Diagnostic Value of Ultrasonic and Computed Tomographic Imaging in Infants with Hypotonia

Infants with hypotonia may have a variety of CNS lesions in addition to many metabolic and peripheral nervous system causes. This article will focus on the CNS causes of hypotonia that can be diagnosed with ultrasound or computed tomography (CT) (Table 1). Ultrasound, computed tomography, and magnetic resonance imaging (MRI) are being used to evaluate the infant's spinal cord directly, but the clinical significance of these evaluations is only now being defined. CHOICE OF MODALITY Specific types of lesions can be studied best with either computed tomography or ultrasound and these will be discussed in detail. In general, if either modality can identify the expected abnormality, ultrasound would be the method of choice because it is portable and less expensive, and it requires no sedation. Computed tomography will be the best modality for studying posttraumatic lesions because they are commonly peripherally located, eg, subdural or epidural hemorrhage. The amount of radiation exposure for a CT scan is similar to that for a routine skull series so that this should not be a constraint unless a large number of scans are being done serially. In these cases, ultrasound may substitute in many situations as long as the anterior fontanel is open. Equipment Limitations Using CT scans, the entire brain and skull of an infant can be evaluated.