Optical Detection of Intracranial Pressure and Perfusion Changes in Neonates With Hydrocephalus

Abstract

Objective: To demonstrate that a novel noninvasive index of intracranial pressure (ICP) derived from diffuse optics-based techniques is associated with intracranial hypertension.

Study design: We compared noninvasive and invasive ICP measurements in infants with hydrocephalus. Infants born term and preterm were eligible for inclusion if clinically determined to require cerebrospinal fluid (CSF) diversion. Ventricular size was assessed preoperatively via ultrasound measurement of the fronto-occipital (FOR) and frontotemporal (FTHR) horn ratios. Invasive ICP was obtained at the time of surgical intervention with a manometer. Intracranial hypertension was defined as invasive ICP ≥15 mmHg. Diffuse optical measurements of cerebral perfusion, oxygen extraction, and noninvasive ICP were performed preoperatively, intraoperatively, and postoperatively. Optical and ultrasound measures were compared with invasive ICP measurements, and their change in values after CSF diversion were obtained.

Results: We included 39 infants, 23 with intracranial hypertension. No group difference in ventricular size was found by FOR (P = .93) or FTHR (P = .76). Infants with intracranial hypertension had significantly higher noninvasive ICP (P = .02) and oxygen extraction fraction (OEF) (P = .01) compared with infants without intracranial hypertension. Increased cerebral blood flow (P = .005) and improved OEF (P < .001) after CSF diversion were observed only in infants with intracranial hypertension.

Conclusions: Noninvasive diffuse optical measures (including a noninvasive ICP index) were associated with intracranial hypertension. The findings suggest that impaired perfusion from intracranial hypertension was independent of ventricular size. Hemodynamic evidence of the benefits of CSF diversion was seen in infants with intracranial hypertension. Noninvasive optical techniques hold promise for aiding the assessment of CSF diversion timing.

Keywords: diffuse correlation spectroscopy; near-infrared spectroscopy; shunt.

Figure 1.

(A) Schematic of optical probe placement, as it was manually held against the forehead during data acquisition. (B) Timeline of the study’s preoperative, intraoperative, and postoperative measurements encompassing cerebrospinal fluid (CSF) diversion surgery. (C) Study design for intraoperative measurements, which include right and left hemisphere optical measurements, a cuff blood pressure (BP) measurement, and an invasive intracranial pressure (ICP) measurement obtained during cerebrospinal fluid (CSF) diversion surgery. (D) Study design for preoperative and postoperative measurements.

Figure 2.

Patient flow chart.

Figure 3.

Association of noninvasive optical and ultrasound biomarkers with intracranial hypertension defined as an invasive intracranial pressure (ICP) measurement of ≥15 mmHg. Units for CBF and CMRO₂ indices are 10⁻⁹ cm²/s and 10⁻⁴ μM cm²/s, respectively. All boxplots show the median ± interquartile range.

Figure 4.

(A) Intraoperative non-invasive ICP (nICP) was correlated with ICP acquired during CSF diversion surgery (solid line is the linear best fit, dashed line is line of unity). (B) Bland-Altman plot of the difference between nICP and ICP (solid line indicates the mean difference; dashed lines indicate the 95% limits of agreement, i.e., the mean ± 1.96 times the standard deviation of the difference). (C) Preoperative fronto-occipital horn ratio (FOR) and (D) fronto-temporal horn ratio (FTHR) as measured on brain ultrasound were not correlated with ICP (solid lines are the linear best fit).

Figure 5.

Changes in optical biomarkers from before to after cerebral spinal fluid (CSF) diversion surgery, dichotomized by our definition of intracranial hypertension as an intracranial pressure (ICP) of ≥ 15 mmHg. ΔnICP is the difference between postoperatively and intraoperatively measured non-invasive ICP (nICP). Relative oxygen extraction fraction (rOEF), cerebral blood flow (rCBF), cerebral metabolic rate of oxygen (rCMRO₂), and total hemoglobin (rTHC) are expressed as postoperative-to-intraoperative ratios. ΔStO₂ is the difference between postoperatively and intraoperatively measured tissue oxygen saturation. P-values indicate whether the mean change was different from zero. All boxplots show the median ± interquartile range.