Birefringent Crystals

Early Lesion of Silicosis

This early silicotic lesion consists of a collection of histiocytes filled with black pigment and crystals. Viewing the section with polarized light shows the crystals. (See below.)

Later, collagenous scar is deposited centrally to form a silicotic nodule.

Silica Particles

When viewed by polarized light, the above section reveals numerous small crystals that tend to be granular rather than needle-shaped as are silicates, which often accompany silica particles in tissue. Further, the silica crystals tend to be less bright than silicates. Thus, the presence of granular, dull crystals confirms the diagnosis of silicosis when typical silicotic nodules are present in the lung and the patient has a history of exposure to silica.

Confirmation of Silica in Tissues

By correlating findings on light microscopy, scanning electron microscopy, and energy-dispersive x-ray microanalysis (for elemental analysis), it has been shown that silica particles, as well as silicate particles, can be seen by light microscopy. The crystalline form of silica (whether alpha quartz, cristobalite, or tridymite) can be determined by X-ray diffraction [1].

 

Silicate Particles

Most of the particles in this section are elongate and more brightly birefringent than those above. These features are typical of silicates, particles which are also common in the soil. Some of the fainter, granular particles may represent silica.

Reference:

1. McDonald J, Roggli V. Detection of silica particles in lung tissue by polarizing light microscopy. Arch Pathol Lab Med 1995: 119:242-246. abstract

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