Imaging diagnosis and clinical outcomes of eight horses with sinus gas expansion

Summary Background Sinus gas expansion is a rare condition in equine patients, resulting in progressive deformity of the facial bones. The condition is sparsely documented in veterinary literature. Similar lesions are categorised as sinus pneumocele or pneumosinus dilatans in human patients, based on the presence or absence of sinus wall erosion. Objectives To describe imaging findings in horses with gas expansion of the paranasal sinuses. Study design Multicentric retrospective descriptive case series. Methods Horses with a computed tomographic (CT) description of sinus gas expansion were included. Computed tomography changes were described, and lesions were categorised as sinus pneumocele or pneumosinus dilatans. Signalment, history and clinical signs were recorded, as well as radiological signs, histology and follow‐up information, when available. Results Eight horses met the inclusion criteria, including seven diagnosed with sinus pneumocele and one with pneumosinus dilatans. Clinical signs were variable, depending on the affected bones and sinuses. The conchofrontal sinus was the most frequently affected. Irregular sinus wall erosion, marginal separation of the bone diploe and abnormal septation were consistent imaging findings in horses with sinus pneumocele. Active bone remodelling was confirmed by histology in one patient. Based on CT, the sinus mucosa was thickened adjacent to the sinus wall erosion in 5/7 patients, with hazy dystrophic mineralisation in three horses. One horse had a follow‐up CT at 26 months, showing progression of the lesion. The horse with pneumosinus dilatans had minor facial bone deformity and severe gas expansion of all left‐sided paranasal sinuses, largely encroaching on the right paranasal sinuses, without bone erosion. Conclusion Diagnostic imaging and more particularly CT is valuable for identifying and characterising abnormal gas expansion of the paranasal sinuses in horses. Based on this small case series, the condition is slowly progressive and inconsistently associated with clinical signs. Its pathophysiology remains unclear, warranting further exploration.