title: New insights into the anatomy of the lacrimal gland using 7T MRI, micro-computed tomography and cinematic rendering
Creators: name: Singh Swati
Publisher: name: Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU)
Year: 2024
Subjects: subject: Lacrimal gland, Tears, Ocular surface

description: 1.1 Background The lacrimal gland, a contributor to the aqueous component of the tear film, has two lobes, an orbital and a palpebral lobe, which are connected via an isthmus. The secretions of this gland are drained onto the ocular surface via the palpebral lobe. There are missing links in its anatomical description, including the isthmus contents, the number of ducts in the orbital lobe, the relationship between the ducts and the palpebral lobe, and the internal vascular anatomy. Anatomical studies depict that the orbital lobe continues into the palpebral lobe around the edge of the aponeurosis of levator palpebrae superioris (LPS). Furthermore, vascular anatomy studies have explored the origin of the lacrimal artery; however, its vascular branches inside the lacrimal gland have not been studied. Therefore, in the current research, the isthmus constituents, the relationship between the palpebral lobe and the conjunctiva, and the internal vascular anatomy have been investigated using histology, scanning electron microscopic (SEM), 7-Tesla MRI (7T MRI), and micro-computed tomography (micro- CT) imaging. 1.2 Material and methods Lacrimal glands (n=10) from Caucasian body donors (n=5; mean age 78.7 years) were examined with 7T-MRI and 3D cinematic rendering (CR) (N=5; scanned at 75-μm intervals), histology, and electron microscopy (N=5). One lacrimal gland from an unfixated body donor was used to study the internal vascular branches with a lead oxide-latex mixture and was examined using micro-CT and 3D CR. 1.3 Results The 3D CR images showed similar-sized lobules (the largest lobule diameter was 1.68±0.19 mm in the orbital lobe and 1.68±0.17 mm in the palpebral lobe) , which were separated by septae (size 0.29 ± 0.09 mm) in both lobes. The inner gland framework resembled a honeycomb pattern. CR and histology showed that the isthmus contained a few acini, large blood vessels, nerves, and up to two ducts passing into the palpebral lobe. The colour images of the rendered lacrimal glands showed a branch of lacrimal artery originating 5 mm posterior to the hilum that ran across the isthmus to the palpebral lobe. This finding was also confirmed using micro-CT. An SEM of the palpebral lobe-conjunctiva complex showed gland lobules and lymphoid follicles located within loosely arranged collagen bundles and a compact subepithelial layer. The central substance of the orbital and palpebral lobes was located at 9.4± 0.2 mm and 2.8± 0.7 mm from the conjunctiva, respectively. Micro-CT and CR images showed five branches of the main lacrimal gland artery, which included an orbital adipose tissue branch, two orbital lobe branches (medial and lateral), and two palpebral lobe branches (medial and lateral). The main artery terminated as palpebral and orbital lobe branches in the lateral half of the lacrimal gland. 1.4 Conclusion This is the first study to provide a detailed anatomical description of the isthmus of the lacrimal gland. The Isthmus contains the main lacrimal artery that runs along the LPS edge and supplies the two lobes via its branches. The orbital lobe has two ducts that enter the palpebral lobe. The lacrimal gland has a honeycomb-like structure that can serve as a template for bioprinting the lacrimal gland. Contrast-enhanced micro-CT can be explored to visualise the internal vascular anatomy of the gland, butfurther studies are required with a larger sample size.