Objective: To determine the distinction between a comedo and an infundibular cyst of Favre-Racouchot disease.
Setting: A university hospital.
Patients: From the 8 patients included in the study, 19 cysts and comedones were evaluated.
Main outcome measure: The distinguishing features between the cysts and comedones of Favre-Racouchot disease.
Results: All lesions were histologically indistinguishable from the primary comedones of acne vulgaris, except for the presence of a marked actinic elastosis in the surrounding dermis. The presence of a variable number of hair shafts and an abundant amount of bacteria, which was positive in the results of Gram staining and periodic acid-Schiff reaction and intermingled with sebum and eosinophilic laminated horny material within the dilated infundibulum, characterizes a comedo and differentiates it from an infundibular cyst.
Conclusions: The cysts and comedones of Favre-Racouchot disease are closed and open comedones. They can be easily differentiated from an infundibular cyst by the histopathologic features rather than by the connection to the surface.