Important structures involved in the pathogenesis of occipital headache include
the aponeurotic attachments of the trapezius and semispinalis capitis muscles
to the occipital bone. The greater occipital nerve (GON) can become entrapped
as it passes through these aponeuroses, causing symptoms of occipital neuralgia.
The aim of this study was to identify topographic landmarks for accurate
identification of GON, which might facilitate its anaesthetic blockade. The course
and distribution of GON and its relation to the aponeuroses of the trapezius and
semispinalis capitis were examined in 100 formalin-fixed adult cadavers. In addition,
the relative position of the nerve on a horizontal line between the external
occipital protuberance and the mastoid process, as well as between the mastoid
processes was measured. The greater occipital nerve was found bilaterally in all
specimens. It was located at a mean distance of 3.8 cm (range 1.5–7.5 cm)
lateral to a vertical line through the external occipital protuberance and the
spinous processes of the cervical vertebrae 2–7. It was also located approximately
41% of the distance along the intermastoid line (medial to a mastoid
process) and 22% of the distance between the external occipital protuberance
and the mastoid process. The location of GON for anaesthesia or any other
neurosurgical procedure has been established as one thumb’s breadth lateral to
the external occipital protuberance (2 cm laterally) and approximately at the
base of the thumb nail (2 cm inferior). This is the first study proposing the use of
landmarks in relation to anthropometric measurements. On the basis of these
observations we propose a target zone for local anaesthetic injection that is
based on easily identifiable landmarks and suggest that injection at this target
point could be of benefit in the relief of occipital neuralgia
