Thoracic Imaging 2003 - Society of Thoracic Radiology

THURSDAY
258
Imaging of Coccidioidomycosis
William Berger, M.D.
Objective: To illustrate the various imaging findings related to
thoracic Coccidioides immitis infection.
Coccidioidomycosis is an infection caused by Coccidioides
immitis, a dimorphic soil-inhabiting fungus. The disease occurs
in endemic areas, essentially confined to the Western Hemisphere,
particularly the southwestern United States. Approximately
100,000 new cases of coccidioidomycosis occur in endemic
regions each year. Knowledge of the various imaging findings
related to coccidioidomycosis is important for radiologists outside
of endemic regions as the southwestern United States is a popular
tourism destination, and consequently patients with coccidioidomycosis
may seek medical attention in nonendemic regions.
Pulmonary manifestations are particularly common, as 99%
of coccidioidomycosis infections are acquired by inhalation of
arthrospores contained in dust. Approximately 30-40% of
patients will develop symptoms following a 1-3 week incubation
period, usually mild respiratory illness characterized by pleuritic
chest pain and dry cough. Systemic manifestations may occur
and include fever, night sweats, and myalgia. “Valley” or
“Desert” fever usually implies primary disease combined with
characteristic skin lesions such as erythema nodosum.
Resolution of the infection usually occurs over 2-6 weeks, after
which immunocompetent patients develop immunity. About
three quarters of patients with primary coccidioidal pneumonia
will go on to complete recovery. Persistent primary or chronic
pulmonary Coccidioidomycosis occurs in about 5% of patients.
Approximately 0.5% of white and 10-15% of African American
and Philipino patients develop disseminated disease.
A diagnosis of Coccidioidomycosis in endemic areas may be
established if typical clinical or radiographic findings are present.
In nonendemic areas, a travel history is of great importance
as the diagnosis may be delayed without knowledge of previous
travel to an endemic region. Serolgic tests for C. immitis are of
benefit in establishing the diagnosis of avute or primary coccidioidomycosis,
as they are accurate, and generally considered to
be the most reliable among currently available serologic markers
for mycoses. Occasionally, bronchoscopy, or biopsy of a
lymph node, skin lesion, or pulmonary nodule is needed to
establish the diagnosis.
Treatment with antifungal medication is usually not necessary,
but is often indicated for immunocompromised patients
and in those with severe primary or disseminated coccidioidomycosis.
Antifungal medication is usually not required for
treatment of a nodule or cavity, or following resection of a lung
lesion. Symptomatic patients with cavities may be treated with
oral azole therapy. Further, cavities that are large, persist, or are
subpleural (predisposing to rupture into the pleural space) are
usually treated operatively. Chronic coccidioidal fibrocavitary
disease is usually treated with azole antifungal therapy.
Primary Coccidioidomycosis occurs after inhalation of the
arthrospores, which induce an exudative reaction, producing a
typical bronchopneumonia, which eventually is accompanied by
a granulomatous reaction. The pneumonia usually remains relatively
localized, and frequently completely resolves.
Radiographic findings in primary coccidioidomycosis vary from
no abnormalities to areas of air space consolidation, which are
usually unilateral (80%) and often confined to the parahilar and
basal regions. Consolidation is the most common radiographic
abnormality and may be dense or hazy and ill defined.
Occasionally, areas of consolidation may resolve in one area
and develop in another, producing so-called “phantom infiltrates”.
Mediastinal (5%) and hilar (15%) adenopathy may
occur, and small effusions (typically ipsilateral to consolidations)
occur in about 10%. Large effusions are rare. Less commonly,
a cavity or one or more nodules may be present during
the primary phase of the disease.
Chronic Coccidioidomycosis is typically defined when clinical
and radiographic manifestations last for longer than 6
weeks. Most commonly, a single nodule develops, frequently in
the same area as a pre-existing consolidation, a finding that is
particularly suggestive of Coccidioidomycosis. The nodules are
usually less than 4 cm, frequently occur in mid to apical portions
of the lung (including the anterior segments of the upper
lobes in contrast to tuberculosis), and almost never calcify.
These nodules may spontaneously cavitate and resolve, remain
stable, or enlarge slowly. Less frequently multiple nodules may
develop. Multiple nodules are almost always randomly distributed,
small, and occasionally show microcavitation. Marked
contrast enhancement of Coccidioidal nodules has been reported.
Most patients with nodules are asymptomatic and frequently
serum coccidioidal antibodies are negative.
Occasionally biopsy of a nodule may be necessary to exclude a
malignant etiology if a previous pneumonia in the same location
can not be documented. Cavities are usually the result of cavitation
of a nodule or excavation of a pneumonia. The cavities
are also usually less than 4 cm and frequently have thin-walled
“grape skin” morphology, though thick or irregular cavity wall
morphology may also be observed. They are well circumscribed
and rarely contain air-fluid levels. They also have a
propensity for the upper lungs and frequently resolve spontaneously.
About half of patients with cavities are asymptomatic,
25% have hemoptysis or respiratory complaints. Subpleural
cavities may rupture into the pleural space producing pneumothorax
and associated empyema. The most serious form of chronic
Coccidioidomycosis is progressive and persistent pneumonia,
which may ultimately prove fatal, especially in immunocompromised
patients. Chronic progressive coccidioidal pneumonia
occurs in less than 1% of patients, and may simulate chronic
pulmonary tuberculosis or histoplasmosis due to presence of
apical fibronodular changes, cavities, and volume loss.
Disseminated Coccidioidomycosis usually occurs early in
the course of the disease, but may develop from chronic progressive
pneumonia or extrathoracic coccidioidomycosis.
Disseminated disease, is more common in African American
and Filipino patients, as well as the immunocompromised.
Disseminated coccidioidomycosis has been documented in
immunocompetent patients, though is more commonly fatal in
immunocompromised patients. Disseminated thoracic coccidioidomycosis
usually produces a miliary pattern. Associated
mediastinal or hilar adenopathy is common. Extrathoracic disease
is also frequently present, usually related to basal meningitis,
meningoencephalitis, or vertebral osteomyelitis. .