[Development variations of the R. anastomoticus cum a. lacrimali in Japanese]

This report describes the developmental variations of the R. anastomoticus cum a. lacrimali in 150 Japanese cadavers (300 orbits). The orbits were classified into seven types on the basis of the diameters, directions and anastomoses of the ophthalmic artery (OA), lacrimal artery (LA) and R. anastomoticus cum a. lacrimali (RAL). The definitions and frequencies of the seven types were as follows. 1) Normal type: The diameter of the RAL was smaller than that of the LA (240 orbits, 80.0%). 2) Thin type: The diameter of the RAL was comparable to or larger than that of the LA, but smaller than that of the OA (19 orbits, 6.3%). 3) Thick type: The diameter of the RAL was comparable to or larger than that of the OA (5 orbits, 1.7%). 4) OA type: The OA was absent or vestigial, and the blood of the orbital contents was supplied mainly by the RAL instead of the OA (1 orbit, 0.3%). 5) LA type: The LA arose from the RAL instead of the OA (23 orbits, 7.7%). 6) MMA type: The middle meningeal artery (MMA) was absent or vestigial, and the blood of the dura mater was supplied mainly by the RAL instead of the MMA (1 orbit, 0.3%). 7) Absent type: The RAL could not be found (12 orbits, 4.0%). The OA, MMA and LA types are established anomalies of the RAL that have been described anatomically and clinically. However, few studies have investigated the developmental variations of the RAL in detail. The results of this study suggest that the developmental variations of the RAL are more remarkable than reported previously.