DOI: 10.1148/rg.273065122
RadioGraphics 2007;27:641-655
© RSNA, 2007
Imaging Manifestations of Blastomycosis: A Pulmonary Infection with Potential Dissemination1
Wayne Fang, MD,
Lacey Washington, MD, and
Nidhi Kumar, MD
1 From the Departments of Radiology (W.F.) and Pathology (N.K.), Medical College of Wisconsin, 9200 W Wisconsin Ave, Milwaukee, WI 53226; and the Department of Radiology, Duke University Medical Center, Durham, NC (L.W.). Presented as an education exhibit at the 2005 RSNA Annual Meeting. Received June 21, 2006; revision requested August 9 and received September 22; accepted September 29. All authors have no financial relationships to disclose.
Address correspondence to W.F. (e-mail: wafang{at}wi.rr.com).
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Abstract
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Pulmonary blastomycosis is an uncommon pathologic condition that is endemic to Canada and the upper Midwest of the United States. Blastomycosis has a variety of radiologic manifestations, including airspace consolidation, focal masses, intermediate-sized nodules, interstitial disease, miliary disease, and cavitary lesions. Affected patients may be asymptomatic or may present with clinical manifestations ranging from mild chronic cough to acute respiratory distress syndrome–like symptoms. Patients with acute symptoms are more likely to have airspace consolidation, whereas chronic manifestations may be associated with masslike lesions. Intermediate-sized nodules with accompanying airspace consolidation, particularly in the upper lobes, should raise suspicion for fungal disease. Lymphadenopathy and pleural effusions are quite uncommon, and calcification is not often seen. Blastomycosis may be aggressive and require treatment. Dissemination from the lung is not unusual and can involve any organ. Diagnosis is often delayed because blastomycosis can mimic many other disease processes, including bacterial pneumonia, malignancy, and tuberculosis. Radiologists can best contribute to the care of patients who live or travel in endemic areas by maintaining a high degree of suspicion for blastomycosis and being familiar with its myriad manifestations.
© RSNA, 2007
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LEARNING OBJECTIVES
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After reading this article and taking the test, the reader will be able to:- Describe the epidemiologic features, pathogenesis, and radiologic appearance of Blastomyces dermatitidis.
- Discuss the clinical settings in which blastomycosis should be considered.
- Identify common and uncommon radiologic manifestations of pulmonary blastomycosis.
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Introduction
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Blastomyces dermatitidis (also called North American blastomycosis) is endemic to Canada and the upper Midwest of the United States, particularly in moist wooded areas near this region’s many lakes, rivers, and streams. Human exposures occur during outdoor activities when fungal microhabitats existing in soil with high organic content are disturbed. Inhaled airborne spores result in primary lung infection, which may then become disseminated. The clinical presentation of affected patients is extremely variable, and clinical symptoms of pulmonary infection may be absent, chronic, acute, or even fulminant.
In this article, we describe the B dermatitidis organism and discuss blastomycosis in terms of its epidemiologic features, pathogenesis, and clinical course. In addition, we discuss and illustrate the radiologic manifestations of blastomycosis, including airspace consolidation, masses, intermediate-sized nodules, interstitial disease, miliary disease, and cavitary lesions. We also describe various extrapulmonary manifestations of blastomycosis.
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Organism
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B dermatitidis is a thermally dimorphic fungus that grows in a mycelial form at room temperature and in culture at 25°C. After 2–4 weeks of incubation, mycelial colonies develop into white cottony molds. At microscopy, the mycelia possess branching hyphae with right-angled conidiophores ending in single round conidia. Many other fungal mycelial forms share this appearance with B dermatitidis; thus, this appearance is not specific.
B dermatitidis converts to a yeast form within tissues and in culture at 37°C. At gross examination, yeast colonies appear cream or tan with buttery wrinkled surfaces. 
At microscopic examination, the yeast cells are 8–15 µm in diameter and possess thick double refractile cell walls. Reproducing cells are characterized by single broad-based budding. The daughter cells grow nearly as large as the mother cells before detachment (Fig 1). In the yeast form, B dermatitidis is far more likely to have these features than are other fungi. Direct visualization of these cells in sputum or tissue samples at microscopy is the primary method with which a definitive diagnosis is made (1).
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Figure 1a. B dermatitidis. (a) Photomicrograph (original magnification, x100; hematoxylin-eosin stain) shows a typical round B dermatitidis yeast cell (arrow) with a thick double refractile cell wall and surrounded by granulomatous tissue. (b) Photomicrograph (original magnification, x100; Gomori methenamine silver stain) shows reproducing B dermatitidis cells, which are characterized by broad-based budding and large daughter cells that are nearly as large as the mother cell before separation.
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Figure 1b. B dermatitidis. (a) Photomicrograph (original magnification, x100; hematoxylin-eosin stain) shows a typical round B dermatitidis yeast cell (arrow) with a thick double refractile cell wall and surrounded by granulomatous tissue. (b) Photomicrograph (original magnification, x100; Gomori methenamine silver stain) shows reproducing B dermatitidis cells, which are characterized by broad-based budding and large daughter cells that are nearly as large as the mother cell before separation.
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Making the diagnosis after growing the fungus in culture is also highly reliable but time consuming, requiring weeks (2). Unlike Candida and Aspergillus species, B dermatitidis is not associated with human colonization (3).
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Epidemiologic Features
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B dermatitidis is very difficult to isolate directly from its native environment. Only a few reports of successful isolation have been published, and still fewer reports are associated with outbreaks of disease. In these reports, organisms were found in soil containing decayed vegetation and in decomposing wood. Recent rainfall and proximity to water appear to be important in promoting the growth of the organism (1). B dermatitidis grows in a microclimate of warm, moist soil in wooded areas and flourishes briefly when the proper ecologic conditions are met. When conditions change, the microclimate disappears (1,3).
North American blastomycosis (as distinguished from South American blastomycosis, a different fungus) is considered endemic to regions of North America that have the highest prevalence of disease outbreaks. The majority of cases occur in (a) the states bordering the Mississippi and Ohio rivers, (b) the Midwest states, (c) the Canadian provinces bordering the Great Lakes, and (d) a narrow strip of New York and Canada bordering the St Lawrence River (Fig 2). Prevalence is reported to be 1 in 100,000 persons in these regions. Small hyperendemic areas have been documented within the endemic regions; in these hyperendemic regions, the prevalence may be as high as 40 in 100,000 persons, supporting the hypothesis that specific environmental conditions are important (4,5). Outside of North America, blastomycosis has been found in Africa, India, Israel, and Saudi Arabia, as well as in Central and South America. South American blastomycosis is caused by the fungus Paracoccidioides brasiliensis and is a similar but distinct disease. Notably, infection with P brasiliensis is considered to be an acquired immunodeficiency syndrome (AIDS)–defining illness (6). North American blastomycosis is found infrequently in AIDS patients or other immunocompromised patients, much less frequently than either histoplasmosis or coccidioidomycosis (7).
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Figure 2. Satellite map illustrates the endemic regions of North American blastomycosis (brown), defined as areas of high disease prevalence: the Ohio and Mississippi River valleys, the St Lawrence River area, the Great Lakes region, and part of central Canada. (Courtesy of the National Aeronautics and Space Administration, The Visible Earth [http://visibleearth.nasa.gov].)
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Outdoor activities like hunting, camping, and logging are associated with blastomycosis infection. A male-female ratio as high as 10:1 has been reported in the patient population. This difference is attributed to higher exposure rates for males, who have historically been more likely to perform these activities (3,4). More recent reports and analyses of single outbreaks with multiple cases of infection do not suggest a gender difference in terms of susceptibility to infection (1,3,4,8). Infections have been diagnosed in animals, especially in dogs, but also in horses, cats, ferrets, lions, wolves, sea lions, and polar bears (9). Transmission between human beings or between humans and animals is not considered a significant vector of infection, although there are reports of transmission through dog bites and even of sexual transmission (10,11).
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Pathogenesis
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In the environment, B dermatitidis grows in the mycelial form. The conidia are easily aerosolized (2–10 µm in diameter) and inhaled into the lungs when the microclimate is disturbed. Given their small size, the conidia are capable of reaching the lung periphery but may also settle more centrally. There, they initiate a granulomatous reaction mediated by neutrophils, monocytes, and macrophages. This host response is usually capable of destroying the conidia and inhibiting conversion of mycelia to yeast. However, conidia that overwhelm host defenses rapidly convert to the yeast form and become more resistant to destruction (1). Hematogenous dissemination reportedly occurs less often than in histoplasmosis but is more frequently symptomatic (7). The most common extrathoracic site is the skin, followed by bone, the male genitourinary system, and the central nervous system (CNS). It is generally accepted that the primary site of infection is the lung, with subsequent dissemination to other sites. Rare reported cases of cutaneous inoculation in laboratory workers and veterinarians are thought to be the exception to this rule. Skin findings are often reported on the face, although the etiology of this phenomenon is not clear (1).
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Clinical Course
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The clinical manifestations of blastomycosis may range from asymptomatic infection to a fulminant clinical course. The ability to mimic other diseases is a hallmark of blastomycosis and often leads to erroneous or delayed treatment. In asymptomatic patients, blastomycosis has been found both incidentally and at screening of individuals during epidemics. When blastomycosis is symptomatic, it can have either an acute or a chronic clinical course.
Clinically acute blastomycosis manifests with fever, chills, and cough, similar to bacterial pneumonia. Often, treatment is begun for presumed community-acquired pneumonia, and sputum or tissue culture is obtained only after the patient fails to respond to therapy.
Chronic pulmonary symptoms occur more frequently than acute ones (7). Patients present with intermittent low-grade fevers, mild persistent productive cough, chest pain, and hemoptysis. General symptoms of malaise, fatigue, and weight loss are also often present. These symptoms have been mistakenly diagnosed as tuberculosis or atypical pneumonia.
In a small percentage of cases, blastomycosis has a fulminant course, manifesting as fevers, chills, and shortness of breath. Rapid systemic dissemination and progression to acute respiratory distress syndrome result within 1 week, often leading to death. Patients often require ventilator assistance within a few days of admission. The fulminant manifestation occurs in both immunocompetent and immunocompromised patients. Blastomycosis is not considered an opportunistic fungal infection, but immunocompromised patients with AIDS or a history of either transplantation or steroid use more often have diffuse disease and a higher mortality rate.
At tertiary referral centers, blastomycosis is sometimes found in patients sent for evaluation of presumed malignancy. Most commonly, the evaluation is for suspected lung cancer, but breast, skin, CNS, and laryngeal masses have been diagnosed as blastomycosis infection after pathologic assessment (1). Although pulmonary findings are generally more common, patients may present initially with disseminated extrathoracic infections such as skin lesions, osteomyelitis, prostatitis, CNS abscesses, or meningitis, with few or no pulmonary symptoms.
Disseminated disease should be treated with systemic antifungal medications, but clinicians may choose to observe patients with isolated pulmonary disease, since mild clinical symptoms often resolve without treatment. These untreated patients should be observed for several months to document resolution. Previously treated or untreated thoracic or extrathoracic infections may reactivate, sometimes years after the initial infection (7).
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Radiologic Manifestations of Pulmonary Infection
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The imaging features of blastomycosis are highly variable. The major radiologic features of pulmonary involvement fall into the following categories: airspace consolidation, masses, intermediate-sized nodules, interstitial disease, miliary disease, and cavitary lesions. Regardless of the category, the disease may be unilateral or bilateral and multifocal or solitary. There is no characteristic lobar predilection, although some reports suggest a tendency for blastomycosis to affect the upper lobes over a basal distribution (12). Multiple manifestations may occur in the same patient.
Airspace Consolidation
Airspace consolidation is the most common radiologic manifestation of blastomycosis. Its reported prevalence varies between 26% and 76%, but the consensus is that the majority of cases of blastomycosis manifest with consolidation (7,13). The usual findings consist of patchy, ill-defined opacities or densities. Although areas of confluence can become quite large, lobar consolidation is considered uncommon. Frequently, air bronchograms are found within these areas of consolidation (Figs 3–7). Several reports have noted a correlation between acute manifestation and airspace consolidation (12,14). Predictably, this manifestation is most likely to be mistaken for community-acquired pneumonia. If a patient has a suspicious clinical history or resides in an endemic region, slow recovery from community-acquired pneumonia should raise suspicion for blastomycosis. The fulminant course of blastomycosis rapidly progresses to bilateral diffuse areas of alveolar consolidation (Fig 8). Finally, in reports of epidemic cases, airspace consolidation is seen at radiography in a large majority of patients (1).
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Figure 3. Airspace consolidation from blastomycosis in a young boy with acute fever and productive cough. Anteroposterior chest radiograph shows a large confluent left upper lobar–lingular consolidation obscuring the left border of the heart. Air bronchograms can be seen faintly.
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Figure 4. Airspace consolidation from blastomycosis in a different patient. Computed tomographic (CT) scan shows a large confluent area of consolidation with prominent air bronchograms.
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Figure 5a. Airspace consolidation from blastomycosis in a 45-year-old woman with persistent chronic cough. (a) Chest radiograph shows patchy consolidation in the retrocardiac region. Patchy consolidation is the most common finding in blastomycosis. (b) Magnified view more clearly shows the patchy infiltrate. (c) CT scan shows irregular consolidation in the left lower lobe.
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Figure 5b. Airspace consolidation from blastomycosis in a 45-year-old woman with persistent chronic cough. (a) Chest radiograph shows patchy consolidation in the retrocardiac region. Patchy consolidation is the most common finding in blastomycosis. (b) Magnified view more clearly shows the patchy infiltrate. (c) CT scan shows irregular consolidation in the left lower lobe.
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Figure 5c. Airspace consolidation from blastomycosis in a 45-year-old woman with persistent chronic cough. (a) Chest radiograph shows patchy consolidation in the retrocardiac region. Patchy consolidation is the most common finding in blastomycosis. (b) Magnified view more clearly shows the patchy infiltrate. (c) CT scan shows irregular consolidation in the left lower lobe.
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Figure 6a. Airspace consolidation from blastomycosis in a 20-year-old man. Anteroposterior (a) and lateral (b) chest radiographs show right middle and lower lobar consolidation, an uncommon manifestation of blastomycosis. Patchy consolidation is also seen in the right upper lobe.
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Figure 6b. Airspace consolidation from blastomycosis in a 20-year-old man. Anteroposterior (a) and lateral (b) chest radiographs show right middle and lower lobar consolidation, an uncommon manifestation of blastomycosis. Patchy consolidation is also seen in the right upper lobe.
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Figure 7a. Airspace consolidation from blastomycosis in a 26-year-old man who presented with right lower lobar consolidation after several months of treatment with antibiotics. CT scan (a) and coronal reformatted image (b) show round low-attenuation lesions that are suggestive of small cavities. The patient also developed extensive cutaneous lesions.
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Figure 7b. Airspace consolidation from blastomycosis in a 26-year-old man who presented with right lower lobar consolidation after several months of treatment with antibiotics. CT scan (a) and coronal reformatted image (b) show round low-attenuation lesions that are suggestive of small cavities. The patient also developed extensive cutaneous lesions.
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Figure 8. Fulminant blastomycosis in a 48-year-old immunocompetent man with fever, cough, and dyspnea. Radiograph shows bilateral diffuse areas of alveolar consolidation, which developed rapidly and required intubation after 2 days of hospitalization. The patient died 10 days later.
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Masses
Masses are the second most common radiologic finding in blastomycosis. Their reported prevalence varies, but they occur in up to 31% of cases (13). Masses are usually well circumscribed and between 3 and 10 cm in diameter (Fig 9). They have a tendency to be paramediastinal or perihilar (7). Some reports have found a correlation between masses and more chronic manifestations of blastomycosis (14). These manifestations can be difficult to differentiate from lung malignancy. In a series of 35 cases reported at the Mayo Clinic, masses were resected in 55% due to high suspicion for bronchogenic carcinoma (13). Unlike histoplasmosis, blastomycotic infections rarely have parenchymal or lymph node calcifications. Lymph node enlargement and chest wall invasion are also rare. Pleural effusions are uncommon and are small when seen (10). No effusions were found in our collection of cases. The Blastomycosis Cooperative Study of the Veterans Administration described four pleural effusions in 198 cases of blastomycosis (15).
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Figure 9a. Blastomycotic mass in a 51-year-old male heavy smoker who was referred by a community clinic. (a) Chest radiograph shows a mass in the left upper lobe. (b) Corresponding CT scan shows the mass to be well circumscribed and round with irregular borders. The results of CT-guided biopsy were inconclusive, and the patient underwent left upper lobectomy and mediastinal lymph node dissection for suspected lung carcinoma. Blastomycosis was diagnosed.
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Figure 9b. Blastomycotic mass in a 51-year-old male heavy smoker who was referred by a community clinic. (a) Chest radiograph shows a mass in the left upper lobe. (b) Corresponding CT scan shows the mass to be well circumscribed and round with irregular borders. The results of CT-guided biopsy were inconclusive, and the patient underwent left upper lobectomy and mediastinal lymph node dissection for suspected lung carcinoma. Blastomycosis was diagnosed.
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Intermediate-sized Nodules
Nodules between 0.5 and 3 cm are reported as occurring infrequently (only 6% in a small series [13]). These nodules can be numerous, as demonstrated in Figures 10 and 11, but patients may also have only one or two nodules. Identification of intermediate-sized nodules in combination with other manifestations such as consolidation should raise suspicion for fungal disease and may help make the diagnosis (13).
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Figure 10. Intermediate-sized nodules from blastomycosis in a 44-year-old man who presented with pneumonialike symptoms. Early chest radiograph shows bilateral diffuse intermediate-sized nodules along with patchy consolidations at the lung bases. The disease progressed to a fulminant course, requiring many days of ventilator support for the patient.
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Figure 11. Intermediate-sized nodules from blastomycosis in a 40-year-old woman with persistent cough, chest pain, and intermittent fevers. The patient had experienced progression of symptoms over several months. CT scan shows multiple bilateral intermediate-sized nodules. A large cavitary lesion (not shown) was also present in the right middle lobe.
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Interstitial Disease
A chest radiographic pattern that is classically described as reticulonodular can be seen in approximately 6%–9% of cases of blastomycosis (13). This pattern is usually bilateral and diffuse; often accompanies a more focal area of consolidation, a mass, or a cavity; and is thought to represent intrapulmonary endobronchial dissemination mimicking endobronchial spread of tuberculosis. The pattern usually has a "tree-in-bud" appearance at CT (Fig 12). A fibrotic interstitial pattern also occurs, although uncommonly. This fibrotic appearance is associated with chronic manifestations, perhaps related to the development of scarring, and is often found with an upper lobe distribution (Fig 13) (13).
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Figure 12a. (a) Reticulonodular pattern in blastomycosis. Radiograph shows bilateral reticulonodular opacities, with a large cavitary lesion in the right upper lobe. (b) Magnified view more clearly depicts the interstitial opacities in the right lower lung. (c) On a CT scan, the reticulonodular opacities seen in a have a tree-in-bud appearance.
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Figure 12b. (a) Reticulonodular pattern in blastomycosis. Radiograph shows bilateral reticulonodular opacities, with a large cavitary lesion in the right upper lobe. (b) Magnified view more clearly depicts the interstitial opacities in the right lower lung. (c) On a CT scan, the reticulonodular opacities seen in a have a tree-in-bud appearance.
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Figure 12c. (a) Reticulonodular pattern in blastomycosis. Radiograph shows bilateral reticulonodular opacities, with a large cavitary lesion in the right upper lobe. (b) Magnified view more clearly depicts the interstitial opacities in the right lower lung. (c) On a CT scan, the reticulonodular opacities seen in a have a tree-in-bud appearance.
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Figure 13. Fibrotic interstitial changes in a 49-year-old woman with chronic dry cough. CT scan demonstrates fibrotic interstitial changes in the left upper lobe. Biopsy of a skin lesion on the right cheek revealed blastomycosis.
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Miliary Disease
Miliary disease has a relatively low reported prevalence (11%–28% in small series) and is usually associated with acute and severe clinical manifestations (7,13). The disease usually manifests as bilateral and diffuse nodules less than 3 mm in size (Fig 14). Immunocompromised individuals have been found to have miliary disease more frequently, although airspace consolidation and masses are more common than miliary disease in these patients.
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Figure 14a. Miliary blastomycosis in an acutely ill patient, who also had dissemination to the sacrum and a phalanx of the hand. (a, b) Posteroanterior (a) and lateral (b) chest radiographs demonstrate bilateral diffuse miliary changes. (c) CT scan shows innumerable tiny nodules with a random distribution in both lungs.
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Figure 14b. Miliary blastomycosis in an acutely ill patient, who also had dissemination to the sacrum and a phalanx of the hand. (a, b) Posteroanterior (a) and lateral (b) chest radiographs demonstrate bilateral diffuse miliary changes. (c) CT scan shows innumerable tiny nodules with a random distribution in both lungs.
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Figure 14c. Miliary blastomycosis in an acutely ill patient, who also had dissemination to the sacrum and a phalanx of the hand. (a, b) Posteroanterior (a) and lateral (b) chest radiographs demonstrate bilateral diffuse miliary changes. (c) CT scan shows innumerable tiny nodules with a random distribution in both lungs.
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Cavitary Lesions
Uncommonly, blastomycosis manifests as cavitary lesions (7). Although its prevalence varies widely, cavitation occurs less frequently in blastomycosis than in histoplasmosis and tuberculosis. The specific appearance of the cavities varies, and they may have either thin or thick walls. The cavities can be multiple or single and may be located centrally or peripherally. They have been associated with both acute and chronic symptoms and have been found incidentally (Figs 15–17). Brown et al (13) reported that the cavities usually mimic tuberculosis and other granulomatous disease, being located in the upper lobes and resulting in posttreatment scarring.
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Figure 17. Cavitary blastomycotic lesion in a 29-year-old man with a 3–4-week history of fever, chills, dyspnea, and productive cough. CT scan shows a large, apical, thick-walled cavitary lesion. Cavitary lesions can be found in both acutely ill and asymptomatic patients.
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Extrapulmonary Manifestations
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Multiorgan involvement in North American blastomycosis is not uncommon, occurring in 17%–30% of cases in two reports (5,16). The most common extrapulmonary site of dissemination of blastomycosis is the skin, believed to occur in 20%–40% of cases of disseminated disease (4). At clinical examination, cutaneous lesions may appear verrucous (warty) or ulcerative. Both types of skin lesions usually occur over microabscesses located deeper in the cutaneous tissues. At CT, these microabscesses appear as subcutaneous areas of soft-tissue and fluid attenuation with associated skin thickening (Figs 18–20).
Bone involvement has been reported in up to 25% of extrathoracic cases by Bradsher (1). Although any bone may be involved, the vertebrae, pelvis, sacrum, skull, ribs, and long bones are most frequently affected (1). Areas of osseous involvement usually appear as lucent (radiography) or low-attenuation (CT) lesions with indistinct margins but have no radiologically specific features to help distinguish them from other forms of osteomyelitis (Figs 21, 22). Most bone lesions will resolve with antifungal treatment alone, but some require debridement.
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Figure 21a. Osseous involvement by blastomycosis in a young adult. (a) Radiograph shows an osteolytic lesion with indistinct margins in the middiaphysis of the humerus. (b) Magnified view more clearly delineates the lesion and its margins. (c) Radiograph shows an osteolytic lesion in the distal metaphysis of the ulna that crosses the physis. Solid uninterrupted periosteal reaction is evident along the lateral ulna. (d) On a bone scintigram, both lesions show increased radiotracer uptake.
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Figure 21b. Osseous involvement by blastomycosis in a young adult. (a) Radiograph shows an osteolytic lesion with indistinct margins in the middiaphysis of the humerus. (b) Magnified view more clearly delineates the lesion and its margins. (c) Radiograph shows an osteolytic lesion in the distal metaphysis of the ulna that crosses the physis. Solid uninterrupted periosteal reaction is evident along the lateral ulna. (d) On a bone scintigram, both lesions show increased radiotracer uptake.
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Figure 21c. Osseous involvement by blastomycosis in a young adult. (a) Radiograph shows an osteolytic lesion with indistinct margins in the middiaphysis of the humerus. (b) Magnified view more clearly delineates the lesion and its margins. (c) Radiograph shows an osteolytic lesion in the distal metaphysis of the ulna that crosses the physis. Solid uninterrupted periosteal reaction is evident along the lateral ulna. (d) On a bone scintigram, both lesions show increased radiotracer uptake.
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Figure 21d. Osseous involvement by blastomycosis in a young adult. (a) Radiograph shows an osteolytic lesion with indistinct margins in the middiaphysis of the humerus. (b) Magnified view more clearly delineates the lesion and its margins. (c) Radiograph shows an osteolytic lesion in the distal metaphysis of the ulna that crosses the physis. Solid uninterrupted periosteal reaction is evident along the lateral ulna. (d) On a bone scintigram, both lesions show increased radiotracer uptake.
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Figure 22. CT scan shows B dermatitidis of the pelvis involving the sacroiliac joint and the surrounding bone on both sides of the joint. The lesion is permeative with indistinct margins. Cortical destruction is also seen.
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Prostatitis and epididymo-orchitis are the most common forms of genitourinary involvement (1). These infections are not usually diagnosed radiographically, but the discovery of one of them should prompt chest radiography regardless of the lack of pulmonary symptoms. Indeed, chest radiography should be performed when any extrathoracic blastomycosis is discovered.
Involvement of the CNS occurs in 5%–10% of cases of blastomycotic dissemination (1). The most common manifestation is epidural or parenchymal abscess, with meningitis being the next most common. At CT, abscesses are usually low in attenuation (Fig 23); at MR imaging, they are hypo- or isointense on T1-weighted images and hyperintense on T2-weighted images (Fig 24). Peripheral and dural enhancement is also characteristic, similar to other cerebral abscesses. Early cases of meningitis usually have normal findings, whereas advanced cases show enlarged cerebrospinal fluid spaces, generalized cerebral swelling, and diffuse meningeal enhancement. In a small series, ventricular fluid samples had a higher diagnostic yield than lumbar puncture samples (1).
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Figure 24a. Blastomycosis in a 26-year-old man with chronic cough who developed a headache. Two weeks earlier, skin lesions that the patient thought were acne had appeared on his face, later spreading to the upper body. Axial fluid-attenuated inversion recovery (a) and coronal gadolinium-enhanced fat-saturated (b) MR images show multiple enhancing high-signal-intensity T2 lesions. Blastomycosis was found in sputum, urine, and skin lesion samples.
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Figure 24b. Blastomycosis in a 26-year-old man with chronic cough who developed a headache. Two weeks earlier, skin lesions that the patient thought were acne had appeared on his face, later spreading to the upper body. Axial fluid-attenuated inversion recovery (a) and coronal gadolinium-enhanced fat-saturated (b) MR images show multiple enhancing high-signal-intensity T2 lesions. Blastomycosis was found in sputum, urine, and skin lesion samples.
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Conclusions
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Although uncommon, blastomycosis may be aggressive and require treatment. It has a reputation for mimicking many other disease processes, including bacterial pneumonia, malignancy, and tuberculosis. The majority of cases of blastomycosis will manifest radiologically as consolidation or a mass, although there are few specific rules or patterns associated with this disease entity. The discovery of intermediate-sized nodules with accompanying airspace consolidation should raise suspicion for fungal disease. There may be a predilection for the upper lobes. Patients with acute symptoms are more likely to have airspace consolidation, whereas chronic manifestations may be associated with masslike lesions. Lymphadenopathy and pleural effusions are notably uncommon. Unlike with histoplasmosis, calcification is not often seen.
Radiologists may contribute to the care of patients who live or travel in endemic areas by maintaining a high degree of suspicion for blastomycosis and an awareness of its myriad manifestations.
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Acknowledgments
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The authors wish to thank G. Carrera, MD, L. Goodman, MD, M. Laguna, MD, and M. Peng, MD, Medical College of Wisconsin, Milwaukee, Wis.
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Footnotes
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Abbreviations: AIDS = acquired immunodeficiency syndrome, CNS = central nervous system
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References
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