Anatomical study of occipital triangles: the ‘inferior’ suboccipital triangle, a useful vertebral artery landmark for safe postero-lateral skull base surgery

Background: Vertebral artery (VA) identification within the suboccipital triangle is a key step in craniocervical junction surgery. Often VA exposition at this level is arduous (space-occupying lesions, previous surgery); to identify VA more proximally may prove useful in complex cases. An alternative triangle is present just below the suboccipital one, where VA can be easily controlled; we named it the inferior suboccipital triangle (IST). The aim of the study is to identify IST anatomical relations and VA space orientation and evaluate its practical utility in surgery. Methods: An anatomical study was performed on ten sides of five injected cadaverdic specimens. Relevant anatomical data were databased. Results: The IST is limited superiorly by the inferior oblique muscle, inferolaterally by the posterior intertransversarii muscle and inferomedially by the C2 lamina; VA at this level has a vertical course with a slight medial to lateral direction (mean 10.8°) and minor posterior to anterior inclination (mean 3.4°). VA within the IST has a constant course without significant loops or kinkings; periarterial venous plexus is less represented at this level. The IST measures an average of 1.89 cm², and VA at this level has an average length of 98 mm. Conclusions: IST is a significantly large anatomical space where the VA course is rather regular, and its length is sufficient for vascular proximal control purposes. Periarterial venous plexus is less evident at this level, easing the surgical exposure. VA exposition within the IST can be used as an alternative option when space-occupying lesions, scars and stabilisation devices make arterial dissection hazardous in more cranial V3 segments.