Fungal Pulmonary Infections and CT Findings
Yes, fungal pulmonary infections can present with no findings on CT of the chest, although this is uncommon as CT is generally more sensitive than other imaging modalities for detecting early fungal infections. 1
Sensitivity of CT for Fungal Pulmonary Infections
CT scans are significantly more sensitive than conventional chest radiographs for detecting fungal pulmonary infections, with chest radiographs frequently showing normal or non-specific findings (29% and 71%, respectively) in the early stages of invasive pulmonary aspergillosis 2
In immunocompromised patients with febrile neutropenia, approximately 50% of patients have pathological findings on high-resolution CT scans when chest radiographs appear normal 1
CT with IV contrast for the diagnosis of invasive pulmonary aspergillosis has a sensitivity of 79%, specificity of 85%, positive predictive value of 76%, and negative predictive value of 87% in pediatric patients with febrile neutropenia 1
Typical CT Findings When Present
When visible on CT, fungal infections typically present with:
- Nodules (present in 90% of patients with fungal infections) 3
- Halo sign (ground-glass attenuation surrounding nodules) - seen in 95% of early invasive pulmonary aspergillosis cases 2
- Air-crescent sign (delayed finding) 1
- Consolidation 1
- Reversed halo sign (relatively specific for mucormycosis) 1
- Cavitary lesions 1
For Pneumocystis pneumonia specifically, findings often include:
- Diffuse bilateral perihilar infiltrates
- Patchy areas of ground-glass attenuation with peripheral sparing
- Cysts and septal thickening 1
Why Fungal Infections May Not Be Visible on CT
Early-stage infections may not yet have produced visible structural changes in the lung parenchyma 1
In severely immunocompromised patients, the inflammatory response may be blunted, resulting in less pronounced radiographic findings 1
Autopsy studies have shown that up to 75% of invasive fungal infections are not detected ante mortem, suggesting limitations in current imaging techniques 1
The sensitivity of CT for fungal infections, while high (92.18% in one study), is not 100%, meaning some infections will be missed 4
Clinical Implications
The German Society of Hematology and Medical Oncology recommends CT scans for patients with prolonged (>96 hours) febrile neutropenia when there is concern for invasive fungal disease, even when chest radiographs are normal 1
The Society of Clinical Oncology makes a strong recommendation to obtain a chest CT for patients with prolonged febrile neutropenia when there is concern for invasive fungal disease, as the lungs are the most commonly affected site 1
Follow-up CT scans should generally not be ordered less than 7 days after starting treatment, as pulmonary infiltrates may initially increase in volume despite effective antifungal therapy 1
In patients with suspected fungal infection but negative CT findings, additional diagnostic procedures such as bronchoalveolar lavage (BAL) may be necessary 1
Pitfalls and Caveats
A negative CT scan does not rule out a fungal pulmonary infection, particularly in the early stages 1, 2
CT findings of fungal infections can overlap with other conditions including bacterial pneumonia, tuberculosis, nocardiosis, and malignancies 1
Comparison with previous CT scans is essential to detect subtle changes that may indicate early infection 1
In cases where CT is not feasible or desired, MRI of the lungs may represent an alternative imaging modality 1
Early empirical antifungal treatment should be considered in high-risk patients with persistent fever despite negative imaging findings 5