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Respiratory Tract Infections, Neoplasms, and Childhood Disorders
549
node granulomas is called a
Ghon complex
(Fig. 22-6).
The Ghon complex eventually heals, undergoing shrink-
age, fibrous scarring, and calcification, the last of these
being visible radiographically. However, small num-
bers of organisms may remain viable for years. Later, if
immune mechanisms decline or fail, latent tuberculosis
infection has the potential to develop into secondary
tuberculosis.
PrimaryTuberculosis
Primary tuberculosis is a form of the disease that devel-
ops in previously unexposed, and therefore unsensi-
tized, persons.
2,13,32,33
It typically is initiated as a result of
inhaling droplet nuclei that contain the tubercle bacil-
lus (Fig. 22-7). Most people with primary tuberculosis
are asymptomatic and go on to develop
latent tuber-
culosis infection
in which T lymphocytes and macro-
phages surround the organism in granulomas that limit
their spread. Individuals with latent tuberculosis do not
have active disease and cannot transmit the organism to
others.
34
In approximately 5% of newly infected people, the
immune response is inadequate; these people go on to
develop progressive primary tuberculosis with continued
destruction of pulmonary tissue and spread to multiple
sites within the lung.
2,32,33
This usually occurs in young
children, whose immune systems are immature, or in
adults with HIV infection or other immunodeficiency
disorders. Sometimes the onset of symptoms is abrupt,
with high fever, pleuritis, and lymphadenitis. As the dis-
ease spreads, the organism gains access to the sputum,
allowing the person to infect others.
In rare instances, tuberculosis may erode into a blood
vessel, giving rise to hematogenic dissemination.
Miliary
tuberculosis
describes minute lesions, resembling millet
seeds, resulting from this type of dissemination that can
involve almost any organ, particularly the brain, menin-
ges, liver, kidney, and bone marrow.
SecondaryTuberculosis
Secondary tuberculosis represents either reinfection
from inhaled droplet nuclei or reactivation of a previ-
ously healed primary lesion
2
(see Fig. 22-7). It often
occurs in situations of impaired body defense mecha-
nisms. The partial immunity that follows primary tuber-
culosis normally affords protection against reinfection
and helps localize the disease should reactivation occur.
After the development of hypersensitivity, the infection
becomes quiescent in the majority of patients. Cavities
are formed as a result of the immune response walling
off the infection. These cavities may coalesce to a size
of up to 10 to 15 cm in diameter (Fig. 22-8). In vulner-
able patients such as the very young or immunocom-
promised adults, the primary infection can progress into
FIGURE 22-6.
Primary tuberculosis. A healed Ghon complex
is represented by a subpleural nodule and involved hilar
lymph nodes. (From Beasley MB,TravisWD, Rubin E.The
respiratory system. In: Rubin R, Strayer DS, eds. Rubin’s
Pathology: Clinicopathologic Foundations of Medicine. 6th ed.
Philadelphia, PA: Wolters Kluwer Health | Lippincott Williams &
Wilkins; 2012:550.)
Secondary
tuberculosis
Inhalation of
tubercle bacillus
Development of
cell-mediated
immunity
Positive skin
test
Primary
tuberculosis
Progressive
or disseminated
tuberculosis
Reactivated
tuberculosis
Cell-mediated
hypersensitivity
response
Granulomatous
inflammatory
response
Ghon
complex
Healed dormant
lesion
Reinfection
FIGURE 22-7.
Pathogenesis of tuberculosis infection.
