Evaluation of the hilar and mediastinal lymph nodes is part of the surgical treatment of non-small cell lung cancer (NSCLC). It is also vital to the staging of lung cancer, which determines the need for adjuvant chemotherapy to improve survival odds in certain stages of NSCLC. Lymph nodes are evaluated according to the AJCC staging system.
Lymph node sampling is decided upon and based on the radiologic appearance of the primary tumor and the nodes. Thus biopsy is typically performed if:
- Mediastinal lymph nodes are larger than 1 cm (short axis) or show positive on fluorodeoxyglucose PET
- There are large, central or bilateral synchronous primary tumors
- Lymph nodes in the hilum of the same side show avidity on PET
Preoperative evaluation of lymph nodes
The gold standard for pre-resection staging of lymph nodes in the mediastinum is anterior mediastinotomy, also called the Chamberlain procedure, and cervical mediastinoscopy. Through a parasternal incision, an endoscope is inserted to evaluate the tissue in the space between the sternum, the heart and the lungs.
This helps differentiate early stage disease from locally advanced disease before resection. It may be done in the same or separate sittings, depending on the level of pathologic evaluation available and require general anesthesia.
Endoscopic transbronchial mediastinal lymph node sampling is also possible, either as is or guided by live endobronchial ultrasound. The advantages of ultrasound-guided endoscopy include:
- It is less invasive
- Can be done without general anesthesia
- Gives access to station 10 nodes unlike mediastinoscopy
- No mediastinal scarring, which allows for repeating the procedure after treatment
Intraoperative evaluation of lymph nodes
During the resection, all interlobar and intralobar lymph nodes, corresponding to stations 10 to 4, are removed while dissecting the hilar and fissural regions.
Lymph node evaluation may be done in two ways: systematic mediastinal lymph node sampling (MLNS), which involves the resection of nodes from each ipsilateral mediastinal station, or a formal mediastinal lymphadenectomy (mediastinal lymph node dissection, MLND), which involves removing all the mediastinal nodes and soft tissue within anatomical landmarks.
The latter is often cited as a complement to standard treatment for NSCLC.
The value of MLND lies in its ability to provide accurate staging, remove undetected micrometastases and thus delay recurrence and complete resection of the lesion. It also allows for better patient selection in relation to adjuvant therapy.
However, it carries higher risks of morbidity and requires a longer operative time, without any obvious survival benefit. Studies show that both procedures confer a similar survival rate, have the same rate of local recurrence and show comparable rates for distant metastasis.
The adverse results of lymph node sampling or dissection have not been found to be very severe. There is no associated mortality.
The common complications include pneumonia, arrhythmias and air leakage from the chest for a prolonged period. Mediastinoscopy may be associated with paralysis of the recurrent nerve, chylothorax, and rarely, hemorrhage.
Importance of lymph node evaluation
The significance of lymph node evaluation relates to its predictive value or, in other words, its ability to help predict the odds of patient survival after the NSCLC is resected. More accurate staging is possible with a full evaluation because it is less probable that positive nodes will be missed.
An important factor in this respect is the lymph node ratio – the ratio of positive lymph nodes to the total number of nodes resected – which better reflects survival odds post-resection.
In NSCLC, any increase in the lymph node ratio predicts lower survival chances and faster recurrence after curative resection. In addition, the choice to undergo adjuvant chemotherapy or radiotherapy is facilitated by the knowledge of the extent of lymph node involvement.