Anatomical variations in internal jugular vein splitting patterns: a theoretical framework for a classification system.

The internal jugular vein (IJV) is in the fibrous carotid sheath, together with the common carotid artery and the vagus nerve. Various splitting patterns, such as fenestration, bifurcation or duplication of this vein are typically incidental surgical or radiological findings. Even though there are some approaches to define such patterns in medical literature, the terminologies are still used interchangeably by authors. Three different landmarks; the posterior belly of the digastric muscle, the hyoid bone and the intermediate tendon of the omohyoid muscle are applied to divide the IJV into four levels. The proposed classification uses these levels to define the IJV splits located in a single level as a fenestration, across two consecutive levels as a bifurcation, three as a partial duplication and all four as a total duplication. In addition, multiple venous splits in a single IJV can be possible which can align in parallel or at different levels. This new classification also considers the definition of rare but possible cases of such variations. This theoretical framework seeks to redefine the terminology in medical literature, to not only promote uniformity but also to enhance anatomical understanding and precision.