Piggyback mycosis: pulmonary hydatid cyst with a mycotic co-infection.

The lungs are common sites for the occurrence of saprophytic or invasive mycosis as well as hydatid cysts. The two diseases seldom coexist, and the manifestation is seen as a fungal ball (usually aspergilloma) formed in the cavity left behind after hydatid cystectomy. Active invasion and proliferation of the fungi in the laminated ectocyst or sometimes the pericyst of the hydatid is very unusual. We report such a unique coexistence identified in two of the six surgically excised pulmonary hydatid cysts in the past 2 years. Both were immunocompetent males, who had presented with non-specific symptoms of cough, haemoptysis and chest pain. The septate slender hyphae of the invading fungus resembled those of Aspergillus.