Today’s pulmonary infections pose multidimensional challenges for radiologists

March 10, 2009

Radiologists should be clinically focused when handling HIV cases, according to a leading chest expert. They must know if patients are drug-naïve or whether they are already on antiretroviral therapy. It is also important to determine how they acquired their HIV, whether onset is acute or more gradual, and how profoundly unwell the patients feel.

Radiologists should be clinically focused when handling HIV cases, according to a leading chest expert. They must know if patients are drug-naïve or whether they are already on antiretroviral therapy. It is also important to determine how they acquired their HIV, whether onset is acute or more gradual, and how profoundly unwell the patients feel.

"If you have all this information, you are much more likely to make a more meaningful contribution to the management of the patient," said Dr. Simon Padley, consultant radiologist at the Chelsea and Westminster Hospital and Royal Brompton Hospital in London.

Pulmonary infection is the commonest cause of infection-related death, and the sixth commonest cause of death overall. It is particularly important in HIV, he commented during Sunday's special focus session on the new face of pulmonary infections in Europe.

Chest x-rays remain the frontline imaging tool for HIV infection.

"We use CT in a much more limited and tailored way," he said. "Sometimes we use CT when the chest x-ray is being debated: Is it normal or isn't it normal? CT can be very useful for solving that argument."

CT is also used if there are complex or atypical features on a chest radiograph that are difficult to interpret. It is used increasingly for staging and restaging of neoplasms associated with HIV rather than for the assessment of infection. Occasionally CT is used for biopsy planning and biopsy guidance when there is a lesion that may be infected, Padley noted.

Two of the most important infections, pyogenic pneumonia and tuberculosis, occur above the point at which the patient is susceptible to opportunistic infections.

"How are these opportunistic infections acquired? The same way that you get that cold flying across the Atlantic. It's that person two rows behind you who sneezes and aerosolizes the pathogen, which you then inhale," he said. "It used to be that if you were an intravenous drug user, you may acquire your pulmonary infection via perhaps bacterial encodarditis or some other route, but aerosolized droplets are the most common cause of pathogen exposure."

His overall advice for HIV infection is to be aware of overlapping radiological appearances, remember noninfective causes, and put imaging in a clinical context. Microbiology is usually diagnostic, he said.

During the same session, Prof. Christian J. Herold, department of radiology at the University of Vienna, discussed community-acquired and nosocomial pneumonia.

"Imaging plays an important role in the detection, classification, and follow-up of patients with pneumonia," he said. "A solid knowledge of the radiographic features of pneumonia and a fundamental understanding of the epidemiologic, pathophysiologic, and clinical features of pulmonary infections are necessary. The chest x-ray is the primary imaging modality, but CT is increasingly used to detect pneumonia and evaluate complications." Pneumonia acquired in the community tends to occur in otherwise healthy persons, in individuals with co-existing diseases, or in nursing-home residents. The mode of infection is by person-to-person transmission of mucus droplets laden with viruses or bacteria.

Modifying factors that increase the risk of infection with specific pathogens include: age over 65 years, alcoholism, immune-suppressive illness, underlying cardiopulmonary disease, multiple medical comorbidities, structural lung disease (bronchiectasis), corticosteroid therapy (>10 mg prednisolon/day), and recent broad-spectrum antibiotic therapy.