Typical Bacterial Pneumonia Imaging

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Typical Bacterial Pneumonia Imaging

Author: Shakeel Amanullah, MD; Chief Editor: Kavita Garg, MD more...

Updated: May 25, 2011

Overview

Pneumonia is the sixth leading cause of death, and the number 1 cause of death from infectious disease, in the United

States.[1, 2, 3, 4, 5, 6, 7] The image below depicts typical bacterial pneumonia.

Image in a 49-year-old woman with pneumococcal pneumonia. The chest radiograph reveals a left lower lobe opacity with pleural

effusion.

Typical versus atypical syndromes

The classification of pneumonias as either typical or atypical arose from the observation that the presentation and

natural history of some patients with pneumonia were different compared with those with pneumococcal infection.

Pathogens like Haemophilus influenzae, Staphylococcus aureus, and gram-negative enteric bacteria cause clinicalsyndromes similar to that due to Streptococcus pneumoniae. However, other pathogens cause an atypical pneumonia

syndrome, and this was initially attributed to Mycoplasma pneumoniae.

Other pathogens, including bacteria and viruses are now known to cause similar syndromes indistinguishable from that

due to M pneumonia. Therefore, the term atypical pneumonia represents diverse etiologic entities and may have

limited clinical value.

Preferred examination

Chest radiography with posteroanterior and lateral views is the preferred imaging examination for the evaluation of

typical bacterial pneumonia.[8]

Radiography

When patients present with fever, chills, or cough, pneumonia is suggested on the basis of focal or diffuse opacities.

Controversy exists with regard to the time required for an opacity to appear on chest radiographs. The vast majority of

opacities appear within 12 hours. When patients are referred from the community to the radiologist, adequate time has

usually lapsed for its detection. However, when nosocomial pneumonia is suspected, these patients may undergo

chest radiography within a few hours, when opacities may not yet be visible on radiographs.[9, 10, 11, 12, 13, 14, 15, 16, 17,

18, 19]

In immunosuppressed patients, especially those with coexistent neutropenia, diabetes, alcoholism, or uremia, the

appearance of infiltrates may also be delayed.

Other findings that suggest the presence of pneumonia include air bronchograms; the silhouette sign; parapneumonic

effusions; and complications of pneumonia, such as lung abscesses, and atelectasis.

Findings that have been associated with an increased mortality, as shown in the multicenter trial by Hasley and

colleagues, are bilateral pleural effusion and multilobar pneumonia.

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Resolution of radiographic findings

The change in infiltrates on chest radiographs is not necessarily correlated with the activity of clinical disease. In some

patients, chest infiltrates may worsen with the start or treatment, despite clinical improvement.

Pneumonia that is slow to resolve after appropriate antibiotic therapy can be a problem. Nonresolving pneumonia has

been variously defined by Amberon in 1943, Henden in 1975, and Fein and colleagues in 1987 and 1993. In general,

this entity is thought to be present when a patient does not improve clinically or when a radiographic infiltrate resolves

slowly despite adequate and appropriate antibiotic therapy. About 10% of diagnostic bronchoscopy procedures and

15% of pulmonary consultations are performed to evaluate a nonresolving infiltrate.

The most common cause of unnecessary invasive evaluation is a failure to appreciate the length of time that infections

need to clear radiologically. Studies have shown that impaired host defenses are more important determinants of

delayed resolution than the infecting pathogen.

Host factors responsible for delayed resolution of pneumonia include age older than 50 years, smoking; and chronic

illnesses, such as diabetes mellitus, renal failure, chronic obstructive pulmonary disease (COPD), and alcoholism.

Bacterial pneumonias usually tend to be unilobar and have cavitary lesions and effusions. Atypical pathogens can

cause multilobar involvement with nodular or reticular infiltrates, lobar or segmental collapse, or perihilar adenopathy.

S pneumoniae pneumonia

S pneumoniae causes 10-50% of all cases of community-acquired pneumonia (CAP). Radiographic consolidation ofthe alveoli begins in the peripheral airspaces, as in the image below. The disease usually causes a lobar or segmental

pattern, and a patchy bronchopneumonic pattern involving the lower lobes is seen in the elderly. A striking

characteristic ofS pneumoniae infection is its tendency to involve the pleura. Parapneumonic effusions are common

in pneumococcal pneumonia.[20]

Image in a 49-year-old woman with pneumococcal pneumonia. The chest radiograph reveals a left lower lobe opacity with pleural

effusion.

In patients with bacteremic pneumococcal patients, 50% had clear radiographs at 9 weeks, compared with 5 weeks in

nonbacteremic pneumococcal pneumonia.

In patients older than 50 years with both alcoholism and COPD, 60% have an abnormal chest radiograph at 14 weeks.

In patients younger than 50 years with bacteremia and no underlying illness, 40% have an abnormal chest image at 2

weeks. For the group as a whole, 37% have residual consolidation at 4 weeks, with complete resolution by 18 weeks

in almost all patients.

Despite therapy during the initial phase of illness, 52% of bacteremic patients compared with 26% of nonbacteremicpatients had radiographs showing deterioration. Jay and colleagues recommended that an appropriate interval for

serial radiographic examination is 6 weeks, unless otherwise indicated by a patient's worsening clinical status.

H influenzae pneumonia

H influenzae pneumonia, shown in the image below, is commonly seen in COPD patients who are smokers; in the

elderly; and in those with alcoholism diabetes, sickle cell anemia, or immunocompromise. This organism can be

present in up to 38% of outpatients and 10% of hospitalized patients with CAP.


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Image in a 48-year-old patient with Haemophilusinfluenzae pneumonia. The chest radiograph shows bilateral opacities with a

predominantly peripheral distribution.

In most patients, radiographs demonstrate a patchy bronchopneumonic pattern, but segmental and lobar consolidation

may be seen. Therefore, H influenzae pneumonia is indistinguishable from pneumococcal pneumonia. Pleural

effusion is a common finding.Radiographs usually show a multilobar infiltrate and pleural effusions in 50% of cases.Resolution is usually slow.

Klebsiella pneumoniae pneumonia

The radiographic patterns seen in Klebsiella pneumonia include patchy bronchopneumonia and dense lobar

consolidations. The alveoli are filled with large amounts of fluid and mucoid suppurative exudates that may cause the

volume of the affected lung to increase with bulging of the interlobar fissures, has a rare feature. Although these

findings are thought to be characteristic ofKlebsiella pneumonia, they may be seen in other causes of pneumonia.

There is a strong tendency for abscess formation as well as pleural involvement. Cavities may develop rapidly after the

onset of illness, and these may be associated with massive lung gangrene.

Pseudomonas aeruginosa pneumonia

P aeruginosa pneumonia has a characteristic predilection for the lower lobes. Patchy bronchopneumonia or extensive

consolidation may be present. Involvement may be unilateral or bilateral and extensive. Extensive necrosis may beseen, with the formation of parenchymal abscesses. Massive bilateral consolidation is usually associated with a poor

prognosis. Nodular infarcts may occur in the lung parenchyma.

S aureus pneumonia

This type of pneumonia may be seen as a complication of influenza, particularly during an epidemic. S aureus

pneumonia usually begins in the peripheral airways rather than in the acini proper. In adults, patchy bronchopneumonia

is more common and often bilateral, though lobar consolidation may be seen. Late development of abscesses is

relatively common. When staphylococcal pneumonia occurs as a complication of influenza, it is usually rapidly

progressive with extensive bilateral pneumonia that resembles pulmonary edema.

In children, it is usually a lobar or multilobar consolidation, rapidly progressing with the development of pneumatoceles

and/or empyema. The presence of pneumatoceles in children is virtually diagnostic of staphylococcal pneumonia.Rapid progression is seen with lobar or multilobar consolidation. Pneumatoceles may rapidly develop, and empyema

is frequent.[21]

Degree of confidence

In patients with underlying structural lung disease, the appearance of the various signs of pneumonia may not be

straightforward.

Narrowing the differential diagnosis of pneumonia into typical and atypical forms on the basis of radiographic

appearance alone is not reliable, as shown in a prospective study by Fang et al.[22]

Computed Tomography

Computed tomography (CT) scanning is increasingly used in clinical practice, but various groups have questioned its

usefulness in evaluating pneumonia. Their reports have suggested that its usefulness in the diagnosis of pneumonia is

limited to the following settings:

Evaluation of an indistinct, abnormal opacity depicted on a chest radiograph

Assessment of patchy, ground-glass, or linear/reticular opacities on chest radiographs

Confirmation of pleural effusion

Examination of neutropenic patients with fever of unknown origin (with the use of ultrathin-section CT

scanning)

In clinical practice, coinfection with multiple organisms is not rare, and underlying abnormalities of the lung

parenchymal usually predispose patients to pneumonia. Hence, the overall clinical and radiologic picture must be

considered.[23]

CT scans of typical bacterial pneumonia are provided below.


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Image in a 49-year-old patient with pneumococcal pneumonia. This chest CT shows a left upper lobe opacity extending to the periphery.

Image in a 50-year-old patient with Haemophilus influenzaepneumonia. The chest CT shows a very dense round area of consolidation

adjacent to the pleura in the left lower lobe.

Ultrasonography

The literature indicates that ultrasonography can aid in the differentiation of consolidation and effusion. Consolidated

lung tissue may appear as hypoechoic areas with blurred margins. The texture varies with the amount of aeration,

being more heterogeneous with aeration and homogenous with dense consolidation.[24] Ultrasonography may also

help in diagnosing empyema and abscesses.

Degree of confidence

The role of ultrasonography in clinical practice is limited to the identification and quantification of parapneumonic

effusions. This area can then be marked for subsequent diagnostic or therapeutic thoracentesis.

Contributor Information and DisclosuresAuthor

Shakeel Amanullah, MD Consulting Physician, Pulmonary, Critical Care, and Sleep Medicine, Lancaster GeneralHospital

Shakeel Amanullah, MD is a member of the following medical societies:American College of Chest Physicians,

American Thoracic Society, and Society of Critical Care Medicine

Disclosure: Nothing to disclose.

Coauthor(s)

David H Posner, MD Assistant Professor of Medicine, New York University School of Medicine; Assistant Chief of

Pulmonary Diseases, Instructor, Intensive Care Unit, Education Coordinator for Pulmonary Fellowship, Lenox Hill

Hospital


Mina Farhad, MD PhD, Clinical Instructor of Radiology, New York University School of Medicine; Head of Thoracic

Imaging, Department of Radiology, Lenox Hill Hospital

Mina Farhad, MD is a member of the following medical societies: Radiological Society of North America


Klaus-Dieter Lessnau, MD, FCCP Clinical Associate Professor of Medicine, New York University School of

Medicine; Medical Director, Pulmonary Physiology Laboratory; Director of Research in Pulmonary Medicine,

Department of Medicine, Section of Pulmonary Medicine, Lenox Hill Hospital

Klaus-Dieter Lessnau, MD, FCCP is a member of the following medical societies:American College of Chest

Physicians,American College of Physicians,American Medical Association,American Thoracic Society, and

Society of Critical Care Medicine


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Disclosure: Sepracor None None

Specialty Editor Board

Satinder P Singh, MD, FCCP Professor of Radiology and Medicine, Chief of Cardiopulmonary Radiology,

Director of Cardiac CT, Director of Combined Cardiopulmonary and Abdominal Radiology, Department of

Radiology, University of Alabama at Birmingham


Bernard D Coombs, MB, ChB, PhD Consulting Staff, Department of Specialist Rehabilitation Services, Hutt

Valley District Health Board, New Zealand


Eric J Stern, MD Professor of Radiology, Adjunct Professor of Medicine, Adjunct Professor of Medical Education

and Biomedical Informatics, Adjunct Professor of Global Health, University of Washington School of Medicine

Eric J Stern, MD is a member of the following medical societies:American Roentgen Ray Society,Association of

University Radiologists, European Society of Radiology, Radiological Society of North America, and Society of

Thoracic Radiology


Robert M Krasny, MD Resolution Imaging Medical Corporation

Robert M Krasny, MD is a member of the following medical societies:American Roentgen Ray Society and

Radiological Society of North America


Chief Editor

Kavita Garg, MD Professor, Department of Radiology, University of Colorado Health Sciences Center

Kavita Garg, MD is a member of the following medical societies:American College of Radiology,American

Roentgen Ray Society, Radiological Society of North America, and Society of Thoracic Radiology


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