suggests chronic intracranial hypotension. However, other imagine techniques, such as myelography, will be required to identify the site of cerebrospinal fluid (CSF) leakage.4

Treatment of spontaneous intracranial hypotension can be complicated. Often this disorder is self-limited and can be treated with conservative measures such as supine positioning, caffeine supplementation, and oral or intravenous hydration. Conservative measures may not be successful and therefor patients may need to undergo epidural blood patch therapy. Patients who do not respond to conservative measures or epidural blood patch may need to undergo surgical dural repair. 

In both epidural blood patch treatment and surgical repair of the dura, it is important to localize the area of CSF leakage. At our institution, if the site of CSF leakage is not identified by traditional myelography, our radiologists perform positive pressure computerized tomographic (CT) myelograms to enhance the sensitivity of traditional myelography to localize the site of CSF leak or a CSF-venous fistula. The procedure begins with a lumbar intrathecal injection of around 70 ml of sterile saline to increase the CSF pressure to 60-70 mmHg. The idea is that the rapid increase in CSF pressure before the subsequent intrathecal contrast injection will drive the contrast out of the dural defect or fistula allowing for rapid diagnosis and localization of the CSF leak.

Increasing the CSF pressure to 60-70 mmHg transmits throughout the intrathecal space, potentially causing a significant elevation in intracranial pressure (ICP) to the same goal pressure as that in the lumbar intrathecal space.  With the elevation in ICP, cerebral perfusion pressure can potentially be impaired if there is if changes in systemic blood pressure do not compensate for the elevated ICP, potentially resulting in cerebral ischemia.   

Our current anesthetic management involves performing general anesthesia for each patient undergoing a positive pressure myelogram. This allows for adequate anesthetic coverage for the discomfort that is likely to accompany elevating the CSF pressure to 60 mmHg. In addition to utilizing standard ASA monitors, we employ continuous intra-arterial pressure monitoring for close calculation of cerebral perfusion pressure. Given the potential for cerebral ischemia, we also employ a cerebral oximeter as a guide for blood pressure management to aid in adequate cerebral perfusion. Blood pressure augmentation is often achieved with a phenylephrine infusion. However, some patients seem to maintain autoregulation and increase their systemic blood pressure without the need for augmentation.

Given the numerous potential changes in physiological parameters (elevated ICP, systemic hypertension, vasopressor augmentation of blood pressure) throughout these procedures it is important for each patient to be screened prior to the procedure to ensure they are a candidate. This often falls into the anesthesiologist’s responsibility as the person with the most knowledge about the physiologic changes occurring. Patients should not have regurgitant valvular heart disease or severe coronary artery disease where systemic vasoconstriction could lead to worsening of the regurgitant volume or increased afterload. Patients should not have cerebral or other vascular aneurysms as increasing systemic pressure could lead to aneurysmal rupture. 

Positive pressure myelograms are a new and developing procedure for diagnosis and localization of CSF leaks and dural-venous fistulas.  If this technique is proven to be more accurate and successful at diagnosis and localization, it may become more prevalent in the neuroradiology suites. Neuroanesthesiologists and neurointensivists should be aware of this procedure and the possible physiologic consequences. Proper patient screening and selection is of utmost importance to ensure patient safety. The anesthetic management continues to develop along with the procedure but as always, the goal is to provide safe anesthetic care.

References:

  1. Forghani R, Farb RI. Diagnosis and temporal evolution of signs of intracranial hypotension on MRI of the brain. Neuroradiology, 2008; 50(12):1025-34.
  2. Schievink WI,  Nuño M, Rozen TD, et al: Hyperprolactinemai due to sponataneous intracranial hypotension. J Neurosurg, 2015; 122(5):1020-25.
  3. Sainani NI, Lawande MA, Pungavkar SA, et al. Spontaneous intracranial hypotension: A study of six cases with MR findings and literature review. Australas Radiol, 2006; 50(5):419-23.
  4. Verdoorn JT, Luetmer PH, Carr CM, et al. Predicting high-flow spinal CSF leaks in spontaneous intracranial hypotension using a spinal MRI-based algorithm: Have repeat CT myelograms been reduced? Am J Neuroradiol 2015; 37:185-88.

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