PMC6020650_01
Eurasian eagle owl, ventrodorsal radiographs. Increased soft tissue opacity in left lung (arrow).
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Workup of the dyspnea problem included radiographs which revealed increased areas of soft tissue opacity within the coelom, especially in the lung fields (Figure 1).
Eurasian eagle owl, coelomic cavity. The abdominal air sac (A) thickened by friable tan to grey exudate. The caudal aspect of the thoracic air sacs coated by black fuzzy material (black arrows). Numerous 1-2 mm yellow-tan plaques on the serosal surfaces of the abdomen (grey arrow). The heart (H) and liver (L) are labeled for anatomic orientation.
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On gross examination of the coelom, the left thoracic air sacs were thickened by friable grey exudate and collapsed upon manipulation, revealing lumina filled with brown friable debris that extended into the subjacent pulmonary parenchyma (Figure 2). Dozens of 1-2 mm raised yellow-tan, less sharply defined foci, sometimes with a fuzzy surface, covered the serosal surfaces of abdominal (Figure 2) and cranial thoracic viscera and the lining of cervical air sacs.
Eurasian eagle owl, air sac. (a),(b) The air sac wall was diffusely thickened by an exudate of fibrin, heterophils, and fewer macrophages with entrapped oxalate crystals. H&E stained section (a) with comparable view under polarized light (b). Polarized light with lower light intensity to better visualize the birefringent, entrapped oxalate crystals. Original objective 4x. (c) Oxalate crystals entrapped within the air sac wall (arrow). Crystals have the characteristic wheat sheaf and rosette arrangement for calcium oxalate. Original objective 20x.
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Using a Leica DM 1000 light microscope, examination of hematoxylin and eosin stained histology slides revealed the abdominal air sac wall was diffusely thickened by an exudate of fibrin, heterophils, and fewer macrophages with entrapped oxalate crystals (Figure 3). The oxalate crystals were characterized by translucent, pale yellow, highly birefringent, anisotropic linear shapes arranged in sheaves and rosettes (Figure 3).
Eurasian eagle owl, air sac. Pigmented conidial heads mixed with fungal hyphae. (a) Visualization of conidiophores of Aspergillus section Nigri on routine H&E section. Original objective 40x. (b) Fungal mats characterized by dark black outlines with Grocott's methenamine silver (GMS) stain. Original objective 40x.
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Fruiting bodies (conidiophores) were visible, including the stalk (variably present), central vesicle with circumferentially biseriate, radiating linear metulae and phialides, and peripheral round, pigmented conidia (Figures 4(a) and 4(b)) and Grocott's methenamine silver stain rarely demonstrated septae.