Spread and metastasis of laryngeal cancer

Laryngeal cancer can spread and metastasize in the following three ways depending on its degree of differentiation and primary site.

1. Direct Infiltration

Early cancers often expand along the mucosal surface and then spread to the submucosal infiltration. Due to some factors, they have their own diffusion rules within a certain period of time. It has been confirmed that the larynx originates from two embryonic bases. The supraglottic area originates from the buccal pharyngeal embryonic base, and the glottic area and subglottic area originate from the tracheal and bronchial primordia. The differences in embryogenesis and the barrier effect of laryngeal cartilage, elastic membrane, and ligaments on tumor spread, as well as the differences in the distribution of lymphatic vessels and blood vessels in the larynx, make the direct infiltration and spread of laryngeal cancer in different parts different.

1. Supraglottic laryngeal cancer

(1) Suprahyoid epiglottic cancer: It usually grows exophytically. In the early stage, it rarely destroys the cartilage or spreads to adjacent tissues. It can grow larger. In the late stage, it invades and destroys the cartilage, causing the epiglottis to deform or disappear. It can also invade the vallecula and pre-epiglottic space, the lateral wall of the pharynx, and other parts above the glottis.

(2) Subhyoid epiglottic cancer: Tumors on the laryngeal surface of the epiglottis can penetrate the small holes in the epiglottic cartilage or destroy the epiglottis and pre-epiglottic space to the tongue root, or spread to the surrounding areas to invade the ventricular band, aryepiglottic folds, and finally to the piriform sinus, pharyngeal epiglottic folds, and vocal cords. However, downward spread to involve the glottis is rare.

(3) Laryngeal ventricular cancer: It is usually an infiltrative and ulcerative type. It is not easy to detect due to its hidden location. It can infiltrate into the deep surface of the ventricular band, causing the ventricular band to bulge. Laryngeal ventricular cancer is prone to invade the paraglottic space and expand backward to involve the medial wall of the pyriform sinus. It develops into the laryngeal cavity and a tumor may appear between the ventricular bands. Vocal cord fixation is usually in the late stage, and subglottic invasion is less common.

(4) Laryngeal ventricular band cancer: Tumors at the anterior edge of the ventricular band can destroy the thyroid cartilage and spread outward, invading the base of the epiglottis and affecting the anterior end of the contralateral ventricular band. Laryngeal ventricular band cancer often affects the vocal cords.

(5) Aryepiglottic fold cancer: In the early stage, it grows exophytically. As the lesion progresses, it may lead to fixation of the vocal cords. In the late stage, the lesion may invade the thyroid cartilage, cricoid cartilage, tongue base, and lateral wall of the pharynx.

2. Glottic cancer

It usually originates from the free edge and upper surface of the junction of the front and middle 1/3 of the vocal cord on one side, and then invades deeply along the long axis and vertical axis of the vocal cord. The tumor may involve the anterior commissure forward, and spread to the opposite vocal cord by breaking through the anterior commissure tendon, invade the arytenoid cartilage backward, invade the laryngeal ventricle, ventricular band and epiglottis upward, break through the elastic cone downward to the subglottic area, and deeply invade the vocal cord muscle, paraglottic space and thyroid cartilage. In the late stage, the tumor may penetrate the thyroid cartilage to the muscle layer and skin, or invade the cricothyroid membrane, pyriform fossa and other parts.

3. Subglottic cancer

Primary subglottic cancer is rare. Due to the lack of muscle layer in the subglottic area, tumors in this area often spread along the mucosa to the surrounding area in the early stages, spread downward to the trachea, invade the vocal cords upward, and may also penetrate the cricothyroid membrane to invade the anterior neck muscles or thyroid gland, and invade the esophagus backwards.

(ii) Cervical lymph node metastasis

Whether or not laryngeal cancer patients have cervical lymph node metastasis has an important impact on their prognosis. The time of cervical lymph node metastasis is closely related to the primary site of the tumor, the degree of differentiation of tumor cells and the patient's immunity to the tumor. Generally speaking, the worse the degree of differentiation of the tumor and the lower the patient's immunity, the earlier the cervical lymph node metastasis occurs. The lymphatic drainage on both sides of the larynx is completely separate, and rarely crosses or mixes.

1. Supraglottic cancer

The supraglottic region is rich in lymphatic vessels and the tumor is poorly differentiated, so the incidence of cervical lymph node metastasis is high. At the time of diagnosis, 55% of patients have clinically positive lymph nodes, 16% are bilateral, and the pathologically positive lymph node rate of selective neck dissection is 16%-26%. In patients who did not touch the enlarged lymph nodes during surgery and did not undergo neck dissection, 33% of patients had positive lymph nodes during postoperative follow-up. Tumor spread to the pyriform sinus, epiglottic valley, and tongue root can increase the rate of lymph node metastasis. The rate of lymph node metastasis of subhyoid epiglottic cancer is lower than that of other supraglottic cancers. The site of supraglottic cancer lymph node metastasis is mostly found in the lymph nodes at the bifurcation of the common carotid artery in the ipsilateral deep upper neck group, and then develops up and down along the internal jugular vein lymph node chain.

2. Glottic cancer

The vocal cords have few lymphatic vessels and the cancer is usually well differentiated. At diagnosis, the metastasis rate of T1 lesions in the glottis is close to 0%, while the metastasis rate of T2 and smaller T3 tumors is 2% to 5%. The metastasis rate of larger lesions and T3 lesions increases to 20% to 30%. Tumors in the anterior commissure and the anterior subglottic region are prone to metastasis to the anterior laryngeal lymph nodes.

3. Subglottic cancer

The metastasis rate of cervical lymph nodes in subglottic cancer is 20%-25%. Subglottic laryngeal cancer often metastasizes to the paratracheal lymph nodes first, and then to the middle and lower groups of deep cervical lymph nodes. The metastasis of paratracheal lymph nodes is directly related to the recurrence of cancer at the fistula. There is evidence that lymphatic vessels in the supraglottic and subglottic regions do cross the midline, and there is a high possibility of spontaneous contralateral lymphatic drainage from the subglottic region. Therefore, the metastasis pattern of subglottic tumors is rarely consistent.

It is worth noting that not all palpable lymph nodes in the neck are tumor metastases; on the contrary, some metastatic lymph nodes cannot be palpated before surgery and can only be confirmed by intraoperative or postoperative biopsy. Therefore, the scope of surgery often needs to be determined according to the intraoperative findings. For those poorly differentiated supraglottic laryngeal cancers with negative lymph node palpation before surgery, we routinely perform lymph node exploration at the carotid bifurcation during surgery, and perform rapid pathological section examinations during surgery. Depending on the results of the pathological examination, we determine whether neck lymph node dissection should be performed at the same time.

(III) Hematogenous metastasis

A small number of patients with advanced disease may have hematogenous metastasis, which is mostly caused by cancer invading blood vessels and allowing cancer cells to enter the blood. It may also invade lymphatic vessels and then enter veins. Distant metastasis may occur to the lungs, liver, kidneys, bones, pituitary gland, etc.