imaging in primary tuberculosis

7/29/2019 Imaging in Primary Tuberculosis

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Imaging in Primary Tuberculosis

Primary tuberculosis is said to occur when clinically manifest infection follows the

first exposure to the organism. Ultimately, the ability of MTb to cause human

infection is related to the organism's ability to survive dormant within hostmacrophages for long periods of time, and to incite a T-cell-mediated, delayed

hypersensitivity response by the infected host. Under normal circumstances, the host

will sequester the MTb organism by forming granulomas. Usually, these granulomas

show caseous necrosis, a pattern characteristically, but not exclusively, associated

with tuberculous infection. The initial infection site has been termed the Ghon focus.

Shortly after the infection occurs, organisms may spread through the lymphatics to

hilar and mediastinal lymph nodes. Both sites usually heal with fibrosis and

calcification. The combination of the lung parenchymal and lymph node MTb

infection sites has been termed the Ranke or Ghon complex (figure 1).

Figure 1.

Ranke (Ghon)

Complex

Frontal chest

radiograph

shows acalcified right

lung nodule

with associated

calcified hilar

lymph nodes.

Organisms within the active Ghon focus often gain access to the bloodstream and may

disseminate to extrathoracic organs; but, usually, host defenses are sufficient to

prevent overt infection from developing in extrathoracic sites. It is important to

remember that, although the pulmonary, lymphatic, and extrathoracic foci of infection

are usually inactive at this point, organisms remain viable and may serve as the nidus

for reactivation of disease when circumstances become favorable. Primary MTb

infection in children is usually asymptomatic, and may be detected only with the

conversion of skin tests. When symptoms occur, cough and fever are most common.

In contrast, adults with primary MTb infection are usually symptomatic, and may

present with weight loss, failure to thrive, fever, cough, and hemoptysis. Night sweatsmay also occur.

Patients with primary MTb most often show no radiologic abnormalities. If overt

infection occurs, the pattern is usually one of air-space consolidation (figure 2), often

involving an entire lobe. The right lung is more commonly affected than the left,

although no definite zonal predominance is seen. Cavitation in primary MTb is

unusual, and miliary dissemination is similarly uncommon.


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Figure 2.

Primary MTb

Frontal chest

radiograph

shows left lower

lobe

consolidation

with a small left

pleural effusion.

MTb organisms

were recoveredfrom sputum

cytology.

Atelectasis is often encountered in children with primary MTb (figure 3), and may be

related to airway compression by enlarged lymph nodes. Less commonly, rupture of

an infected lymph node into an adjacent bronchus may cause endobronchialdissemination of infection associated with atelectasis. Adults with primary MTb

uncommonly present with pulmonary atelectasis.

Figure 3. MTb

Infection

Causing

Bronchial

Stenosis

Right upper lobe

atelectasis in a

child with right

upper lobe

bronchial

compression

due to MTb

adenitis.

Radiographic abnormalities in primary MTb infections are often slow to resolve, even

with the institution of prompt treatment. Air-space opacities may take more than 6

months to clear, and lymphadenopathy may take even longer to resolve.

Lymphadenopathy commonly occurs in children with primary MTb infection. Usually

hilar lymph nodes are involved, and mediastinal lymph nodes, particularly in the right

paratracheal region, may be enlarged, as well. Unilateral lymphadenopathy is more

often seen than is bilateral disease, and occasionally lymph node enlargement may be

the only radiographic finding present. Lymphadenopathy is uncommon in adults with


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primary MTb, unless they are immunocompromised (see later). Lymph nodes actively

infected with MTb quite commonly show central low attenuation, representing

necrosis, on contrast-enhanced CT. Pleural effusion may occur in patients with

primary MTb infection. Often, when tuberculosis is discovered as the cause of pleural

effusion, no parenchymal focus of disease is radiographically evident; this pattern is

considered characteristic of primary MTb pleural infection. Usually such effusions are

small and unilateral.

Progressive Primary Tuberculosis

Rarely, a parenchymal focus of primary MTb infection becomes rapidly progressive.

Extensive consolidation and cavitation develop, either at the site of the initial

pulmonary parenchymal focus of infection or in the apical and posterior segments of

the upper lobes. Thus, progressive primary MTb infection may closely resembles

postprimary MTb infection.

References: To return to reference section after viewing abstract, clickhere before

clicking on "abstract".

Kim H, Song K, Goo J, Lee J, Lee K, Lim T. Thoracic sequelae and complications of

tuberculosis. Radiographics 2001; 21:839-858; discussion 859-860. Text

Lee K, Im J. CT in adults with tuberculosis of the chest: characteristic findings and

role in management. AJR 1995; 164:1361-1367. Abstract

Primack S, Logan P, Hartman T, Lee K, Muller N. Pulmonary tuberculosis and

Mycobacterium avium-intracellulare: a comparison of CT findings. Radiology

1995;194:413-417. Abstract

Leung A. Pulmonary tuberculosis: the essentials. Radiology 1999; 210:307-322. Text

Lee J, Lee K, Jung K, Han J, Kwon O, Kim J, Kim T. Pulmonary tuberculosis: CT

and pathologic correlation. J Comput Assist Tomogr 2000; 24:691-698. Abstract
http://pathhsw5m54.ucsf.edu/cts/unknown19/primarytb.html#referencehttp://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=11452057http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=7754873http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=7824720http://radiology.rsnajnls.org/cgi/content/full/210/2/307http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=11045687http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=11452057http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=7754873http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=7824720http://radiology.rsnajnls.org/cgi/content/full/210/2/307http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=11045687http://pathhsw5m54.ucsf.edu/cts/unknown19/primarytb.html#reference

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