Cartilage invasion

Why cartilage invasion matters

For laryngeal SCC, the critical distinction is generally between limited inner thyroid-cartilage involvement and transcartilaginous/extralaryngeal extension:

The NCI summary describes T3 disease as tumor limited to the larynx with vocal-cord fixation, paraglottic-space invasion, and/or inner thyroid-cartilage cortex involvement; extension through the outer thyroid-cartilage cortex or into extralaryngeal tissues is T4a. For radiology reporting, it is therefore much more useful to state the depth and side of cartilage involvement than simply writing “cartilage invasion present.”[cancer]

Relevant laryngeal anatomy and spread

Thyroid cartilage

The thyroid cartilage is the key cartilage for imaging staging, especially for glottic/anterior commissure and supraglottic cancers.

Important routes include:

• Anterior commissure: Thin or absent perichondrium and close relationship to the thyroid cartilage make this a classic route for transcartilaginous spread.
• Paraglottic space: Tumor reaching or replacing paraglottic fat is associated with impaired cord mobility and provides a route toward thyroid-cartilage invasion.
• Pre-epiglottic space: Supraglottic tumors can fill this fat space and subsequently extend toward the thyrohyoid membrane or thyroid cartilage.
• Thyrohyoid membrane / neurovascular foramina: Can provide pathways to extralaryngeal soft-tissue extension.

Be cautious with the common shorthand that “anterior commissure involvement equals cartilage invasion.” It increases risk, but invasion requires direct imaging evidence of abnormal cartilage signal/density, cortical breakthrough, or tumor on both sides of the cartilage.

Cricoid cartilage

Cricoid involvement is particularly relevant in subglottic and postcricoid/hypopharyngeal tumors. It may be subtle because of variable mineralization and because tumor can track in the subglottic paraglottic region. In laryngeal staging, cricoid-cartilage invasion is T4a.[radiopaedia]

Arytenoid cartilage

Arytenoid sclerosis can be reactive or related to altered stress/loading, particularly in the setting of vocal-fold paralysis. A combination of findings is more convincing than sclerosis alone: tumor contact/encasement, focal erosion or lysis, abnormal marrow replacement, loss of contour, and additional abnormal cartilage findings. An AJNR study found that impaired arytenoid mobility and more than one CT cartilage abnormality were relatively reliable indicators of neoplastic cartilage invasion.[ajnr]

Epiglottic cartilage

The suprahyoid epiglottis is fibroelastic rather than hyaline cartilage. For supraglottic tumors, report the involvement of:

• Lingual and laryngeal epiglottic surfaces
• Pre-epiglottic space
• Vallecula/base of tongue
• Aryepiglottic folds
• Paraglottic space
• Hyoid or extralaryngeal extension

“Epiglottic cartilage invasion” should not be treated as equivalent to thyroid or cricoid cartilage invasion for T staging.

CT technique and findings

Preferred CT acquisition

For primary laryngeal staging, use thin-section contrast-enhanced multidetector CT with reconstructions in axial, coronal, and sagittal planes. Images should be obtained during quiet respiration rather than phonation or swallowing, with the patient avoiding motion and swallowing during acquisition.

A practical approach:

• IV contrast unless contraindicated.
• Thin isotropic acquisition, ideally allowing approximately 1 mm reconstructions.
• Soft-tissue and bone/cartilage algorithms.
• Coverage from skull base through thoracic inlet, with a standard nodal neck survey.
• Coronal and sagittal reformats aligned to the laryngeal axis when possible.

CT is fast, accessible, less affected by swallowing artifacts than MRI, and excellent for cortical erosion, gross lysis, mineralized cartilage, extralaryngeal extension, nodal disease, and chest staging.[thieme-connect]

CT signs of cartilage invasion

Use a hierarchy of confidence rather than treating every sclerosis as invasion.

High-specificity CT findings

• Definite focal cortical erosion or destructive lysis.
• Tumor visible on both the endolaryngeal and extralaryngeal sides of a cartilage.
• Through-and-through cartilage destruction with extralaryngeal soft-tissue mass.
• Definite cortical breakthrough, especially with contiguous enhancing tumor beyond the laryngeal framework.
• Major cartilage destruction or “blowout.”

Intermediate/suspicious findings

• Focal medullary replacement or loss of normal fatty marrow in an ossified cartilage.
• Focal irregular cartilage contour adjacent to tumor.
• Asymmetric sclerosis, especially when combined with a second abnormality.
• Focal abnormal enhancement within an ossified cartilage.
• Tumor abutting cartilage at a high-risk location, such as the anterior commissure, with subtle adjacent structural abnormality.

Low-specificity / pitfalls

• Isolated thyroid-cartilage sclerosis.
• Symmetric or age-related ossification.
• Post-biopsy inflammation.
• Chondronecrosis or inflammatory chondritis after radiation/chemoradiation.
• Arytenoid sclerosis in the setting of altered mechanics or vocal-fold paralysis.
• Partial-volume effects at the anterior commissure or subglottis.

Historically, sclerosis has been sensitive but nonspecific—particularly in the thyroid cartilage, where mineralization is highly variable. Erosion, lysis, and especially extralaryngeal tumor are more specific but generally later findings.[academic.oup][pmc.ncbi.nlm.nih]

MRI technique and findings

MRI is particularly valuable for:

• Nonossified cartilage, where CT may be insensitive.
• Suspected early medullary cartilage invasion.
• Equivocal CT findings with potential treatment implications.
• Defining paraglottic and pre-epiglottic space involvement.
• Distinguishing the extent of local soft-tissue disease when CT is limited by dental artifact.

A practical laryngeal MRI protocol includes:

• Small field-of-view axial T1-weighted imaging.
• Axial and coronal fat-suppressed T2-weighted imaging.
• Axial and coronal fat-suppressed T1-weighted post-gadolinium imaging.
• DWI/ADC as an adjunct for the primary tumor and nodal assessment.
• Thin slices, typically 3–4 mm or less depending on scanner/protocol.

MRI criteria for cartilage invasion

The classic concept is to compare cartilage signal/enhancement directly with the adjacent tumor:

• Normal ossified cartilage marrow: High T1 marrow signal.
• Suspicious/invaded cartilage: Focal loss of normal high T1 marrow signal, T2 hyperintensity similar to tumor, and enhancement similar to the adjacent tumor.
• More definitive invasion: Tumor-related signal replacing cartilage plus cortical breach or contiguous extralaryngeal soft-tissue extension.

A commonly used MRI pattern is: tumor abuts cartilage with reduced intrachondral T1 signal, increased T2 signal matching tumor, and postcontrast enhancement matching tumor.[epos.myesr]

MRI strengths and limitations

MRI is more sensitive for cartilage invasion, particularly early intrachondral tumor spread and nonossified cartilage. A systematic review/meta-analysis of 14 studies and 776 patients found pooled sensitivity of 88% for MRI versus 66% for CT; pooled specificity was 81% for MRI versus 90% for CT, without a statistically significant specificity difference in that analysis.[pubmed.ncbi.nlm.nih]

However, MRI can overcall invasion because edema, inflammation, perichondritis, reactive hyperemia, biopsy-related change, and treatment effects may produce T2 hyperintensity and enhancement that resemble tumor. The key MRI false-positive pattern is diffuse or ill-defined cartilage edema/enhancement adjacent to bulky mucosal disease without a discrete tumor-matched marrow-replacement pattern or cortical/transcartilaginous extension.

CT versus MRI

The evidence supports a complementary strategy: CT for most patients and MRI when cartilage involvement is uncertain or would materially alter organ-preservation versus surgical decision-making.[thieme-connect][pubmed.ncbi.nlm.nih][academic.oup]

Practical reporting approach

For a laryngeal or hypopharyngeal SCC, avoid a binary “cartilage invasion: yes/no” statement unless unmistakable. Instead, report the specific cartilage, imaging confidence, and whether there is outer cortical/transcartilaginous extension.

Copy-ready report elements

Primary tumor

• Subsite: supraglottic, glottic, subglottic, transglottic, pyriform sinus, postcricoid, or posterior pharyngeal wall.
• Cranio-caudal extent and maximal dimensions.
• Anterior commissure involvement.
• Paraglottic-space involvement.

Reporting checklist limitation: The supplied checklist ends after paraglottic-space involvement. No additional checklist items were supplied.