CTICasesPulmonary Mucormycosis (Cunninghamella) in a Stem Cell Transplant Recipient
Imaging findings
Serial imaging in a stem cell transplant recipient shows an initially clean right upper lobe, then subtle smudging of the upper lobe vessels. CT at that point demonstrates a peripheral ground-glass lesion lying against the pleura anteriorly. A few days later this has evolved into a well-formed bird's nest pattern.
Key takeaways
The bird's nest sign is characteristic of mucormycosis; the organism here was Cunninghamella bertholletiae. Mucor has become notably more common than Aspergillus in this stem cell transplant population, plausibly because voriconazole prophylaxis suppresses Aspergillus while mucor breaks through it, and mucor responds poorly to voriconazole. Some cases behave indolently, taking weeks rather than days to form a bird's nest, and may arise in the lower lobes rather than the usual mid and upper lung. Mucor is notoriously hard to recover on bronchoscopy and lavage — possibly because the lesion is essentially an infarct with necrotic tissue and no communicating airway — so a negative lavage does not exclude it. Serologic testing for pathogen DNA fragments has recovered mucor from blood where lavage failed.
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