The external occipital protuberance (EOP) is a bony projection on the occipital bone, serving as an attachment point for muscles and ligaments [1].

It varies in shape due to mechanical forces, with an enlarged variant called the occipital spur or knob, which can cause symptoms like pain or remain asymptomatic. EOP is important in procedures such as nerve blocks, occipitocervical fusion, and sex determination [2].

It can be classified into three types: flat (Type 1), crest (Type 2), and spine (Type 3), with distinct gender associations [3](Fig 1).

Imaging techniques like computed tomography (CT) are more sensitive than traditional radiography in detecting EOP variations.

This study investigates the morphometric characteristics of the EOP, its relationship with the foramen magnum, and its potential role in sex determination.