The suprasternal space, which is also known as the “Burns space,” is a narrow space between the superficial and deep layers of the investing layers of the deep cervical fascia above the manubrium of the sternum. According to Gray’s Anatomy, it contains a small amount of areolar tissue, the lower parts of the anterior jugular veins, and the jugular venous arch, as well as the sternal heads of the sternocleidomastoid muscles and occasionally lymph nodes. The result of this study showed the suprasternal lymph node metastasis is associated with tumors located in the inferior pole and level IV lymph node metastasis. The suprasternal lymph node metastasis can be predicted when there are two or more level IV lymph node metastasis. Level IV LNR > 0.125 and level VI LNR > 0.357 were also associated with suprasternal lymph node metastasis.
Sun et al. first defined the lymph node area between the sternocleidomastoid and sternohyoid muscle as follows: its anterior boundary as the sternocleidomastoid muscle, its posterior as the sternohyoid muscle, its superior as the intersection of sternocleidomastoid and sternohyoid muscle, and its inferiors as suprasternal fossa and clavicle, its external and internal boundary as the lateral and internal borders of the sternohyoid muscle, respectively. They mentioned that this space is part of the suprasternal space, and they found up to 5 (average, 3) lymph nodes pathologically. In this study, up to 4 (average, 1.4) lymph nodes were pathologically confirmed in the suprasternal space. Although the number of lymph nodes is small, it is certain that lymph nodes are present in the suprasternal space.
A prognostic significance of lymph node metastasis has been reported for low-risk as well as high-risk patient.[15-17] However, whether prophylactic central neck dissection is beneficial in patients with well-differentiated PTC is controversial because of a greater risk of postoperative complications, such as transient or permanent hypoparathyroidism and unintentional recurrent laryngeal nerve injury. In contrast to central neck dissection, lateral neck dissection should be performed on patients who have PTC with clinically apparent cervical lymph node metastasis detected on palpation or imaging studies.[19-21] The extent of lateral neck dissection is still controversial, but a thorough lymph node dissection is required. Therefore, suprasternal lymph node metastasis is rare but should be routinely included in the lateral neck dissection because there are few complications during dissection.
The etiology of suprasternal lymph node metastasis is not clear. Sun et al. reported that, without exception, patients with suprasternal space metastasis also had lateral cervical lymph node metastasis, and level III and IV metastases were significantly correlated with suprasternal space metastasis. They speculated that suprasternal space metastasis could be a result of the increasing tumor load after lateral cervical metastasis. Homma et al. speculate that fibrofatty tissue, including the level III and IV metastatic lymph nodes, moves into the suprasternal space gradually due to the daily motion of the neck. We present two theories through the anterior jugular node chain. First, level IV metastatic lymph nodes move into the suprasternal space laterally. Second, central lymph nodes, especially the pretracheal and paratracheal metastatic lymph nodes, move into the suprasternal space medially (Fig. 4). In this study, all patients with suprasternal lymph node metastasis had level IV and VI metastasis. However, only level IV metastasis was significantly correlated with suprasternal lymph node metastasis, and two or more level IV metastatic lymph nodes had the best predictive value. Therefore, it is important to dissect the suprasternal lymph node adjacent to the level IV lymph node, as the first theory is more convincing.
Suprasternal lymph node metastasis can be recognized by preoperative ultrasonography or CT; however, there is little clinical interest. Therefore, suprasternal lymph nodes are not routinely dissected because they are not included in the central and lateral neck compartment. Sun et al. reported that the positive rate for the suprasternal space was 22.6% among 115 patients with clinically node-positive PTC who underwent neck dissection that included the suprasternal space. In this study, the positive rate for the suprasternal space was 12.9% among 85 patients.
The number of metastatic lymph nodes and LNR are risk factors for locoregional recurrence in PTC.[9, 10] Suprasternal lymph node metastasis was associated with level IV lymph node metastasis and can be predicted when there are two or more level IV lymph node metastasis. Level IV LNR > 0.125 and level VI LNR > 0.357 were also associated with suprasternal lymph node metastasis. Although the frequency of suprasternal lymph node metastasis is low, prophylactic suprasternal lymph node dissection is less invasive, easier to achieve, and less time consuming than central compartment dissection, which increases the risk of recurrent laryngeal nerve palsy and hypocalcemia. In this study, it did not take much longer to dissect the suprasternal lymph nodes, and there were no intraoperative or postoperative complications such as bleeding or pain.
PTC has an excellent prognosis, with a 10-year overall survival rate > 90%. However, in rare cases, nodal recurrence may occur in the suprasternal lymph nodes. Because locoregional recurrence can affect quality of life, it is important to reduce the risk of locoregional recurrence by complete resection of the lymph nodes during surgery. Suprasternal lymph node metastasis is relatively rare, but dissection is safe and easy.