Ultrasonographically guided, compartment-oriented lymph node dissection in the management of papillary thyroid cancer

Abstract

Lymphatic metastases are common in papillary thyroid cancer (PTC) at the time of diagnosis [1]. In the presence of synchronous cervical lymphadenopathy, diagnosed clinically or ultrasonographically, the standard surgical approach has been the modified radical lymph node dissection (MRLND), performed at the time of initial total thyroidectomy. This strategy achieves optimal local control of the disease (thereby minimizing local recurrence rates), improves the efficacy of postoperative radioactive therapy (aiming to eradicate potential residual microscopic disease) and facilitates patient’s monitoring during follow-up by measuring serum thyroglobulin [2]. During recent decades, a modern classification of neck lymph nodes has been widely adopted, based on findings and landmarks from cross-sectional anatomic imaging; this is a useful aid in mapping nodal surgical intervention. This classification system is composed of six major nodal regions (levels or compartments I to VI) and defines a compartment-oriented neck dissection. Sublevel classification is also used when certain zones within the larger levels have independent biological significance [3]. Current evidence suggests specific patterns of lymphatic metastases in PTC. Central (compartment VI) lymph nodes are often the first site for lymphatic metastases from PTC, since this level is considered as the first lymphatic basin draining thyroid parenchyma. The most common lateral lymph node regions harboring metastases are levels III and IV [4,5]. Metastases to levels II and V are more rarely observed [6]. Finally, metastases to level I nodes are extremely rare in PTC [6,7]. Recent advances in imaging allow – with acceptable accuracy – the recognition of the presence of pathological lymph nodes within the different compartments of the neck. Currently, high-resolution ultrasonography (US) is being used extensively in the preoperative assessment of cervical lymph nodes (sensitivity 97%, specificity 93%) [8]. The US characteristics of a suspicious lymph node include increased size, round shape (short axis to long axis ratio ≥0.5), absent echogenic hilum, irregular margins, thickened hypoechoic cortex, intranodal calcifications, cystic necrosis, peripheral or mixed vascularity and increased elasticity score. The accuracy of US in recognizing pathologic neck lymph nodes is higher for the lateral nodal compartments, while US evaluation of central compartment lymph nodes has been proved to be of lower sensitivity in detecting metastatic lymph nodes especially in patients with coexistent chronic