Optic Nerve Sheath Diameter
Optic Nerve Sheath Diameter (ONSD) has been used to estimate intracranial pressure since the late 1990s, but a cut off in children has been hard to determine. These authors from India attempted to find such a cut off.
What did they do? They took 125 children (aged 1-12, average age 6 years) admitted to the PICU and broke them up into 3 groups. There was a group with neurologic complaints found to have increased ICP (Group A- 40 patiens) based on symptoms AND fundoscopy (performed by an ophthalmologist) or CT scan findings consistent with ICP, a second group with neurologic complaints without evidence of increased ICP (Group B- 45 patients), and a third group without any neurologic complaints (Group C- 40 patients). They measured the ONSD in all of these patients and made note of optic-disc elevation (ODE) as well as "crescent sign" (a hypoechoic shadow within the optic nerve). Notably this was a very sick cohort, with 16% mortality in the cohort.
What did they find? Group A had an average ONSD of 5.48mm, Group B had an average of 5.14mm, and Group C had an average of 4.5mm. Crescent sign and ODE were significantly more common in Group A, but also notable in Group B. They calculated a cut off of 4.9mm to be 90% specific and 46% sensitive, with an area under the curve of 0.67.
Another interesting thing they did is to measure the ONSD 30 minutes after the patients were given hypertonic saline or mannitol. They found a significant reduction in ONSD in both Group A and Group B.
Bottom line: ONSD is a great screening tool for increased ICP. It is highly sensitive, but very non-specific. I will start using ~4.9mm as my cut off for considering further work-up.
What did they do? They took 125 children (aged 1-12, average age 6 years) admitted to the PICU and broke them up into 3 groups. There was a group with neurologic complaints found to have increased ICP (Group A- 40 patiens) based on symptoms AND fundoscopy (performed by an ophthalmologist) or CT scan findings consistent with ICP, a second group with neurologic complaints without evidence of increased ICP (Group B- 45 patients), and a third group without any neurologic complaints (Group C- 40 patients). They measured the ONSD in all of these patients and made note of optic-disc elevation (ODE) as well as "crescent sign" (a hypoechoic shadow within the optic nerve). Notably this was a very sick cohort, with 16% mortality in the cohort.
What did they find? Group A had an average ONSD of 5.48mm, Group B had an average of 5.14mm, and Group C had an average of 4.5mm. Crescent sign and ODE were significantly more common in Group A, but also notable in Group B. They calculated a cut off of 4.9mm to be 90% specific and 46% sensitive, with an area under the curve of 0.67.
Another interesting thing they did is to measure the ONSD 30 minutes after the patients were given hypertonic saline or mannitol. They found a significant reduction in ONSD in both Group A and Group B.
Bottom line: ONSD is a great screening tool for increased ICP. It is highly sensitive, but very non-specific. I will start using ~4.9mm as my cut off for considering further work-up.
