Diagnostic Imaging for the Emergency Physician E-Book

Joshua S. Broder

• Editore: Saunders
• Anno: 2011
• ISBN:
  9781437735871
• Argomento: Medicina
• Categoria: Medicina de emergencia y cuidado crítico

Diagnostic Imaging for the Emergency Physician, written and edited by a practicing emergency physician for emergency physicians, takes a step-by-step approach to the selection and interpretation of commonly ordered diagnostic imaging tests. Dr. Joshua Broder presents validated clinical decision rules, describes time-efficient approaches for the emergency physician to identify critical radiographic findings that impact clinical management and discusses hot topics such as radiation risks, oral and IV contrast in abdominal CT, MRI versus CT for occult hip injury, and more. Diagnostic Imaging for the Emergency Physician has been awarded a 2011 PROSE Award for Excellence for the best new publication in Clinical Medicine.

• Consult this title on your favorite e-reader, conduct rapid searches, and adjust font sizes for optimal readability.
• Choose the best test for each indication through clear explanations of the "how" and "why" behind emergency imaging.
• Interpret head, spine, chest, and abdominal CT images using a detailed and efficient approach to time-sensitive emergency findings.
• Stay on top of current developments in the field, including evidence-based analysis of tough controversies - such as indications for oral and IV contrast in abdominal CT and MRI versus CT for occult hip injury; high-risk pathology that can be missed by routine diagnostic imaging - including subarachnoid hemorrhage, bowel injury, mesenteric ischemia, and scaphoid fractures; radiation risks of diagnostic imaging - with practical summaries balancing the need for emergency diagnosis against long-terms risks; and more.
• Optimize diagnosis through evidence-based guidelines that assist you in discussions with radiologists, coverage of the limits of "negative" or "normal" imaging studies for safe discharge, indications for contrast, and validated clinical decision rules that allow reduced use of diagnostic imaging.
• Clearly recognize findings and anatomy on radiographs for all major diagnostic modalities used in emergency medicine from more than 1000 images.
• Find information quickly and easily with streamlined content specific to emergency medicine written and edited by an emergency physician and organized by body system.

Chapter 1 Imaging the Head and Brain

Joshua Broder, MD, FACEP, Robert Preston, MD

Emergency physicians frequently evaluate patients with complaints requiring brain imaging for diagnosis and treatment. The diversity of imaging modalities and variations of these modalities may be daunting, creating uncertainty about the most appropriate, sensitive, and specific modality to evaluate the presenting complaint. An evidence-based approach is essential, with modality and technique chosen based on patient characteristics and differential diagnosis. In this chapter, we begin with a brief summary of computed tomography (CT) and magnetic resonance (MR) technology. Next, we present a systematic approach to interpretation of head CT, along with evidence for interpretation by emergency physicians. Then, we discuss the cost and radiation exposure from neuroimaging, as these are important reasons to limit imaging. We review the evidence supporting the use of CT and magnetic resonance imaging (MRI) for diagnosis and treatment of emergency brain disorders, concentrating on clinical decision rules to target imaging to high-risk patients. We also consider adjunctive imaging techniques, including conventional angiography, plain films, and ultrasound. By chapter’s end, we consider the role of neuroimaging in the evaluation of headache, transient ischemic attacks (TIAs) and stroke, seizure, syncope, subarachnoid hemorrhage (SAH), meningitis, hydrocephalus and shunt malfunction, and head trauma.

Neuroimaging Modalities

Indications for neuroimaging are diverse, including traumatic and nontraumatic conditions (Table 1-1). The major brain neuroimaging modalities today are CT and MRI, with adjunctive roles for conventional angiography and ultrasound. Plain films of the calvarium have an extremely limited role, as they can detect bony injury but cannot detect underlying brain injury, which may be present even in the absence of fracture.

TABLE 1-1 Clinical Indications, Differential Diagnoses, and Initial Imaging Modality

Clinical Indication	Differential Diagnosis	Initial Imaging Modality
Headache	Mass, traumatic or spontaneous hemorrhage, meningitis, brain abscess, sinusitis, hydrocephalus	Noncontrast CT
Altered mental status or coma	Mass, traumatic or spontaneous hemorrhage, meningitis, brain abscess, hydrocephalus	Noncontrast CT
Fever	Meningitis (assessment of ICP), brain abscess	Noncontrast CT
Focal neurologic deficit—motor, sensory, or language deficit	Mass, ischemic infarct, traumatic or spontaneous hemorrhage, meningitis, brain abscess, sinusitis, hydrocephalus	Noncontrast CT, possibly followed by MRI, MRA, or CTA, depending on context
Focal neurologic complaint—ataxia or cranial nerve abnormalities	Posterior fossa or brainstem abnormalities, vascular dissections	MRI or MRA of brain and neck; CT or CTA of brain and neck if MR is not rapidly available
Seizure	Mass, traumatic or spontaneous hemorrhage, meningitis, brain abscess, sinusitis, hydrocephalus	Noncontrast CT, possibly followed by CT with IV contrast or MR
Syncope	Trauma	Little indication for imaging for cause of syncope, only for resulting trauma
Trauma	Hemorrhage, mass effect, cerebral edema	Noncontrast CT—if clinical decision rules suggest need for any imaging
Traumatic loss of consciousness	Hemorrhage, DAI, mass effect, cerebral edema	Little indication when transient loss of consciousness is isolated complaint
Planned LP	Increased ICP	Noncontrast head CT—limited indications

Computed Tomography

CT has been in general clinical use in emergency departments (EDs) in the United States since the early 1980s. The modality was simultaneously and independently developed by the British physicist Godfrey N. Hounsfield and the American Allan M. Cormack in 1973, and the two were corecipients of the Nobel Prize for Medicine in 1979.^1,2 Advances in computers and the introduction of multislice helical technology (described in detail in Chapter 8 in the context of cardiac imaging) have dramatically enhanced the resolution and diagnostic utility of CT since its introduction. CT relies on the differential attenuation of x-ray by body tissues of differing density. The image acquisition occurs by rapid movement of the patient through a circular gantry opening equipped with an x-ray source and multiple detectors. A three-dimensional volume of image data is acquired; this volume can be displayed as axial, sagittal, or coronal planar slices or as a three-dimensional image. CT does raise some safety concerns with regard to long-term biologic effects of ionizing radiation and carcinogenesis, which we describe later. The radiation exposure to the fetus in a pregnant patient undergoing head CT is minimal.³ Most commercially available CT scanners have a weight capacity of approximately 450 pounds (200 kg), although some manufacturers now offer units with capacities up to 660 pounds (300 kg).⁴ Portable dedicated head CT scanners with acceptable diagnostic quality and no weight limits are now available.^4a

Noncontrast Head CT

Noncontrast CT is the most commonly ordered head imaging test in the ED, used in up to 12% of all adult ED visits.^5,6 It provides information about hemorrhage, ischemic infarction, masses and mass effect, ventricular abnormalities such as hydrocephalus, cerebral edema, sinus abnormalities, and bone abnormalities such as fractures. Although dedicated facial CT provides more detail by acquiring thinner slices through the region of interest or by changing the patient’s position in the scanner during image acquisition, general information about the face and sinuses can be gleaned from a generic noncontrast head CT, as described in detail in Chapter 4 on facial imaging. The American ...