General Characteristics and Morphology of Hematins
The formation of hematins is based on the chemical process of oxyhemoglobin hydrolysis. This transformation yields pigments possessing unique physicochemical and morphological properties.
Under microscopic examination, hematins are visualized as characteristic structures. They can take the form of rhomboid crystals or appear as clusters of fine granules. The color palette of these formations ranges from saturated dark brown to deep black.
A crucial diagnostic criterion for hematins is their behavior in polarized light. These pigments exhibit anisotropy — they demonstrate distinct birefringence. Furthermore, a fundamental property of hematins is that the iron within their structure remains strictly in a bound state.
Classification of Hematins
In pathological anatomy, when studying hemoglobin-derived pigments, three main forms of hematins are traditionally distinguished:
- Hemomelanin (also known as malarial pigment or hemozoin).
- Hydrochloric acid hematin (often referred to in literature as hemin).
- Formalin pigment.
Etiology and Pathogenesis of Malarial Pigment
Hemomelanin has an infectious etiology. Its appearance is inextricably linked to the life cycle of the malarial parasite belonging to the genus Plasmodium.
The pathogenesis of this pigment's formation represents a strict sequence of events:
- First, merozoites of the parasite actively penetrate erythrocytes.
- Once inside, the parasite hydrolyzes hemoglobin.
- During this process, a specific amorphous brown pigment is formed from the prosthetic group of the hemoglobin molecule.
- As the pigment accumulates, infected erythrocytes rupture, releasing the pigment into the bloodstream.
- Finally, the circulating pigment undergoes phagocytosis by macrophages.
Localization and Macroscopic Appearance
Following phagocytosis by macrophages, systemic distribution of hemomelanin occurs within organs of the reticuloendothelial system (RES). The primary targets for deposition are the spleen, liver, bone marrow, and lymph nodes.
Special attention should be given to the localization of the pigment in the central nervous system. In cases of cerebral malaria leading to coma, hemomelanin is found directly within glial cells of the brain.
The macroscopic appearance of affected organs is highly specific. Due to massive pigment accumulation, tissues lose their natural color and acquire a pronounced slate-gray hue. It should also be noted that alongside the malarial pigment, concomitant deposition of other pigments may be observed in tissues.