A nonpigmented membrane-bound vesicle in a melanocyte that contains tyrosine and matures into the melanin-filled melanosome; prominent in melanocytes of albinos.
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Similarly, Stone et al (16) detected HMB-45 and NK1-C3 immunoreactivity predominantly in epithelioid and spindle cells and premelanosome -like structures in epithelioid cells in 9 cases by electron microscopy.
12) Electron microscopy may identify the presence of melanosomes or premelanosomes.
There were no recognizable lipid droplets, premelanosomes, fusiform densities, or micropinocytotic vesicles.
2) In 2 reported cases, transmission electron microscopy was used to identify melanosomes, premelanosomes, and discrete aggregates of intermediate filaments distending the cytoplasm.
Ultrastructurally, epithelioid cells in AML show evidence of melanogenesis by the presence of intracytoplasmic membrane-bound dense bodies, crystalloids, or granules consistent with premelanosomes (Figure 4).
Ultrastructurally, melanosomes and premelanosomes can be seen.
Ultrastructural studies have documented abundant cytoplasmic glycogen, premelanosomes, thin filaments with occasional dense bodies, hemidesmosomes, and poorly formed intercellular junctions in PEComas.
The term perivascular epithelioid cell was first proposed by Bonetti and colleagues (13) in 1992 as an explanation for the presence of HMB-45 immunoreactivity and premelanosomes in both clear cell "sugar" tumors of the lung and AML.
In fact, tyrosinase protein or its messenger RNA (mRNA) can be detected even in undifferentiated amelanotic melanomas, (135-137) including those lacking premelanosomes, as documented at the ultrastructural level.
Secretory granules, melanosomes, and premelanosomes were absent.
This study, based on 27 cases of renal angiomyolipoma, supports the findings of previous studies that demonstrated HHF-35 and HMB-45 immunoreactivity in renal angiomyolipoma and that described the presence of premelanosomes by ultrastructural examination.