The mixed dust lesion is stellate, more cellular, and less fibrotic than the round, fibrotic, silicotic nodule, which results from inhalation of dust with a high content of silica. Radiographs showed pneumoconiosis, and histologically the lesions showed black silicotic nodules. The major differential diagnosis was tuberculosis. Exposure to mixtures of silica and less fibrogenic dusts produces a lesion with more cellularity and less fibrosis than that which occurs after exposure to silica alone. Typically, a stellate lesion is composed of macrophages, lymphocytes, plasma cells, and a variable amount of black pigment.
Birefringent crystals are present.
The mixed dust lesion is located around the respiratory bronchiole or in the pleura. Hut lung is a form of pneumoconiosis characterized by mixed dust lesions containing black pigment, silicates, and silica. It is domestically acquired by persons living in primitive, rural areas. Smoke from cooking fires in poorly ventilated houses is one factor in developing disease. Grobbelaar and Bateman measured quartz dust from grinding maize and found safe levels, but total dust generated by grinding and the smoke concentrations in the huts were unacceptably high.