Orbital lymphoma and subacute or chronic inflammatory pseudotumor: Differentiation with two-phase helical computed tomography

Objective: The differentiation between orbital lymphoma and subacute or chronic inflammatory pseudotumor (SCIPT) may be difficult clinically and radiologically. The aim of this study was to evaluate the enhancement characteristics of orbital lymphoma and SCIPT with two-phase helical computed tomography (CT) and delayed coronal CT and to determine whether attenuation measurements on CT can be used to differentiate between the 2 diseases. Methods: Nineteen histopathologically proven orbital lymphomas and 9 SCIPTs were examined with two-phase helical CT. After injecting 90 ML contrast material at a rate of 3 mL/s, early- and late-phase axial CT scans were obtained with scanning delays of 30 and 90 seconds, respectively. Delayed coronal scans were obtained with delays of 4-9 minutes. Attenuation of the lesions at each phase was measured quantitatively. Relative percentages of contrast enhancement (CE) were calculated to determine the cutoff value for differentiating SCIPT from lymphoma. Results: The CT attenuation change over time was significantly different between orbital lymphoma and SCIPT (P < 0.05). Increased CT attenuation between early- and late-phase axial scans was seen in 42% (n = 8) of lymphoma cases, and decreased CT attenuation was seen in 58% (n = 11). In 17 lymphomas (90%), the CT attenuation decreased between late-phase axial and delayed coronal scans. Conversely, in 7 SCIPTs (78%), the CT attenuation increased gradually over time from early-phase axial to delayed coronal scans. The relative percentage of CE at the delayed coronal scan had a cutoff value of -6.97%, a sensitivity of 84%, and a specificity of 100%. Conclusion: Different characteristics of attenuation change on two-phase helical CT and delayed coronal CT can be helpful in differentiating between orbital lymphoma and SCIPT.