Prediction of the ideal point for occipitalis major and occipitalis minor nerve block by injected volume and anatomical dissections

Purpose: Just as there are many pain syndromes that concern the back region of the head and neck, surgical procedures that require an approach from this region also cause postoperative pain and reduce the quality of life of patients. Blockade of the nerves in this area is frequently used in the prevention and treatment of these conditions. Nervus occipitalis major and minor are the most important nerves that provide innervation of this region. The success of blockade of these nerves requires the correct determination of the injection site and the use of the correct injection volume. There is no consensus on the optimal injection volume for successful block. The aim of our study is to compare the spread pattern and nerve involvement of different volumes of injected dye during N. occipitalis major and minor block using cadaver models and anatomical dissections, to provide new information to improve the success and safety of this block. Materials and Methods: In our study, 12 head halves of 6 cadavers, which were found in the laboratories of Ankara University Faculty of Medicine, Department of Anatomy and used in dissection training, were used. Cadavers were randomized to receive 3 or 5 mL injections for GON blocks into the right or left side of the occipital region. On these selected cadavers, 6 GON blocks were applied using 3 mL methylene blue (1% methylthioninium chloride) and 6 GON blocks were applied using 5 mL methylene blue. Post-injection cadaver dissections were performed with an independent anatomist (not involved in block performance) to evaluate the location, vertical distribution, and observed staining of the nerves. Results: In our study, six cadaver heads embalmed with 10% formaldehyde solution in the Ankara University Faculty of Medicine Department of Anatomy laboratory were used. Four of these cadavers were male and two were female, and the average age was 75.5±10.89 (58-91) years. The average biparietal diameter of the cadavers was 151.7±7.53 mm (145-167), the average nasion-inion distance was 380.6±49.91 mm (310-440), and the average head circumference was 611.6±50.45 mm (550 mm). It was calculated as -670). The origin of the GON was found at the level of the atlantoaxial intervertebral area, an average of 18 mm lateral to the midline (min: 16 mm and max: 19 mm). GON appearances were observed to be symmetrical in 2 cadavers. After leaving the intervertebral space, the GON progresses laterally and caudally to the M. obliquus capitis inferior. It goes around this muscle in all cadavers. Subsequently, it was observed in all cadavers that M. semispinalis advanced from the dorsal side of the capitis. The last muscular structure is M. trapezius and GON pierces this muscle. On the left side of Cadaver 1, GON was observed to pierce the aponeurosis of this muscle. The emergence of the GON into the subcutaneous plane was found to be an average of 22.75 mm lateral to the midline (min: 17 mm and max: 27 mm) and an average of 18 mm caudal to the EOP (min: 15 mm and max: 21 mm). It then spreads to the dorsal craniocervical area, where it innervates by giving numerous branches. While GON was seen medial to the OA in 8 dissections; It was detected lateral to the artery in 4 dissections. In 9 of the total dissections, GON and OA intersected at a single point, while in the other 3 dissections, it was observed that OA and GON coursed together in the subcutaneous plane and were in a helical relationship. It was observed that most of the injected methylene blue was confined to the fascial plane between M. obliquus capitis inferior and M. semispinalis capitis, regardless of the injection volume. It was observed that all GONs and TONs were stained. All LONs were stained in the 5 ml injected group; It was observed that LON was stained in 3 cadavers in the 3 ml injected group. It was observed that the dye spread below the M. trapezius in 3 of the cadavers in the 5 ml injected group. In this group, it was determined that the dye spread primarily along the M. semispinalis cervicis in the caudad direction. Although there were different spreading patterns in the muscle and fascial planes, intense staining of the trigonum suboccipitale was observed in every cadaver. In addition, it was observed that N. suboccipitalis, located within this triangle, was stained in all injection groups. Conclusion: GON block is an effective method in the diagnosis and treatment of various painful syndromes. It is a popular application, especially in pain syndromes such as migraine, which do not respond to medical treatment and cause significant disability. There are uncertainties in the literature regarding the localization of GON blockade, the type of local anesthetic to be applied, the type of steroid and the injectate volume. It was determined that with 3 ml GON injection, all proximal GONs and TONs were stained, and LONs were stained in half of the cadavers. Additionally, in 30% of cadavers, the GON was located lateral to the OA. Key words: Nervus occipitalis major, Nervus occipitalis minor, headache, nerve blockade, GON blockade