Idiopathic intracranial hypertension (IIH), sometimes referred to as pseudotumor, occurs when fluid around the brain and spinal cord builds up in the skull, raising intracranial pressure (ICP). This, in turn, puts increased pressure on the optic nerve and may result in vision loss. A recent study pulled data from patients who underwent MRI and lumbar puncture in the Mayo Clinic Study of Aging (MCSA) to determine the prevalence of indirect signs of raised ICP on MRI and whether or not these signs correlated with lumbar puncture opening pressure, the value used to measure IIH. The authors reported that while ICP isn’t a dependable biometric in isolation, associated MRI findings such as decreased pituitary gland size are important to consider when identifying patients with pathologically high ICP.
The researchers included MCSA participants who had had an MRI within three months of a lumbar puncture with opening pressure data. They evaluated MRIs for signs of increased ICP, including pituitary to sella ratio, cerebellar tonsillar ectopia and optic nerve sheath diameter. Potential influences from body mass index and obstructive sleep apnea were also noted as possible correlations.
A total of 597 MCSA patients were included in the analysis (260 female, 43.6%). Median age was 70.7 years and median opening pressure was 152mm H2O (pressures of 200mm H2O to 250mm H2O are considered borderline elevated and those 250 and above are considered elevated). A total of 91 (15.2%) participants had an opening pressure of 200mm H2O or greater. The researchers found empty or partially empty sella in 81 patients (12.8%). They also noted a decreased pituitary to sella ratio with increasing opening pressure, and a weak correlation between opening pressure and average optic nerve sheath diameter, which wasn’t significant when accounting for age, sex and BMI. They found no correlation between opening pressure and cerebellar tonsilar ectopia. Obstructive sleep apnea was associated with increased optic nerve sheath diameter but wasn’t significant after adjusting for age, sex and BMI.
“Smaller pituitary gland size correlated with increasing opening pressure,” the researchers noted. “This study has demonstrated the frequency with which increased optic nerve sheath diameter, empty sella and cerebellar tonsilar ectopia occur in a normal population.”
In isolation, it would seem that any one of these radiologic findings would poorly serve as independent diagnostic signs for increased ICP. Based on the observation that these radiologic features can be seen in normal individuals, [suggesting that ICP is a continuum], using these signs alone in all patients with headaches would lead to an overdiagnosis of IIH because of the relative rarity of IIH compared with headaches in the general population.
“We wouldn’t recommend lumbar puncture unless the clinical suspicion for increased ICP is high, because lumbar punctures have potential risks and the opening pressure can be quite variable,” they added. They noted also that the study population was mostly over the age of 60 and white, limiting the generalizability of the results to a more diverse population.
Witsberger EM, Huston III J, Cutsforth-Gregory JK, et al. Population-based evaluation of indirect signs of increased intracranial pressure. J Neuro-Ophthalmol. July 21, 2021. [Epub ahead of print].