The importance of the greater occipital nerve in the occipital and the suboccipital region for nerve blockade and surgical approaches--an anatomic study on cadavers.

OBJECTIVE: Greater occipital nerve (GON) blockade is an effective method for treatment of occipital neuralgias. Occipital neuralgia or neuropraxis of this region may be seen particularly as a result of compression of the GON. This study shows the relationship between the GON and its external bone landmarks, in order to prevent complications and to perform nerve blockades safely. The study also defines the points where the GON pierces the semispinalis capitis (SSC) and the trapezius, and where the GON passes the obliquus capitis inferior (OCI), and identifies bone landmarks for places where the GON may be entrapped. MATERIALS AND METHODS: In the laboratories of Dokuz Eylül University, Faculty of Medicine Department of Anatomy, 12 GON's belonging to male adult cadavers fixed in formaldehyde were dissected. Colored silicone was injected to all cadavers and then microdissections were performed under a dissection microscope. The lesser occipital nerve, the GON, the greater auricular nerve, and the occipital artery (OA) were dissected. All measurements were made with a 0.1mm sensitive calipometer. RESULTS: The GON's diameter at the point where the GON pierces the SSC was found to be 2.5±0.3 mm. The distance between the point where the GON pierces the SSC and the external occipital protuberance (EOP) was 53.6±5.0 mm. The distance between this point and the midline was 9.0±1.9 mm, the distance between this point and the intermastoid line was 11.5±3.9 mm and the distance between this point and the mastoid process was 65.5±5.9 mm. The distance between the midline and the point where the GON pierces the aponeurosis of trapezius (AT) was 47.9±8.0 mm, the distance between this point and the EOP was 15.1±7.0 mm, the distance between this point and the intermastoid line was 17.1±2.8 mm, and the distance between this point and the mastoid process was 59.4±2.3 mm. We measured the distance between the OA and the intermastoid line to be 8.5±6.1 mm vertically and 32.3±3.9 mm horizontally to the midline. CONCLUSION: In this study, we define the GON's route in the suboccipital and the occipital region where the nerve pierces the SSC and the AT and where blockade or surgery can be performed. These data will help the surgeon and clinician to avoid complications in this region.

Variations in the high division of the sciatic nerve and relationship between the sciatic nerve and the piriformis.

OBJECTIVE: The sciatic nerve (SN) separates into its branches, the tibial and common fibular nerves, outside the pelvis. However, it may rarely be separated within the pelvis. In such cases, the tibial nerve and the common fibular nerve may leave the pelvis through different routes. These variations may cause nerve compressions under other anatomic structures, resulting in non-discogenic sciatica. The aim of this study was to define the level of the SN exit and of the SN division. MATERIAL AND METHOD: 50 gluteal regions were examined in 25 formalin-fixed adult male cadavers. RESULTS: In 52% of the cases, the SN exited the pelvis as a whole nerve without any division, whereas in 48% a high division was observed. Branches of the SN left the pelvis through the infrapiriform foramen (IP) as two separate nerves In 24%. One branch of the SN left the pelvis through the IP and other through a different route in another 24%. CONCLUSION: The differences in the exit routes of these two nerves are important in clarifying the clinical etiology of nondiscogenic sciatica. These variations require reviewing the piriformis syndrome.

Anatomic considerations and the relationship between the piriformis muscle and the sciatic nerve.

UNLABELLED: STATING BACKGROUND: The piriformis syndrome is one of the non-discogenics causes of sciatica. It results from the compression of the sciatic nerve (SN) by the piriformis muscle (PM) in the neutral and piriformis stretch test position. The evidence of the increase in pain in the test position requires a detailed anatomical study addressing the changes that occurred in the SN and PM anatomy during the test position. The aim of this study is to examine this relationship morphometrically. MATERIALS AND METHODS: A total of 20 right and left lower limbs of ten adult cadavers were examined. The SN and the PM were made visible. The location of the SN was evaluated with respect to the consistent bony landmarks, including the greater and the lesser trochanter of the femur, the ischial tuberosity, the ischial spine of the hip bone, the posterior inferior iliac spine of the hip bone and the posterior superior iliac spine of the hip bone. The study was done in both neutral and test positions (i.e., 30 degrees adduction 60 degrees flexion and approximately 10 degrees medial rotation position of the hip joint). RESULTS: The width of the greater sciatic notch was 63.09 +/- 13.59 mm. The length of the lower edge of the PM was 95.49 +/- 6.21 mm, and whereas the diameter of the SN where it emerged from the infrapiriforme was 17.00 +/- 3.70 mm, the diameter decreased to 11.03 +/- 2.52 mm at the level of the lesser trochanter of the femur. The SN intersected the PM most commonly in its medial second quarter anatomically. The vertical distance between the medial edge of the SN-PM intersection point and the ischial tuberosity was 85.62 +/- 17.23 and 72.28 +/- 7.56 mm (P < 0.05); the angle between the SN and the transverse plane was 66.36 degrees +/- 6.68 degrees and 71.90 +/- 8.48 degrees (P < 0.05); and the vertical distance between the medial edge of the SN and the apex of the ischial spine of the hip bone was 17.33 +/- 4.89 and 15.84 +/- 4.63 mm (P > 0.05), before and after the test position, respectively. CONCLUSION: This study provides helpful information regarding the course and the location of the SN. The presented morphometric data also revealed that after stretch test position, the infrapiriforme foramen becomes narrower; the SN becomes closer to the ischial spine of the hip bone, and the angle between the SN and the transverse plane increases. This study confirmed that the SN is prone to be trapped in the test position, and diagnosis of this situation requires dynamic MR and MR neurography study.