I. Computed tomography
Supra-glottis
Supraglottis is delimited superiorly by the hyoid bone and inferiorly by the upper surface of the vocal cords.
1. Epiglottis
Tumors of suprahyoid epiglottis can spread to valleculs, glosso-epiglottic fold and base of the tongue.
Tumors of infrahyoid epiglottis can spread to pre-epiglottic space threw vascular perforations and then infiltrates the para-glottic space and the glottis.
On CT it is analysed on axial images and sagittal reconstructions. Its encroachment is seen as enhanced thickening of its surfaces.
2. Ventricular cords :
From the ventricular cords, the tumor may spread anteriorly to the epiglottis and the pre-epiglottic space, latéraly to the ary-epiglottic folds and inferiorly to the laryngeal ventricls and the vocal cords. Its invasion is seen as asymmetric thickening visualized on phonation acquisition.
3. Laryngeal ventricls :
Laryngeal ventricls are better visualized on phonation maneuver and coronal reconstructions. They are seen as small air‑filled outpouching between ventricular and vocal cords. their invasion is suspected in case of enhanced tissue filling one or two ventricls or absence of their opening during phonation maneuver. Fig. 2
Fig. 2: axial and coronal enhanced Ct with phonation maneuver showing a glottic and supra-glottic mass of the left vocal cord (blue arrow), laryngeal ventricle (red arrow) and ventricular cord (green arrow). We should notice the air-filled right ventricle.
5. Pre-epiglottic space :
The pre-epiglottic space is a fat-filled space containing lymphatic tissues, commonly associated with nodal metastases. It is limited by the hyothyroid membrane anteriorly, the epiglottis posteriorly and the hyoepiglottic ligament superiorly.
It is better analyzed on axial images and sagittal reconstructions. Its invasion is seen as a replacement of its fatty density by an enhanced tissue. Fig. 3
Fig. 3: Coronal and axial enhanced Ct showing a large mass of the left ventricular cord (blue arrow) and para-laryngeal space, reaching the pre epiglottic space (asterix) and the right ventricular cord (red arrow).
I. Glottis :
The glottis is delimited superiorly by the vocal cords and inferiorly by the upper surface of the cricoid cartilage. It comprises vocal cords, anterior and posterior commissures and para-glottic space.
1. Vocal cords :
Invasion of vocal cords is rapidly depicted as it is associated with hoarseness of the voice. Their lymphatic drainage is sparse explaining the rare cases of nodal metastases. Their invasion is seen as an enhanced asymmetric thickening of one or both vocal cords.
2. Anterior commissure :
Threw anterior commissure, the tumor can spread superiorly to the pre-epiglottic space, inferiorly to the subglottis, laterally to the para-glottic spaces and the thyroid cartilage. Its invasion is seen as soft tissue thickening exceeding 1 to 2mm. Fig. 4
3. Posterior commissure :
Its invasion is seen as a thickening exceeding 1 to 2mm.
4. Para-glottic space:
Threw para-glottic space, tumor may spread laterally to the thyroid cartilage. Axial images provide better analyse of its invasion, seen as an enhanced tissue replacing its fatty density. Fig. 4
Fig. 4: Axial (A) and coronal (B) enhanced cervical computed tomography showing a mass of the right glottis and the supra glottis with thickening of the right vocal cord (blue arrow) reaching the anterior commissure (asterix) and the para-glottic space anteriorly associated with sclerosis of the right arytenoid cartilage (red arrow).
III . Sub-glottis :
Sub-glottic tumors are rare and clinically silent, commonly associated with nodal metastases mediastinal nodes. Its invasion is seen as an asymmetric thickening exceeding 5 mm anteriorly and 10 mm posteriorly. Indirect indicators of its invasion are sclerosis and lysis of cricoid cartilage. Fig. 5
Fig. 5: Axial (A) and coronal (B) enhanced cervical CT showing a left transglottic mass with thickening of the ventricular and the vocal cords with extension to subglottic region (asterix), associated with sclerosis of the cricoid cartilage (black arrow).
IV. Laryngeal cartilage :
Cartilage invasion is associated with low response to radiation therapy and high risk of recurrence. It requires total laryngectomy with voice sparing. Thyroid, cricoid and arytenoid cartilages are composed of non-ossified and ossified cartilage. The ossified portion gets bigger with age and exposes the cartilage to tumor invasion.
Criterias used to depict cartilage invasion are sclerosis, erosion, lysis and extra-laryngeal tumor spread Fig. 6 Fig. 7
Sclerosis is a sensitive sign. But in many cases, it is a sign of inflammatory status and bone remodelling. This sign is more specific for arytenoid and cricoid cartilages.
Lysis indicates bone destruction, highly specific but a moderately sensitive as it is associated with advanced tumors.
Extra-laryngeal tumor spread is considered to have the highest specificity but is seen in advanced stages.
Fig. 6: Axial images on cervical enhanced CT :
A: Thickening in the left vocal cord, the anterior commissure (Asterix) and erosion of the thyroid cartilage.
B: Mass of the glottis, the anterior commissure, both vocal cords and extra laryngeal tissues threw a lysis of the thyroid cartilage (blue arrow).
Fig. 7: Figure 2 : axial images on cervical CT focused on the sub-glottis with soft (A) and bone (B) windows showing an asymmetric thickening of the left surface of the sub-glottis (black arrow), lysis of the cricoid cartilage (red arrow) and extra laryngeal spread (blue arrow)
V. Extra-laryngeal tissues :
Extra-laryngeal spread is not avualuated by clinical examination. It upgrades the tumor to T4 and contradicates partial laryngectomy and radio-therapy. It is associated with a high risk of tumor recurrence.
It can occur threw cartilage, hyo-thyroid or thyro-cricoid membranes.
An asymmetric enhanced thickening of extra-laryngeal tissues indicates their invasion. An indirect sign is a lysis of laryngeal cartilages. CT is moderately sensitive but highly specific in their evaluation. Fig. 8
Fig. 8: Axial image (A) and sagittal reconstruction (B) of an enhanced cervical CT showing a transglottic enhanced mass with invasion of aryepiglottic folds (black arrows) pre-epiglottic space (Asterix) and extra-laryngeal tissues threw the hyo-thyroid membrane ( red arrow)
VI. Lymph nodes :
Nodal metastases aret indicators of prognosis. They are better depicted on enhanced CT. They are more common in case of supraglottic tumors. The glottis doesn’t present lymphatic drainage. Therefore, tumors that only affect the glottis are not associated with nodal metastases.
The most commonly affected levels are II, III and IV. Subglottic tumors are associated with mediastinal para-tracheal and pre-tracheal lymph nodes.
The main imaging criteria is the size exceeding 15mm in the level IIa and 12mm in other levels. Other sensitive criterias are heterogeneous enhancement with necrosis, round shape and irregular borders suggesting extra-capsular extension. Fig. 9
Fig. 9: Axial (A) and sagittal reconstruction (B)of an enhanced cervical CT showing a glottic and supra-glottic mass (red arrow) with necrotic lymph node of the right level IV presenting irregular borders suggesting extra capsular spread (blue arrow)
VII. Thoracic acquisition:
An acquisition exploring the thorax is systematic. It permits depicting extension to mediastinal structures, pulmonary and mediastinal lymph nodes. It also permits detecting pulmonary synchronous tumors.
Magnetic resonance imaging :
In laryngeal cancer, MRI is mainly indicated for cartilage exploration.
Its limitation is its sensitivity to movements caused by coughing swallowing or dyspnea, making this examination difficult to interpret in patients with laryngeal cancer. Cartilaginous involvement is seen as low-signal intensity in T1 sequences, high-signal intensity in T2 sequences with enhancement after the administration of gadolinium contrast agent.
MRI permits the evaluation of pre-epiglottic invasion. This space presents a spontaneous high-signal intensity on both T1 and T2 sequences. Its invasion is suspected in case of an enhanced tissue replacement of its fatty signal.