Non-invasiveness, non- ionizing, portability, and cost effectiveness are the factors that render ultrasound more useful than any other modality for imaging ICH. Prematurity and low birth weight are the two major risk factors that make an infant susceptible to ICH. Hypoxia in these infants causes variability in the blood pressure resulting in the tearing of the fragile cerebral vessels, especially in the germinal matrix.
Ultrasound grading of ICH [as I, II, III – A/ B/ C and IV] helps in identifying the infants at risk for developing structural damage and also those who might require intervention. The germinal matrix is recognized as the earliest site for ICH in premature infants. Germinal matrix hemorrhage [GMH- grade I bleed] is recognized as an echogenic mass inferolateral to the frontal horns of the lateral ventricles. It may compress the ipsilateral ventricle, undergo subsequent liquefaction and may form a subependymal cyst.
IVH appears as bright echoes within the ventricles or bulky enlargement of the choroid plexus, and may result from an extension of GMH in premature infants. Early grades of IVH with no ventriculomegaly may be difficult to detect by ultrasound. A blood – CSF level may be noted. In the advanced grades, the entire ventricle may be filled with blood. Resolution of the hemorrhage results in liquefaction of the clot, with decrease in size and echogenicity and retraction of the clot from the wall. Fragmentation may occur and clot pieces may be seen moving within the ventricle. Ventricular enlargement usually resolves, but may persist as obstructive post hemorrhagic hydrocephalus, communicating hydrocephalus secondary to arachnoiditis or due to inflammatory ependymitis.
Intraparenchymal hemorrhage [IPH] i.e. grade IV ICH is the most severe form. IPH is now considered to be a form of periventricular hemorrhagic infarction, which is a venous infarct and is a strong prognosticator of poor neurological outcome. The initial bleed is brightly echogenic, usually fronto-parietal and may cause a mass effect. A porencephalic cyst communicating with the ipsilateral ventricle is usually the sequela to IPH.
In term infants IVH may occur from the choroid plexus, with no associated GMH. In the term infant asphyxia, birth trauma, apnea, seizures and coagulation defects have been implicated in cerebral hemorrhage. Other sites for ICH include subarachnoid space and the cerebellum. Subarachnoid hemorrhage findings are subtle and may be seen as widening of the horizontal portion of the Sylvain fissure with increased echogenicity. Isolated subarachnoid bleed is more common in term infants than neonates. Cerebellar hemorrhage is rare, associated with poor prognosis and is seen as an echogenic area within the cerebellum with non-visualization of the 4th ventricle. Subdural and epidural hemorrhages are difficult to detect with ultrasound, and may necessitate the use of a standoff pad.