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- Could you differentiate paranasal sinus cysts and progressive ethmoid haematomas on CT?
Could you differentiate paranasal sinus cysts and progressive ethmoid haematomas on CT?
J Equine Vet Sci. 2025
Obi Veterinary Education
March 09, 2026
D Berner 1, M Hellige 2, G G Harvey 3, K Gerlach 4, M Iglesias-Garcia 5, G Manso-Diaz 6
Background
Paranasal sinus cysts (PSC) and progressive ethmoid haematomas (PEH) are non-neoplastic lesions in horses' paranasal sinuses, which require accurate differentiation due to differing prognoses and treatment options. Radiography and endoscopy are commonly used but have limitations in detecting the full extent and nature of these lesions. Computed tomography (CT) is considered superior for assessing such lesions. The study aimed to determine whether PSC and PEH can be reliably differentiated on CT images and to describe their distinct CT features.
Methods
This retrospective multicenter study evaluated CT images from 97 horses across four European equine referral centers. Horses included had a confirmed diagnosis of PSC (n=28), PEH (n=24), or sinusitis (n=45, used as controls). CT images were anonymized and evaluated by three experienced observers for diagnostic classification. Two observers further graded CT features in consensus, assessing lesion characteristics such as heterogeneity, mineralization, bone and soft tissue distortion, and dental involvement. Statistical analyses included sensitivity, specificity, and kappa agreement metrics.
Results
There was substantial to almost perfect agreement between CT diagnosis and the confirmed diagnosis among observers (κ = 0.82–0.97). PEH lesions were significantly more heterogeneous and hyperattenuating compared to PSC and sinusitis. PSCs more commonly exhibited features such as a mineralized wall, inner and outer bone distortion, dental distortion, and focal mineralization within the lesion. PSCs were homogeneous in appearance, in contrast to the heterogeneous PEHs. Gas and mucosal thickening were more indicative of sinusitis. The presence of heterogeneous and hyperattenuating lymph nodes was unique to PEH. No significant difference was found in lesion size among the groups.
Limitations
The retrospective, multicenter design led to variations in CT equipment and acquisition protocols. Only cases that underwent surgical confirmation were included, likely representing advanced disease stages. Histological confirmation was not available for all cases, and observers were aware of the diagnostic categories, introducing potential bias. The study did not include neoplastic lesions due to insufficient histological confirmation.
Conclusions
CT imaging reliably differentiates PSC from PEH and sinusitis based on distinct imaging characteristics. PEHs are typically heterogeneous and affect caudal sinus systems more often, while PSCs are homogeneous with notable mineralization and bone distortion. CT imaging allows precise lesion characterization and is valuable for diagnosis and surgical planning in equine sinus disease.
Bone reconstruction CT images of different horses at the level of the caudal maxillary sinus, there is a paranasal sinus cyst (A), progressive ethmoid haematoma (B) and sinusitis (C), the horse’s left is on the right of the images. Note the homogenous pattern of the soft tissue attenuating material in A and C compared to the moderately heterogeneous pattern in B. Thickening of the bone (white arrows) is noted more at multifocal areas and therefore was graded more severely in A than in B and C, where only a focal area was affected. The infraorbital canal (IOC) is affected in all three horses (Please note the * is placed immediately next to the IOC). In A the IOC is severely displaced and the bone shows moderate thinning, in B the IOC shows area of bone thickening laterally and areas of bone thinning medially. In C, the medial bony outline of the IOC is interrupted medially. Additionally, in A, a hyperattenuating thin linear area, representing a mineralised wall (black arrows) and flattening of the dental apices (open black arrow) is seen. In C, gas is visible within the mass (open white arrow) and moderate mucosal swelling in the caudal maxillary sinus (dashed arrows).
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