Essentials of Radiology: Common Indications and Interpretation (Mettler, Essentials of Radiology)

293 Pages·2013·109.296 MB·English

by  Fred A. Mettler Jr. MD MPH

ESSENTIALS OF
RADIOLOGY
Third Edition

ESSENTIALS OF
RADIOLOGY
Third Edition
Fred A. Mettler, Jr., MD, MPH
Department of Radiology
New Mexico Federal Regional Medical Center
and
Clinical and Emeritus Professor
University of New Mexico
School of Medicine
Health Sciences Center
Albuquerque, New Mexico
1600 John F. Kennedy Blvd.
Ste 1800
Philadelphia, PA 19103-2899
Essentials of Radiology ISBN: 978-1-4557-4225-7
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Library of Congress Cataloging-in-Publication Data
Mettler, Fred A., 1945-
Essentials of radiology / Fred A. Mettler, Jr.—3rd ed.
p. ; cm.
Includes bibliographical references and index.
ISBN 978-1-4557-4225-7 (soft cover)
I. Title.
[DNLM: 1. Radiography—methods. WN 445]
RC78
616.07′57—dc23
2013012095
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Preface
Radiology receives little attention in most medical school Uses of computed tomography (CT) scanning have
curricula except perhaps as an elective. The classic gross significantly expanded. CT scanners are now capable of
anatomy laboratory is dead, and most health care providers imaging large portions of the body in a few seconds.
encounter human internal anatomy and function through Applications that previously could not be performed,
radiology. This text is not meant to make you into a radi- because of patient or organ motion, now are no problem.
ologist or to be just a text for a radiology medical student CT scans are rapidly replacing most plain films of
elective. It is intended to be a text that will provide a the abdomen and have completely replaced intravenous
basis for radiologic anatomy, imaging fundamentals, and pyelograms and a number of nuclear medicine proce-
common clinical problems and to be a book that you will dures. All of this has added significant radiation dose to
keep and use in your future practice. Since the first edition, the U.S. population, and unnecessary radiation dose has
this text has been widely used by medical students, nurse become a matter of concern.
practitioners, physician assistants, primary care physicians, With the coming changes to our health care system, it
and first-year radiology residents. will be even more important to order and use imaging
With a basic text containing fundamentals, one may studies wisely, efficiently, and appropriately. Information
wonder why a third edition is needed. Even though many has been added on the appropriate workup of common
aspects of radiology have remained unchanged over the clinical problems such as headache, hypertension, and low
past decade, rapid and significant changes have occurred back pain. Information is also included on current screen-
in both technology and applications. ing guidelines. I have endeavored to include this informa-
With digital imaging systems and rapid dictation with tion without expanding the total volume of the text and
voice recognition technology, there is much less reason for yet retaining the essentials. Because readers often have
a physician to visit the radiology department. In-person questions about the cost and radiation dose associated with
consultations with radiologists have become rare. Greater common examinations, this information has been retained
expertise in radiology will be required because medical in the appendix.
students, residents, and others will be examining digital
images at sites remote from the radiology department. Fred A. Mettler, Jr.
v
Acknowledgments
I thank my colleagues, especially Charles Hickam, MD;
Blaine Hart, MD; and Josh Robertson, MD, for helpful
comments and for providing a number of the images. I
would also like to thank RuthAnne Bump for advice with
images.
vii
1
Introduction
AN APPROACH TO IMAGE “viral cardiomyopathy” in a patient who really has a malig-
INTERPRETATION nant pericardial effusion.
After practicing for 20 years or so, a radiologist knows
The first step in medical imaging is to examine the patient the spots where pathology most commonly is visualized.
and determine the possible cause of his or her problem. Throughout this text, I point out the high-yield areas for
Only after this is done can you decide which imaging study the different examinations. Although no absolute rules
is the most appropriate. A vast number of algorithms or exist, knowing the pathology and natural history of differ-
guidelines have been developed, but no definite consensus ent diseases will help you. For example, colon cancer typi-
exists on the “right” one for a given symptom or disease cally metastasizes first to the liver rather than the lungs,
because a number of imaging modalities have similar whereas sarcomas preferentially metastasize to the lungs
sensitivities and specificities. In this text I provide tables of rather than the liver.
appropriate initial imaging studies for various clinical After reviewing the common causes of the imaging find-
situations. When possible, these tables are based on the ings that you have observed, you should reorder the causes
published literature and recommendations of professional in light of the clinical findings. At this point, you probably
societies. When this is not possible, I give you my opinion think that you are finished. Not so. Often a plethora of
based on 40 years of clinical practice. information is contained in the patient’s image files or in
What should you expect from an imaging examination? the hospital computer information system. This comes in
Typically one expects to find the exact location of a problem the form of previous findings and histories supplied for the
and hopes to make the diagnosis. Although some diseases patient’s other imaging examinations. Reviewing the old
present a characteristic picture, most can appear in a reports has directed me to areas of pathology on the
variety of forms depending on the stage. As a result, image current image that I would have missed if I had not looked
interpretation will yield a differential diagnosis that must into the medical information system. A simple example is
be placed in the context of the clinical findings. a pneumonia that has almost but not completely resolved
Examination of images requires a logical approach. First or a pulmonary nodule that, because of inspiratory differ-
you must understand the type of image, the orientation, ence, is hiding behind a rib on the current examination.
and the limitations of the technique used. For example, You probably think that you are finished now. Wrong
I begin by mentally stating, “I am looking at a coronal again. A certain number of entities could cause the findings
computed tomography (CT) scan of the head done on the image, but you just have not thought of them all.
with intravenous contrast.” This is important, because After I have finished looking at a case, I try to go through
intravenous contrast can be confused with fresh blood in a set sequence of categories in search of other differential
the brain. possibilities. The categories I use are congenital, physical/
Next I look at the name and age on the image label to chemical, infectious, neoplastic, metabolic, circulatory, and
avoid mixing up patients, and it allows making a differen- miscellaneous.
tial diagnosis that applies to a patient of that age and sex.
You would not believe the number of times that this
seemingly minor step will keep you from making dumb X-RAY
mistakes.
The next step is to determine the abnormal findings on Regular x-rays (plain x-rays, also sometimes called
the image. This means that you need to know the normal radiographs) account for about 75% of imaging examina-
anatomy and variants of that particular part of the body as tions. X-ray examinations, or plain x-rays, are made by an
well as their appearance on the imaging technique used. x-ray beam passing through the patient. The x-rays are
After this, you should describe the abnormal areas, because absorbed in different amounts by the various tissues or
it will help you mentally to order a differential diagnosis. materials in the body. Most of the beam is absorbed or
The most common mistake is to look at an abnormal scattered. This represents deposition of energy in the
image and immediately to name a disease. When you do tissue but does not cause the patient to become radioactive
this, you will find your mind locked on that diagnosis or to emit radiation. A small percentage of the incident
(often the wrong one). It is better to say to yourself some- radiation beam exits the patient and strikes a detector.
thing like, “I am going to give a differential diagnosis of The historical imaging receptor was a film/screen com-
generalized cardiac enlargement with normal pulmonary bination. The x-ray beam would strike a fluorescent screen,
vasculature in a 40-year-old man,” rather than to blurt out which produced light that exposed the film, and then the
1
2   Chapter 1 | Introduction
film was developed. Newer systems are called computed Without these, mistakes can easily be made. You must
radiography or digital radiography. In computed radiogra- remember that an object visualized on a specific view is
phy, the x-rays strike a plate that absorbs the x-rays and somewhere in the path of the x-ray beam (not necessarily
stores the energy at a specific location. The plate is then in the patient). If an object projects outside the patient on
scanned by a laser, which releases a point of light from the any view, it is outside the patient. However, even if an
plate. The location is detected and stored in a computer. object projects within the patient on two orthogonal views,
In digital radiography detector systems, the x-ray hits a it can still be located outside the patient (Figs. 1-2 and 1-3).
detector and then is converted to light immediately. Once Each additional view needed to make a diagnosis requires
either type of image is stored in the computer, it can be an additional x-ray exposure and therefore adds to the
displayed on a monitor for interpretation or transmitted patient’s radiation dose. Radiation doses from various
to remote locations for viewing. examinations are given in the Appendix.
Four basic tissue densities, or shades, are visible on plain The terminology used to describe images is usually quite
x-rays. These are air, fat, water (blood and soft tissue), and straightforward. Chest and abdominal radiographs are
bone. Air is black or very dark. On regular x-rays and CT referred to as upright or supine, depending on the position
scans, fat is generally gray and darker than muscle or blood of the patient. In addition, chest x-rays are usually described
(Fig. 1-1). Bone and calcium appear almost white. Items as posteroanterior (PA) or anteroposterior (AP) (Fig. 1-4).
that contain metal (such as prosthetic hips) and contrast These terms indicate the direction in which the x-ray beam
agents also appear white. The contrast agents generally traversed the patient on its way to the detector. PA means
used are barium for most gastrointestinal studies and that the x-ray beam entered the posterior aspect of the
iodine for most intravenously administered agents. patient and exited anteriorly. AP means that the beam
Remember that standard or plain x-rays are two- direction through the patient was anterior to posterior. A
dimensional presentations of three-dimensional informa- left lateral decubitus view is one taken with the patient’s
tion. That is why frontal and lateral views are often needed. left side down.
Air
Soft tissue
FIGURE 1-1 The four basic densities on an x-ray. A lateral 
Fat
view of the forearm shows that the bones are the densest, or 
white; soft tissue is gray; fat is somewhat dark; and air is very 
dark. The abnormality in this case is the fat in the soft tissue of 
the forearm, which is due to a lipoma. 
Bone
FIGURE 1-2 Spatial localization on an x-ray. On both antero-
posterior (AP) and lateral projections, the square and round 
objects will be seen projecting within the view of the chest, even 
though the square object is located outside the chest wall. If you 
can see an object projecting outside the chest wall on at least one 
view (the triangle), it is outside the chest. If, however, an object 
looks as though it is inside the chest on both views, it may be 
either inside or outside. 
Film
Anterior-posterior Lateral
Chapter 1 | Introduction   3
A B
FIGURE 1-3 What is the location of the keys? On both the posteroanterior (PA) view of the chest (A) and the lateral view (B), the keys seem to be within 
the center of the chest. Actually if you look carefully, you will notice that the keys do not change position at all, even though the patient has rotated  
90 degrees. The keys are located on the receptor cassette and are not in the patient. 
Use of contrast agents permits visualization of anatomic
structures that are not normally seen. For example, intra-
venous or intra-arterially injected agents allow visualiza-
Film
tion of blood vessels (Fig. 1-5). If imaging is done with
standard format, the blood vessels appear white. Digital
imaging allows subtraction or removal of unwanted struc-
tures, such as the bones, from an image (see Fig. 1-5, B).
Often the computer manipulation is done in such a way
that the arteries may appear black instead of white, although
this usually does not present a problem in interpretation.
Contrast agents are used to fill either a hollow viscus
(such as the stomach) or anatomic tubular structures that
can be accessed in some way (such as blood vessels, ureter,
and common bile duct). When you see an abnormality on
one of these studies, you must determine whether the
location is intraluminal, mural, or extrinsic. This usually
Anterior-posterior Posterior-anterior
requires seeing the abnormality in perpendicular views
FIGURE 1-4 Typical x-ray projections. X-ray projections are typically 
(Fig. 1-6). Unless you are careful about this determination,
listed as anteroposterior (AP) or posteroanterior (PA). This depends on 
whether the x-ray beam passed to the patient from anterior to posterior  you will make errors in diagnosis.
(AP) or the reverse. Lateral (LAT) and oblique (OBL) views also are com- Contrast agents instilled orally, rectally, or retrograde
monly obtained.  into the ureter or bladder incur little or no risk unless
aspiration or perforation occurs. With the intravenously or
intra-arterially administered agents, a small but real risk
Position is important to note, because it can affect mag- for contrast reaction exists. This is something that you
nification, organ position, and blood flow and therefore should consider before ordering a contrast-enhanced CT
significantly affect image interpretation. For example, the scan. About 5% of patients will experience an immediate
heart appears larger on AP than on PA images because on mild reaction, such as a metallic taste or a feeling of
an AP projection the heart is farther from the detector and warmth; some experience nausea and vomiting, wheeze, or
is magnified more by the diverging x-ray beam. It also get hives as a result of these contrast agents. Some of these
appears larger on supine than on upright images because mild reactions can be treated with 50 mg of intramuscular
the hemidiaphragms are pushed up, making the heart diphenhydramine (Benadryl). Because contrast agents
appear wider. Portable chest images are taken not only in also can reduce renal function, they should not generally
the AP projection but also with the tube closer to the be used in patients with compromised renal function (esti-
patient than on standard upright images. This magnifies mated glomerular filtration rate [eGFR] <50 to 60 mL/
the heart even more. min).