[Histological variants of parasympathetic paragangliomas (chemodectomas) of the neck and morphological variants of their malignancy].

Histotopograms of 28 chemodectomas have been studied. Principal microscopic features of malignancy are as follows: structural atypia (complete in solid or fibrous variants) or partial (alveolar chemodectoma) loss of alveolarity as the most important sign of organotypia; another sign of malignancy is cell cataplasia (cell and nuclear polymorphism, change in nuclear-cytoplasmic relationship in the direction of its increase, nuclear hyperchromatism, appearance of large ungly hyperploid nuclei, mitotic activity of tumour cells in one case. Incomplete angiogenesis characteristic for malignant tumours was also detected. Invasive growth in the majority of chemodectomas in the form of partial growth through the walls of great vessels and ubiquitous growth through the walls of small vessels were present in most chemodectomas. Thus, there is a basis to claim that the chemodectomas studied are malignant tumours although they are characterized by a slow (years) growth and slow progression.