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Invasive pulmonary aspergillosis: frequency and meaning of the "hypodense sign" on unenhanced CT

¹ Department of Diagnostic Radiology, Eberhard-Karls-University, Hoppe-Seyler-Str.3, 72076 Tübingen, ² Department of Internal Medicine-Oncology, Eberhard-Karls-University, Ottfried-Müller-Str. 5, 72070 Tübingen, ³ Institute of Medical Biology, Eberhard-Karls-University, Elfriede-Authorn-Str. 6, 72076 Tübingen, ⁴ Department of Pathology, Eberhard-Karls-University, Liebermeisterstraße 8, 72076 Tübingen and ⁵ Department of Medical Biometry, Eberhard-Karls-University Tübingen, Westbahnhofstrasse 55, 72070 Tübingen, Germany

View larger version (77K): [in a new window]   Figure 1. 63-year-old patient with fever at aplasia following bone marrow transplant for acute leukaemia. Axial unenhanced CT-image (view from below) shows a large area of consolidation in the right upper pulmonary lobe. (a) Using a narrow "soft tissue" window setting, the central hypointensity (white arrow) is easy to delineate (width 120 HU; level 20 HU). (b) Note poor delineation of the infarcted area (white arrow) on the same image viewed by standard "soft tissue" window setting (width 450 HU; level 35 HU). (c) The same lung opacity is viewed by a lung window setting (documented two slices caudally from a,b). This window setting is not suitable for recognition of the central hypointensity, but it demonstrates the halo sign (white arrow).

View larger version (44K): [in a new window]   Figure 2. 17-year-old male patient with leukaemia and fever at aplasia after bone marrow transplant. (a) Axial non-enhanced CT-image shows focal subpleural consolidation in the right pulmonary lower lobe, due to lung parenchymal necrosis by invasive pulmonary aspergillosis. On unenhanced CT the central hypodense parenchymal infarction is though easily distinguishable. It is surrounded by inflammatory reaction (black arrow) and a hyperdense ring in between (white arrow), presumably caused by haemorrhage (confirmed by biopsy). (b) One of the follow-up CT examinations was performed after intravenous contrast material administration, in order to exclude other potential infectious complications in the abdomen. Easier delineation of infarcted lung parenchyma is obvious (white arrow). However, unenhanced CT is also of diagnostic quality.

View larger version (95K): [in a new window]   Figure 3. 63-year-old male patient with fever at aplasia following bone marrow transplant for acute myeloid leukaemia. Axial CT scans show follow-up of a nodular invasive pulmonary aspergillosis lesion in the upper lobe of the left lung. (a) A focal nodular lung parenchymal consolidation with homogeneous density is seen in the left upper lung lobe. By appropriate window setting (same window setting as on Figure 1a), (b) central hypodensity can be recognized. (c) Note delineation of the crescent sign, and (d) corresponding cavitation, following successful antifungal therapy.

View larger version (71K): [in a new window]   Figure 4. Invasive pulmonary aspergillosis in a 55-year-old female patient with chronic myeloid leukaemia. A magnified view of a slice of the right upper lobe shows vital hyphae of Aspergillus fumigatus in a pulmonary lesion with central necrosis. In the periphery of the lesion, beneath the "crescent air", a rim of chronic inflammation is present (black arrow). Note also hyphae in intravascular thrombotic material (white arrow). (a) PAS x 5. (b) Photomicrograph from the area of consolidation shows tissue necrosis. Aspergillus fumigatus hyphae could be identified in necrotic tissue (white arrow). PAS x 400.