CRANIAL ULTRASOUND IMAGING


Ultrasound imaging of the head uses sound waves to produce pictures of the brain and cerebrospinal fluid. It is most commonly performed on infants, whose skulls have not completely formed. A transcranial Doppler ultrasound evaluates blood flow in the brain’s major arteries.

Ultrasound waves can't pass through bones. So an ultrasound to check the brain can't be done after the bones of the skull (cranium) have grown together. Cranial ultrasound can be done on babies before the bones of the skull have grown together. Or it can be done on adults after the skull has been opened with surgery. In adults, the test may be done to see brain masses during brain surgery.

WHAT IS BEING LOOKED FOR:

IN BABIES (USUALLY WHEN PREMATURE)

  • Periventricular leukomalacia (PVL). PVL is a condition in which the brain tissue around the ventricles is damaged. This may be caused by a lack of oxygen or blood flow to the brain that may have occurred before, during, or after birth.

  • Bleeding in the brain. This includes intraventricular hemorrhage (IVH).

  • To check a baby's large or increasing head size. The test can also check for infection in or around the brain such as from encephalitis or meningitis.

  • To check for brain problems that are present from birth such as congenital hydrocephalus

IN ADULTS (AFTER THE SKULL HAS BEEN OPENED):

  • To help find and evaluate brain mass such as a tumour during surgery

TRANSCRAINAL DOPPLER:

Is used to assess the risk of stroke in adults and children with sickle cell disease. It is also used to measure conditions affecting blood flow to and within the brain, such as:

  • Stenosis: a narrowing of a segment of a vessel, most commonly due to atherosclerosis (hardening of the arteries).

  • Vasospasm: a temporary narrowing of a vessel, usually a reaction to blood being present in the spinal fluid spaces surrounding the brain. This condition is known as subarachnoid hemorrhage (SAH).

TRANSCRANIAL DOPPLER ULTRASOUND:

Doppler ultrasound, a special application of ultrasound, measures the direction and speed of blood cells as they move through vessels. The movement of blood cells causes a change in pitch of the reflected sound waves (called the Doppler effect). A computer collects and processes the sounds and creates graphs or color pictures that represent the flow of blood through the blood vessels.

WHAT IS SEEN:

LENGTH OF THE EXAM:

15 to 30 minutes.

THE MEASUREMENTS:

The infant is positioned lying face-up. A clear, water-based gel is applied to the transducer to help the transducer make secure contact with the body and eliminate air pockets that can block the sound waves from passing into the body. The sonographer (ultrasound technologist) or radiologist then gently presses the transducer against the fontanelle (soft spot of the infant's head, which has no bone to block the passage of the sound waves).

If head ultrasound is used during brain surgery, a portion of the skull will be removed and the exposed brain examined for brain masses with the use of a transducer.

During a transcranial Doppler ultrasound, the patient is either positioned on his or her back on an examination table or seated upright in an examination chair. A clear water-based gel is applied on the back of the neck, above and lateral to the cheek bone, in front of the ear or over the eyelid, as these are sites for blood vessels that supply the brain. The transducer is gently pressed over one of these areas to measure the direction and speed of the flowing blood.

The patient will need to remain still during the examination, which may take up to 35 minutes. However, if the patient needs to adjust his or her position on the examination table, there is usually no problem in pausing for that time. If the examination is being performed on an infant, a nurse or radiologic technologist may assist with keeping the infant still to ensure the best imaging quality.

WHAT IS SEEN:

IMAGE: Normal brain and bleeding brain as seen through the fontanelle of a baby

Image: PVL Cranial ultrasound The recommendation for infants less than 30 weeks gestation is a screening ultrasound at 7-14 days and a repeat ultrasound at 30-40 weeks. Echodensities correlate with the acute phase of necrosis. They transition into coalescent echolucencies (cavities) that give the affected white matter a “Swiss cheese” appearance. Ultrasound is best for the detection of cystic PVL.

IMAGE: Encephalitis ultrasound (dog brain)

IMAGE: Thickened meninges. a Coronal sonogram through frontal lobes in an 11-week-old infant with group streptococcus group B meningitis demonstrates diffuse echogenic thickening of the leptomeninges (arrows) and prominent extra-axial fluid spaces (asterisk). b, c Coronal sonogram on a different infant with group streptococcus group B meningitis (b) shows marked thickening of the suprasellar cisterns (arrows), compared to a normal infant (c)

CHALLENGES OF THE TEST:

Ultrasound examinations are very sensitive to motion, and an active or crying child will slow the examination process.

Large patients are more difficult to image by ultrasound, because greater amounts of tissue weaken the sound waves as they pass deeper into the body.

Exam results could be altered, due to:

  • an open wound or recent surgical incision near the area being imaged.

  • changes in blood flow pattern as a result of heart disease or irregular heart rhythms.

IMAGES, TEXT, SOURCES, STUDIES:

https://www.webmd.com/brain/cranial-ultrasound#4

https://www.webmd.com/brain/cranial-ultrasound-2

http://neuropathology-web.org/chapter3/chapter3cPvl.html

#imaging #ultrasound

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