CT of the paranasal sinuses: study of a control series in relation to endoscopic sinus surgery.

A control series of biplane CT scans of the paranasal sinuses, derived from patients examined for orbital tumours, is described. The scans were assessed for the presence of anatomical variants in the middle meatus, said to contribute to meatal stenosis, and for signs of asymptomatic infection revealed by the presence of clouding or mucosal thickening in the sinuses. Of the anatomical variants, only concha bullosa (pneumatisation of the middle turbinate) was associated with a high incidence of infection in the sinuses (85 per cent). Evidence of asymptomatic sinus infection was as high as 39 per cent overall, the highest incidence occurring in the ethmoid cells (28 per cent). Isolated ethmoid clouding on CT was observed in 15 per cent and is likely to be found in as many as one in seven of the adult population in the UK. It is concluded that in the majority of patients clouding confined to a few ethmoid cells shown on CT is without clinical significance. The evidence from the control series did not support the concept that most sinus infection starts in the middle meatus. The presence of a large reservoir of quiescent or chronic sinus infection in the control group suggests that in most instances sinusitis derives from a recrudescence of this pre-existing infection.