Radiology-based diagnosis of fungal pulmonary infections in high-risk hematology patients: are we making progress?

Abstract

Purpose of review: In patients with hematological malignancies, high-resolution computed tomography (CT) is the recommended imaging approach for diagnosis, staging and monitoring of invasive fungal disease (IFD) but lacks specificity. We examined the status of current imaging modalities for IFD and possibilities for more effective applications of current technology for improving the specificity of IFD diagnosis.

Recent findings: Although CT imaging recommendations for IFD are largely unchanged in the last 20 years, improvements in CT scanner technology and image processing algorithms now allow for technically adequate examinations at much lower radiation doses. CT pulmonary angiography can improve both the sensitivity and specificity of CT imaging for angioinvasive molds in both neutropenic and nonneutropenic patients, through detection of the vessel occlusion sign (VOS). MRI-based approaches also show promise not only for early detection of small nodules and alveolar hemorrhage but can also be used to detect pulmonary vascular occlusion without radiation and iodinated contrast media. 18F-fluorodeoxyglucose (FDG) PET/computed tomography (FDG-PET/CT) is increasingly used to monitor long-term treatment response for IFD, but could become a more powerful diagnostic tool with the development of fungal-specific antibody imaging tracers.

Summary: High-risk hematology patients have a considerable medical need for more sensitive and specific imaging approaches for IFD. This need may be addressable, in part, by better exploiting recent progress in CT/MRI imaging technology and algorithms to improve the specificity of radiological diagnosis for IFD.

Box 1

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FIGURE 1

Computed tomography pulmonary angiography for detection of invasive fungal disease. (a) Negative vessel occlusion sign as patent contrast-enhanced vessels are visualized in the right lower lung consolidation of a neutropenic patient with Pseudomonas aeruginosa pneumonia; (b) positive vessel occlusion sign (arrow) in the right lung of a neutropenic patient with positive serum galactomannan (probable aspergillosis); (c) volumetric projection of the pulmonary vessel tree demonstrating obstructed vessel (arrow).

FIGURE 2

Combined low dose computed tomography (LDCT) imaging with pulmonary angiography to diagnose invasive fungal disease. a 42-year-old man who received alloHCT for acute myeloid leukemia developed Gram-negative Pseudomonas aeruginosa sepsis prior to engraftment. Initial LD-CT at the time of initial fever during the first 24 h of neutropenia reveals on axial CT images (a) a small micronodule (<10 mm) in the right lower lung (arrow). Patient developed persistent fever with a repeat LD-CT 10 days later (b) demonstrating enlarged (>10 mm) right lower lobe infiltrate amenable to CTPA pulmonary angiography (arrow). CTPA revealed (c) arterial vessel occlusion (d, inset magnified image) suggestive of angioinvasive fungal disease. Modified with permission from reference [30^▪]. CT, computed tomography; CTPA, CT pulmonary angiography; HCT, hematopoietic cell transplantation.