Semi-Automated Segmentation on Computed Tomography Datasets for Three-Dimensional Reconstruction and Volumetric Analysis of the Paranasal Sinuses in Alpacas (Vicugna pacos) and Their Anatomical Variations.

Understanding the anatomy of alpaca (Vicugna pacos) paranasal sinuses is essential for accurate interpretation of diagnostic imaging and surgical planning, especially given the species' susceptibility to dental disease and associated sinusitis. However, detailed anatomical and volumetric data on alpaca sinuses remain limited. This study aimed to characterise the volumetric properties and anatomical composition of the paranasal sinuses in alpacas using semi-automated segmentation of computed tomography datasets, with the goal of supporting clinical practice in veterinary medicine. Seven adult alpaca heads were scanned using computed tomography, followed by semi-automated segmentation and three-dimensional reconstruction. All specimens displayed the dorsal conchal sinus (sinus conchae dorsalis), middle conchal sinus (sinus conchae mediae), maxillary sinus (sinus maxillaris), frontal sinus (sinus frontalis), and lacrimal sinus (sinus lacrimalis). The sphenoid sinus (sinus sphenoidalis) was present in six out of seven animals. Marked inter-individual anatomical variation was noted, particularly in the frontal sinus and sphenoid sinus. Despite this variability, sinus volumes were generally symmetrical between the left and right sides, with no statistically significant differences. The frontal sinus had the largest mean volume, with values of 13.75 ± 6.70 cm3 on the left and 13.91 ± 7.22 cm3 on the right. Statistical analysis revealed no significant correlations between sinus volume and sex, age, or estimated craniofacial volume. Coefficients of variation exceeded 50% in most sinus compartments, emphasizing substantial individual variability. Three-dimensional models highlighted the complex morphology and spatial variation among specimens. This study provides novel insights into the sinonasal anatomy of alpacas, demonstrating a high degree of individual variation despite general bilateral symmetry. These findings emphasize the need for species-specific anatomical references and can aid in improving diagnostic accuracy and surgical outcomes in clinical settings. The three-dimensional reconstructions offer a valuable educational resource for veterinary professionals.