1) Occipital neuralgia is defined as paroxysmal stabbing pain, with or withoutpersistent aching between paroxysms, in the distributions of the greater, lesser,and third occipital nerves. 2) Occipital neuralgia is a cause of protracted or severe intractable headaches,which occur more frequently in women. 3) Entrapped peripheral nerves typically have increased cross-sectional area.Increases in the cross-sectional areas of nerves in cases of peripheral neuropathyhave been well described. 4) Occipital neuralgia is a headache that may result from greater occipital nerveentrapment. 5) Possible zones of greater occipital nerve irritation and entrapment include thefollowing: A)) Where the greater occipital nerve emerges from the C2 dorsal ramus betweenthe atlas and the axis. B)) Where the nerve courses between the obliquus capitis inferior andsemispinalis capitis muscles. [Its like a sandwich: the 2 muscles are the bread and the nerve is between them] C)) Where the nerve pierces the belly of the semispinalis capitis. D)) Where the nerve exits from the tendinous aponeurosis of the trapezius. 6) The purpose of this study was to measure the cross-sectional area andcircumference of symptomatic and asymptomatic greater occipital nerves inpatients with unilateral occipital neuralgia. Measurements were done withsonography in 17 patients. 7) Persons with a greater body mass index (BMI) had larger cross-sectionalnerves. [This suggests that increased BMI people may be more prone to peripheralnerve entrapment]. 8) This article reports sonographic evidence showing significant increased cross-sectional area and circumference of the symptomatic greater occipital nerve inpatients with unilateral occipital neuralgia: with unilateral occipital neuralgia: Ultrasound Measurements of the Greater Occipital Nerve Symptomatic Side Asymptomatic Side Cross Section 4.1 ± 2.6 mm 2.0 ± 0.7 mm Circumference 8.5 ± 2.7 mm 5.6 ± 1.4 mm 9) There were significant differences between the symptomatic andasymptomatic cross-sectional areas. 10) A significant difference was also noted between the symptomatic andasymptomatic circumferences. 11) A usual site of greater occipital nerve entrapment was within the tight fasciasurrounding the belly of the obliquus capitis inferior near the C2 spinous process[E]. 12) There was a significant difference in the cross-sectional areas andcircumferences of the greater occipital nerves between the symptomatic andasymptomatic sides. These findings are consistent with typical swelling of peripheralneuropathy. [Remember: minor compression collapses the intraneural vein,causing neural swelling, resulting in more internal pressure]. 13) We report sonographic data showing a significant increase in the cross-sectional area and circumference of the greater occipital nerve in patients withoccipital neuralgia.