Emergency Department Neuroimaging for the Sick Child

Introduction

Acute neurological emergencies in children can present with a wide variety of symptoms and signs such as fever, vomiting, headache, poor feeding, seizures, and altered consciousness, ultimately leading to encephalopathy and deep coma. Often, an inevitable deficiency of relevant clinical history and lack of dependable neurological examination in an acutely sick child pose a challenge to the emergency team in delivering a precise diagnosis and instituting the appropriate management as early as possible.

The roles of the radiologist in these emergencies are manifold. The first and foremost role is to determine whether neuroimaging is indicated, as well as which imaging modality is preeminent to answer the clinical question. The choice of imaging modality may also be guided by its availability, the condition of the child, and the requirement for contrast and/or sedation in an emergency setting. Secondly, the radiologist should be cognizant of the key imaging findings to provide a timely and appropriate diagnosis, consider pertinent differentials, and detect complications that warrant urgent medical attention. Any critical imaging findings that can affect the immediate management and prognosis must also be promptly conveyed to the emergency department (ED) physician.

Imaging Techniques

Different imaging modalities can be considered based on clinical status, age, provisional diagnosis, and institutional availability. Radiographs are practically limited to the trauma of the spine. Skull radiographs, once used frequently, are now obsolete and only used as a part of the skeletal survey in suspected nontraumatic brain injury. Transcranial ultrasound is a good initial imaging modality of choice in neonates or infants with open fontanelle to evaluate ventricular size and exclude intraventricular bleed. Computed tomography (CT) is the most commonly used imaging modality due to the easy accessibility, intermediate cost, and rapid acquisition time, which obviates the need for anesthesia. However, CT is of concern in children given the higher radiation susceptibility of rapidly dividing cells and longer life span, during which they may develop long-term cumulative effects of radiation. Cautious optimization of the CT examination using the As Low As Reasonably Achievable (ALARA) principle, based on the age and weight of the child, allows effective acquisition of the best-quality image with the lowest radiation dose possible. While CT may be superior for the evaluation of bone, magnetic resonance imaging (MRI) does not utilize ionizing radiation and allows excellent tissue contrast to assess intracranial pathology. MRI acquisition time is longer and potentially requires anesthesia depending on the age and clinical status of the patient. The introduction of ultrafast MRI offers some flexibility, allowing shorter acquisition time and decreasing the need for sedation. This has come in handy in children with ventriculoperitoneal shunts, where the use of ultrafast MRI protocols has played an important role in avoiding multiple CT examinations for suspected shunt dysfunction. Recently, with improved image resolution, ultrafast MRI protocols have been introduced as the initial imaging modality of choice whenever possible instead of CT. Previously limited to T2-wieghted sequences using single-shot fast spin-echo (SSFSE) or Half-Fourier-Acquired Single-shot Turbo spin Echo, newer ultrafast MRI protocols have additional sequences such as fluid-attenuated inversion recovery (FLAIR), T1-weighted imaging (T2*WI), diffusion-weighted imaging (DWI), and T2-weighted imaging (T2WI) that demonstrate sufficient image quality in comparison with routine brain MRI, with acquisition time ranging from 1 to 5 minutes. The most common pediatric neurological emergencies requiring ED visits are trauma, stroke, and infections, along with headaches.

Traumatic Brain Injury

The impact of traumatic injury on the developing brain mostly depends on the severity of the trauma and the age of the child: the younger the age, the higher the risk. Causes of trauma are also variable and age-dependent, such as an accidental drops in infants and falls in toddlers and older children, while adolescents commonly suffer from sports-related injuries or motor vehicle accidents.

Head injuries are clinically classified as mild, moderate, or severe based on the Glasgow coma scale (GCS) and on the pediatric GCS for nonverbal children (under 2 years of age). Patients with moderate to severe injury undergo a CT examination after clinical stabilization. In mild injury, the need for imaging in children follows further clinical criteria. The clinical tool that is most often used is the Pediatric Emergency Care Applied Research Network (PECARN). PECARN helps ED physicians decide which children require urgent CT and who can be managed conservatively without imaging. The most important pediatric traumatic entities are described below.

Scalp Injury

Soft tissue injuries including scalp hematomas and lacerations are common. Scalp hematomas that can cross midline or sutures are caput succedaneum (superficial to the galea aponeurotica), and subgaleal hematoma (deep to the galea aponeurotica) ( Fig. 11.1 ). Cephalhematoma is often a birth-related finding, located deep to the periosteum, and does not cross suture or midline ( Fig. 11.2 ).

Skull Fractures

Skull fractures are common in children due to the thin calvaria from underdeveloped diploe. Sutural diastasis is also a known complication in children ( Fig. 11.3 ). Calvarial fractures can be linear, comminuted, nondepressed, and depressed. Ping-pong fracture is a unique depressed skull fracture ( Fig. 11.4 ) seen in newborns and infants due to inward buckling of the under mineralized calvaria (analogous to buckle fracture of the appendicular skeleton). Skull base fractures are often related to severe injury and should be suspected with orbitofacial trauma ( Fig. 11.5 ). Vascular injuries involving caroticojugular vessels ( Fig. 11.6 ) and cranial nerve injuries causing facial palsy and hearing loss are common with skull base fractures and may present as an immediate or delayed complication.

Growing Skull Fracture

This is a delayed complication of calvarial fracture with a dural tear, typically seen in children under 3 years of age. The parietal bone is the most common site. Due to dural tear, there is constant transmission of cerebrospinal fluid (CSF) pulsations to the fracture site, resulting in progressive widening and scalloping ( Fig. 11.7 ). This results in herniation of pia-arachnoid, formation of a leptomeningeal cyst, and encephalomalacia of the underlying brain parenchyma.

Imaging Pitfalls

Linear undisplaced fractures can be confused with primary and accessory sutures. Helpful clues that favor sutures are sclerotic borders, interdigitated margins, expected course and location, and the fact that they are frequently bilateral.

Imaging Requisites

All fractures should be evaluated in all three planes, and, when possible, imaging should reconstruct a three-dimensional shaded surface display of the skull. Always rule out a skull base fracture in the presence of pneumocephalus.

Reporting Checklist

Fracture location, extension, crossing the suture or midline, depressed or nondepressed, displaced or undisplaced, width of displacement, and depth of depression. Look for the involvement of orbitofacial, petromastoid, and caroticojugular canal with skull base fractures.

Extraaxial Hemorrhage

There are three types of extraaxial hemorrhage (EAH), and the imaging appearance depends upon age and location of the hemorrhage, admixing of CSF, preexisting collection, and the presence of underlying bleeding diathesis.

Epidural Hematoma

Typical biconvex hematoma ( Fig. 11.2 ) in the epidural space, do not cross suture but may cross the midline (dural venous sinus bleed). Unlike adults, these are commonly venous in origin and can occur without fracture due to malleable bones and unsupported meningeal vessels.

Subdural Hematoma

Classic concavoconvex collection ( Fig. 11.8 ) of blood in the potential subdural space. May cross the suture, but do not cross the midline. The commonest intracranial hematoma in children, particularly in infants and toddlers; unlike in adults, it is frequently bilateral.

Subarachnoid Hemorrhage

Focal and linear hyperdensity along the sulci and cisterns ( Fig. 11.9 ) within subarachnoid space. The most common site is Sylvian fissure.

Imaging Pitfalls

Subarachnoid hemorrhage (SAH) should not be confused with pseudo-SAH secondary to cerebral edema or bilateral subdural hematoma (SDH). Venous epidural hematoma is common in pediatric patients and can cross the midline.

Imaging Requisites

EAHs can be missed with the routine parenchymal window and are best evaluated at subdural window 130 and level 30 (standard brain window 75 and level 20). Triplanar evaluation is necessary.

Reporting Checklist

Hematoma location, extension, size, maximum width, mass effect, midline shift, and brain herniation.

Intraaxial Injury

Cortical Contusions

Occur due to collision of the brain and skull at the site of impact ( Fig. 11.10 ) or opposite to it (coup-countercoup). Usually less common and less severe in children due to smooth and softer calvaria.

Diffuse Axonal Injury

Occurs due to sudden acceleration and deceleration. The younger the age, the more severe and extensive the injury. Typically presents as multifocal hemorrhagic foci with surrounding edema ( Figs. 11.10 and 11.11 ) and can be divided into: grade I: lobar white matter involvement at the grey-white matter junction; grade II: corpus callosum involvement; grade III: involvement of brainstem and posterior fossa structures ( Fig. 11.10 ).

Abusive Head Trauma

Typically seen in children below 2 years of age, with maximum risk in the first 6 months of life. Shaking injury from violent motion of the head results in SDH ( Fig. 11.8 ), SAH, generalized parenchymal injury (cytotoxic edema, laceration, axonal injury), and bridging vein injury ( Fig. 11.12 ), with or without thrombosis. Fractures that are multiple, complex, bilateral, or unexplained with the mechanism of trauma should raise suspicion for abusive head trauma (AHT). CT is usually the primary imaging tool, but MRI is superior for determining the full extent of the injury. A concern of AHT should be raised when there is discordance between the clinical history and the degree of injury. However, AHT is not an imaging diagnosis and requires a multidepartmental approach.

Imaging Pitfalls

In clinically significant trauma with normal-appearing CT, look for secondary signs of edema such as sulcal effacement and cisternal narrowing and herniation.

Imaging Requisites

Diffuse axonal injury and nonhemorrhagic contusions can be difficult to detect on CT. An MRI is to be considered when there are discrepancies between the clinical findings and CT examination.

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