Oral cancer accounts for 30%–40% of all the malignant tumours in India. Owing to widespread tobacco and betel quid consumption, head and neck cancers are very common in our country and cause significant morbidity and mortality.
Overview of general principles in staging of head and neck cancers
The TNM system
• The tumour burden is a key determining factor of the overall prognosis and outcome for a patient that directs the further management for a particular stage group.
• The TNM staging system is the most widely clinically used staging schema, developed by the American Joint Committee on Cancer (AJCC) in collaboration with the Union for International Cancer Control (UICC).
• The AJCC TNM system classifies cancers by the size and extent of the primary tumour (T), involvement of regional lymph nodes (N) and the presence or absence of distant metastases (M).
Categories
The T, N and M designations are referred to as categories. They are defined separately for each tumour and histologic type.
Classifications
The T, N and M categories may be defined at different time points in the care of the cancer patient.
These points in time are termed ‘classifications’, and are based on the point in temporal evaluation and management of the disease.
• Clinical Classification (cTNM)
• Pathological Classification (pTNM)
• Posttherapy or Post Neoadjuvant Therapy (ycTNM and ypTNM)
• Recurrence or Retreatment (rTNM)
• Autopsy (aTNM)
Prognostic stage groups
After synthesizing the patient history and physical examination findings supported by radio-pathological data, the final ‘stage group’ is decided.
The term stage should not be used to describe individual T, N or M category designations that often are mistakenly referred to as ‘stage’.
Approach to imaging head and neck cancers
Imaging in head and neck cancers can be requested for the purpose of locoregional disease burden assessment or for metastatic workup.
Locoregional imaging
• A substantial amount of information needed for staging is procured by means of clinical and/or endoscopic examination. However, imaging plays an indispensable role in completing the lacunae in clinical exam and aiding in assigning final clinical staging. Imaging helps in deciding appropriate management strategy, assessing resectability and providing important prognostic information.
• The role of imaging is not to diagnose the disease but to characterize it further, except for in patients with severe trismus in whom clinical exam is not possible.
The purpose of Locoregional baseline imaging in head and neck cancers include:
1. Assessing burden of primary disease, with focus on:
• Delineating submucosal and deep soft tissue extent (and depth of invasion, when possible).
• Bone erosion and cartilage involvement.
• Vascular relations.
2. Assessing nodal burden, with special attention to:
• Contralateral adenopathy.
• Relation of nodes with surrounding vascular structures (as it may alter resectability).
3. Perineural spread of tumour, along with intracranial extension of disease.
Follow-up imaging in head and neck forms an extensive component of posttreatment surveillance and focuses on assessing response to therapy and status of residual/recurrent disease.
Metastatic workup
• In addition to loco-regional evaluation, Metastatic work-up may include performing noncontrast CT scan of the chest to look for lung metastasis.
• PET/CT is preferred if advanced disease is present at the time of staging or in cases of metastatic adenopathy from unknown primary.
Modalities
Although various modalities may be complimentary to each other in many cases, it may not be possible to perform all imaging tests due to various reasons. We review the merits and demerits of the various available modalities in detection and characterization of head and neck malignancies (Tables 3.37.1 and 3.37.2).
MRI may be needed occasionally as a problem solving tool for perineural spread detection.
Oral cavity – Proper:
Oral tongue
Contrast-enhanced MRI.
CT: If MRI is equivocal for bony erosion.
Oropharynx:
Base tongue, Uvula, Tonsil, oropharyngeal wall.
Contrast-enhanced MRI.
CT: If MRI is equivocal for bony erosion.
Nasopharynx
Contrast-enhanced MRI.
CT:if MRI is equivocal for subtle clival or skull base involvement.
Sinonasal cavity
Contrast-enhanced MRI.
CT: may help as an initial definer of site of origin, depict bony remodelling or destruction, and detect internal calcifications and tumour matrix.
Hypopharynx/Larynx
MDCT with IV contrast.
MRI: If doubtful cartilage erosion, especially unossified.
Salivary gland tumours
• Superficial parotid
• Deep Parotid, Minor salivary glands
High-frequency USG
Contrast-enhanced MRI
Thyroid gland
High-frequency USG with USG guided FNAC.
CT/MRI: Useful to detect extra-thyroidal extension in a loco regionally invasive tumour.
Requisites of head and neck cancer imaging
A. CT and MRI may be complimentary in various scenarios.
B. As a general rule, MDCT is the primary investigation of choice for cancers of the oral vestibule (i.e., oral cavity excluding the oral tongue) and infra hyoid neck (hypopharynx, larynx).
C. MRI is the primary modality to be used for the oral cavity proper (oral tongue), the suprahyoid neck (nasopharynx and oropharynx) and the para nasal sinuses. MR particularly helps in differentiating inspissated sinus secretions from neoplasm.
D. CT study protocol for the head and neck must include sharp kernel bone algorithm images. This facilitates optimal detection of bone erosion – the key clinical question.
E. Multiplanar reconstruction (MPR), with oblique reformats to be utilized as needed (Fig. 3.37.1).
F. Appropriate artefact reduction measures to be taken to minimize metallic artefact due to dental crowns or amalgams, such as reangulation of the gantry or using an MAR protocol.
G. MDCT with ‘puffed cheek’ technique to be used for cancers involving the oral cavity (Fig. 3.37.2). This helps delineate the gingivobuccal sulcus, with better visualization of the mucosal thickening.
H. Cross-sectional imaging for thyroid cancers is indicated to characterize extra thyroidal extension to the oesophagus, trachea and adjoining structures when clinically or radiologically suspected.
I. Degree of vessel involvement in terms of angle of contact is crucial in determining surgical resectability.
J. Perineural spread of disease:
• Perineural spread refers to spread and migration of tumour cells along nerves.
• Upto 40% cases with perineural spread of tumour may remain asymptomatic. Even when asymptomatic, presence of perineural spread confers a grave prognosis.
• As perineural spread cannot be detected clinically, it is of paramount importance for the radiologist to familiarize with pathways of common cranial nerves involved (especially the second, third divisions of the trigeminal, the facial and the glossopharyngeal) and the skull base foramina through which they pass.
• Although perineural spread may be identified on CECT, MRI remains the modality of choice for its detection (Fig. 3.37.3).
• On MRI, features of perineural tumour involvement are:
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