Dr Rajesh Umap Asso Prof Dept of Radiodiagnosis CRANIAL USG Dr Rajesh Umap Asso Prof Dept of Radiodiagnosis

CRANIAL USG v CT AND MRI Possible to perform on critically ill patients. Cranial ultrasound is relatively inexpensive, does not require sedation or radiation, and offers the important benefit of being portable. Past studies comparing the utility of cranial ultrasound to MRI have not taken into account modern technology and rigorous ultrasound scanning technique. Recent studies using such techniques have shown that cranial ultrasound is diagnostically accurate compared with MRI and useful to determine initial clinical management.

TECHNIQUE Linear array transducer via the anterior fontanel in the coronal and sagittal planes. Typically, six to eight coronal images are obtained beginning at the frontal lobes just anterior to the frontal horns and extending to the occipital lobes posterior to the lateral ventricle trigones. The transducer is then rotated 90°, and approximately five images are obtained, including a midline sagittal view of the corpus callosum and cerebellar vermis in addition to bilateral parasagittal images beginning in the midline and progressing laterally through the peripheral cortex

Next, four color Doppler images may be obtained for screening vascular structures . The arterial system is assessed for patency and resistance to flow by obtaining a color Doppler image of the circle of Willis . This image, obtained via the anterior or temporal fontanel, is used to localize the middle or internal cerebral artery to obtain a spectral tracing with peak systolic velocity (PSV), end-diastolic velocity (EDV), and resistive index (RI) The internal cerebral arteries are more easily seen via the anterior fontanelle.

The venous system is evaluated for patency by obtaining a color Doppler image of the sagittal sinus and vein of Galen in the sagittal plane. Visualization of the cerebellar hemispheres is optimized by obtaining images through the right and left mastoid fontanels. This technique has been shown to improve detection of posterior fossa hemorrhages . Adjunct color Doppler images via the posterior fontanelle or foramen magnum can also be used to screen for patency of the transverse sinuses. Finally, completion of the modern cranial ultrasound requires switching from a curved to a linear array transducer, which allows high resolution imaging of the brain.

IMPORTANT PRINCIPLES First, gray matter tends to be hypoechoic and white matter tends to be hyperechoic. When this pattern is reversed, abnormality is indicated. Second, the normal brain is always symmetric, but symmetric is not always normal. A third principle involves visualization of all layers of the normal cortex. The superficial pia mater should be seen as a thin well defined hyperechoic layer overlying the hypoechoic cortical gray matter, which in turn overlies the hyperechoic white matter. Fourth, the periventricular white matter is normally homogeneous in echogenicity and is equal to or less echogenic than the adjacent choroid plexus. Asymmetry or heterogeneity of the periventricular white matter suggests an abnormality, as can occur with periventricular leukomalacia.

Intracranial sonography can demonstrate many unsuspected cranial abnormalities. Demonstration of wide subarachnoid spaces with low‑level internal echoes is observed in intracranial subarachnoid hemorrhages and meningitis

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