• Toshihide Tanaka, Michiyasu Fuga, Akihiko Teshigawara, Yuzuru Hasegawa, Kaichi Nishiwaki, Yuichi Murayama, and Hideaki Yokoo.
• Department of Neurosurgery, Jikei University School of Medicine Kashiwa Hospital, Chiba, Japan. Electronic address: ttanaka@jikei.ac.jp.
• World Neurosurg. 2020 Nov 1; 143: 247-260.

BackgroundWe have reported an extremely rare case of a frontal convexity tumor diagnosed as IgG4-related disease (IgG4-RD) with unique neuroradiological images.Case DescriptionA 64-year-old man with a history of monoclonal gammopathy of undetermined significance and conservative treatment had presented with a left facial spasm. Computed tomography showed a high-density round tumor with perifocal edema in the right frontal convexity. Magnetic resonance imaging demonstrated unique findings, including low signal intensity on T1- and T2-weighted, fluid-attenuated inversion recovery, and diffusion-weighted images, with slight gadolinium enhancement. The tumor was totally removed via right frontal craniotomy. It had been located in the subdural space, was not adherent to the dura, and was less vascular than meningiomas. Histological investigation demonstrated plasma cells that were strongly positive for IgG4 and contained κ and λ light chains at a ratio of 1.5:1. The serum IgG4 level was elevated. The tumor met the diagnostic criteria for IgG4-RD. The patient was followed up for 3 years during postoperative adjuvant steroid therapy. The steroid therapy was discontinued, and during the next 4 years, neither tumor recurrence nor symptoms were observed.ConclusionIntracranial IgG4-RD with smoldering monoclonal gammopathy of undetermined significance is extremely rare. We reviewed the differential diagnosis of plasma cell granuloma and plasmacytoma, therapeutic implications, and clinical outcomes. Complete resection of a conspicuous and solitary IgG4-RD lesion in the frontal convexity is simple and could provide a cure with less-aggressive adjuvant therapy.Copyright © 2020 Elsevier Inc. All rights reserved.

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