Application of high-frequency ultrasound in the diagnosis of brachial plexus injury in children with Narakas type IV obstetrical brachial plexus palsy

Introduction

Obstetrical brachial plexus palsy (OBPP), also known as brachial plexus injury (BPI), is caused by the application of forceful traction during childbirth, resulting in damage to the anterior rami of the brachial plexus. According to pathological changes, plexus injuries OBPP can be classified as avulsion injury (preganglionic injury) or rupture injury (postganglionic injury). In general, the upper trunk is more prone to rupture while the lower trunk is more prone to avulsion (1). Given that nerve injury exerts a considerable impact on the innervated side and that irreversible damage may be caused by long-term denervation, brachial plexus reconstruction surgery involving the lower trunk must be completed within 6 months (2,3) and followed by immediate complex treatment (4). The choice of the procedure is determined by the type of nerve trunk injury (5): rupture injury is treated by nerve grafting (6), while the treatment of avulsion injury involves transfer of a healthy peripheral nerve bundle and subsequent connection to the functionally more important avulsed brachial plexus trunk (7). For traumatic neuromas in the upper trunk, excision and clearance of surrounding relevant lesions followed by nerve reconstruction, regardless of the presence or absence of nerve conduction, has received near-unanimous consensus (6,8,9). Under this premise, accurate assessment of the type and severity of nerve injury in children with OBPP represents a key step in preoperative diagnosis. An accurate preoperative diagnosis is beneficial to the reduction of operative time, determination of surgical exposure, and precise nerve reconstruction. This can lead to improved prognosis and reduction in the degree of disability in the affected limb of patients with OBPP (10,11). Assessment methods commonly used in clinical practice include symptom inquiry and physical examination, while auxiliary examinations include magnetic resonance imaging (MRI) and electromyography (10-15). However, the young age of children with OBPP makes it impossible to perform the aforementioned examinations without sedation.

With the rapid advancement of technology, the resolution of ultrasound imaging techniques has continuously improved, leading to the gradual adoption of ultrasonography for brachial plexus detection among a growing number of clinicians. In 1998, Sheppard et al. (16) first reported the sonographic findings of the normal adult brachial plexus. In 2014, Joseph et al. (17) reported a case of neonatal BPI on the right side, in which the injured segments and type of injury were determined by ultrasonographic examination. Ultrasonography has demonstrated considerable value in the diagnosis and treatment of adult BPI (1,15-17). However, clinical reports on the ultrasonographic examination of BPI in infants with OBPP remain scant.

Our study thus aimed to use high-frequency ultrasound for the exploration of brachial plexus roots in children with Narakas type IV OBPP and to analyze the characteristic ultrasonographic images of nerve injuries in these patients. Our results can serve as a reference for future clinical work, particularly preoperative assessments by pediatric surgeons and hand surgeons. We present this article in accordance with the STROBE reporting checklist (available at https://qims.amegroups.com/article/view/10.21037/qims-2025-479/rc).

Methods

Study participants

A total of 27 infants who were diagnosed with Narakas type IV OBPP at the Children’s Hospital of Fudan University between December 2020 and November 2021 were included in this study. The diagnostic criteria were as follows: (I) indications during childbirth, including dystocia such as macrosomia, forceps delivery, and shoulder dystocia; (II) upper limb dyskinesia after birth, in which the movement of one side of the upper limb is asymmetric or deformed, which manifests as total brachial plexus paralysis, with the functions of the upper arm, forearm, and hand being affected; (III) positive Horner sign, which is a characteristic manifestation of type IV obstetric paralysis, including ptosis, miosis, anhidrosis, etc.; (IV) muscle strength examination indicating obviously weakened or no muscle strength of the upper limb on the affected side, particularly in shoulder abduction, elbow flexion, and wrist and finger extension; and (V) reflex examination indicating a lack of pathological reflexes of the upper limb on the affected side, including the biceps reflex, triceps reflex, etc. The age of the patients ranged from 33 to 202 days (median age 109 days). A total of 24 patients underwent brachial plexus reconstruction at an interval of 2 days to 58 days (median interval 16.5 days) after ultrasonographic examination (see Table 1). Prior to the examination, all patients were sedated via oral administration of chloral hydrate (1 mL/kg body weight). Once asleep, the patients were placed in a supine position for the ultrasonographic examination. Patients who experienced poor sedative effects were calmed by feeding or pacifier use while undergoing the examination. This study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments and was approved by the Ethics Committee of Children’s Hospital of Fudan University (Approval No. [2021]. 335-01). Informed consent was obtained from all the children’s guardians.

Examination equipment

Ultrasonographic examinations were performed with an ACUSON Sequoia ultrasound system (Siemens Healthineers, Erlangen, Germany). An L4–10 high-frequency probe was used to examine the bilateral neck of the patients to determine the condition and type of injury, and the thyroid mode was selected for the exploration process. All examinations were performed by a single sonologist. The coupling agent was heated before use to reduce discomfort to the patients.

Operating methods and judgment criteria

The ultrasonographic exploration of the brachial plexus was performed by a single sonologist with 13 years of experience in ultrasonography and 7 years of experience in musculoskeletal ultrasonography. The sonologist was only provided the basic information of patients, such as the name, age, and the affected side.

During observation of the brachial plexus, ultrasonographic observations were performed in accordance with the standard anatomical landmarks. The probe was placed on the thyroid section to serve as the reference point. With the long axis of the spine serving as the axis for alignment, the probe was subsequently moved laterally toward the back of the patient’s neck. The vertebral artery was then located for use as the examination plane to pinpoint the nerve roots. Nerve roots of the various segments were identified according to the fact that transverse processes of the C2–C6 vertebrae possess anterior and posterior tubercles, while the anterior tubercle of the transverse process of the C7 vertebra is frequently small or absent (18). The nerve roots of each vertebra were identified after the ultrasonographic features of the various vertebrae were clarified (19-21). The course and ultrasonographic features of each nerve root were observed, and the foraminal and postforaminal nerve root thicknesses were measured.

Data acquisition and statistical analysis

All brachial plexus images were collected and transmitted to the picture archiving and communication system of our hospital. Foraminal and postforaminal thicknesses of the brachial plexus were measured, and the measurements were transcribed with Excel 2019 (Microsoft Corp., Redmond, WA, USA). With the intraoperative findings serving as the gold standard, the accuracy of ultrasonographic examination was analyzed in SPSS 25.0 (IBM Corp., Armonk, NY, USA). Statistical analysis was performed via the χ² test, and the differences between the two categorical variables of surgical findings and ultrasound results were compared, with differences considered statistically significant when P<0.05.

Results

The exploration of nerve roots of the bilateral brachial plexus was performed in 27 children with Narakas type IV OBPP. Nerve roots of the bilateral C5–C7 upper trunk segments were accurately and clearly identified in all the patients (100%), but the C8 nerve root was only identified in 10 (37.0%). Moreover, 24 patients underwent nerve exploration and reconstruction surgery after the ultrasonographic examination. Clinical intraoperative data of the remaining three patients who did not undergo surgery at our hospital could not be obtained. Table 2 shows the comparison of ultrasonographic and intraoperative findings of all patients. The normal course of spinal nerves involves emergence from the intervertebral foramen, with nerves appearing as thin, linear hypoechoic structures with uniform thickness. Nerve trunk injury was deemed present when linear hypoechoic structures with nonuniform thicknesses were observed. Nerve trunk injuries identified by ultrasonography were classified into two categories based on the distance from the intervertebral foramen. (I) The first was an abnormality beside the intervertebral foramen, which manifests on ultrasonography as abnormal thinning of the nerve trunk at the intervertebral foramen and slight nerve trunk swelling in the postforaminal zone, corresponding to nerve avulsion. Alternatively, the nerve trunk may show abnormal swelling at the intervertebral foramen. (II) The second was postganglionic abnormality, which manifests on ultrasonography as a lack of significant differences between the nerve trunk at the intervertebral foramen exit and the nerve trunk on the contralateral side, combined with the detection of segmental abnormal swelling along the course of the nerve trunk, which would correspond to nerve rupture (22) (Figures 1,2). Table 2 shows the detailed ultrasonographic exploration results, and Table 3 shows the results of statistical analysis.

Figure 1 A 53-day-old male patient with right-sided OBPP. (A) Exploration of the right brachial plexus: the C5 and C6 nerves exhibited significant swelling after exiting the nerve root, forming a cluster (thin arrows). The C7 nerve had an abnormally thin nerve root, with slight swelling observed along the course of the nerve (thick arrow). Slight swelling of the C8 nerve could be observed after the nerve root (triangle), but the nerve root could not be clearly explored. (B) Exploration of the left brachial plexus: the C5, C6, and C7 nerves had relatively uniform thicknesses along the course from the root to the nerve trunk, while the C8 nerve could not be detected. Intraoperative findings indicated the presence of rupture injury in the C5 and C6 nerves, along with avulsion injury in the C7 and C8 nerves. OBPP, obstetrical brachial plexus palsy.

Figure 2 A 73-day-old male patient with right-sided OBPP. Exploration of right brachial plexus: Extra-foraminal swelling could be observed in the C5 and C6 nerves, with the C6 nerve exhibiting bead-like swelling (thin arrows). The C7 nerve showed swelling at the root. This was followed by significant narrowing, which was in turn followed by a second swelling (thick arrows). The C8 nerve exhibited swelling in the nerve root (triangle). Intraoperative findings indicated the presence of rupture injury in the C5 and C6 nerves, along with avulsion injury in the C7, C8, and T1 nerves. OBPP, obstetrical brachial plexus palsy.

Ultrasonographic examination of the C5 nerve root revealed the presence of enlargement beside the nerve root in 7 patients and postganglionic enlargement in 20. Intraoperative findings of the 24 patients who underwent surgery indicated the presence of avulsion injury in 3 and rupture injury in 21 patients. The results of the χ² test indicated that differences between the ultrasonography and intraoperative findings were not statistically significant (χ²=4.367; P=0.037). The accuracy of ultrasonography in diagnosing the type of C5 injury was 83.3% (20/24).

Ultrasonographic exploration of the C6 nerve root revealed the presence of abnormality beside the nerve root in 12 patients and postganglionic abnormality in 15. Intraoperative findings of the 24 patients who had undergone surgery indicated the presence of avulsion injury in 10 and rupture injury in 14. The results of the χ² test indicated that differences between the ultrasonography and intraoperative findings were not statistically significant (χ²=5.662; P=0.017). The accuracy of ultrasonography in diagnosing the type of C6 injury was 75.0% (18/24).

Ultrasonographic exploration of the C7 nerve root revealed the presence of abnormality beside the nerve root in 19 patients and postganglionic abnormality in 7. Intraoperative findings indicated the presence of avulsion injury in all 24 patients who underwent surgery. The accuracy of ultrasonography in diagnosing the type of C7 injury was 75.0% (18/24).

Ultrasonographic exploration of the C8 nerve root led to confirmed detection in 10 patients, all of whom eventually underwent surgery. The ultrasonographic findings included negative findings in two patients and the presence of abnormality beside the nerve root in eight. Intraoperative findings of the 24 patients who underwent surgery revealed negative findings in 2 patients and the presence of avulsion injury in 22. The ultrasonographic detection rate for the C8 was 37.0% (10/27), and the accuracy of ultrasonographic diagnosis in the 10 suspected cases was 100%.

Discussion

The brachial plexus belongs to the peripheral nervous system and arises from the interweaving and convergence of anterior rami of the C5–C8 spinal nerves and the T1 spinal nerve (23). Branches of the brachial plexus are distributed on muscles of the pectoral region; muscles of the shoulder girdle; superficial back muscles (except for the trapezius); and the muscles, joints, bones, and skin of the arm, forearm, and hand. They are responsible for sensory and motor innervation of the aforementioned areas and also serve autonomic functions.

In many OBPP cases, hand function can be restored spontaneously without surgical intervention (24-26). Multimodal conservative treatment methods have been recently applied to children with OBPP, some for postoperative rehabilitation and some for training therapy, depending on the degree of nerve damage (26-28). However, only those with mild nerve injury and who ultimately achieve complete restoration of nerve functions within 1 month are able to experience normal development in the affected limb (29). The consequences of Narakas type IV OBPP, including morphological and functional abnormalities, gradually manifest after a short window period of 1 month after birth; these include upper limb shortening, joint contractures and deviation (30), shoulder dislocation (31), subtle differences in upper limb coordination (32), and even brain neurostructure change (33). In some cases, such abnormalities may persist to a certain extent even with good recovery of hand function (34). Under this premise, nerve reconstruction surgery should be performed in a timely manner to avoid obvious morphological and functional abnormalities and reduce deformity and disability. Approximately 10–30% of the children with OBPP are unable to achieve restoration of ideal motor function and thus require surgical intervention (29,35). At present, the primary method of surgical intervention adopted in clinical practice is brachial plexus exploration followed by reconstruction. The method of reconstruction is typically determined by the type of nerve injury observed during intraoperative exploration, which also serves as the current gold standard for validating relevant auxiliary examinations. In short, nerve trunk rupture injury is treated by nerve grafting, in which healthy peripheral nerves are connected to both ends of the ruptured brachial plexus trunk. Avulsion injury is treated by nerve transfer, with the injured brachial plexus trunk being connected to other healthy peripheral nerves to achieve reinnervation of the brachial plexus. Given that the surgical approach is dependent on the type of nerve injury, hand surgeons are constantly seeking auxiliary examination methods that enable accurate and rapid preoperative determination of nerve injury and condition. This allows for comprehensive preoperative planning that can reduce the operative time and offer precise control of the surgical field, thereby ultimately reducing complications, enhancing surgical treatment outcomes, and maximizing the restoration of limb function on the affected side of patients.

Traditional brachial plexus imaging techniques include magnetic resonance (MR) water imaging and high-resolution MRI (14,31). The use of computed tomography has been phased out in clinical practice due to the need for lumbar puncture for spinal cord imaging and other disadvantages, such as radiation injury. However, MR techniques also possess shortcomings such as long examination time and a requirement for high patient compliance. In addition, limitations also exist in MR-based examinations when used for detecting postganglionic injuries such as upper trunk avulsion. In our study, the patients had not undergone preoperative MRI of the brachial plexus due to the risks and benefits of sedation in such young patients. Ultrasonographic examination offers advantages such as the absence of radiation, noninvasiveness, short examination time, and low requirement for patient compliance. Therefore, it is an ideal imaging modality for repeated examinations. Ultrasonographic imaging techniques have been adopted for nerve imaging examinations primarily due to their ability to provide sufficient resolution (36). Karmakar et al. (37) clearly visualized the entire brachial plexus course above the clavicle via high-definition ultrasonographic imaging, thereby providing a key basis for assessing the development and injuries of the brachial plexus. Compared with MR, ultrasound has advantages in delineating the internal structure and direction of extravertebral nerves (38), especially for neonates who usually cannot undergo MR examinations smoothly without sedation.

Narakas type IV injury is a type of OBPP involving injury to all anterior rami of the C5–T1 spinal nerves and Horner syndrome (39). Such OBPP cases are characterized by extensive and severe injury to the brachial plexus, which is often clearly identifiable on ultrasonography. In this study, the accuracy rates of high-frequency ultrasonography in locating nerve trunk injury and identifying the type of injury in the C5, C6, and C7 nerves were 83.3%, 75.0%, and 75.0%, respectively. These results adequately demonstrate the good diagnostic performance of current ultrasonographic techniques in examining the upper trunk injury of the brachial plexus in neonates. Therefore, ultrasonography can be used as a clinical screening tool, especially for patients with OBPP with injury limited to the upper and middle trunk. Effective preoperative ultrasonographic examinations executed by experienced sonologists specializing in superficial ultrasonography, combined with other patient information obtained from physical examinations, can contribute to relatively accurate preoperative assessment results. This may facilitate the formulation of surgical plans with greater accuracy by hand surgeons, thus optimizing surgical approaches and enhancing surgical outcomes (40).

However, in our study, ultrasonography exhibited inadequate diagnostic ability for the lower trunk of the brachial plexus. For instance, the detection rate of the C8 nerve was only 37% (10/27), and the T1 nerve could not be identified at all. These drawbacks are primarily attributed to the short neck length of the infants, resulting in the inability to achieve a snug fit between the linear array–shaped high-frequency probe and the base of the neck. Similar findings were reported in a study on the use of ultrasonography involving healthy children conducted by Wang W and Wang Q (41) and a study involving infants conducted by Gunes et al. (42). The poor diagnostic ability of ultrasonography in examining nerve root lesions in the lower trunk has also limited its application in the diagnosis of BPI in infants, especially in cases of complete BPI. Although the diagnostic accuracy of ultrasonography for the C8 nerve was 100%, the possibility of the occurrence of statistical bias due to an excessively small sample size cannot be ruled out.

Nevertheless, we have accumulated experience in the ultrasonographic exploration of trunks of the brachial plexus through examination of the upper and middle trunks in children with Narakas type IV OBPP. We additionally summarized the ultrasonography manifestations of different types of nerve injury, including avulsion and rupture injuries. The noninvasiveness, radiation-free nature, and low patient compliance of ultrasonography make it suitable for repeated nerve explorations. When performed before brachial plexus reconstruction surgery for OBPP, ultrasonographic nerve exploration can assist hand surgeons in clarifying the nerve injury condition, assessing patient prognosis, and designing accurate surgical plans. When performed after nerve reconstruction surgery, this enables the assessment of surgical outcomes and the timely discovery of surgical complications. In the rehabilitation of patients with OBPP, ultrasonographic nerve exploration can also be used to determine the status of nerve bundle recovery, which can assist rehabilitation physicians in formulating training plans.

Conclusions

In this study, we performed ultrasonographic examinations of the brachial plexus in children with Narakas type IV OBPP to assess the affected nerve trunks and injury type, and compared the ultrasonographic findings with intraoperative findings. Our results indicated that ultrasonography achieved high accuracy in the determination of nerve course and injury type in the upper and middle trunks of the brachial plexus. Therefore, it can be applied in repeated examinations and can serve as an objective imaging modality for preoperative and postoperative diagnosis and assessment of children with OBPP.

Acknowledgments

Acknowledgments for Professor Jia Bing, whose guidance during his lifetime has benefited me a great deal.

Footnote

Reporting Checklist: The authors have completed the STROBE reporting checklist. Available at https://qims.amegroups.com/article/view/10.21037/qims-2025-479/rc

Data Sharing Statement: Available at https://qims.amegroups.com/article/view/10.21037/qims-2025-479/dss

Funding: This study is funded by Program of Shanghai Academic/Technology Research Leader (No. 23XD1403100) and National Clinical Key Specialty Construction Project (No. 10000015Z155080000004).

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://qims.amegroups.com/article/view/10.21037/qims-2025-479/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. This study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The study was approved by the Ethics Committee of Children’s Hospital of Fudan University (No. [2021]. 335-01), and informed consent was obtained from all children’s guardians.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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