Unusual morphologies of Cryptococcus spp. in tissue specimens: report of 10 cases

Abstract

SUMMARYTen cases of cryptococcosis due to unusual microscopic forms of Cryptococcus sp. observed over a twenty-eight year period ) are presented. The most important clinicopathological and laboratory data are tabulated. The uncommon forms of cryptococcal cells given are: structures resembling germ tube (one case), chains of budding yeasts (one case), pseudohyphae (two cases) and nonencapsulated yeast-like organisms (eight cases). The diagnosis was based on the histopathological findings. The causative organism was isolated and identified in seven cases; five were due to C. neoformans, and two to C. gattii. In addition, the importance of using staining histochemical techniques -Grocott's silver stain (GMS), Mayer's mucicarmine stain (MM) and Fontana-Masson stain (FM) -in the diagnosis of cryptococcosis is argued.

Cryptococcus neoformans Hyperfilamentous Strain Is Hypervirulent in a Murine Model of Cryptococcal Meningoencephalitis

“…Although C. neoformans hyphae are rare in vivo and are associated with low virulence, pseudohyphae have been observed in histological samples and they were found to confer resistance to Acanthamoeba spp. phagocytosis [27], [78], [79], [80]. Although pseudohyphae are dispensable for virulence [81], stochastic transitions from yeast to pseudohyphae may serve as an escape strategy and confer resistance to phagocytosis by mammalian macrophages similar to giant/titan cells.…”

Pseudohyphal Growth of Cryptococcus neoformans Is a Reversible Dimorphic Transition in Response to Ammonium That Requires Amt1 and Amt2 Ammonium Permeases

“…Like most fungi, Cryptococcus neoformans changes growth morphology: in rich nutrients, round yeast form growth predominates, whereas during mating, C. neoformans forms dikaryotic hyphae. Several decades ago, pseudohyphal or hyphal morphogenesis of C. neoformans was reported in infected animal tissues and during interaction with amoebae (11,14,15,39,48,49,54). Recently, Magditch and colleagues found that RAM pathway mutants form pseudohyphae, which survive better during coculture with amoeba (40).…”

“…When cocultured with amoeba, C. neoformans cells form pseudohyphae, where yeast C. neoformans cells are engulfed by amoebae and pseudohyphal C. neoformans cells are free from amoebae, either having not been engulfed or having escaped (4,41). C. neoformans also forms atypical pseudohyphae during host infection, where pseudohyphal or hyphal growth has been observed in infected host tissues (11,14,15,39,48,49,54). These observations may imply that C. neoformans cells form pseudohyphae as a survival strategy to escape from natural predators or host defenses.…”

Cryptococcal lymphadenitis in a human immunodeficiency virus-infected patient: A diagnostic role of fine needle aspiration cytology and special stains

“…[15] Classically, C. neoformans on cytology smears appear as intracellular and/or extracellular tear drop-shaped or ovoid to spherical yeast-like cells, some of which show budding daughter yeast cells attached by a narrow base, with a refractile halo-like thick mucopolysaccharide capsule. [123456] Granulomatous inflammation and giant cell reaction may be slight or absent. [6] Sometimes, cryptococci can be missed or overlooked because of small size, scanty load of organisms, and necrosis.…”

“…[123456] Granulomatous inflammation and giant cell reaction may be slight or absent. [6] Sometimes, cryptococci can be missed or overlooked because of small size, scanty load of organisms, and necrosis. [14] Unusual cryptococcal morphology (seen in approximately 33% of cases) can give rise to a diagnostic dilemma.…”