Neonatal Neurosonography

 

 

 

Neonatal Neurosonography is a very important and indispensable tool for evaluating pre-term and term neonates for intracranial pathology. It is readily available, portable, relatively inexpensive and safe. Premature infants are at a heightened risk for Intracranial hemorrhage. Up to 67% of pre-term infants born before 32 weeks gestational age develop intracranial bleeds. There is also a variety of intracranial pathologies that can be detected via ultrasound like; Hydrocephalus, Vascular anomalies, developmental abnormalities, and conditions related to infectious processes.

SbF7K6W7Phm9zmfQqoRM1T2B.pngAnatomy

A robust knowledge of Neuroanatomy is required for the execution and interpretation of these exams. The brain is divided into 3 main areas the cerebrum, cerebellum and brain stem. It has many convolutions called sulci and gyri that increase the surface area.
The Cerebrum is the most cephalad portion and consists of 4 lobes: frontal, parietal, temporal and occipital lobes. The separation of these lobes is by way of fissures, which are large grooves. Important ones that pertain to sonographic imaging are the Sylvian Fissures, Cingulate Gyrus and the Interhemispheric Fissure, which divides the brain into right and left hemispheres.
These hemispheres are connected by the Corpus Callosum (CC), a large bundle of nerver fibers that allow the hemispheres to communicate. There is a fluid filled sturcture right below that CC called the Septum Pellucidum. This structure is an important marker in the fetal brain to rule out structural anomalies.

VbkuJNhCWOlgCJpltgcDZQ_Ventricles_of_the_brain.png

Ventricular System

The ventricular system is a series of chamber deep within the brain the collect and allow the flow of cerebrospinal fluid. The main components are the paired lateral, third and fourth ventricles.

Within the ventricles are the choroid plexi, which line the bodies of the lateral ventricles, the roof of the third ventricle and a little bit in the fourth ventricle. The choroid plxus creates the cerebospinal fluid.

brain coronal.jpgBasal Ganglia

The basal ganglia is a group of grey matter structures found in the base of the brain that relate to the Thalamus and are important to movement and coordination.

Sonographically important structures:

Caudate Nucleus and Thalamus which form the Caudo-thalamic groove an area where grade I Hemorrhages occur due to the highly vascularized and fragile germinal matrix which lies just above it in the subependymal (under the ventricular lining), region.

Cerebellum

The cerebellum is another occipital bi-lobe structure which is also important motor control. It is located in the posterior fossa.

brain coronal with scan planes3.jpg

Technique

Scanning is usually performed with small footprint high frequency transducers for optimal resolution. The younger the neonate the higher the frequency that can be used. Full term and older babies may require a 5-7 mhz frequency to assure penetration to the deep structures in the Brain. Higher frequency linear transducers may be used to evaluate superior cortical structures/lesions and vasculature including the Superior Sagital Sinus.

We use primarily the anterior fontanelle using a coronal, sagittal and parasagittal views. Also we scan through the mastoid fontanelle (for the posterior fossa and cerebellar views) and posterior fontanelle (for posterior structures especially the occipital horn to detect dependent hemorrhage) and temporal views for further evaluation.

The exam should be done with the patient in the supine position, though you may encounter patients in various positions depending on their care. If the patient is in lateral decubitus the exam can still be done.
Patients may have multiple lines including venous and arterial lines, nasogastric and endotracheal tubes. Extra care must be taken when scanning these babies to avoid potentially dislodging of these catheters.

Paraventricular white matter should be less echogenic than the Choroid plexus
<32 weeks, brain is smoother
36 and greater more sulci and gyri and the ventricles are more slit like

Grade IV hemorrhage.png

Intracranial Hemorrhage of Prematurity

Germinal Matrix/Subependymal bleeds are believed to happen due to poor autoregulation of premature infants, sudden changes in pressure or oxygen saturation can cause sudden reperfusion which ruptures of the tiny delicate vessels

Etiologic Factors
Gestational Age
<32 weeks up 67% will have bleeds
Term Infants 5%
Low birth Weight <1500 gm
Hypoxia

Most of the Bleeds occur early
Day 1 50%
Day 2 25%
Day 3 15%
Day 4 10%
95% of all bleeds occur by day 9

The IVH is typically categorized into 4 grades

  • Grade I – Limited to the subependymal/germinal matrix, no blood in ventricle
  • Grade II – Blood ruptures the lining and starts to fill the ventricle, no ventriculomegaly
  • Grade III – Intraventricular blood with ventriculomegaly
  • Grade IV – Intraparenchymal (thought to occur from venous infarction)

Subependymal bleed will eventually liquify and undergo cystic degeneration. 80% extend into the Intraventricular region. 15% of bleeds will also develop in the parenchyma. It was though that Intraprenchymal bleeds started in the germinal matrix but now it is thought that they occur from venous infarcts.

 

Sequlae of ICH
Cysts
Encephalomalacia (necrosis of white matter with liquefaction and cavitation)               Ventricular Dilatation
-70% infants with IVH resolve or be mild
-15% will be severe
-15% or less require shunts

Outcomes of Grade Bleeds

Mortality                     Cerebral Palsy
Grade 1   0-12                                      15%
Grade 2   2-24 %                                 25%
Grade 3    8-32 %                                 50%
Grade 4   22-45                                    75%

Henry Suarez

Sources:

“State-of-the-Art Cranial Sonography: Part 1, Modern Techniques and Image Interpretation : American Journal of Roentgenology: Vol. 196, No. 5 (AJR).” State-of-the-Art Cranial Sonography: Part 1, Modern Techniques and Image Interpretation : American Journal of Roentgenology: Vol. 196, No. 5 (AJR). N.p., n.d. Web. 07 Nov. 2016.

Intracranial Neonatal Neurosonography An Update.

 

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