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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_2664_Библиотеки_им_академика_М_И_Перельмана
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USMLE Step 2 CK
l Internal Medicine
Seborrheic Dermatitis
Pathogenesis. An oversecretion of sebaceous material and a hypersensitivity reaction to a
superficial fungal organism, Pityrosporum ovale, underlie seborrheic dermatitis.
Clinical Presentation. These patients present with “dandruff,” which may also occur on the face.
Scaly, greasy, flaky skin is found on a red base on the scalp, eyebrows, and in the nasolabial fold.
Treatment. Therapy consists of low-potency topical steroids, such as hydrocortisone, or topical antifungals in the form of shampoos, such as ketoconazole or sulfide. Zinc pyrithione is
also used as a shampoo.
Stasis Dermatitis
Pathogenesis. Stasis dermatitis is a hyperpigmentation built up from hemosiderin in the tissue. It occurs over a long period, from venous incompetence of the lower extremities leading
to the microscopic extravasation of blood in the dermis.
Treatment. There is no way to reverse this problem. Prevention of progression is with elevation of the legs and lower-extremity support hose.
Contact Dermatitis
Pathogenesis. Contact dermatitis is a hypersensitivity reaction to soaps, detergents, latex, sunscreens, or neomycin over the area of contact. Jewelry is a frequent cause, as is contact with
the metal nickel from belt buckles and wristwatches.
Clinical Presentation. It can occur as linear, streaked vesicles, particularly when it is from
poison ivy.
Diagnosis. A definitive diagnosis can be determined with patch testing.
Treatment. Identify the causative agent and treat with antihistamines and topical steroids.
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phil.cdc.gov
Figure 12-10. Contact Dermatitis Due to Poison Ivy
Pityriasis Rosea
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Pathogenesis. Pityriasis rosea is a pruritic eruption that begins with a “herald patch” 70 to
80% of the time. It is mild, self-limited, and usually resolves in 8 weeks without scarring.
Clinical Presentation. It is erythematous, salmon colored, and looks like secondary syphilis, except that it spares the palms and soles and has a herald patch. The lesions on the back
appear in a pattern like a Christmas tree (if the observer is especially imaginative).
Diagnosis. The VDRL/RPR is negative. This is a clinical diagnosis.
Treatment. Very itchy lesions may be treated with topical steroids.
DECUBITUS (PRESSURE) ULCERS
Pathogenesis. Decubitus ulcers are chronic sores that occur in the pressure areas of the body,
where bone is closer to the skin. It is often associated with patients who are immobilized or
bedridden.
Clinical Presentation. Stage I lesions consist of nonblanchable redness. Stage II lesions result
in destruction of the superficial epidermis or partial destruction of the dermis. Stage III
lesions have destroyed the full thickness of the skin, but not the fascia, and stage IV lesions
show destruction all the way to the bone.
Chapter 12
l Dermatology
Diagnosis. Never culture a swab of the superficial ulcer or drainage from the ulcer. It will be
impossible to determine whether it is a genuine infection or simply colonization. A definitive
microbiologic diagnosis is often obtained only in the operating room after debridement.
Treatment. The major theme of management is to relieve pressure. If the lesions are definitely
infected, then antibiotics are useful.
HAIR
Alopecia Areata
Pathogenesis. This is an autoimmune disease in which antibodies attack the hair follicles and
destroy hair production.
Treatment. The majority will resolve spontaneously over time. Immediate therapy is with
localized steroid injection into the area of hair loss.
Telogen Effluvium
Pathogenesis. This is the loss of hair in response to an overwhelming physiologic stress, such
as cancer or malnutrition.
Treatment. The management is to correct the underlying stress or disease.
431
USMLE Step 2 CK
l Internal Medicine
ACNE
Pathogenesis. The contributing organism is Propionibacterium acnes. Pustules and cysts
occur, which rupture and release free fatty acids, which in turn causes further irritation. Acne
is more common in girls, but boys have more severe disease.
Clinical Presentation. There are both closed comedones, which are white, and open comedones, which are black. The discharge, although purulent, is odorless.
Treatment. Mild disease is treated with topical antibiotics, such as clindamycin, erythromycin,
or sulfacetamide. In addition, the bacteriostatic agent benzoyl peroxide is used. Topical retinoids are applied if the attempts to control the load of bacteria locally are ineffective.
Moderate disease treatment combines benzoyl peroxide with the retinoids tazarotene, tretinoin, and adapalene. Severe cystic acne is treated with oral antibiotics, such as minocycline,
tetracycline, clindamycin, and oral isotretinoin. Oral retinoic-acid derivatives are a strong
teratogen.
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Radiology/Imaging
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Chapter Title
Learning Objectives
❏ List the indications and common abnormal findings for chest X-ray, abdominal
X-ray, PET scan, bone scan
❏ Answer questions about different approaches to visualizing the CNS
This concise section should help you understand when to order each of the different types of
tests in radiology. A description of what is found on each type of test is provided. For example, What does a sonogram show, and what doesn’t it show? When does one use a CT scan or
an MRI? When is contrast the best answer in a test question?
CHEST X-RAY
The most basic radiologic examination is a chest x-ray. Standard x-rays are based on the degree
of density of tissue and how much x-ray energy each type of tissue will absorb. The closer a
bone structure is in density, the greater the energy it will absorb. Therefore, because bones block
the most amount of x-ray energy, they will come out white on the film. Conversely, air absorbs
or blocks the least amount of energy and thus will appear darkest.
00
13
Chest x-rays are not routine screening tests. There is no routine screening of the general population for cancer or tuberculosis. You can do a chest x-ray if the PPD skin test is positive, but
this is not the same thing as just doing a general screening.
Most x-rays are posterior-anterior (PA) films. The x-ray plate is placed in front of the chest,
and the patient is leaning forward against the plate. The x-ray beam is directed from posterior
to anterior. The patient must be able to stand for a PA film to be performed.
Anterior-posterior (AP) films are less accurate but must be done in patients who are too ill or
unstable to stand up. All patients with central venous lines or chest tubes, or unstable patients,
such as those in the intensive care unit, undergo AP films. The single greatest difference on AP
films is that the heart size is artificially enlarged on them because the heart is more anterior
in the chest and will therefore cast a wider shadow. On a normal PA film, the heart should
be <50% of the total transthoracic diameter. This is increased to >50% on an AP film. (This
phenomenon is no different than holding your hand in a light shined against a wall. The farther your hand is away from the wall, the larger your hand’s shadow will appear.)
433
USMLE Step 2 CK
l Internal Medicine
Technical Aspects of Normal Film Quality
When examining a chest x-ray, first assess the film for its technical quality. If the patient’s
body is abnormally rotated, then the film will be less accurate. You can determine this by seeing if the trachea and the spinous apophysis are midway between the clavicles.
Chest x-rays should be performed when the patient is holding in a full inhalation. There
should be at least 10 ribs visible, counting from top to bottom.
An underexposed film will have the structures appearing too white. An overexposed film will
have the blood vessels appearing too dark, preventing one from accurately assessing the blood
vessels.
Note that on a PA film, the right hemidiaphragm is typically higher than is the left hemidiaphragm. This is because the liver is underneath the right hemidiaphragm, pushing it up.
Expiratory Films
Expiratory films are used when one is looking for a pneumothorax. The lungs will appear smaller
because less air will remain in the lungs on expiration. Because a pneumothorax is air outside the
lungs in the pleural space, this air will appear relatively larger. The volume of air in the pleural
space does not decrease on exhalation.
Note
The right hemidiaphragm will
appear higher on a lateral
x-ray and a PA film because
the liver pushes it upward.
Lateral Chest X-ray
Lateral chest x-rays will determine whether a structure in the chest is more anterior or posterior.
For example, they can determine whether a mass that is visible in the center of the mediastinum on a PA film is posterior, making it more likely to be a neurally derived tumor attached to
the spinal cord or an anterior mass. Anterior mediastinal masses are from the thymus, thyroid,
lymph nodes, or a teratoma.
Lateral x-rays also have a greater sensitivity for the detection of small pleural effusions. On
a PA film, you need at least 100 to 200 mL of fluid present to even begin to see an effusion.
Each hemithorax can contain 3 liters of fluid if it is filled to capacity. A lateral chest x-ray can
detect as little as 50 mL. These figures represent the amount of fluid needed to barely begin
seeing “blunting,” or obliteration, of the costophrenic angle.
On a lateral x-ray, the right hemidiaphragm is the one crossing the heart shadow.
Decubitus Films
Decubitus films help detect the presence of a pleural effusion. These are taken with the patient
lying on his or her side and are employed when blunting or obscuration of the costophrenic
angle is seen on a PA or lateral x-ray. Effusions will move and form a layer on the side of the
chest wall. Infiltrates from alveolar disease do not move with gravity. You cannot determine if an
effusion is infected just from its appearance on an x-ray.
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Chapter 13
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APPEARANCES OF COMMON DISORDERS ON CHEST X-RAY
COPD/Emphysema
The most common appearance of COPD on a chest x-ray is related to hyperinflation of the
lung. This leads to a darkening of the lung fields because more air is present. This trapped air
also flattens the diaphragm and gives the impression of an elongated or tubular-shaped heart
because it has been stretched down. There is an increased anterior/posterior diameter, or “barrel chest.” Further, bullae are large, air-filled cavities that can give thin, white lines on a chest
x-ray as the walls of the cavities press up against each other.
l Radiology/Imaging
Pneumonia
Lobar pneumonia causes a whitening of each individual lobe of the lung because of the
greater density of the lung. The “silhouette” sign is present, which is when the border
between the affected lobe and the surrounding denser structure is obscured. (The density of
the lung increases because of alveolar infiltration to the point where it takes on the density
of the nearby heart or diaphragm; hence, one can no longer tell where the lung ends and
the denser structure nearby begins). Lower lobe pneumonia gives a silhouette over each half
of the diaphragm. Right middle-lobe pneumonia obscures the right heart border and will
not pass the minor or horizontal fissure seen on a PA chest x-ray. Upper-lobe infiltration
will not pass the major fissure, and this is more easily seen on a lateral x-ray. You cannot
determine a specific microbiologic etiology from the x-ray alone.
Diseases of the lung outside the airspace but in the interstitial membrane give a fine, lacy appearance visible in most, if not all, of the lobes. Examples of disorders that give interstitial infiltrates are Pneumocystis pneumonia, Mycoplasma, viruses, chlamydia, and sometimes Legionella.
Noninfectious etiologies of an interstitial infiltrate are pulmonary fibrosis secondary to silicosis,
asbestosis, mercury poisoning, berylliosis, byssinosis (from cotton), or simply idiopathic pulmonary fibrosis. As the long-standing disorders become worse and more chronic, a greater degree of
fibrosis occurs. This leads to greater thickening of the membrane. The terms that are used for this
more chronic, thicker appearance are reticular-nodular and, later, honeycombing.
Note
Interstitial Syndromes of the
Lung include:
Sarcoidosis
Histiocytosis X
IPF (interstitial pulmonary
fibrosis)
Tumor
Failure
Asbestosis
Collagen disorders
Environmental
Dust
Drugs
Wikipedia, James Heilman, MD
Figure 13-1. Pneumonia
435
USMLE Step 2 CK
l Internal Medicine
Congestive Heart Failure
The majority of pulmonary vascular flow is normally at the base of the lungs because of gravity. When there is fluid overload, the blood vessels toward the apices become fuller. This is
known as pulmonary vascular congestion, or “cephalization” of flow. The term cephalization is
used because more flow is moving toward the head. The other findings associated with CHF
are cardiomegaly, effusions, and Kerley B lines.
Kerley B lines are the least important. They are small, horizontal lines at the bases that represent
fluid in the interlobular septa. Each lung has several lobes. When fluid builds up outside the lobes,
this is known as a pleural effusion. When fluid builds up within each lobe, in between the lobules,
this is known as a Kerley B line. This type of subtle radiologic finding is less important in the
evaluation of congestive heart failure since the advent of the widespread use of echocardiography.
Position of Lines and Tubes
Chest x-rays are routinely used to determine the appropriate position of central venous lines
and both endotracheal and chest tubes. The proper position of the tip of an endotracheal
tube is 1 to 2 cm above the carina. It is important to keep some space above the carina so that
when the head moves forward, the tube does not push into the carina, which is extremely
uncomfortable and will provoke coughing. The tip of central venous lines is at the junction of
the superior vena cava and the right atrium, at the point where the right mainstem bronchus
is seen. The tip of the line should not be fully inside the atrium because this can irritate the
heart and may provoke an arrhythmia.
Air under the Diaphragm
When there is perforation of an abdominal hollow organ, such as the duodenum, air is
released and is visible under the diaphragm. The proper film to detect this is a chest x-ray
taken in the upright position. This will allow the air to collect under the diaphragm, which
should be easily visible. Abdominal x-rays do not always visualize the top of the diaphragm
because of differences in body size. Chest x-rays always visualize the top of the diaphragm.
436
Wikimedia, Clinical Cases
Figure 13-2. Pneumoperitoneum
Chapter 13
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Imaging Tools for Lung Parenchyma
High resolution CT scan provides greater detail than a chest x-ray or CT scan because of 1 mm
cut. This has a sensitivity of 95% and a specificity of close to 100% for lung parenchymal disease. High resolution CT scan is indicated in the following conditions:
• Symptomatic patients with a normal chest x-ray
• Detecting metastatic lesions, solitary nodules, bullae, bronchiectasis, and diffuse
parenchymal disease (i.e., idiopathic lung diseases)
• To determine the type of lung biopsy required and site of biopsy
ABDOMINAL X-RAYS
Compared with chest x-rays, standard abdominal films without barium contrast provide
far less information. Abdominal x-rays are beneficial only in the detection of an abdominal
obstruction, such as an ileus or a volvulus; they do not reliably detect mass lesions, polyps,
cancer, ascites, or inflammatory bowel disease. Mass lesions in all abdominal organs are best
detected with CT scan or MRI of the abdomen. Polyps are best detected by colonoscopy.
Ascites are visualized by sonography (U/S) or CT scanning. Inflammatory bowel disease, diverticulosis, and cancer are best detected by either endoscopy or barium studies of the bowel.
Although 80 to 90% of kidney stones (nephrolithiasis) can be seen on abdominal films, they
are also best detected by sonography or CT scanning. Only 10 to 15% of gallstones can be
detected on an abdominal film because most of them do not calcify. Pancreatic calcifications
can be detected in 30 to 50% of patients with chronic pancreatitis.
l Radiology/Imaging
Sonography (U/S)
Sonography is used for evaluation of abdominal and pelvic pathology. Sonograms should
be employed first for evaluation of the biliary tract because of their accuracy in evaluating
dilation and obstruction of the ducts. The majority of cholelithiasis should be detected with
sonography because cholesterol gallstones should be easily visible by sonography. The majority of nephrolithiasis is visible by sonography, although there is less accuracy in detecting
stones in the ureters because they become retroperitoneal structures.
Sonography is useful in the evaluation of masses in the liver, spleen, pancreas, and pelvis,
as well as for evaluating the presence of ascites. Despite this accuracy, CT scanning tends to
have a greater sensitivity and specificity for the abdomen and pelvis. Sonography is particularly valuable in the evaluation of pregnant patients because it avoids radiation exposure
to the fetus. Although less accurate, sonography is also practical in patients who have an
absolute contraindication to the use of IV contrast. A total of 1:10,000 patients have a lifethreatening reaction to the use of iodinated contrast agents.
There is very little utility of sonography in the evaluation of thoracic structures because the
ribs block the sound waves. Also, sonography in the evaluation of intracranial structures, such
as the brain, is not recommended because the skull blocks the sound waves.
Endoscopic U/S involves introducing a sonographic device into the abdomen at the end of an
endoscope. Endoscopic U/S is extremely accurate in evaluating pancreatic pathology that is not
easily visualized on CT scanning, such as a gastrinoma. Pancreatic lesions can also be effectively
evaluated in this way.
437
USMLE Step 2 CK
l Internal Medicine
Endoscopic Retrograde Cholangiopancreatography
Endoscopic retrograde cholangiopancreatography (ERCP) is an endoscopically introduced
contrast procedure designed to visualize the biliary tract and pancreatic structures. ERCP is for
therapy. The endoscope is introduced into the small bowel, and a catheter is placed through
the sphincter of Oddi. Contrast is injected through the catheter. This allows extremely accurate visualization of the pancreatic ductal and biliary systems. ERCP is excellent for detecting
strictures, stones, and neoplastic causes of obstruction. The other advantages of ERCP are the
ability to perform therapy with the removal of these stones, to dilate strictures, and to perform
biopsies. The scope does not routinely go up the sphincter of Oddi because it is too large to
pass. MRCP is an MRI alternative to ERCP. It is less invasive than ERCP but does not allow an
intervention.
The most common complication of ERCP is acute pancreatitis (around 10% in some series).
Most of the time the pancreatitis is mild.
Note
MRCP: diagnosis
ERCP: treatment
Clinical Pearl
Capsule endoscopy is not
a screening test to detect
colon cancer. Perform capsule
endoscopy to evaluate
obscure small bowel GI
bleeding.
Barium Studies
Barium studies of the large bowel are never as accurate for colonic pathology as is endoscopy.
In addition, you cannot biopsy with barium studies or perform therapeutic procedures, such
as cautery or epinephrine injection for bleeding. The upper GI series is never as accurate as is
upper endoscopy for the same reasons.
However, barium studies of the esophagus are a good test to start with for the evaluation of
esophageal pathology. Barium esophagram is particularly good for the detection of strictures,
rings, and webs, or Zenker diverticulum. Barium is not as accurate as an upper endoscopy for
the detection of esophageal cancer because a biopsy is required. (Endoscopy is far superior for
the detection and therapy of esophageal varices as well.) Barium is not as accurate as manometry for the confirmation of the diagnoses of achalasia or muscular disorders, such as diffuse
esophageal spasm and nutcracker esophagus.
Capsule Endoscopy
The ileum and jejunum are the hardest parts of the bowel to visualize by radiologic studies
or endoscopy. In the past, a “push enteroscopy” was performed by introducing an extremely
long, thin scope into the small bowel. Capsule endoscopy is a new technology that allows
direct visualization of the small bowel by swallowing a camera that electronically relays
thousands of photographic images from the small bowel to a receiver outside the body. The
drawback of this procedure is that it is not possible to perform therapeutic interventions in
this way. If a patient has GI bleeding that is serious and both upper and lower endoscopy do
not reveal the source, then answer “capsule endoscopy” on the exam.
438
HIDA Scanning
This is a nuclear medicine scan useful only in the detection of acute cholecystitis. HIDA scanning is most useful in patients in whom the diagnosis of cholecystitis is not clear. An abnormal or positive test is the lack of visualization of the gallbladder. This is because the neck
of the gallbladder or cystic duct becomes too edematous to allow the passage of the nuclear
material. A normal scan will visualize the gallbladder. An abnormal scan will not visualize or
fill the gallbladder.
Chapter 13
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l Radiology/Imaging
Wikimedia, Myo Han
Figure 13-3. HIDA Scan
Virtual Colonoscopy
This procedure uses CT scan or MRI to provide a computer-simulated bidimensional or
tridimensional image of the air-filled, distended colon.
PET SCANNING
Positron emission tomography (PET) scans are useful in the detection of cancer. They are
particularly useful in determining whether lesions that are visible on a CT scan of the chest
are malignant or benign. Cancer is typically associated with the increased uptake of fluorodeoxyglucose. PET scanning is used after chemotherapy to assess for the presence of residual
cancer in some patients and can also be used to determine whether a patient is an operative
candidate to remove a primary cancer. If the PET scan does not reveal malignancy, then the
resection of certain primary cancers, such as lung cancer, is more likely to be successful.
Remember that slow-growing cancers (e.g., broncheoalveolar) may have a negative PET scan.
Be careful when evaluating pulmonary nodules with PET scanning.
Clinical Pearl
Always check the patient’s
glucose before doing a PET
scan. If the glucose is elevated,
the PET scan can be falsely
negative.
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