<prompt> A patient is a known case of polyarteritis nodosa. On examination of biopsy, accumulation of amorphous, basic, proteinaceous material in the vessel wall was seen. This finding is suggestive of:Fibrinoid necrosisLeucocytoclastic vasculitisHyaline arteriosclerosisCaseous necrosis  <response>: Ans. a Fibrinoid necrosisFibrinoid necrosis is a form of necrosis, or tissue death, in which there is accumulation of amorphous, basic, proteinaceous material in the tissue matrix with a staining pattern reminiscent of fibrin.How to differentiate from hyaline arteriosclerosis?- please remember in fibrinoid necrosis, pink material has fibrin like quality as opposed to glassy homogenous hyaline in hyaline arteriosclerosis, refer to image 2 