by the Editors
March 8, 2022
The Hyams grade is a system that divides olfactory neuroblastomas into four levels or grades in order to help predict how the tumour will behave over time. Hyams grade 1 and 2 tumours are called low-grade while Hyams grade 3 and 4 tumours are called high-grade. The Hyams grade is important because higher grade (grade 3 and 4) tumours are more likely to grow into areas of the head outside of the nasal cavity and to spread to other parts of the body.
In order to determine the Hyams grade, pathologists look for the following six microscopic features: pattern of growth, mitoses (tumour cells dividing to create new tumour cells), necrosis (dead or dying tumour cells), pleomorphism (tumour cells that vary in size and shape), neuropil, and rosettes. Low-grade olfactory neuroblastomas will typically be growing in round nests or lobules but will have very few mitoses, no necrosis, and very little pleomorphism. Low-grade tumours will also contain some neuropil and may have Homer Wright rosettes. High-grade olfactory neuroblastomas often grow in large sheets and with mitoses, necrosis, and pleomorphism. High-grade tumours also contain less neuropil and Flexner–Wintersteiner rosettes may be seen.