Pediatric Head CT

Introduction

Neuroradiological imaging of the pediatric patient has undergone tremendous change since the late 2000s. Although the use of magnetic resonance imaging (MRI) is on the rise, in part because of concerns over exposing children to medical radiation, there is still an important role for pediatric head computed tomography (CT), which provides fast imaging, often without the need for sedation. CT therefore remains an important tool for evaluating patients in the emergency department, especially in cases of acute trauma and critically ill inpatients who may be too unstable to undergo a lengthier MRI examination ( ). MRI also carries the additional risk of sedation and anesthesia for young children who have limited or no verbal skills and have difficulty remaining still in the magnetic resonance (MR) scanner long enough for the technologist to produce diagnostically useful images. At our institution, CT can be performed portably, making it an accessible test for children who cannot be transported to the radiology department. In addition, for patients who cannot undergo MRI secondary to implanted devices or external monitoring hardware, CT serves as the only available cross-sectional imaging modality.

The aim of this chapter is to provide an approach for interpreting pediatric head CT scans with a focus on recognizing intracranial structures in the developing brain while highlighting common disease entities seen in children. We will not, however, describe all potential neurological diseases of childhood that may be detected on head CT. As with the other chapters in this book, our goal is to present key findings that will enable the busy clinician to arrive at an appropriate or probable differential diagnosis by using a systematic approach to interpreting head CTs that will aid in clinical decision making.

Computed Tomography Techniques and Radiation Awareness

As CT use continues to grow among all age groups, the risks associated with exposure to ionizing radiation must be disclosed, as well as the fact that children experience disproportionate sensitivity to the effects of radiation. CT now accounts for the largest contribution to medical radiation dose in the United States. Children are at a greater risk for both short- and long-term effects of radiation, in part because their smaller bodies and organs are more susceptible to damage from higher doses and in part because their developing tissues and rapidly dividing cells are more radiosensitive than those of adults. These factors, combined with longer life expectancy, place children at higher risk for eventually developing cancers as a result of exposure to ionizing radiation, especially when CT must be repeated over months or years.

As a medical community, we can all play a role in minimizing radiation exposure through a variety of techniques. For example, shielding tissues outside of the imaging field can reduce the dose delivered to adjacent organs. Proper protocols should be selected for pediatric patients that take into account smaller body size with adjustments in the milliampere (mA) and peak kilovoltage (kVp). Protocols can also be further tailored depending on the clinical indication. Often a lower-dose scan can yield sufficient diagnostic information to answer a specific clinical question. At our institution, we select different scanning parameters for patients who are being followed for hydrocephalus where visualization of fine anatomic detail at the expense of a higher radiation dose does not add value to the clinical decision-making process ( ; ; ). Single-phase contrast examinations should be part of the routine standard of care because additional information is rarely captured from the noncontrast or delayed phases to justify the added radiation dose. The scanning parameters for children must also be adjusted to image only the region of interest, with care taken to minimize imaging of any collateral tissues or organs.

With the promotion of the Image Gently campaign, numerous resources are now available to help guide the selection of appropriate CT parameters for clinical practice ( ). At our institution, CT imaging protocols are continually reviewed by a team of radiologists, medical physicists, and radiology technologists to ensure scans are being optimized to achieve images of the highest diagnostic quality at the lowest possible levels of radiation exposure ( ). The parameters selected for our head CT protocol are presented in Table 25.1 . Modern multidetector scanners enable the acquisition of submillimeter (mm) thin-section images, which can then be reformatted into multiple viewing planes, but with no additional radiation dose delivered to the patient. Three-dimensional (3D) rotating models can also be generated from the axial data. These 3D models can both aid the radiologist in detecting pathology and provide surgeons and clinicians with a helpful visual aid for future disease management.

Special Computed Tomography Examination Considerations

As in adults, CT angiography (CTA) is also used for specific indications in the work-up of the pediatric patient. CTA is used to evaluate children with acute, nontraumatic parenchymal or subarachnoid hemorrhage; to evaluate for intracranial aneurysms, vascular malformations, or intracranial arterial dissections; or when concern exists for acute stroke where intravascular thrombolysis is being considered. At our institution, a single-phase, arterial-phase CT is performed that omits the noncontrast phase of the examination often performed in adult patients. CT venography is performed at some institutions for the evaluation of venous sinus thrombosis when MRI is either unavailable or contraindicated ( ).

Occasionally contrast-enhanced CT may also be performed for the work-up of a mass, for assessing metastatic spread of disease, or for evaluating infectious processes. In pediatric patients with headache in the setting of sinusitis or mastoiditis, contrast-enhanced CT may be used to evaluate for intracranial complications. In most instances, MRI is preferred for these indications; however, as mentioned previously, in patients for whom MRI is not indicated, contrast-enhanced CT can play a vital role in reaching a diagnosis. Under these circumstances, the noncontrast portion of the examination is generally omitted because postprocessing techniques can evaluate cases where there is a question of enhancement in the presence of hemorrhage or mineralization.

Key Imaging Questions

In order to systematically approach pediatric head CTs we have organized this chapter around key imaging questions and finding encountered in clinical practice.