The “Azzopardi phenomenon” in high-grade astrocytoma with a PNET-like component

The "Azzopardi phenomenon" refers to the deposition of deeply basophilic, smudged material on the stromal blood vessels of highly cellular malignant tumors, and the material is considered to be derived from the nuclear chromatin liberated from necrotizing tumor cells. This phenomenon was observed in a case of high-grade astrocytoma with a primitive neuroectodermal tumor (PNET)-like component that arose in the frontal lobe of a 44-year-old man. The deeply basophilic material was deposited from the media to the adventitia of small or medium-sized blood vessels, and vascular smooth muscle cells largely disappeared. Endothelial cells were relatively preserved. The material was positive for the Feulgen reaction and immunoreactive for histone H3. The Azzopardi phenomenon is frequently seen in small cell lung carcinoma or retinoblastoma, but rare in tumors arising in the CNS. The present case is the first case of an astrocytic tumor that showed this phenomenon. This is also the first example in which histone protein was demonstrated to be co-deposited in the vascular walls in the Azzopardi phenomenon.