Page 194 - Concise Pathology for Exam Preparation ( PDFDrive )

7 Infections 179

Septate thin hyphal
showing acute-angled
branching

FIGURE 7.11. Septate filaments of Aspergillus showing branching at acute angles (PAS;
2003).

• The three primary sites of invasion are nasal sinuses, lungs and gastrointestinal tract,
depending on whether spores (which are widespread in dust and air) are inhaled or
ingested.
• Most commonly in diabetics, the fungus may spread from nasal sinuses to orbit and
brain, giving rise to rhinocerebral mucormycosis. The zygomycetes cause local tissue
necrosis, invade arterial walls and penetrate periorbital tissues and cranial vault. Menin-
goencephalitis follows, sometimes complicated by cerebral infarctions when fungi
invade arteries and induce thrombosis.
• Lung involvement with zygomycetes (Fig. 7.12) may be secondary to rhinocerebral
disease, or it may be primary in patients with haematologic neoplasms. Lung lesions are
a combination of haemorrhagic pneumonia with vascular thrombi and infarcts.

Broad aseptate
hyphal invading
lung tissue

Right-angled
branching

FIGURE 7.12. Lung parenchyma showing invasion by broad aseptate hyphae of zygomycetes
branching at right angle (Silver stain’ 4003).

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