Joint segmentation of sternocleidomastoid and skeletal muscles in computed tomography images using a multiclass learning approach.

Deep-learning-based methods can improve robustness against individual variations in computed tomography (CT) images of the sternocleidomastoid muscle, which is a challenge when using conventional methods based on probabilistic atlases are used for automatic segmentation. Thus, this study proposes a novel multiclass learning approach for the joint segmentation of the sternocleidomastoid and skeletal muscles in CT images, and it employs a two-dimensional U-Net architecture. The proposed method concurrently learns and segmented segments the sternocleidomastoid muscle and the entire skeletal musculature. Consequently, three-dimensional segmentation results are generated for both muscle groups. Experiments conducted on a dataset of 30 body CT images demonstrated segmentation accuracies of 82.94% and 92.73% for the sternocleidomastoid muscle and entire skeletal muscle compartment, respectively. These results outperformed those of conventional methods, such as the single-region learning of a target muscle and multiclass learning of specific muscle pairs. Moreover, the multiclass learning paradigm facilitated a robust segmentation performance regardless of the input image range. This highlights the method's potential for cases that present muscle atrophy or reduced muscle strength. The proposed method exhibits promising capabilities for the high-accuracy joint segmentation of the sternocleidomastoid and skeletal muscles and is effective in recognizing skeletal muscles, thus, it holds promise for integration into computer-aided diagnostic systems for comprehensive musculoskeletal analysis. These findings are expected to enhance medical image analysis techniques and their applications in clinical decision support systems.

Sternalis featuring tendomuscular fusion to the contralateral sternocleidomastoid: a cadaveric case report.

PURPOSE: To report the morphologic and spatial relationships of a bilateral sternalis muscle variant. METHODS: Routine cadaveric dissection in an undergraduate anatomy laboratory revealed two sternalis muscles parasternal to the sternal body. Subsequent fine prosection of the anterior thoracic wall and neck was carried out to uncover the soft tissue attachments of both sternalis muscles. Positional relationship to neighboring anterior thoracic and neck structures, and geometric dimensions of the muscle bellies and tendons, were documented. RESULTS: Both sternalis muscles were imbedded in the pectoral fascia, with their muscle fibers running obliquely to the midsternal line. The right sternalis muscle was notably larger in length, width, and thickness compared to the sternalis muscle on the left. The right sternalis muscle featured a distinct superior cord-like intermediate tendon that traversed superolateral and fused directly with the contralateral sternomastoid and sterno-occipital portions of the left sternocleidomastoid muscle. The superior tendon of the left sternalis muscle was aponeurotic and affixed to the cord-tendon of the right sternalis muscle. A distinct tendinous entheses for the sternal head for both sternocleidomastoid muscles were noted at the manubrial body. CONCLUSIONS: This case report describes a unique bilateral sternalis muscle variant with conjoined sternocleidomastoid muscle integration. This anatomical description of a sternalis-sternocleidomastoid muscle morphology may supplement radiographic interpretations and support diagnostic accuracy.

Branchial Cyst Masquerading as Myositis and Abscess of Sternocleidomastoid Muscle and Necrotic-Cystic Lymphadenopathy.

Branchial cleft cysts are considered one of the most common cystic lesions in neck and are commonly seen in pediatric age group and young adulthood with most of the cases presenting within second and third decade. Here we intend to discuss a case of a 43 year old male who presented with a very short history of a painful lateral neck mass and was clinico-radiologically suggested as either myositis and abscess of sternocleidomastoid muscle or necrotic/cystic lymphadenopathy. An ultrasound guided needle aspiration cytology did not show any microorganism thus an excisional biopsy of the mass was done suspecting it to be lymph nodal mass. However the histopatholgical examination confirmed it to be an inflamed branchial cyst. Thus we would like to highlight the importance of keeping branchial cleft cysts as a possible differential while managing lateral neck masses of any duration in adults as well as in children.

Accessory Head of Sternocleidomastoid Muscle in Indian Cadavers: A Report of Three Cases.

During dissection sessions for undergraduate students, the unilateral accessory clavicular head of the sternocleidomastoid muscle was observed in three cadavers. These accessory heads extended from the middle third of the clavicle and joined the sternocleidomastoid muscle in the middle third. The variations in the sternocleidomastoid muscle may be attributed to abnormal mesodermal splitting or fusion failure during the development of the post-sixth branchial arch. Anomalies of the sternocleidomastoid may be misdiagnosed as cervical dystonia, fibromatosis colli, or muscular spasm. In rare cases, an accessory head could result in torticollis in adults. These anomalies warrant particular attention during interventional procedures conducted by anesthesiologists. The internal jugular vein is accessed at the lesser supraclavicular fossa for cannulation during central venous access and temporary hemodialysis. Variations in its anatomy can pose challenges during these procedures. Moreover, the clavicular head may be utilized for muscle flaps in the upper neck and occipital regions.

A Case of Refractory Tracheocutaneous Fistula Successfully Treated With the Combination of Auricular Cartilage Grafting and Sternocleidomastoid Muscle Flap.

The tracheotomy site usually closes spontaneously after decannulation, but in rare cases, it develops into tracheocutaneous fistula. We experienced a case of tracheocutaneous fistula that was successfully treated with the combination of auricular cartilage grafting and sternocleidomastoid muscle flap. In this case, we performed the closure of tracheocutaneous fistula with a view to filling the tissue defect with soft tissue to prevent recurrence. The surgical procedure performed in this case was unique, which to our knowledge, has not been described previously. Herein, we report some findings obtained, together with a literature review. The patient was a 73-year-old male. Starting five months after tracheotomy, the closure of a tracheocutaneous fistula was attempted twice at an otolaryngology clinic, which resulted in recurrence. The patient visited our department with the desire to close the tracheocutaneous fistula. At the initial examination, we found a cutaneous fistula with a diameter of approximately 2 mm on the cranial side of the sternal notch and thinning of the surrounding tissue. Preoperative computed tomography (CT) showed a tracheal defect with a size of approximately 10 mm on the caudal side of the sternal notch. The surgery was performed under general anesthesia 10 months after tracheotomy. The platysma muscle was attached to elevate the skin flap, and the scarring at the cutaneous fistula opening was removed. The cartilage defect was 10×12 mm in size. A piece of cartilage was harvested from the posterior surface of the auricle (navicular fossa) and grafted to the tracheal opening. A part of the left sternocleidomastoid muscle body of the sternal head was dissected from the mandibular side using the sternal attachment site as a stalk and elevated. The muscle flap was rotated, with its tip folded back, doubled over, and fixed on top of the auricular cartilage graft. The platysma muscles were sutured together during which the skin flap suture line was shifted so that the suture line would not coincide with the tracheal fistula site. The course was favorable, with no recurrence for three years. In the closure of a tracheocutaneous fistula, two sides need to be considered: the trachea and the skin. The tracheal defect in the present case was larger than 10 mm in size and thus auricular cartilage grafting was performed. In addition, we filled the tissue defect with the soft tissue of a sternocleidomastoid muscle flap, which was a unique step. The combined use of auricular cartilage grafting and sternocleidomastoid muscle flap was effective for the closure of a refractory tracheocutaneous fistula.

Hypoglossal nerve involvement and sternocleidomastoid muscle atrophy in chronic inflammatory demyelinating polyneuropathy with Hashimoto's thyroiditis: A case report and literature review.

Chronic inflammatory demyelinating polyneuropathy (CIDP) is an immune-mediated neuropathy. While CIDP typically affects the peripheral nerves in the limbs, involvement of cranial nerves is atypical, and cases of muscle atrophy secondary to cranial nerve involvement are exceptionally rare. A 30-year-old female patient, who complained of numbness and weakness in her limbs, was diagnosed with CIDP after experiencing atrophy of the tongue and sternocleidomastoid muscles, along with tongue muscle fibrillation during a neurological examination. Additionally, the patient had hypothyroidism caused by Hashimoto's thyroiditis. Cerebrospinal fluid tests indicated albumincytological dissociation. Electrophysiological examination results confirmed the diagnosis of typical CIDP. Glucocorticoid treatment, a standard therapy for CIDP, led to a significant improvement in the patient's symptoms, including the regeneration of her tongue muscles. A literature review revealed only eight cases of CIDP with hypoglossal nerve involvement, and this case represents the first documentation of concurrent sternocleidomastoid muscle atrophy. Although muscle atrophy from cranial nerve involvement is infrequent in CIDP, the positive response to treatment is encouraging.

Ectopic parathyroid adenoma on sternocleidomastoid muscle: a case report.

A 54-year-old woman was admitted to the hospital with a left neck mass. Enhanced CT and ultrasound examinations revealed a lesion in the left sternocleidomastoid muscle. The patient undergone right thyroid lobe resection 8 years ago. Interestingly, the lesion on the sternocleidomastoid muscle, along with the left lobe of the patient's thyroid, visually appears to form a displaced and complete thyroid in the early Tc-99m-MIBI parathyroid scintigraphy. Combined with Tc-99m-MIBI scintigraphy and abnormal PTH and blood calcium levels, the consideration was given to the lesion in the sternocleidomastoid muscle as an ectopic parathyroid adenoma. Subsequent surgical pathology confirmed this suspicion.

Soft Tissue Dissection in the Transcondylar Approach: A Modified Layered Technique to Maximize Lateral Access.

Objective While the transcondylar approach is technically challenging, it provides generous ventral and caudal exposure to the craniovertebral junction. This approach requires navigation around multiple eloquent neurovascular structures including the lower cranial nerves, vertebral artery and its branches, and the brainstem. Superficial exposure, including incision location and muscle dissection, can dramatically affect the surgical angle and maneuverability at depth. Methods We demonstrate the transcondylar approach in a step-by-step fashion in a formalin-embalmed, latex-injected cadaver head. Dissection within each layer of the suboccipital muscles was performed. A small cohort with an illustrative case is also included herein. Results The sternocleidomastoid (SCM) muscle was retracted anteriorly; the splenium capitis, semispinalis capitis, and longissimus capitis muscles were disconnected from the superior nuchal line and reflected inferomedially. The suboccipital muscle group was fully exposed. The superior and inferior oblique muscles were disconnected from the transverse process of C1. The superior oblique and the rectus capitis posterior major muscles were then dissected off the inferior nuchal line, and the suboccipital muscle group was retracted inferomedially en bloc . The greater auricular nerve was retracted laterally with the SCM, and the greater occipital nerve was retracted inferomedially with the suboccipital muscle group. Conclusion This technique avoids the obstructive muscle bulk that results from a myocutaneous approach while maximizing deep exposure. Understanding the detailed muscular anatomical relationship with the insertion location and suboccipital nerves is key to complete and safe extracranial dissection. Diligent dissection helps minimize postoperative pain and muscle spasm while optimizing the closure technique.

Tracheal repair with sternocleidomastoid flap in mediastinoscopic surgery for esophageal cancer.

Tracheal injury during mediastinoscopic esophagectomy is a life-threatening complication that is challenging to manage. However, no precise treatment has been defined. An 80-year-old male patient with upper esophageal cancer underwent a mediastinoscopic esophagectomy and gastric tube reconstruction through the posterior mediastinal route. When the esophagus was separated from the trachea using a bipolar vessel sealing system, the left side of the membranous trachea incurred a 3-cm defect 7 cm below the sternal notch. We successfully repaired the tracheal injury not by directly suturing the defect but by reinforcing it with a pedicle sternocleidomastoid flap. The gastric tube was placed over the tracheal repair for esophageal reconstruction via a posterior mediastinal route. As a result, the patient recovered well and was discharged. A sternocleidomastoid flap might be another surgical option for reinforcement flaps in tracheal injuries.

A novel minimally invasive endoscopic approach of thyroid surgery-endoscopic thyroidectomy via sternocleidomastoid muscle posteroinferior approach.

Background: Since the endoscopic thyroidectomy was firstly reported by Hüscher in 1997, there has been an ongoing debate regarding whether mainstream endoscopic thyroidectomy can be classified as minimally invasive surgery. In this study, we innovatively proposed the endoscopic thyroidectomy via sternocleidomastoid muscle posteroinferior approach (ETSPIA), a novel minimally invasive surgical technique, and compared its efficacy with the well-established transoral endoscopic thyroidectomy vestibular approach (TOETVA). Methods: We retrospectively analyzed 50 patients who underwent ETSPIA and 50 patients who underwent TOETVA at Beijing Tongren Hospital, comparing their clinical characteristics, operative duration, blood loss, postoperative alterations in parathyroid hormone (PTH) and serum calcium, recovery post-surgery, complications, and follow-up data. Results: The ETSPIA group had a shorter operation time compared to the TOETVA group (243.40±58.67 vs. 278.08±78.50 min; P=0.01). The ETSPIA group also had less intraoperative blood loss than the TOETVA group (20.60±10.58 vs. 33.00±11.11 mL; P<0.001). More central lymph nodes were dissected in the ETSPIA group compared to the TOETVA group (5.90±4.72 vs. 3.36±2.80; P=0.002). However, the difference in the number of positive central lymph nodes dissected was not statistically significant (1.38±2.33 for ETSPIA vs. 0.94±1.39 for TOETVA; P=0.26). The ETSPIA group had a shorter length of stay (LOS) compared to the TOETVA group (6.82±2.02 vs. 8.26±2.72 days; P=0.003). The alteration in PTH levels 1 day after surgery was less pronounced in the ETSPIA group compared to the TOETVA group (-26.38%±18.43% vs. -35.75%±22.95%; P=0.04). At the 1-month postoperative mark, the ETSPIA group showed a marginal increase in PTH levels, whereas the TOETVA group exhibited a slight decrease (10.12%±35.43% vs. -11.53%±29.51%; P=0.03). Regarding the average percentage change in serum calcium level 1 day after surgery, the ETSPIA group showed a smaller change, though this difference was not statistically significant (-4.79%±5.47% vs. -5.66%±3.90%; P=0.40). Furthermore, the incidence of hoarseness attributable to transient recurrent laryngeal nerve (RLN) injury in postoperative patients was lower in the ETSPIA group compared to the TOETVA group, but this difference did not reach statistical significance (0% vs. 4%; P=0.15). Conclusions: Overall, compared to TOETVA, the ETSPIA is characterized by a shorter operative route, enhanced protection of the parathyroid glands, reduced trauma, and expedited postoperative recovery.

Intramuscular Lipoma of the Sternocleidomastoid Muscle: A Rare Entity Revisited.

Intramuscular lipomas, typically found in subcutaneous tissue, rarely affect deeper muscular planes, especially those of the head and neck region. The following are 3 cases of intramuscular lipomas involving the sternocleidomastoid muscle. The first 2 patients presented with painless, palpable masses confirmed by diagnostic imaging as well-circumscribed intramuscular lipomas. One was treated surgically, while the other was managed conservatively with monitoring and close follow-up. The third patient reported dysphagia associated with occasional dyspnea and mild pain. The mass was identified as infiltrative lipoma and was resected surgically. Complete tumor removal with no recurrence at 6 months was observed for the first and last cases. The second case was serially followed at 3 and 6 months with no interval changes. We report the largest case series on intramuscular lipomas of the sternocleidomastoid muscle to enhance our understanding of this rare entity.

Sternocleidomastoid Muscle Flap in an Older Patient With Congenital Muscular Torticollis.

Congenital muscular torticollis (CMT) is caused by muscle damage during childbirth, tumors, or masses within the muscles and generally resolves with physical therapy during infancy. In this study, we performed reconstruction after resection of a parotid gland tumor using a sternocleidomastoid muscle (SCMM) flap in an older patient with neglected CMT. The patient was a 64-year-old woman who had had a left-sided oblique neck since infancy but had never received any treatment, including physical therapy. She underwent parotid tumor resection and SCMM flap transfer. The SCMM flap can be safely elevated using indocyanine green fluorescence angiography, with the middle pedicle serving as the feeding vessel to fill the parotid defect. Three months after surgery, the torticollis had improved and the cheek depression was not noticeable, indicating the effectiveness of surgical treatment for CMT in older patients and the possibility of using SCMM as a muscle flap.

Effect of sternocleidomastoid flap repair and endoscopic injection of emulsified adipose tissue stromal vascular fraction in the treatment of refractory cervical anastomotic leak contaminating mediastinum.

Mediastinal infection caused by anastomotic leak is hard to cure, mainly because the poor drainage at the site of mediastinal infection leads to persistent cavity infection, which in turn becomes a refractory mediastinal abscess cavity after minimally invasive esophagectomy (MIE)-McKeown. Herein, we explored sternocleidomastoid (SCM) muscle flaps and emulsified adipose tissue stromal vascular fraction containing adipose-derived stem-cells to address this issue. We studied 10 patients with esophageal cancer who underwent MIE-McKeown + 2-field lymphadenectomy and developed anastomotic and mediastinal leak and received new technology treatment in the Affiliated Cancer Hospital of Zhengzhou University from June 2018 to March 2022. The clinical data and prognosis of the patients were collected and analyzed. A total of 5 patients received this surgery, and no other complications occurred during the perioperative period. Among the 5 patients, 1 patient was partially cured, and 4 patients were completely cured. During the follow-up 3 months postoperatively, all these 5 patients could eat regular food smoothly, and no relapse of leak and mediastinal infection occurred. The new surgical method has achieved good results in the treatment of anastomotic leak. Compared with the traditional thoracotomy, it is a less invasive and feasible surgical approach, which can be used as a supplement to the effective surgical treatment of cervical anastomotic leak contaminating the mediastinum.

Intramuscular nerve distribution of the sternocleidomastoid muscle for the botulinum toxin injection.

PURPOSE: The aim of this study is to define the intramuscular nerve distribution of the sternocleidomastoid muscle (SCM) and the innervation zones (IZ) to describe the optimal botulinum toxin injection sites. METHODS: The cricoid cartilage (CC), laryngeal prominence (LP) and hyoid bone (HB) and angle of mandible (AM) were determined as landmarks. The length of the muscles were measured between the sternoclavicular joint and tip of the mastoid process. SCM was evaluated in two parts as anterior and posterior divided by the line where the length of the muscle was measured. Measurements were made to define the relationships of the SCM with common carotid artery, internal and external jugular veins. IZ were described according to these vessels. Afterwards, Modified Sihler's staining technique was applied to expose the intramuscular nerve distribution. RESULTS: The average length of SCM was 160,1 mm. Motor entry point of the accessory nerve fibers were between the AM-HB lines, in the range of 30-40% of the muscle length, and in the posterior part of the muscles. IZ were between the HB-CC lines in the anterior and posterior part. When this interval was examined according to the vessels, the optimal injection sites were between the LP-CC lines. CONCLUSIONS: This study shows the position of the intramuscular nerve fibers endings of the SCM according to the chosen landmarks and the relationship of the IZ with the vessels to prevent complications. These results can be used as a guide for safe and effective botulinum toxin injections with optimal quantities.

Epidemic Myalgia Presenting as Cervical Pain: A Case Report.

A 53-year-old female visited our hospital because of cervical and abdominal pain preceding fever and upper respiratory symptoms. Severe tenderness was noted over the bilateral sternocleidomastoid muscles, the superior portion of the trapezius muscle, and the umbilical region of the abdomen. The patient reported exacerbation of posterior neck pain in the supine position and during the transition from sitting to the supine position. The diagnosis of epidemic myalgia was finally made. This case highlights the presence of the cervical variant of epidemic myalgia.

Transaxillary endoscopic subfascial operation for persistent muscular torticollis in pediatric patients: A 13-year retrospective study in Taiwan.

BACKGROUND: The endoscopic surgery for persistent muscular torticollis has been well-described and most are subcutaneous working caverns. As the sternocleidomastoid muscle is located beneath the deep cervical fascia that corresponds to the pectoral fascia, this study aimed to review our results of the transaxillary approach under the pectoral fascia and the deep cervical fascia. METHODS: Between November 2009 and January 2022, pediatric patients with persistent muscular torticollis receiving transaxillary endoscopic subfascial operation were retrospectively reviewed and analyzed. RESULTS: There were thirty-three consecutive patients with median age of 6.5 years (range, 5.5 months-15.7 years). The median operating time was 90.0 min. With a median follow-up of 14.8 months (range, 5.0-127.7), the final outcomes showed excellent-to-good results in 90.9%, fair results in 6.1%, and poor results in 3.0%. Univariate analysis revealed that the long-term outcomes of the operation were independent of gender, age, involved side and previously open myotomy (p = 0.662, 0.818, 0.740 and 0.596, respectively). CONCLUSIONS: The subfascial working cavern would be technically achievable for the transaxillary endoscopic approach with good functional and cosmetic outcomes.

Anatomical variations in the course of spinal accessory nerve in the neck triangles: A descriptive study.

BACKGROUND: Spinal Accessory Nerve (SAN), which innervates the sternocleidomastoid (SCM) and trapezius muscles, is closely related to the internal jugular vein (IJV) in the anterior triangle of the neck and passes superficially in the posterior triangle. Injury to SAN is a major complication of level II neck dissection, leading to shoulder syndrome. The present study aims to assess the course and its relation to the SCM muscle and IJV in the Tamil ethnolinguistic groups in South India. METHODS AND MATERIALS: The anterior and posterior triangles of the neck were dissected in 28 formalin-fixed adult cadavers. The course of the SAN and the entry and exit points of SAN along the SCM muscle were assessed using the mastoid process as the reference. Recorded data was analyzed using SPSS software. RESULTS: The SAN was anteriorly related to the IJV in 58.73%, posteriorly in 37.5%, and pierced through the IJV in 3.57% of the specimens. The entry and exit points of SAN from the mastoid process were 37.86±7.26mm and 48.55±8.22mm, respectively. In 86.67% of the cases, the SAN traversed through the SCM muscle, and in 13.33%, it was deep to the SCM. CONCLUSION: The present study reports that the SAN is variable in its course, and relation to SCM and IJV. Knowledge about the variant anatomy of the SAN in the triangles of the neck is important and it aids surgeons to prevent iatrogenic injuries to SAN or IJV and enhance surgical safety in neck procedures.

Sternocleidomastoid muscle-splitting method for high cervical carotid endarterectomy: illustrative cases.

BACKGROUND: The number of cervical carotid endarterectomies (CEAs) has decreased as carotid artery stenting (CAS) has increased. However, CEA and CAS both have advantages and disadvantages; therefore, appropriate procedures must be selected for individual patients. High-positioned carotid artery stenosis presents technical challenges for CEA and is occasionally managed by performing CAS. However, CAS is associated with a high risk of thrombosis in patients with soft plaques, suggesting a clinical need for a better procedure. Consequently, appropriate surgical treatment for patients requiring high-level CEAs is essential. OBSERVATIONS: In this study, a novel and straightforward method was devised. The primary concept underlying this technique is separation of the sternocleidomastoid muscle (SCM) from other anatomical structures to ensure a wider surgical field. By anatomically separating the SCM into the sternal and clavicular head groups, the objective of the wider surgical field can be met. Herein, we report technical innovations in high-positioned carotid artery stenosis and evaluate their efficacy in two patients. LESSONS: In conclusion, high CEA surgery using this new method is valuable and may eliminate barriers to more advanced approaches.

Evaluation of patients with chronic obstructive pulmonary disease by maximal inspiratory pressure and diaphragmatic excursion with ultrasound sonography.

BACKGROUND: Decreased respiratory muscle strength and muscle mass is key in diagnosing respiratory sarcopenia. However, the role of reduced diaphragm activity, expressed as the maximal level of diaphragmatic excursion (DEmax), in diagnosing respiratory sarcopenia in patients with chronic obstructive pulmonary disease (COPD) remains unclear. This study aimed to characterize patients with COPD and low DEmax and maximal inspiratory pressure (MIP), a measure of inspiratory muscle strength, and assess the role of DEmax in respiratory sarcopenia. METHODS: Patients with COPD underwent spirometry, exercise tolerance (VO2peak) test, and MIP measurement. DEmax and sternocleidomastoid thickness at the maximal inspiratory level (TscmMIL) were assessed using ultrasound sonography. RESULTS: Overall, 58 patients with COPD (median age, 76 years; median %FEV1, 51.3 %) were included, 28 of whom showed a %MIP of ≥80 %, defined as having preserved MIP. Based on the %MIP of 80 % and median value of DEmax (48.0 mm) as thresholds, the patients were stratified into four groups: both-high (n = 18), %MIP-alone low (n = 11), DEmax-alone low (n = 10), and both-low (n = 19) groups. The both-low group exhibited the lowest %FEV1, Δinspiratory capacity, VO2peak, and TscmMIL, and these values were significantly lower than those of the both-high group. Except for %FEV1, these values were significantly lower in the both-low group than in the %MIP-alone low group despite adjusting DEmax level for body mass index. CONCLUSION: Measuring DEmax along with MIP can characterize patients with COPD, reduced exercise capacity, and decreased accessory respiratory muscle mass and can help diagnose respiratory sarcopenia.

Spinal accessory nerve anatomy in the posterior cervical triangle: A systematic review with meta-analysis.

This study aimed to investigate the anatomy of the spinal accessory nerve (SAN) in the posterior cervical triangle, especially in relation to adjacent anatomical landmarks, along with a systematic review of the current literature with a meta-analysis of the data. Overall, 22 cadaveric and three prospective intraoperative studies, with a total of 1346 heminecks, were included in the analysis. The major landmarks relevant to the entry of the SAN at the posterior border of the SCM muscle (PBSCM) were found to be the mastoid apex, the great auricular point (GAP), the nerve point (NP), and the point where the PBSCM meets the upper border of the clavicle. The SAN was reported to enter the posterior cervical triangle above GAP in 100% of cases and above NP in most cases (97.5%). The mean length of the SAN along its course from the entry point to its exit point from the posterior triangle of the neck was 4.07 ± 1.13 cm. The SAN mainly gave off 1 or 2 branches (32.5% and 31%, respectively) and received either no branches or one branch in most cases (58% and 23%, respectively) from the cervical plexus during its course in the posterior cervical triangle. The major landmarks relevant to the entry of the SAN at the anterior border of the TPZ muscle (ABTPZ) were found to be the point where the ABTPZ meets the upper border of the clavicle and the midpoint of the clavicle, along with the mastoid apex, the acromion, and the transverse distance of the SAN exit point to the PBSCM. The results of the present meta-analysis will be helpful to surgeons operating in the posterior cervical triangle, aiding the avoidance of the iatrogenic injury of the SAN.