Hyalin

Hyalin is a histopathologic term describing material that appears glassy, homogeneously eosinophilic, and structureless under light microscopy. The word hyalin (from Greek hualos, glass) is used both as a noun and within compound terms to denote a glassy, protein-rich appearance in tissues. Hyaline change is a non-specific process reflecting protein deposition, aggregation of cytoskeletal elements, or fibrotic remodeling with basement membrane material.

In pathology, hyaline material can accumulate in various locations, including blood vessel walls, glomeruli, interstitium, and extracellular spaces. Hyaline arteriolosclerosis, for example, involves hyaline deposition in small arteries and arterioles and is commonly associated with long-standing hypertension and diabetes mellitus. In the kidney, hyaline deposition can present as arteriolar hyalinosis or nodular glomerulosclerosis (Kimmelstiel-Wilson nodules). In the lung, hyaline membranes line alveoli in diffuse alveolar damage such as acute respiratory distress syndrome. In the liver, Mallory hyaline refers to Mallory-Denk bodies, eosinophilic cytoplasmic inclusions seen in alcoholic liver disease. In urine, hyaline casts, composed largely of Tamm-Horsfall protein, may be observed in the distal nephron.

Because hyaline change is a descriptive, non-specific finding, it usually indicates chronic injury, protein leakage, or degenerative processes rather than a single disease entity. Hyaline material is distinct from hyaline cartilage, a normal type of cartilage with a glassy extracellular matrix.

See also: hyaline cartilage, hyaline membranes, hyalinosis, Mallory hyaline.