External occipital protuberance classification with special reference to spine type and its clinical implications

This investigation aimed to study the types of external occipital protuberance (EOP) with special reference to Type 3 (spine type). Detailed information will be useful for clinicians to manage occipital headaches or issues related to the biomechanics of the neck and for accurate radiological interpretations.

Thirty-one dry intact cadaveric skulls were studied for EOP classification. In Type III EOP cases, the size of EOP was noticed using different modalities and compared. The superior nuchal lines and external occipital crest were observed for their prominence and any variation.

42% of the skulls belong to Type 1, 51.5% to Type 2, and 6.5% to Type 3 EOP. Superior nuchal lines and external occipital crest were more prominent in Types 2 and 3 EOP. In Type 3 EOP cases, the mean length, width, and thickness of the spine as measured directly on the skull were 16.63 mm; 20.1 mm, and 7.82 mm respectively, the same as radiograph findings. CT examination revealed the average volume as 0.95 cm³. Out of two Type 3 EOP cases, the spine with larger values for its size was having a lesser volume value in CT.

Plain lateral radiography is a reliable method to measure the length and thickness of spinous EOP. However, more values of these parameters for morphometry of the EOP spine do not mean more volume of EOP and vice versa. Detailed information regarding the occurrence of occipital spur and its morphology will be of great importance to neurosurgeons, sports, physicians, emergency departments, and radiologists.