Differentiation of equine paranasal sinus cysts and progressive ethmoid haematomas on computed tomographic images

Paranasal sinus cysts (PSC) and progressive ethmoid haematomas (PEH) are regularly observed in the paranasal sinus system. Due to their different prognosis and treatment options, differentiation of both lesions prior to surgery on computed tomographic (CT) images is important for guidance. It was hypothesised that PSC and PEH can be reliably differentiated on CT images. The database of four European equine referral centres were retrospectively searched for horses that had undergone a CT examination of the head and had a confirmed PSC or PEH. Additionally, cases with confirmed sinusitis were selected as control cases. Images were anonymised and evaluated by different observers to investigate their ability to differentiate these diseases. Multiple imaging characteristics were evaluated for all diseases. Ninety-seven horses were included, final diagnosis was PEH in 24, PSC in 28, and sinusitis in 45 horses. Substantial to almost perfect agreement between CT diagnosis and final diagnosis for all three observers was found. Heterogeneity and attenuation of the lesion were graded significantly higher in PEH. Mineralisation within the soft tissue structure, inner and outer distortion of bone and soft tissues, a mineralised wall, and dental distortion were significantly more common in PSC. Only cases that subsequently underwent treatment were included, therefore, most cases were at an advanced stage. Histological examination was not available in all cases. Differentiation between PEH and PSC on CT images was excellent, and the reported different characteristics might help clinicians to distinguish between both diseases.