Imaging in Thoracic Blastomycosis

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Blastomyces dermatitidis is a thermally dimorphic fungus that causes the systemic pyogranulomatous disease termed blastomycosis. This pathogen is endemic to North America, particularly in the states bordering the Mississippi and Ohio rivers, the Great Lakes, and the St. Lawrence Seaway. ^[1] Blastomycosis is the least common of the endemic systemic mycoses; the other, more common mycoses include histoplasmosis and coccidioidomycosis. Lungs, and to a lesser extent, skin and bone, are the most common organs involved with this fungus. Hematogenous dissemination can occur. ^{[2, 3, 4, 5, 6, 7, 8, 9]}

See the images below.

In a 2014 study, according to the United States Agency for Healthcare Research and Quality, states within the Mississippi and Ohio River valleys had the highest age-adjusted hospitalization incidence of blastomycosis cases, with Wisconsin having the highest incidence (2.9 hospitalizations per 100,000 person-years). From 2000 to 2011, blastomycosis-associated hospitalizations increased significantly in Illinois and Kentucky, with an average annual increase of 4.4% and 8.4%, respectively. Overall, 64% of blastomycosis-associated hospitalizations were among men, and the median age at hospitalization was 53 years. ^[7]

The diagnosis of thoracic blastomycosis is made on the basis of a demonstration of organisms in culture or on fungal stains (10% potassium hydroxide) of sputum, bronchoscopy specimens, or secretions obtained from cerebrospinal fluids or dermal, subcutaneous, or other lesions. ^[6] Cultures are positive in more than 90% of cases. Culture growth may take from 1 to several weeks.

Radiographic findings are nonspecific and variable, with radiographic patterns of thoracic blastomycosis being indistinguishable from those of other mycotic infections.

Chest radiography is the first imaging study performed. The most common pattern observed is acute, nonspecific focal lung opacity, which is found in 25-75% of patients. ^{[10, 11, 12, 13, 14]}

For excellent patient education resources, see eMedicineHealth’s patient education article Bronchoscopy.

Chest radiographs usually reveal focal lung opacities in the upper lobes (seen in 25-75% of patients); these opacities are often nodular in character. In adults, the upper lobes are affected more frequently than the lower lobes; the ratio is approximately 2:1. In children, opacities most commonly involve the lower lobes. Lung opacities may be patchy or confluent; they may be subsegmental, segmental, or nonsegmental (see the images below). The radiographic appearance is similar to that seen with community acquired pneumonia; slow improvement, lack of change, or even progression of disease over time should raise the possibility of granulomatous infection.

The next most common radiographic presentation (occurring in as many as 30% of patients) is that of a focal discrete mass, either single or multiple. The mass is usually well circumscribed; such masses are variable in size and occasionally contain air-bronchograms. When solitary, a mass may mimic primary carcinoma, especially when associated with unilateral lymph node enlargement or bone destruction (see the images below).

Cavitation occurs less commonly in patients with blastomycosis than in patients with tuberculosis or chronic histoplasmosis; the reported incidence is approximately 15-20% (see the images below).

In a minority of patients, a miliary or diffuse interstitial disease pattern is seen at presentation; patients have respiratory failure and need mechanical ventilation. This pattern may be observed in previously healthy immunocompromised patients. In many patients, the focal lung opacities or mass may be observed in association with the diffuse interstitial pattern, a finding that supports the hypothesis that pulmonary dissemination occurs from a focal pulmonary site (see the image below).

In contrast to histoplasmosis, hilar and mediastinal adenopathy and calcification are uncommon (occurring in 10-20% of cases).

Pleural involvement and significant effusion are uncommon (20%). Rarely, lung or pleural involvement extends into adjacent bones or soft tissues. Pleural thickening without free effusion is a more common radiographic finding.

Osteolytic lesions in the skeleton usually are associated with superficial abscesses. Rarely, mediastinal involvement results in superior vena cava obstruction or brachial plexopathy.

Computed tomography (CT) scan findings of thoracic blastomycosis are variable. As with chest radiography, nonspecific lung parenchymal opacification is most commonly observed, followed by mass lesions (see the images below).

In a review of CT findings in 16 patients with pulmonary blastomycosis, Winer-Muram et al reported the following ^[15] :

A localized mass – 14 patients (88%)

Consolidation – 9 patients (56%)

Masses ranging from 3-16 cm in diameter (mean, 8 cm)

A majority of masses containing air bronchograms – 12 of 14 patients (86%)

Unilateral abnormalities – 11 patients

Abnormalities involving both lung – 5 patients

In addition, no lobar predominance was noted. Cavitation was observed in 2 patients; calcified hilar nodes was observed in 7 patients (44%); and enlarged noncalcified nodes was observed in 1 patient.

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Alkrinawi S, Reed MH, Pasterkamp H. Pulmonary blastomycosis in children: findings on chest radiographs. AJR Am J Roentgenol. 1995 Sep. 165(3):651-4. [Medline].

Brown LR, Swensen SJ, Van Scoy RE, et al. Roentgenologic features of pulmonary blastomycosis. Mayo Clin Proc. 1991 Jan. 66(1):29-38. [Medline].

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Sheflin JR, Campbell JA, Thompson GP. Pulmonary blastomycosis: findings on chest radiographs in 63 patients. AJR Am J Roentgenol. 1990 Jun. 154(6):1177-80. [Medline].

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Winer-Muram HT, Beals DH, Cole FH Jr. Blastomycosis of the lung: CT features. Radiology. 1992 Mar. 182(3):829-32. [Medline].

Dimar JR 2nd, Puno RM, Nowacki MR, Carreon LY. Surgery for blastomycosis of the spine. Am J Orthop (Belle Mead NJ). 2014 Nov. 43 (11):E266-71. [Medline].

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Fahad M Al-Hameed, MD, AmBIM, FCCP, FRCPC Chairman, Intensive Care Department, Director, Ambulatory Care Center (Services), Professor Associate of Medicine/Critical Care, College of Medicine, King Saud Ben Abdulaziz University for Health Sciences; Consultant in Critical Care and Pulmonary Medicine, King Khalid National Guard Hospital, King Abdulaziz Medical City, Saudi Arabia

Fahad M Al-Hameed, MD, AmBIM, FCCP, FRCPC is a member of the following medical societies: American College of Chest Physicians, American Thoracic Society, Canadian Medical Association, Royal College of Physicians and Surgeons of Canada, Saudi Association for Venous Thrombo-Embolism

Disclosure: Nothing to disclose.

Sat Sharma, MD, FRCPC Professor and Head, Division of Pulmonary Medicine, Department of Internal Medicine, University of Manitoba Faculty of Medicine; Site Director, Respiratory Medicine, St Boniface General Hospital, Canada

Sat Sharma, MD, FRCPC is a member of the following medical societies: American Academy of Sleep Medicine, American College of Chest Physicians, American College of Physicians-American Society of Internal Medicine, American Thoracic Society, Canadian Medical Association, Royal College of Physicians and Surgeons of Canada, Royal Society of Medicine, Society of Critical Care Medicine, World Medical Association

Disclosure: Nothing to disclose.

Bruce Maycher, MD 

Bruce Maycher, MD is a member of the following medical societies: American Roentgen Ray Society, Canadian Medical Association, Radiological Society of North America, Society of Thoracic Radiology

Disclosure: Nothing to disclose.

Bernard D Coombs, MB, ChB, PhD Consulting Staff, Department of Specialist Rehabilitation Services, Hutt Valley District Health Board, New Zealand

Disclosure: Nothing to disclose.

Eugene C Lin, MD Attending Radiologist, Teaching Coordinator for Cardiac Imaging, Radiology Residency Program, Virginia Mason Medical Center; Clinical Assistant Professor of Radiology, University of Washington School of Medicine

Eugene C Lin, MD is a member of the following medical societies: American College of Nuclear Medicine, American College of Radiology, Radiological Society of North America, Society of Nuclear Medicine and Molecular Imaging

Disclosure: Nothing to disclose.

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 School of Medicine

Disclosure: Nothing to disclose.

Imaging in Thoracic Blastomycosis

Research & References of Imaging in Thoracic Blastomycosis|A&C Accounting And Tax Services
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