Anatomy of the greater occipital nerve: implications in posterior fossa approaches

Purpose Because of its superficial location in the dorsal regions of the scalp, the greater occipital nerve (GON) can be injured during neurosurgical procedures, resulting in post-operative pain and postural disturbances. The aim of this work is to specify the course of the GON and how its injuries can be avoided while performing posterior fossa approaches. Methods This study was carried out at the department of anatomy at Bordeaux University. 4 specimens were dissected to study the GON course. Posterior fossa approaches (midline suboccipital, paramedian suboccipital, retrosigmoid and petrosal) were performed on 4 other specimens to assess potential risks of GON injuries. Results The GON runs around the obliquus capitis inferior (100%), crosses the semispinalis capitis (100%) and the trapezius (75%) or its aponeurosis (25%). Direct GON injuries can be seen in paramedian suboccipital approaches. Stretching of the GON can occur in midline suboccipital and paramedian suboccipital approaches. We found no evidence of direct or indirect GON injury in retrosigmoid or petrosal approaches. Conclusion Our study provides interesting data regarding the risk GON injury in posterior fossa approaches. Direct GON injuries in paramedian suboccipital approaches can be avoided with careful dissection. Placing retractors in contact with the periosteum and performing a minimal retraction may help to avoid excessive GON stretching in midline suboccipital and paramedian suboccipital approaches. Furthermore, the incision for retrosigmoid approaches should be as lateral as possible and not too caudal. Finally, avoiding extreme patient positioning reduces the risk of GON stretching in all approaches.