Transorbital Ultrasonographic Measurement of Optic Nerve Sheath Diameter in Brain Death

Ultrasonographic measurement of optic nerve sheath diameter (ONSD) can successfully be used to estimate intracranial pressure (ICP) elevation. Its utility in corroboration of brain death (BD) was herein studied.

ONSD was measured in 29 subjects with BD; in 19 comatose patients (with raised ICP in 11), 20 patients with various neurological diseases, and 40 healthy control subjects. The distance between the inner and outer edges of the echolucent lines around hyperechoic area surrounding the optic nerve (ON) was identified as ONSD external (ONSDe) and ONSD internal (ONSDi).

Compared to patients with neurological diseases (5.75 ± .79 mm) or healthy controls (5.98 ± .63 mm), ONSDe was significantly higher in comatose patients (7.61 ± .97 and 6.71 ± 1.07 mm in those with and without raised ICP) and BD subjects (8.34 ± .66 mm). ONSDi showed similar trends across the groups: 6.09 ± .71 mm in BD; 5.89 ± .37 mm in comatose control with elevated ICP; 5.16 ± .49 mm in comatose control with normal ICP; 4.36 ± .68 mm in neurological control; 4.69 ± .67 mm in healthy control. The accuracy of ONSDe measurements in differentiating patients with ICP elevation (n = 40) was .965 as determined by area under the curve (AUC) of receiver-operator characteristics curves. Similarly, accuracy in discrimination of BD was .952. However, ONSDe showed limited yield to identify BD cases among comatose patients with Glasgow coma scale score of 3, where accuracy was .803 (95% CI: .709-.816) and decreased further to .722 (95% CI: .610-.816) when analyses were restricted to comatose patients with ICP elevation. AUC values for ONSDi was similar or lower.

ONSD is significantly greater in subjects with BD. However, quantification of ONSD cannot discriminate BD subjects from comatose ones with raised ICP with 100% certainty.