Aggregates of pigment laden macrophages within the lamina propria
The glands remain intact.
The macrophages are strongly stained by pigment and contain bland round nuclei. There is no abnormal pattern of inflammation.
Melanosis coli is found in the colonic mucosa as a result of chronic ingestion of anthraquinones and plant derived laxatives. Anthraquinones cause cellular apoptosis, the debris of which is phagocytosed by macrophages and results in lipofuscin pigment accumulation.
The colon appears dark brown, with a predominance of the effect in the right colon.