Nervio occipital mayor: trayecto, relaciones anatómicas e implicancias clínicas de sus posibles sitios de atrapamiento / Great occipital nerve: course, anatomical relations and clinical implications of their potential entrapment sites

RESUMEN: El nervio occipital mayor (NOM) se forma del ramo dorsal del nervio espinal C2 y asciende entre la musculatura cervical posterior para inervar la piel del cuero cabelludo. Diversos autores han descrito su recorrido, sin embargo, es escasa la información referente a la relación que presenta este nervio con el músculo oblicuo inferior de la cabeza (OIC) y su trayecto intramuscular. El objetivo de este estudio fue determinar el recorrido y relaciones que el NOM estableció en el intervalo existente entre los músculos OIC y músculo trapecio (T). Para ello, se midieron las distancias verticales y horizontales a la altura de la protuberancia occipital externa y línea mediana, y se dividió al músculo OIC en tercios para observar variaciones del recorrido de este nervio. Junto con medir el diámetro del NOM, se midieron las distancias vertical y horizontal de este nervio a través de cinco puntos de referencia muscular y un punto de referencia vascular. Estos puntos musculares fueron: a) sobre el vientre del músculo OIC (punto 1); b) en la cara profunda del músculo semiespinoso de la cabeza (SEC) (punto 2); c) en la cara superficial del músculo SEC (punto 3); d) en la cara profunda del músculo T (punto 4); y e) en la cara superficial del músculo T (punto 5). A este se sumó el punto 6, en el cual se establecieron las distancias vertical y horizontal con la arteria occipital a la altura de la cara superficial del músculo T. Para ello se disecaron 18 cabezas (36 triángulos suboccipitales) de cadáveres adultos brasileños pertenecientes al laboratorio de Anatomía de la Universidade Federal de Alagoas (UFAL), Maceió, Brasil. Las distancias verticales y horizontales obtenidas respecto de los seis puntos fueron: 63,67 y 27,15 mm (punto 1); 53,89 y 21,44 mm (punto 2); 30,61 y 14,49 mm (punto 3); 20,39 y 22,8 mm (punto 4); 5,86 y 33,46 mm (punto 5); 5,99 y 35,56 mm (punto 6), respectivamente. En relación al músculo OIC, el NOM se ubicó en un 72,22 % de las muestras en el tercio medio de este músculo, 19,44% en su tercio lateral y un 8,33 % en su tercio medial. Todos estos hallazgos deben ser considerados al momento de diagnosticar correctamente posibles atrapamientos del NOM en la región cervical profunda, siendo además, una contribución para el éxito de procedimientos quirúrgicos de esta región.

SUMMARY: The great occipital nerve (GON) is formed from the dorsal branch of the C2 spinal nerve and ascends between the posterior cervical musculature to innervate the skin of the scalp. Various authors have described its course, however, there is little information regarding the relationship that this nerve presents with the obliquus capitis inferior (OCI) and its intramuscular path. The objective of this study was to determine the route and relationships that the GON established in the interval between the OCI muscles and the trapezius muscle (T). For this, the vertical and horizontal distances were measured at the height of the external occipital protuberance and median line, and the OCI muscle was divided into thirds to observe variations in the path of this nerve. Along with measuring the diameter of the GON, the vertical and horizontal distances of this nerve were measured through five muscle reference points and one vascular reference point. These muscle points were: a) on the belly of the OCI muscle (point 1); b) in the deep face of the semispinalis capitis muscle (SCM) (point 2); c) on the surface of the SCM (point 3); d) on the deep face of the T (point 4); and e) on the surface face of the T (point 5). To this was added point 6, in which the vertical and horizontal distances were established with the occipital artery at the height of the superficial face of the T. For this, 18 heads (36 suboccipital triangles) of Brazilian adult corpses belonging to the Anatomy laboratory of the Universidade Federal de Alagoas (UFAL), Maceió, Brazil, were dissected. The vertical and horizontal distances obtained with respect to the six points were: 63.67 and 27.15 mm (point 1); 53.89 and 21.44 mm (point 2); 30.61 and 14.49 mm (point 3); 20.39 and 22.8 mm (point 4); 5.86 and 33.46 mm (point 5); 5.99 and 35.56 mm (point 6), respectively. In relation to the OCI, the GON was located in 72.22 % of the samples in the middle third of this muscle, 19.44 % in its lateral third and 8.33 % in its medial third. All these findings should be considered when correctly diagnosing possible entrapments of GON in the deep cervical region, being a contribution to the success of surgical procedures in this region.

Efficacy of the Greater Occipital Nerve Block for Cervicogenic Headache: Comparing Classical and Subcompartmental Techniques.

AIM: The aim of the study was to compare the efficacy of the greater occipital nerve (GON) block using the classical technique and different volumes of injectate with the subcompartmental technique for the treatment of cervicogenic headache (CH). METHODS: Thirty patients acted as his/her own control. All patients were submitted to the GON block by the classical technique with 10 mg dexamethasone, plus 40 mg lidocaine (5 mL volume). Patients were randomly allocated into 1 of 3 groups (n = 10) when pain VAS was > 3 cm. Each group was submitted to a GON subcompartmental technique (10 mg dexamethasone + 40 mg lidocaine + nonionic iodine contrast + saline) under fluoroscopy using either 5, 10, or 15 mL final volume. Analgesia and quality of life were evaluated. RESULTS: The classical GON technique resulted in 2 weeks of analgesia and less rescue analgesic consumption, compared to 24 weeks after the subcompartmental technique (P < 0.01). Quality of life improved at 2 and 24 weeks after the classical and the suboccipital techniques, respectively (P < 0.05). The data revealed that groups were similar regarding analgesia when compared to volume of injection (P > 0.05). CONCLUSIONS: While the classical technique for GON block resulted in only 2 weeks of analgesia, the subcompartmental technique resulted in at least 24 weeks of analgesia, being 5 mL volume sufficient for the performance of the block under fluoroscopy.