[Ultrasound evaluation of the greater occipital nerve]

To demonstrate the appearance of the greater occipital nerve on ultrasound.

The greater occipital nerve was evaluated in 21 patients (9 males-12 females; mean age=52 years, range: 20-71; mean weight=74.5kg, range: 50-125) at the time of carotid duplex ultrasound. All examinations were preformed by the same sonographer using a single ultrasound unit. The anatomical landmark used to locate the nerve was the inferior obliquus capitis muscle. MRI and CT images were available in two cases and anatomical cadaver sections were also available.

The greater occipital nerve could be identified at the level of the inferior obliquus capitis muscle in 90.47% (19/21) of cases, even in obese patients. In three slender patients (14.38%), the nerve could be identified at the level of the trapezius aponeurosis and next to the V3 segment of the vertebral artery. The mean anteroposterior diameter of the nerve at the level of the inferior obliquus capitis muscle was 1.65mm (range: 1.14mm-2.8mm).

The greater occipital nerve could be detected at the level of its first genu by ultrasound in 90% of patients, even in obese patients.