[Imaging of the paranasal sinus].

The paranasal sinus is an aerated space constructed of bones. Its draining pathway for secreted mucus is narrow and surrounded by structures such as the palate, orbit, and anterior cranial fossa. Many minute openings traverse the bony structure for innervation and blood supply. Therefore, CT and MRI play a complementary role in diagnosing sinonasal disease. When paranasal sinusitis is suspected, CT is conducted to evaluate the drainage passages, deviation of the nasal septum or normal variants, and bone sclerosis for preoperative planning of endoscopic sinus surgery. When a unilateral space-occupying lesion or bone destruction is detected by CT, malignancy may be considered. However, contrast resolution on CT is limited, and the procedure should be complemented by MRI. MRI is superior to CT in contrast resolution, and is more helpful in illustrating tumor extension or invasion into soft tissues such as the masticator space or into the orbital or intracranial space. The present report discusses sinonasal non-neoplastic and neoplastic diseases that have typical and characteristic findings on CT and MRI.