To the Editor.
—Biondi ring tangles (BRTs) (pseudotangles) of the ependymal and choroid plexus epithelia of the aging brain, originally described by del Rio Hortega1 and Biondi,2 appear as serpentine, curled, or annular profles (Fig 1) with silver impregnation and thioflavine S stains.3 They also exhibit birefringence with Congo red stain4 and increase in number with age. The above light microscopic characteristic resemble those of the neurofibrillary tangles and of senile plaque amyloid fibers of normal aging brains and brains of patients with Alzheimer's disease. Our ultrastructural study of BRTs has revealed that they are composed of tightly packed bundles of long, straight, 10-nm (in diameter) intracellular filaments (Fig 2), assuming parallel arrangements for a long distance. This configuration is different from the 20-nm (in diameter) paired helical intracellular filaments reported in aging choroid epithelium by Eriksson and Wester-mark.5 The BRT fibers differ also from those of cerebrovascular and plaque amyloid, which are composed of short bundles of 10-nm (in diameter) fibers oriented in all directions.4
Wen GY, Rudelli RD, Kim KS, Wisniewski HM. Tangles of Ependyma-Choroid Plexus Contain B-Amyloid Protein Epitopes and Represent a New Form of Amyloid Fiber. Arch Neurol. 1988;45(12):1298–1299. doi:10.1001/archneur.1988.00520360016002
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