Foramen on the sacral ala and the lumbar transverse process: reviewing not a very common observation

Introduction A recently published study in this journal reported an example of a vertically oriented foramen at the sacral ala as a ‘new’ finding [1]. The current study/review is based on a brief survey of previously published literature on the occurrence of such foramina in the neural arches of the lumbosacral vertebrae, with discussion of the accepted clinical and embryologic significance of these foramina. Several perpendicularly oriented foramina have been reported running lateral or postero-lateral to the axial plane of the spinal canal at the lumbo-sacral region [2]. These formina reported by De Beers et al. in 1984, were from CT scans obtained from individuals suffering from low back pain. This included a foramen at the bases of the transverse and superior articular process of the L5, and vertical foramina passing through the medial part of the transverse process of L5, at the base of the sacral ala. Investigators have linked formation of these foramina due to osteoarthritic changes at the base of the facet joints [3–4], due to ossification of the mamillo-accessory ligament [5], or incomplete union of the costal and transverse ‘elements’ forming the transverse processes, during embryogenesis [6–7]. Case Report This study reports one such foramen occurring on the left sacral ala. This sacral sample was detected from the osteology collection at the Department of Forensic Medicine, Gandhi Medical College, Bhopal during a study conducted to investigate the morphology of sacra associated with lumbosacral transitional variations. This particular foramen (Figure 1) led to a bony tunnel that was about 17 mm in length. The cranial opening of the foramen was approximately 6 mm and 4 mm at its maximum and minimum diameters, respectively. The foramen was placed like a transversely oval gap on the left sacral ala about 4 mm lateral to the margin of the first sacral vertebral body. Situated just anterior to the mid-alar transverse plane, this bony tunnel ran inferiorly (slightly in an antero-medial direction) and opened caudally into the first anterior sacral foramen (Figure 1, inset) on the left side –and hence connected with the sacral canal, at the same level.