Copyright @ 2009 . Unauthorized reproduction of this article is prohibited. American Society of Regional Anesthesia and Pain Medicine Evaluation of the Longus Colli Muscle in Relation to Stellate Ganglion Block Ye zim Ate z, MD,* Ibrahim Asik, MD,Þ Enver O ¨ zgencil, MD,* Halil I brahim A0ar, MD,þ Banu Ya?murlu, MD,§ and I brahim Tekdemir, MDþ Background and Objectives: The longus colli (LC) muscle is an important structure of the anterior cervical spine and has a critical role in stellate ganglion block. This technique involves withdrawing the needle to locate its port for injection above the anterior surface of the LC muscle; however, its exact thickness at the C5, C6, and C7 levels has not been measured. The aim of this anatomic and magnetic resonanceYsupported study was to evaluate the thickness of the LC muscle at these levels from the anterior tubercle of each vertebra toward the vertebral body at 5-, 10-, and 15-mm distances to provide precise anatomic data for stellate ganglion block. Methods: Ten cadavers, 60 vertebral body specimens, and cervical magnetic resonance imaging (MRI) scans of 40 adult patients were used for measurements. Results: The main findings of this study are that the thickness of the LC muscle varies between 5.0 and 10.0 mm at C6 and C7 in cadavers and between 8.0 and 10.0 mm in MRI scans. Sex has an important role; MRI scans revealed that male patients have a considerably thicker LC muscle at each vertebral level. Conclusion: We found a highly variable thickness of the LC muscle in anatomic and imaging studies, which may lead to negative block results. (Reg Anesth Pain Med 2009;34: 219Y223) S tellate ganglion blocks are commonly performed as diagnostic or therapeutic procedures for complex regional pain syndrome. 1 Techniques described for stellate ganglion block involve anterior paratracheal, lateral, anterolateral, supe- rior, and posterior approaches. Although stellate ganglion blocks have been used in clinical practice for more than 70 years, the literature indicates a variable success rate (16%Y100%). 2Y4 Some of this unpredictability has been attributed to the methods used for the evaluation of the sympathetic blockade; however, considering the complex anatomy of the region, technical concerns have also been addressed. 2,5,6 Although the longus colli (LC) muscle has been described in some studies investigating neck anatomy, its anteroposterior thickness at different cervical vertebral levels has never been determined. 7,8 The LC muscle is an important landmark on the anterior cervical spine. This muscle extends from the anterior tubercle of the atlas to the third thoracic vertebral body. 9 The stellate ganglion is located on the anterior surface of the LC muscle. Therefore, using the anterior paratracheal approach, the practitioner has to withdraw the needle until the port for local anesthetic egress is anterior to the anterior surface of the muscle. Either there is considerable variability (2Y5 mm) in the reported distance that the needle should be withdrawn to prevent an injection into the LC muscle for stellate ganglion block with the paratracheal approach, or it has never been properly measured. 10,11 Therefore, practitioners do not know precisely how far to withdraw the needle. We therefore measured the exact thickness of the LC muscle. This study was performed on cadavers and magnetic resonance imaging (MRI) scans of adult patients to evaluate the actual thickness of the LC muscle at different levels of the transverse processes of the cervical vertebra related to the stellate ganglion block. METHODS Institutional review board approval and written informed consent were obtained for the clinical part of this study. Data for this study were obtained from 10 cadavers with intact neck anatomy, 60 cervical vertebral body specimens, and cervical MRI scans of 40 adult patients. All measurements (cadaveric and radiologic) were performed 3 times by 2 investigators blinded to each other. Data were recorded in millimeters. Cadaver Study Ten adult white male cadavers were obtained from the Department of Anatomy (Ankara University, Ankara, Turkey). Cadavers had been embalmed in 10% formaldehyde and were kept in 5% formaldehyde. The medical histories of the subjects with intact neck anatomy revealed no findings of cervical or muscle disease. They were aged 54 years (SD, 7 years) at the time of death. Mean height and weight of cadavers were 168 cm (SD, 11 cm) and 71 kg (SD, 4 kg), respectively. The cadaver was placed in a supine position, and a longitudinal incision was made lateral to the sternocleidomastoid muscle, beginning at the level of the hyoid bone and descending to the clavicles, allowing access to the space by medial retraction of the carotid sheath and midline structures of the neck. The stellate ganglion was found lying on or just lateral to the lateral border of the LC between the base of the seventh cervical transverse process and the neck of the first rib, which were both posterior to the stellate ganglion, and the vertebral vessels were located anteriorly. The stellate ganglion was separated from the posterior aspect of the cervical pleura by the suprapleural membrane; the costocervical trunk branches were located near its lower pole. C4 to T1 were then exposed bilaterally. The vertebral levels were determined using anatomic landmarks including the first rib and anterior tubercles of C6 transverse processes. The medial border of the LC and the most lateral palpable part of the anterior tubercle for C5 and C6 were identified (Fig. 1). Once the LC muscle was revealed, the thickness of this muscle was measured in situ without dissecting the muscle or removing it, every 5 mm from the tip of transverse process to the medial border of the LC muscle (Fig. 2). Measurements were performed at the C5, C6, and C7 vertebral levels. The parameters were gauged using a digital caliper (Mitutoyo Corporation, Kanagawa, Japan) accurate to 0.01 mm. ORIGINAL ARTICLE Regional Anesthesia and Pain Medicine & Volume 34, Number 3, May-June 2009 219 From the Departments of *Anesthesiology and Reanimation, †Anesthesiology and Algology, ‡Anatomy, §Radiology, University of Ankara, Ankara, Turkey. Accepted for publication August 26, 2008. Address correspondence to: Ibrahim Asik, MD, University of Ankara, Faculty of Medicine (e-mail: iasik@yahoo.com). Copyright * 2009 by American Society of Regional Anesthesia and Pain Medicine ISSN: 1098-7339 DOI: 10.1097/AAP.0b013e3181a32a02