Medical Imaging and Timely Diagnosis of Invasive Pulmonary Aspergillosis

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Abstract
Reliable and timely diagnosis of invasive pulmonary aspergillosis (IPA) remains an interesting clinical challenge. At present, the in vivo clinical diagnosis of IPA is based on (1) host risk factors for the acquisition of this disease; (2) microbiological data, including the results of molecular diagnostic techniques; and (3) clinicoradiological data. The European Organization for Research and Treatment of Cancer/Mycoses Study Group incorporated these criteria into consensus diagnostic guidelines intended for clinical and epidemiological research involving patients with hematological malignancies or stem cell transplants [1]. In this issue of Clinical Infectious Diseases Greene et al. [2] present high-resolution CT imaging data from a large series of patients with definite and probable IPA from the Global Comparative Aspergillosis Study, to assess the prevalence of the halo sign and to correlate imaging findings at presentation with therapeutic response. This study corroborates the importance of the CT scan in the diagnostic elaboration of infection and respiratory symptoms in a population of patients with a high a priori likelihood of developing invasive, opportunistic fungal infections. The majority of the patients had hematological immunosuppressive conditions; only 14% of patients had nonhematological immunosuppressive conditions. It was found that most patients (94%) presented with nodular lesions, and 61% of patients presented with a halo sign. Furthermore, the outcomes of patients presenting with a halo sign were significantly better than those of patients with other radiological abnormalities. This study provides large-scale confirmation of the diagnostic value of early CT scanning of the chest in patients with severe neutropenia who are developing respiratory symptoms and signs suggestive for IPA, as was established by Caillot et al. [3]. Timely recognition of IPA shortens the delay before institution of appropriate therapy, creating an opportunity for curing the disease at an early stage with an inoculum amenable to antifungals. The CT halo sign appears early during the course of IPA, whereas the air crescent sign occurs later and is less useful for early diagnosis [4]. Approximately half of the patients in the Global Comparative Aspergillosis Study did not have neutropenia at the time of enrollment in the treatment protocol. The high prevalence of the halo sign in this series of patients supports its diagnostic value even for severely immunocompromised patients without severe neutropenia.

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