PVL typically begins with numerous, small areas of necrosis, followed in more severe cased by cystic formation and more diffuse white matter injury. Newborns typically exhibit few or no signs of white matter injury, and PVL can easily be missed if routine screening is not performed. Furthermore, prematurity, extreme stiffness, and / or poor ability to suckle should alert the physician that there may be white matter damage.
The preliminary diagnosis of PVL often is made using head imaging technologies. Soon after an at-risk baby is born, physicians typically order an ultrasound to determine if the baby has white matter damage. However, the low sensitivity of an ultrasound allows for some white matter injury to be missed. Magnetic resonance imaging (MRI) is much better than an ultrasound at identifying PVL. MRI can show lesions that are less than 0.5 cm, as well as noncystic PVL, while an ultrasound typically cannot. An MRI should be performed on infants who had a difficult course of development, especially if there was prematurity, maternal or fetal infection, a known hypoxic / ischemic event during or right after birth, or a traumatic head injury.
Computed tomography, or CT scanning, is less useful for the diagnosis of PVL in very preterm infants because it detects fewer lesions than does MRI or ultrasound. In older infants, however, CT can identify the loss of periventricular white matter, as well as ventricular enlargement. Even with the best head imaging, however, some white matter damage will be missed and films will be read as normal.
Modes and timing of diagnostic techniques include the following:
- Although PVL often cannot typically be seen on an initial ultrasound scan in the first 24 hours after brain insult, the scan will usually show periventricular damage after 24 hours of life. If there are cystic changes they will usually be seen after approximately 1 – 3 weeks. This emphasizes the importance of serial scans.
- Routine ultrasound screening should be performed on all infants with a gestational age less than 33 weeks, or with birth weight less than 1500 grams to identify abnormalities in the brain. Screening should also be performed in all births where birth trauma is suspected.
- Screening should be performed to detect IVH (brain bleeds), with an initial scan being performed on extremely low birth weight infants at risk for abnormalities.
- When abnormalities are detected, more frequent examinations are performed to assess the progression of PVL.
- MRI should be used for better assessment of the extent of white matter damage. An MRI has better sensitivity and specificity than ultrasound and CT scans and can show injury at 1 day of age.