Positional relationship between the lacrimal sac and the base of the skull: implication of the risk of cerebrospinal fluid leakage during dacryocystorhinostomy
Experimental cadaver study
Ethics approval/consent to participate
All cadavers included in this study had given written informed consent prior to death, allowing their bodies to be donated to our university for the advancement of clinical science. The format of the approval was in accordance with the Japanese law regarding the “Law on Donation of Body for Medical and Dental Education”. All corpses were donated and registered with the Corpse Department of Aichi Medical University. The methods used to secure human tissue were humane and consistent with the principles of the Declaration of Helsinki.
This study was approved by the Institutional Review Board (IRB) of Aichi Medical University Hospital (approval number, 2021-042) and followed the principles of the 1964 Declaration of Helsinki. request of the IRB, an overview of this study publicly available on the Aichi Medical University website has been published. This public display also allowed the families of the donors to refuse to participate in this study, although no refusals were reported to us.
Study plan and corpses
This experimental anatomical study included cadavers fixed in 10% buffered formalin. None of the cadavers had gross eyelid, orbital, lacrimal, cranial, paranasal or facial disorders, nor any history of eyelid, orbital, lacrimal, cranial, paranasal or facial surgery during their lifetime. Sides on which an ethmoidectomy or skull base surgery was performed for another experimental study were excluded from this study.
Dissection and measurements of cadavers
All cadaver dissections and measurements were made by one of the authors (YT). All measurements were performed using a digital caliper (DigitalCaliper 19975; Shinwa Rules CO. Ltd., Niigata, Japan). Photographs were taken with a digital camera (D3100; Nikon, Tokyo, Japan).
The skin and orbicularis oculi muscle were removed until the MCT and lacrimal sac were exposed. After opening the lacrimal sac, a probe was inserted from the punctum to confirm the position of the CCO (Fig. 1a). The cranial bone was partially removed to the horizontal level of the base of the skull above the lacrimal sac (Fig. 1a). The presence or absence of frontal sinus interposition was confirmed (Fig. 1b). The vertical width of the MCT was measured. The vertical distances between the superior border of the MCT and the CCO, the bottom of the lacrimal sac, the base of the skull and the top of the frontal sinus were measured (Fig. 1a–c). The thicknesses of the base of the skull and the frontal bone at the horizontal level of the base of the skull and that at the top of the frontal sinus were measured, respectively (Fig. 1b,c).
Ethics approval/consent to participate
This study was approved by the IRB of Aichi Medical University Hospital (approval number, 2021-372) and followed the principles of the 1964 Declaration of Helsinki. The IRB granted a waiver of informed consent for this study based on the ethical guidelines for medical and health research involving human subjects established by the Japanese Ministry of Education, Culture, Sports, Science and Technology and the Ministry of Health , work and well-being . The waiver was granted because the study was a retrospective chart review and not an interventional study and because it was difficult to obtain consent from patients who had been treated several years prior to the study. Nonetheless, at the request of the IRB, we have published an outline of the study, which is available for public viewing on the Aichi Medical University Hospital website. This public posting also allowed patients to opt out, although none of the patients did. Personal identifiers were removed from all records prior to data analysis.
Study design and patients
This retrospective observational study included all patients in whom a CT scan was performed for the differential diagnosis of lacrimal sac tumors before DCR for primary unilateral nasal lacrimoduct obstruction +/- dacryocystitis between January 2018 and July 2021. Patients with missing data were excluded from this study. Patients whose CT slice thickness was greater than 1 mm were also excluded from this study.
Data on age, sex, affected side and clinical diagnosis were collected from the medical records of all patients. Patency of the lacrimal drainage system on the unaffected side, as verified by lacrimal syringe, was also confirmed from the medical records of all patients.
Measurements on CT images
1 mm continuous axial CT images (Aquilion Precision; Canon, Tokyo, Japan) were obtained using a bone window algorithm (width, 2,500; level, 500). Axial CT images were obtained based on Reid’s baseline and coronal images were reconstructed based on planes parallel to the face. To obtain symmetrical axial images, the positions of the face, shoulders and soles of the feet were fixed without creases in the patient’s neck. All measurements were made on the unaffected side using the digital caliper tool of the image viewing software (ShadeQuest/ViewR; Yokogawa Medical Solutions Corporation, Tokyo, Japan) and that of the processing system three-dimensional (3D) images (Aquarius NET; TeraRecon Incorporated, NC, US) by one of the authors (YT).
On the anterior plane, the presence or absence of frontal sinus interposition was confirmed (Fig. 2a,b). The vertical distance between the bottom of the lacrimal sac and the base of the skull and the thickness of the skull base bone were measured (Fig. 2a). Then, the cursor was positioned and fixed at the bottom of the lacrimal sac, and the coronal slice images moved backward to the posterior plane (Fig. 2c,d)13. On the posterior plane, the vertical distance between the position of the cursor and the base of the skull, the horizontal distance between the vertical line passing through the cursor and the cribriform plate, the vertical distance between the horizontal line passing through the position of the cursor and the cribriform plate, the thicknesses of the skull base bone and that of the cribriform plate at the lateral margin were measured (Fig. 2d).
Using the 3D image processing system, the cursor intersection was positioned and fixed at the bottom of the lacrimal sac on the anterior plane, and the coronal section images moved to the back of the image showing no ethmoid sinus interposition. In this situation, the anteroposterior distance from the lacrimal crest posterior to the position of the cursor was measured on the axial image (Fig. 2e). In patients without frontal sinus interposition, the anteroposterior distance from the posterior lacrimal crest to the point where the cribriform plate forms a lower border of the olfactory pit was measured.
Patient age and measurement results were expressed as means ± standard deviations. Vertical distances were expressed as positive values when the measurement points were above the reference points (the upper edge of the TCM and the bottom of the lacrimal sac). Sex-related differences in cadaver age at death, patient age, and measurement results were analyzed using Student’s t-test or Mann-Whitney’s U-test. Cadaver age at time of death, patient age, gender ratio and measurement results were compared between cadavers/patients with and without frontal sinus interposition of the frontal sinus using the test Mann-Whitney U and Fisher’s exact test. Patient age, sex ratio, and measurement results were compared between patients with and without the cribriform plaque positioned above the horizontal level of the bottom of the lacrimal sac (Fig. 2f) using the test Mann-Whitney U and Fisher’s exact test. All statistical analyzes were performed using SPSS™ ver. 26 software (IBM Japan, Tokyo, Japan). PA–a value
Presentation of the conference
Part of this study was presented at the 36th Congress of the Asia-Pacific Academy of Ophthalmology (APAO) held September 5-11, 2021.