Orbital granulomatosis with polyangiitis: MRI discriminators from IgG4-related disease and lymphoma
Elif Gunay Bulut, Ekim Gumeler, Jale Karakaya, Levent Kilic, Omer Karadag, Kader Karli OguzAbstract
Objectives
To evaluate the distinguishing MRI features of orbital granulomatosis with polyangiitis (GPA) from IgG4-related orbital disease (IgG4-ROD) and lymphoma.
Methods
This retrospective study included 53 patients (10 GPA, 21 IgG4-ROD, 22 lymphoma) who underwent MRI at disease onset. Two blinded radiologists independently evaluated morphological characteristics including; laterality, location, margins, T2 signal, contrast enhancement, necrosis, and extraorbital findings. Quantitative analysis involved ADC measurements and cortex-normalized ADC ratios. Statistical analysis comprised analysis of variance with post-hoc testing, receiver operating characteristic analysis, and intraclass correlation coefficients (ICC).
Results
Bilaterality was more common in GPA than other cohorts (p = 0.038). GPA was significantly differentiated from lymphoma by a higher frequency of ill-defined margins and extraconal fat infiltration (p = 0.001 and p = 0.004, respectively), as well as by marked T2 hypointensity (p < 0.001). Contrast enhancement further distinguished the cohorts (p = 0.017), with hyperintense enhancement (relative to muscle) restricted to the inflammatory cohorts. Necrosis was exclusive to GPA (20%, p = 0.033). Extraorbital findings including sinonasal neoosteogenesis were significantly more frequent in GPA than other cohorts (p = 0.001). Both GPA and IgG4-ROD showed significantly higher mean ADC values/ratios than lymphoma (p < 0.001), with excellent ICC (>0.95). ADC measurements did not differ significantly between GPA and IgG4-ROD.
Conclusion
MRI reliably discriminates orbital GPA from lymphoma through multiple descriptive features and ADC measurements. Although IgG4-ROD shares overlapping imaging characteristics with GPA, necrosis and extraorbital findings serve as highly suggestive differentiating markers.
Advances in knowledge
This study offers a detailed MRI description of orbital GPA and its first comparative analysis with IgG4-ROD and lymphoma.