Laryngeal and hypopharyngeal cancers, like other head and neck cancers, begin as mucosal lesions, and their mucosal extent is far better assessed by clinical and endoscopy at presentation. Imaging plays a complementary role in the clinical workup. The extent of the local tumour and the various patterns of spread can be identified, as can the complex and intricate anatomy of the larynx and the hypopharynx. Features which may upstage the T staging of these tumours can be identified, and thus assist in treatment planning. Nodal staging is also better performed with imaging, again assisting in treatment planning.

Traditionally performed with CT, MRI now plays a greater role in the staging of these neoplasms. The superior soft tissue resolution, together with new hardware and software capable of achieving thin sections within a reasonable amount of time has contributed to this paradigm shift. Cartilage invasion in particular, one of the important criteria determining T staging of laryngeal carcinoma is better assessed at MRI. This is less well assessed with CT, as reactive peritumoral inflammatory change can be difficult to differentiate from actual tumour invasion. There are some drawbacks to MRI, being more costly and laborious and takes longer to perform, although there is no radiation burden. The extent of submucosal spread and soft tissue invasion (e.g. paraglottic space involvement by hypopharyngeal carcinomas, pharyngeal constrictor invasion) is also better seen with MRI. In post-treatment cases, the soft tissue changes induced by surgery and chemoradiotherapy (CRT) make it more difficult to identify recurrent tumours, especially with CT. Here, the superior soft tissue resolution in MRI plays a role in helping to identify recurrent lesions, although this still remains challenging.

When performing MRI for the larynx and hypopharynx, meticulous attention to technique and the use of surface coils with a small field of view (FOV) greatly enhances the accuracy of this examination. Pre-imaging patient preparation is important. Coaching and practicing with the patient beforehand familiarizes the patient with the examination requirements, with greater cooperation, resulting in better quality images. Use of thin slice techniques is preferred. Slice planning for the T1 and T2 images should be identical, allowing more accurate evaluation. Surface coils placed over the larynx and hypopharynx are essential; their proximity to the small structures of the larynx and hypopharynx ensures less signal loss and increased conspicuity of anatomic structures. Gadolinium administration is also helpful, although this may not be in patients with severe renal impairment. DWI sequences can also be of use in identifying subtle tumours.

Accurate T staging of these tumours is important in directing therapy. T1 and T2 tumours may be treated by radiotherapy (RT) or surgery, while T3 and T4 tumours may be treated with surgery and RT, or chemotherapy, with our without salvage surgery. Features that need to be identified include:

• cartilage erosion – minor (T3) vs major (T4a)

• pre-epiglottic / paraglottic invasion – T3

• extralaryngeal spread (e.g. thyroid gland) – T4

• prevertebral invasion – T4

• carotid encasement – T4

• mediastinal involvement – T4

With regards to laryngeal invasion, the use of high-resolution imaging with surface coils better visualizes the laryngeal cartilages, including the small arytenoid cartilages. Accurate identification of laryngeal cartilage invasion is important, as cartilage invasion alters staging and prognosis, and may preclude voice-sparing surgical techniques. Extensive cartilage invasion and extralaryngeal spread is also an unfavourable prognosticator for radiotherapy. Normal laryngeal cartilage may be ossified or unossified. At MRI, unossified cartilage shows low T1W signal, low T2W signal and no enhancement post-contrast. In comparison, normal ossified cartilage shows high T1W signal, high T2W signal and no enhancement post-contrast.

Early studies evaluating the accuracy of MRI using standard neurovascular coils showed MRI was no better than CT at identifying cartilage invasion. However, these examinations employed large FOVs and adopted the following criteria to determine cartilage invasion - low T1 signal within the cartilage, intermediate/high T2 signal within the cartilage and any enhancement. However, with the adoption of new criteria for identifying cartilage invasion, and the use of surface coils and a small FOV, the accuracy of MRI was increased. Currently used imaging criteria for the evaluation of laryngeal cartilage invasion (using the tumour as the reference structure) are:

• Low T1

• Inflammation: T2 & enhancement greater than tumour

• Invasion: T2 & enhancement similar to tumour

Subtle infiltration of the pharyngeal constrictor muscles and infiltration of the paraglottic fat, particularly by hypopharyngeal carcinomas, is also better demonstrated. This can appear as subtle disruption and signal change in these soft tissue structures and their presence affects the T staging of the primary tumour. Again, the greater soft tissue resolution with MRI allows the radiologist to better identify these features.

In the post-treatment scenario, MRI is superior to CT in differentiating between post treatment scar and recurrent tumour, thereby making it more useful for follow up studies. Post-treatment changes such as Reinke’s oedema may be identified, while it is easier to differentiate recurrent tumour from post-treatment scarring. MR-PET may also play an important role in the future.

In conclusion, MRI plays an important role in the staging of laryngeal and hypopharyngeal cancers. The superior soft-tissue contrast resolution, coupled with meticulous attention to technique allows for improved anatomic and tumour delineation, demonstration of cartilage invasion and identification of recurrent tumours.