IgG 4 Overexpression Is Rare in Meningiomas with a Prominent Inflammatory Component: A Review of 16 Cases

Meningiomas with prominent inflammation are traditionally classified as “lymphoplasmacyte‐rich meningioma” ( LPM ). Both inflammatory and neoplastic meningeal proliferations have recently been linked to IgG 4 disease, although a potential association with LPM has not been previously explored. Sixteen meningiomas with inflammatory cells outnumbering tumor cells were further characterized by CD 3, CD 20, CD 68 and/or CD 163, CD 138, kappa, lambda, IgG and IgG 4 immunostains. There were 11 female and 4 male patients, ranging from 22 to 78 (median 59) years of age. Tumors consisted of 10 World Health Organization ( WHO ) grade I , 5 grade II and 1 grade III LPMs . Immunohistochemically, the most numerous cell type was the macrophage in all cases followed by CD 3‐positive T cells and fewer CD 20‐positive B cells. Plasma cells ranged from moderate‐marked (N = 5) to rare (N = 7), or absent (N = 4). Maximal numbers of IgG 4 plasma cells per high power field (HPF) ranged from 0 to 32, with only two cases having counts exceeding 10/HPF. The IgG 4/ IgG ratio was increased focally in only two cases (30% and 31%). Additionally, plasma cells represented only a minor component in most examples, whereas macrophages predominated, suggesting that “inflammation‐rich meningioma” may be a more accurate term. The inflammatory stimulus for most cases remains to be elucidated.