Our review focuses on the anatomical concepts and patterns of tumor spread and the means to detect this with optimal crosssectional imaging.

This allows an excellent depiction of the intricate anatomy of the larynx in order to study ventricular complex, submucosal laryngeal spaces, anteroposterior extension, laryngeal cartilage involvement and metastatic spread permitting to establish a TNM staging, and to recognize its impact above the array of therapeutic options.

1. Anatomical recall:  Fig. 1,  Fig. 2,  Fig. 3, Fig. 4  

The larynx is a 5-7 cm long hollow tube lined by mucosa and adapted for protection of the airway and phonation. The cartilaginous scaffolding of the larynx is composed of the thyroid, cricoid, and arytenoid cartilages surrounded by connective and muscular tissue that form its walls.

Superiorly, its upper boundary starts at the tip of the epiglottis which demarcates the boundary with the pharynx, in front of the third - fourth cervical vertebra.

Inferiorly, the larynx extends to the lower margin of the cricoid cartilage.This lies opposite the sixth cervical vertebra.

The larynx is divided into three regions: supraglottis, glottis and subglottis regions.

• Supraglottis (Fig. 5,  Fig. 6,  Fig. 7,  Fig. 8,  Fig. 9,  Fig. 10,  Fig. 11) :

from the tip of the epiglottis to the laryngeal ventricles. Its content are:

• Vestibule
• Epiglottis
• Pre-epiglottic fat
• Aryepiglottic folds
• False vocal cords
• Paraglottic space
• Arytenoids cartilages
• Ventricles

• Glottis : Fig. 12,  Fig. 13,  Fig. 14

• True vocal cords
• Anterior commissure
• Posterior commissure

 • Subglottis (Fig. 15,  Fig. 16) from the true vocal cords to cricoid cartilage.

• Mucosal surface at the level of cricoid cartilage
• Conus elasticus
• Quadrangular membrane

The framework of the soft tissue structures of the larynx are the cricoid, thyroid and arytenoids cartilages.

2/ Epidemiology : 

Cancers of the larynx predominate in men between 45 and 70 years.

The incidence increases in young adults and in women, especially in urban areas.

Tobacco is the essential carcinogen.

Squamous cell carcinoma is the most common histological type.

The clinical signs are more or less present according to the starting point and the evolution of the tumor (dysphonia, dysphagia, dyspnea ...)

3/ Diagnosis :

Endoscopy is performed under general anesthesia and is essential for the assessment of laryngeal cancers  as well as for any other localization of the upper aerodigestive tract. Its objectives are to specify the local extension of the tumor, to guide biopsy and thus to provide an histologic grading (Fig. 17) and examine the entire mucosa of the UADT (Upper AeroDigestive Tract) in search of another simultanous localization. But alone, it is insufficient in the evaluation of locoregional extension. Hence the interest of the scanner.

CT is currently the most commonly used exam to evaluate the initial extent of these cancers through thin sections and reconstructions in different planes of space.

CT imaging protocol :

Evaluation of laryngeal cancer requires a contrast Computed Tomography study of the neck. Excellent images can be obtained using a multidectector CT (MDCT) following the injection of an iodinated contrast agent. The contrast may be hand injected or an automated power injector may be used, in which case sufficient delay should elapse before scan acquisition begins. The patient lies in supine position, breathing quietly and is asked to refrain from coughing or swallowing. Axial scanning is performed from the skull base to the aortic arch with the acquisition plane parallel to the plane of hyoid bone, to obtain scans parallel to the true vocal cords. The raw axial image dataset is reconstructed with a section thickness of as little as 0.75 mm to obtain high quality sagittal and coronal reformatted images. A 512 × 512 matrix is used with a small field of view (FOV) between 16 and 20 cm. All images are reviewed in soft tissue and bone windows. An additional examination for better assessment of the tumor in laryngeal ventricle, anterior commisure and aryepiglottic folds may be done with e‑phonation.

The use of a scanner in this context requires a thorough knowledge of the protocol, the endoscopic data, the locoregional anatomy and the preferred pathways of laryngeal cancer spread depending on the initial location.

In case of doubt on a cartilaginous lesion it is necessary to make fine cuts in high resolution centered on the suspect region. The usual tissue windows will be supplemented by bone windows for the study of ossified cartilages to confirm sclerosis.

The phonatory maneuvers allow to study the mobility of the arytenoid cartilages.

The Valsalva maneuver is necessary to dilate the ventricles, vallecles and light of the piriform sinuses when needed.

The MDCT allows:

• Exploring the entire larynx in less than 20 seconds

• Reduction of motion artifacts

• Realization of dynamic maneuvers

• The realization of two-dimensional reconstructions.

• Optimization of the injection of cotrast agent which allows a good tumor impregnation

• Exploring all ganglionic areas

Input of the scanner:

• Specifies deep local extension to fatty spaces, cartilage, perilaryngeal tissue when endoscopy is insufficient.

• Studies ganglionic extension in all territories, some of which are clinically less palpable (retro pharyngeal ganglia, under the base of the skull or in the mediastinum).

• Provides information on areas that are difficult to explore clinically (by endoscopy) such as the underlying glottis, the bottom of the piriform sinus and the laryngeal ventricle.

• Orients the therapeutic decision, in fact, certain criteria of extension in CT are considered as factors prognostic and make it possible to modify the conventional treatment regimens.

Tumor CT Signs:

Tumor process / tissue thickening taking contrast and deforming the laryngeal duct

Reduction of laryngeal lumen

Locoregional extension:

Depending on the region

Importance of sagittal and coronal reconstructions

Good technique

Points of weakness of the evaluation of tumor extension: petiole or "stem of a leaf" of epiglottis, epiglottic cartilage, crico-thyroid membrane, calcified cartilages (It is difficult to affirm the tumoral invasion of the cartilage due to the randomness of normal calcifications and ossifications)

Elements of analysis:

•Implicated regions:

1 / Supraglottis tumors : Fig. 18

-Extension to the vallecles and to the base of the tongue

-Infiltration of the pre-epiglottic box and the HTE region

-Cartilage: Sclerosis / Erosion / Lytic process 

2 / Glottic tumors : Fig. 19,  Fig. 20

-Extension to the anterior and posterior commissures

-Lesion of the opposite vocal cord

-Invasion of the petiole of the epiglottis

-Invaion of the pre-epiglottic chamber, para glottic fatty space

-Cartilaginous infringement 

-Extension in height: laryngeal ventricle, ventricular band

3 / Subglottic tumors : Fig. 21

-Infringement of cricoid cartilage

-Extension to extra-laryngeal soft tissues

-Extension to the trachea

• Anterior Commissure (AC) :

- Determining factor in therapeutic choice.

- Its impairment means the possibility of tumor spread to the opposite cord, the thyro-arytenoid muscle or the paraglottic space.

- At CT, a tissue thickness greater than 1 to 2 mm of the AC signifies its invasion. On the other hand, the presence of air against the cartilage is a good element to eliminate its infringement.

- However, the presence of tissue in this region is a source of false positives by the anterior accretion of the vocal cords.

- The effectiveness of CT in the study of this region is less than 80%.

• Extension to the other hemilarynx.

  • Ventricular bands:

- In the glottic tumor assessment, extension to the ventricular bands shifts the tumor from a T1 stage to a T2 stage.

- This extension is better appreciated during the phonation maneuver.

  • Sub-glottis:

- Tumor extension to the subglottis is found in 13 to 20% of glottic cancers.

- It is a contraindication to any conservative surgery of the larynx.

- Difficult to access endoscopy, this extension must be perfectly analyzed in CT.

- The extension to the subglottis results in CT by a tissue thickening taking the contrast, in continuity with the tumor and coming into contact with the cricoid cartilage.

- An invasion of this region> 5mm in posterior, and to 1 cm in anterior means its attack.

- Sclerosis of the cricoid cartilage is a sign of a tumorous process on contact.

- The loss of the symmetry of the subglottic region on the coronal reconstructions in phonation is also a good sign of subglottic involvement.

• Hyo-thyro-epiglottic region (HTE).

- This lodge is not accessible for endoscopic examination.

- It must be finely analyzed in imaging because a massive extension at this level is a contraindication to conservative surgery.

- Massive tumor infiltration may mask the lodge.

- However, the fibro-edematous reaction in the vicinity of the tumor can simulate extension in this region.

• Paraglottic spaces and para laryngeal fat:

- The para-glottic space has a major carcinological importance in the exploration of pharyngo-laryngeal cancers.

- An extension at its level may be at the origin of an extension towards the aryepiglottic folds and the HTE region forward, and towards the piriform sinuses in the back.

- The disappearance of the paraglottic fatty edema at CT is a predictive sign of invasion.

• Cartilage invasion:

- The performances of the CT with evaluation of integrity of the cartilage are average.

- It is sometimes difficult to affirm the tumoral invasion of the cartilage due to the random nature of normal calcifications and ossifications.

- CT tends to overestimate the infringement of arytenoid cartilage and underestimate the invasion of thyroid cartilage.

• Extra-laryngeal soft tissue infiltration:

- The difficulty of deciding between inflammatory reaction and tumor infiltration in case of minimal invasion of the muscular structures often arises.

- However, the asymmetry of the muscular mass remains a reliable sign in the more evolved infiltrations especially if it is located opposite to the tumor.

• Adenopathies (Ganglionic Extension):

- The presence of adenopathies is considered pathological when they measure more than 12 mm of smaller transverse diameter at the upper jugular level and 10 mm in the other regions.

- The presence of a heterogeneous ganglion, a central hypodensity and a peripheral contrast enhancement evoking necrosis, are strongly suggestive of the metastatic character, in particular for the borderline ganglia.

- Capsular rupture is a frequent feature of hypopharyngeal tumors, which are usually associated with very large adenopathies.

- Spiral CT also allows the complete study of the ganglionic territories, including at the level of the base of the skull, in the search for retro pharyngeal ganglia that can modify the therapeutic management.

- It allows, thanks to a good opacification of the vessels, to analyze the relations between the ganglionic block and the carotid that influence the surgical management.

MRI:

- Used as second intention in special cases.

- Failure in 10 to 15% due to movement artifacts.

- Informative for the cartilages, the base of the tongue and the subglottis.

- However, no recommendations reported for the realization of MRI in the preoperative exploration of pharyngolaryngeal tumors.

KEY POINTS

Endoscopy and CT are two complementary examinations in the initial extension of laryngeal cancer. The accuracy of laryngeal cancer staging  by using a combination of clinical examination and CT has been reported to be between 73 and 88% compared with 55 to 64% by clinical examination alone. The endoscopy allows to examine the ventricular bands and ventricles of Morgani, while CT permits to evaluate the involvement of other anatomic structures such as pre-epiglottic space, cartilaginous destruction or extralaryngeal spread, permiting so the establishment of TNM staging  (Fig. 22, Fig. 23)

Prognosis elements & therapeutic involvement :

• Infringement of the anterior commissure contraindicates a cordectomy.
• Invasion of the HTE region, opposite vocal cord and cricoid contraindicates conservative voice therapy
• Glottic involvement requires total laryngectomy
• Invasion of the tracheal rings requires a surgical gesture enlarged to the trachea.

Surveillance:

• Search for complications
• Search for recidivism
• Virtual endoscopy:

               Technique of the Future

               Total safety
               Ability to explore downstream stenosis
               Ability to get any angle