Congo red
Histochemical stain used to identify amyloid deposits. Shows characteristic apple-green birefringence under polarized light.
Full Definition
Congo red is a specialized histochemical stain essential for the identification of amyloid deposits in tissue sections. When applied to amyloid-containing tissue, Congo red produces a salmon-pink coloration under standard light microscopy. However, the definitive diagnostic feature is the characteristic apple-green birefringence observed when the stained tissue is examined under polarized light. This optical property is virtually pathognomonic for amyloid and distinguishes it from other protein deposits. In neuropathology, Congo red staining is crucial for diagnosing cerebral amyloid angiopathy, identifying senile plaques in Alzheimer's disease, and detecting other amyloidoses affecting the nervous system.
Usage
Usage note: Must specify examination under polarized light to confirm birefringence.
In Context
- "Congo red staining confirmed the presence of amyloid in the vessel walls, supporting a diagnosis of cerebral amyloid angiopathy." — Neuropathology consultation
- "The plaques showed Congo red positivity with apple-green birefringence under polarized light." — Alzheimer disease case