**Evaluate the Di**ff**erences in CT Features and Serum IgG4 Levels between Lymphoma and Immunoglobulin G4-Related Disease of the Orbit**

**Wei-Hsin Yuan 1,2,3,\*, Anna Fen-Yau Li 3,4, Shu-Yi Yu 2,3, Ying-Yuan Chen 3,5, Chia-Hung Wu 2,3, Hui-Chen Hsu 6, Jiing-Feng Lirng 2,3 and Wan-You Guo 2,3**


Received: 14 June 2020; Accepted: 27 July 2020; Published: 29 July 2020

**Abstract:** Background: Benign immunoglobulin G4 (IgG4)-related orbital disease (IgG4-ROD) characterized as tumors mimicking malignant orbital lymphoma (OL)—responds well to steroids, instead of chemotherapy, radiotherapy and/or surgery of OL. The objective of this study was to report the differences in computed tomography (CT) features and- serum IgG4 levels of IgG4-ROD and OL. Methods: This study retrieved records for patients with OL and IgG4-ROD from a pathology database during an eight-year-and-five-month period. We assessed the differences between 16 OL patients with 27 lesions and nine IgG4-ROD patients with 20 lesions according to prebiopsy CT features of lesions and prebiopsy serum IgG4 levels and immunoglobulin G (IgG) levels This study also established the receiver-operating curves (ROC) of precontrast and postcontrast CT Hounsfield unit scales (CTHU), serum IgG4 levels, serum IgG levels and their ratios. Results: Significantly related to IgG4-ROD (all *p* < 0.05) were the presence of lesions with regular borders, presence of multiple lesions—involving both lacrimal glands on CT scans—higher median values of postcontrast CTHU, postcontrast CTHU/precontrast CTHU ratios, serum IgG4 levels and serum IgG4/IgG level ratios. Compared to postcontrast CTHU, serum IgG4 levels had a larger area under the ROC curve (0.847 [95% confidence interval (CI): 0.674–1.000, *p* = 0.005] vs. 0.766 [95% CI: 0.615–0.917, *p* = 0.002]), higher sensitivity (0.889 [95% CI: 0.518–0.997] vs. 0.75 [95% CI: 0.509–0.913]), higher specificity (0.813 [95% CI: 0.544–0.960] vs. 0.778 [95% CI: 0.578–0.914]) and a higher cutoff value (≥132.5 mg/dL [milligrams per deciliter] vs. ≥89.5). Conclusions: IgG4-ROD showed distinct CT features and elevated serum IgG4 (≥132.5 mg/dL), which could help distinguish IgG4-ROD from OL.

**Keywords:** immunoglobulin G4-related orbital disease (IgG4-ROD); orbital lymphoma (OL); computed tomography (CT); Hounsfield unit
