Squamous cell carcinoma, head and neck

Histopathology

Squamous cell carcinomas are mucosal lesions and as such are usually visible at the surface; rarely they develop beneath an intact-appearing mucosa. They can be preceded by a premalignant stage, in which the epithelial cells lose their normal appearance and resemble malignant cells; however, infiltration of surrounding tissues is lacking. Infiltration or invasion occurs when the basal membrane of the epithelium is disrupted. Initially only the subepithelial fibrous tissue is infiltrated; the type of tissue invaded in later stages depends on the site of the tumour. Muscle invasion is a common feature. These tumours are usually diverted by bone or cartilaginous structures and various fascial layers to easier pathways of extension; bone and/or cartilage invasion is mostly a late phenomenon. Perineural tumour spread head and neck and/or perivascular spread can be encountered in all head and neck sites. Locoregional extension is often due to invasion of capillary lymphatics, with subsequent metastatic deposits in neck lymph nodes (see lymphadenopathy head and neck). Some primary tumour locations are associated with a high incidence of metastatic lymph nodes (e.g. nasopharyngeal carcinoma), while others rarely show such spread (e.g. glottic carcinoma). Distant spread is not often seen in squamous cell carcinoma of the head and neck; the lung is the most common site of metastasis.

Apart from the 'classical' squamous cell carcinoma, some other types of carcinoma are encountered in the head and neck region. Verrucous carcinoma is a well differentiated papillomatous tumour. Lymphoepithelioma is a carcinoma with a lymphoid stroma, predominantly occuring in the nasopharynx. Other carcinomas (e.g. spindle cell carcinoma) resemble sarcomas.

Epidemiology

Generally these tumours are first seen in middle age, with a rising incidence up to the age of 70-80 years. The incidence of these tumours is clearly affected by environmental factors. The relative risk is strongly increased by cigarette smoking. High alcohol consumption has a synergistic effect together with smoking. These factors explain the higher incidence in men; changing habits over the past few decades have led to a higher frequency of these tumours in women. Occupational exposure to substances such as nickel and wood dust also has a carcinogenic effect, well-known for sinonasal tumours. There seems to be an association between nasopharyngeal carcinoma and Epstein - Barr virus infection; but a causal link has not been proven.

Smoking and alcohol abuse irritate the entire mucosa of the respiratory tract, inducing premalignant and malignant lesions. This has led to the concept of field cancerization or 'condemned mucosa'. A second primary malignant tumour may be detected during the diagnostic work-up or follow-up of the first malignant tumour (index tumour).

Diagnostic imaging

Mucosal abnormalities can be far better evaluated by the clinician than by even sophisticated imaging methods such as CT or MRI; often the pathology will already be known by the time the patient has a radiological examination. However, extension into the deeply lying tissue planes may be impossible to detect by clinical examination.

Some regions such as the base of the skull, pterygopalatine and infratemporal fossa, orbits and brain are beyond clinical evaluation, but critical management decisions have to be made based on the involvement of these structures; imaging findings are of the utmost importance in such cases. Perineural tumour spread, head and neck and/or perivascular tumour spread, eventually leading to tumour progression or recurrences at distance from the primary tumour, can be detected. Bone or cartilage invasion or destruction can be visualized using CT or MRI. Metastatic adenopathies can be identified (see lymphadenopathy, head and neck), sometimes still in a subclinical stage or in places not accessible to clinical examination, such as the retropharyngeal lymph nodes. All these findings can profoundly influence the staging and management of the patient. Finally, imaging may be used to monitor tumour response and to try to detect recurrent or persistent disease before it becomes clinically evident, possibly allowing a better chance of successful salvage.

For a more detailed description of imaging findings in squamous cell carcinoma, see  hypopharynx cancer, nasopharynx cancer, oropharynx cancer, sinonasal cavities cancer, supraglottic cancer, subglottic cancer.

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