Nasal and temporal intraconal orbital fat densities differ on computerized tomographic scans of normal orbits

Background and Aim: The anatomy and function of different areas within the intraconal fat remain poorly understood. A potential difference between nasal and temporal orbital fat densities in normal eyes may assist clinicians and radiologists in more accurately interpreting computerized tomographic (CT) scans and making more informed diagnostic and therapeutic decisions for patients with orbital pathologies. Patients and Methods: Data from randomly selected patients who underwent orbital CT scans at Sheba Medical Center in 2022 were analyzed. Patients with abnormal imaging findings in either orbit were excluded. Intraconal orbital fat density was measured in six nasal and temporal sites by means of Hounsfield units (HU). Results: The study included 54 patients (mean age 45.3 ± 25.5 years, 29 [54%] females) who were scanned for ophthalmologic etiologies unrelated to the orbit. Non-contrast-enhanced (NCE)-CT scans were available for 36 patients (67%), CE-CT scans for 31 patients (57%), and both CE and NCE scans for 13 patients. HU values were significantly higher in the nasal orbit compared to the temporal orbit on both NCE-CT (-75.8 ± 7.5 nasal vs. -78.1 ± 8.4 temporal, P < 0.001) and CE-CT (-72.7 ± 6.7 nasal vs. -74.6 ± 8.6 temporal, P 5 0.02). Age, sex, and laterality had no effect on the HU values. Conclusions: The density of nasal intraconal fat is higher compared to temporal intraconal fat, as observed on both CE and NCE-CT scans of normal eyes. These results suggest the presence of anatomical differences between these compartments and could have significant clinical implications in the diagnosis of various orbital pathologies.