**5. Assessment of intracranial hypertension and hydrocephalus syndrome**

#### **5.1 CSF infusion test or infusion-load test (ILT)**

ILT with the calculation of resorption resistance of the CSF was one of the fundamental methods in choosing of surgical treatment of patients with hydrocephalus [9].

#### **Figure 3.**

*A—Bolus INT circuit with recorded parameters: Po—initial liquor pressure; Pp—maximum pressure after bolus injection. Pt—liquor pressure after bolus injection after 1 minute in the relaxation phase; ΔV—volume of injected fluid. B is the type of pulse wave of ICP with a compensated state of intracranial compliance. P1—Systolic peak, P2—Vascular peak, P3—Diastolic peak. C—pathological Lundberg waves of type B caused by an increase in ICP without depletion of intracranial compliance. D—pathological Lundberg waves of type A caused by increased ICP with depletion of intracranial compliance.*

During ILT, the bolus infusion technique of A. Marmarou is used. To do this, a ventricular catheter is inserted into the cavity of the lateral ventricle. The distal part of the ventricular catheter is connected to the ILT system. Within 2 minutes the background intracranial pressure, background spectral components of wave oscillations are recorded. Next, a saline solution is injected with a bolus volume of 2 ml at a rate of 1 ml/sec with an interval between boluses of 1 min [4, 10, 15, 17] (**Figure 3**, **A**).

From the ratio of the injected volume, the magnitude of the maximum increase in pressure and pressure after 1 minute during the relaxation period, according to A. Marmarou's formula, both the production rate (A) and the resorption resistance index (R) (a value proportional to the inverse value of its absorption) are calculated using an infusion-liquor test, which is based on excretion and administering a certain volume of CSF by boluses or once and measurement of the time during which the cerebrospinal pressure is restored as a result of CSF production or suction [15, 25].

The calculation is carried out according to the formulas:

1.CSF production rate (A) (Eqs. (3) and (4)):

$$\frac{\Delta V\_1 \cdot \lg\left(\frac{P\_1}{P\_m}\right)}{t\_1 \cdot \lg\left(\frac{P\_0}{P\_m}\right)}\tag{3}$$

2.CSF resorption resistance (R) (Eq. (4)):

*CSF Bypass Surgery in Children with Hydrocephalus: Modern Possibilities, Prospects… DOI: http://dx.doi.org/10.5772/intechopen.110871*

$$
\Delta V\_2 \cdot \lg \left[ \frac{P\_2 \cdot \left( P\_p - P\_0 \right)}{P\_p \cdot \left( P\_2 - P\_0 \right)} \right] \tag{4}
$$


The evaluation of ILT results consists in the determination of intracranial pressure, fluctuations of CSF (amplitude-frequency changes), as well as registration of resorption resistance of CSF, followed by obtaining one of the variants of pressure-volume curves (P/V): normotensive, hypertensive, and atrophic [15].

#### **5.2 Monitoring biomechanical properties of CSS in case of ICH**

Currently, discrete values of intracranial pressure are of low practical importance, since they do not display indicators of intracranial compliance (ICC). To assess the severity of the pathological process in patients with increased ICP of various etiologies, including hydrocephalus and congenital malformations of the skull bones, an assessment of the pulse curve recorded when measuring ICP is used. These changes are typical of ICC changes of any etiology and characterize the amplitude of pulse oscillations, the morphology of pulse curve peaks, and the formation of plateau waves with a significant decrease in compliance. The classical view of the pulse curve is shown in **Figure 3**, **B**.

One cardiac cycle forms three peaks due to the increase in intracranial volume in the systole and its decrease in the diastole.

Accordingly, the P1 (systolic) peak turns out the most pronounced one on the normal ICP curve. Immediately upon reaching the pulse wave of the microcirculatory bed of the brain, a P2 peak should appear as the reaction of the arterial bed muscular layer to compensate systolic pressure and normalize the curve, and reduce the amplitude of pulse oscillations. At the moment of diastole, a dicrotic P3 peak is formed, which characterizes a decrease in intracranial blood volume and relaxation of the vascular bed. The morphology of the pulse curve depends on the initial state of the ICC and the volume of increase in the intracranial contents, which manifests clearly and underlies the infusion-load testing.

Formulas were used for discrete assessment of biomechanical properties and liquor circulation [15]:

$$PVI\_d = \frac{dV\_b}{\lg\frac{\left(meanICP\_p\right)}{\left(meanICP\_o\right)}}\tag{5}$$

where PVId is the discrete value of the PVI index; meapISRo is the average liquor pressure before bolus administration; mean ICPp is the average liquor pressure after bolus administration; dVb is injected (with a plus sign)/output volume (with a minus sign) of the bolus, ml.

$$C\_d = \frac{0,4343 \cdot PVI\_d}{memICP\_o} \tag{6}$$

where *Cd* is a discrete assessment of craniospinal compliance.

$$I\_d = \frac{PVI\_d \lg\left[\frac{\left(memICP\_p\right)}{\left(memICP\_t\right)}\right]}{dT} \tag{7}$$

where Id is a discrete estimate of the rate of resorption/production of CSF; dT is the time interval in minutes from the moment of bolus injection/withdrawal to the current meanICPt average pressure.

$$R\_d = \frac{dT \cdot meanICP\_o}{PVI\_d \lg\left[\frac{meanICP\_t\left(meanICP\_p - meanICP\_o\right)}{(meanICP\_t - meanICP\_o)meanICP\_p}\right]}\tag{8}$$

where Rd. is a discrete estimate of the resorption resistance of the CSF.

In addition to changes in the pulse curve, the classic signs of an increase in ICP and a decrease in ICC are the appearance of pathological plateau waves (Lundbergwaves) on the ICP monitoring chart. There are three types of waves—A, B, C—while only type B and C waves are indicative of this or that change in compliance. Type C waves are associated with respiratory and cardiac cycles, manifested by an increase in ICP of a small amplitude. Their duration does not exceed the specified cycles. Type B waves are manifested by an increase in ICP to 30–50 mmHg and a duration of 1–5 minutes (**Figure 3**, **C**). Most often, the appearance of these waves is considered to provoke ICC without its obvious depletion. The appearance of type A waves—prolonged, up to 40 minutes, persistent increases in ICP up to 50 mmHg and above—is associated with the depletion of ICC (**Figure 3**, **D**).

The universality of these parameters resulting from compliance changes of any etiology seems to be significant. The identification of the ICP increase plateau is a significant diagnostic criterion for "latent" ICH, which is most often encountered in the long course of the pathological process. HCG in hydrocephalus can serve as an example of such condition, developing in patients with congenital malformations of the skull bones, or in patients with subcompensated forms of hydrocephalus in the neonatal period, when classical clinical signs of ICH are extremely rare.

#### **5.3 Imaging methods, indices of the ventricular system of the brain**

Modern imaging methods make it possible to identify hydrocephalus, establish the cause of the development of this process, conduct dynamic observation, and evaluate the effectiveness of the performed liquor bypass surgery. Currently, magnetic spiral computed tomography (MSCT) is considered to be the optimal method of radiation diagnosis of hydrocephalus, the use of which allows you to quickly measure the size and count the indices of the ventricular system of the brain, which is especially important in childhood when planning surgical treatment [26, 27].

*CSF Bypass Surgery in Children with Hydrocephalus: Modern Possibilities, Prospects… DOI: http://dx.doi.org/10.5772/intechopen.110871*

When interpreting the conducted radiation examination, the symmetry, degree of expansion, configuration, and contours of the ventricular system are taken into account.

**The index of the anterior horns of the lateral ventricles** is calculated in relation to the maximum distance between the most distant external parts of the anterior horns and the maximum bitemporal diameter of the skull multiplied by 100. Normally, the value of this index ranges from 25.4 (under the age of 5 years) to 29.4–31.0 (aged 71 to 80 years) (**Figure 4**, **A**).

**The index of the central sections of the lateral ventricles** is calculated with respect to the smallest distance between their outer walls in the recess area and the maximum bitemporal diameter of the skull on the same slice multiplied by 100. Normally, the value of this index ranges from 18.2 to 26.0 (**Figure 4**, **B**).

**The index of the III ventricle** is estimated in relation to its maximum width in the posterior third at the level of the pineal gland to the largest transverse diameter of the skull on the same section, multiplied by 100. Normally, the value of this index increases with age, reaching 3.0 at the age of 5 years and 4.8—from 71 to 80 years (**Figure 4**, **C**).

**The index of the IV ventricle** is calculated in relation to its largest width to the maximum internal diameter of the posterior fossa of the skull on the same slice. Normal indicators of this index are 11.9–14.0 (**Figure 4**, **D**).

Intraventricular hypertension is characterized by the appearance of periventricular edema, there are four stages of these changes:

Stage 1—blurring of the contours of the upper-outer corners of the anterior horns or a clearly limited border of reduced density of the same localization;

#### **Figure 4.**

*MSCT of the brain. Measurement for calculating the index of the anterior horns of the lateral ventricles (A), measurements for calculating the index of the central divisions of the lateral ventricles (B). Measurement for calculating the index of the III ventricle (C), measurements for calculating the index of the IV ventricle (D).*

Stage 2—reduction of density in the anterior and posterior horns;

Stage 3—edema along the perimeter of the lateral ventricles;

Stage 4—scalloped contours of the lateral ventricles and thinning of the brain substance.

Conducting magnetic resonance imaging (MRI) or MSCT with ventriculometry, in combination with a CSF examination, allows to timely diagnose hydrocephalus, to determine the severity and evaluate the results of the treatment.
