Clinical history: A 39-year-old woman was admitted to the pulmonary service with fever and productive cough. Chest x-ray showed bilateral diffuse infiltrates. History was notable for a renal transplant 8 months previously. A bronchoalveolar lavage was performed. Cytologic evaluation was requested to rule out infection due to fungi, Pneumocystis, acid-fast bacilli, cytomegalovirus and malignancy.
Pathology: 35 mls of BAL fluid was processed for routine cytospins which showed a mixed cellular population including macrophages, moderate numbers of neutrophils and scattered bronchial epithelial cells. Staining for acid-fast bacilli was negative. The Gomori methenamine silver (GMS) stain revealed the following at 400X magnification:
Diagnosis?