Chapter 15

Although recent improvements in neuroimaging and neuromonitoring have added insight into the developing brain and have brought information to the bedside to help the clinician identify infants at risk for poor neurologic outcome, available techniques continue to be limited in their ability to predict future intelligence and motor, language, and problem-solving skills accurately. Moreover, given the enormous plasticity of the neonate's brain, even significant defects detectable with these tests may result in "normal" neurodevelopmental outcomes. Nevertheless, these modalities hold future promise in assisting clinicians to better identify and refer patients at risk.

1. Neuroimaging

1. Ultrasonography

• Definition. By using the bone window of a fontanelle, sound waves are directed into the brain and reflected according to the echodensity of the underlying structures. The reflected waves are used to create two- and three-dimensional images.

• Indication. Ultrasonography is the preferred tool for identification and observation of germinal matrix/intraventricular hemorrhage and hydrocephalus and is valuable in detecting midline structural abnormalities, hypoxic-ischemic injury, subdural and posterior fossa hemorrhage, ventriculitis, tumors, cysts, and vascular abnormalities. Ultrasonography of the developing cingulate sulcus has been suggested to reflect gestational age (see sample studies in Chapter 10).

• Method. A transducer is placed over the anterior fontanelle, and images are obtained in coronal and parasagittal planes. The posterior fontanelle is the preferred acoustic window for the imaging of the infratentorium, including brainstem and cerebellum. Advantages of this technique include high resolution, convenience (performed at the bedside), safety (no sedation, contrast material, or radiation), noninvasiveness, and low cost compared with other imaging studies. Disadvantages include the lack of visualization of nonmidline structures, especially in the parietal regions, and the lack of differentiation between gray and white matter.

• Results. The integrity of the following structures may be evaluated with ultrasonography: all four ventricles, the choroid plexus, caudate nuclei, thalamus, septum pellucidum, and corpus callosum.

1. Doppler ultrasonography

• Definition. Like regular ultrasonography, this technique uses a bone window to direct sound waves into the brain. Moving objects (eg, red blood cells) reflect sound waves with a shift in frequency (Doppler shift) that is proportional to their speed. These changes are measured and expressed as the pulsatility index. The angle of the probe in relation to the flow affects the Doppler shift and requires exact standards for serial measurements.

• Indication. Knowing the cross section of the vessel (area), Doppler ultrasonography can provide information on cerebral blood flow (CBF) and resistance.

Changes in CBF and resistance have been noted in a variety of pathologic states. Doppler ultrasonography is of clinical value in states of cessation of CBF (eg, brain death or cerebrovascular occlusion), states of altered vascular resistance (eg, hypoxic-ischemic encephalopathy, hydrocephalus, or arteriovenous malformation), and ductal steal syndrome.

• Method. Combined with conventional ultrasonography to identify the blood vessel, Doppler ultrasonography produces a color image indicating flow (red, toward the transducer; blue, away from the transducer). CBF velocity is measured as the area under the curve of velocity waveforms. Small body weight and low gestational ages negatively influence the success ...

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