Computed tomographic imaging of the normal immature California sea lion head (Zalophus californianus)

Different computed tomography (CT) protocols were tested to optimize imaging of the head of the California sea lion. Transverse mode images were superior to helical mode images. Bone structures were best imaged using 1 mm slice width combined with a high-frequency image reconstruction algorithm and best viewed using a wide window setting. Soft tissue structures were generally difficult to differentiate with the exception of the orbital region, which was best imaged using 2mm slice width combined with a medium-frequency image reconstruction algorithm and best viewed using a narrow window setting. Anatomic features specific to the California sea lion were identified on CT images and were consistent with previously published data. These included absence of the lacrimal bone, nasolacrimal ducts, and paranasal sinuses. Upon qualitative assessment of the orbit and nasal cavity, there was a triangular-shaped interorbital nasal cavity on transverse images, and extensive, highly convoluted ethmoid turbinates. The permanent dental formula was identical to previous reports. In conclusion, we provide a detailed description of the anatomy of the immature California sea lion head and a definition of two imaging protocols.