Three horses with bilateral sinonasal progressive haematomas not associated with the ethmoidal labyrinth

Summary Progressive haematomata (PH) are a rare cause of equine paranasal sinusitis and are thought to result from recurrent haemorrhage within the respiratory submucosa of the ethmoidal labyrinth. Clinical signs of PH are variable but mostly attributable to rupture of the mass with haemorrhage, occlusion of nasomaxillary drainage and secondary infection. Almost all affected horses have unilateral or bilateral, intermittent, serosanguinous nasal discharge. Radiographic examination is useful in identifying large PH, but small masses can be overlooked because of superimposition. Computed tomography (CT) has the benefit of producing cross‐sectional images of the sinuses, overcoming the limitations of radiography. The cases in this report suffered from bilateral PH not associated with the ethmoidal labyrinth. They highlight the benefit of CT in the diagnosis, surgical planning and evaluation of the architecture of the sinuses. Preoperative treatment with formalin to desiccate the mass prior to removal can be performed more safely when guided by CT.