Value of unenhanced CT in an opacified sinus

click image to enlarge Value of unenhanced CT in an opacified sinus

1- The real value of unenhanced CT is the following: if you see an opacified sinus with hyper dense contents, it is usually a sign of benign disease. Tumor is not hyper-dense. The hyper density is due to one or a combination of the following:
· inspissated secretions
· fungus
· blood

The CT shows hyper density and the MRI shows hyper intensity on T2WI, both of which you will remember are benign signs in sino-nasal disease, indicating a Proteinaceous substance.

2- In general bright signal on T2 is a sign of benign disease, since fluid and mucosal disease usually have high water content. Secretions do not have solid enhancement. If you have an enhancing mass, you must rule out tumor.
3- MRI can discern secretions and mucosa from masses. When you understand the signal characteristics, you are readily able to distinguish soft tissues masses from inspissated secretions. The signal intensity of secretions can vary and mainly depends on the ratio of water to protein and the viscosity. Different protein contents result in different signal intensities on T1 and T2W-images (figure).

The signal intensity of sinus secretions depends on the protein content
4- When it comes to imaging of neoplasms of the paranasal sinuses, CT and MRI play complementary roles. It is not about the histology but about answering the question 'is it tumor or not?' and then determining the extent of the disease, for example intracranial or orbital extension. Use MRI to differentiate inspissated secretions from neoplasms.