Comparison of Imaging Findings between Granulomatosis with Polyangiitis and Eosinophilic Granulomatosis with Polyangiitis on Sinus CT: Importance of High-Density Opacification of the Paranasal Sinuses.

Background and purpose: Granulomatosis with polyangiitis (GPA) and eosinophilic granulomatosis with polyangiitis (EGPA) are the most common causes of chronic sinusitis from systemic granulomatous diseases. While both are small- to medium-sized vasculitis with necrotizing granulomas, they have different clinical courses and prognoses. High-density sinus opacification has been reported in allergic fungal sinusitis with eosinophilic infiltrates. Given that EGPA also has eosinophilic tissue infiltrates, we evaluated the differences in sinus CT findings, focusing on the sinus secretion attenuation between patients with GPA and EGPA, along with other previously described findings.

Materials and methods: This study included 31 patients with GPA and 22 patients with EGPA who underwent sinus CT. The attenuation of secretions within the paranasal sinuses was visually assessed, and the Hounsfield unit (HU) of the highest-density portions within each sinus was measured. Lund-Mackay scores (LMS), bony destruction, sclerotic wall changes, adjacent organ involvement, and nasal polyps were evaluated and compared between patients with GPA and EGPA. Multiple logistic regression analyses were conducted to determine which factors independently discriminated GPA from EGPA, and the diagnostic ability to differentiate between these 2 diseases was evaluated by using a receiver operating characteristic curve analysis.

Results: More patients in the GPA group showed bony destructions, bone sclerosis, and involvement of organs adjacent to paranasal sinuses than in the EGPA group (P = .006, 0.048, and 0.035, respectively). The EGPA group had higher LMS and more nasal polyps than the GPA group (P = .078 and 0.333, respectively). More patients in the EGPA group showed internal high-density opacification than in the GPA group, and patients with EGPA had higher mean HUs (both P < .0001). The presence of high-density opacification or mean HUs independently distinguished GPA from EGPA (OR, 53.67 and 1.07; 95% CI, 4.07-708.03 and 1.02-1.13, respectively) and showed a greater ability to discriminate between these diseases compared with other findings.

Conclusions: Patients with EGPA had more high-density sinus opacification and higher mean HU on sinus CT than the patients with GPA. In addition to the previously reported CT findings, such as bony destruction, bone sclerosis, and adjacent organ involvement, evaluating secretion attenuation can assist in distinguishing between GPA and EGPA.