Besides smoking, additional risk factors that predispose to aneurysm formation include fenestrated arteries (Fig. 1.6), fibromuscular dysplasia, neurofibromatosis, alpha-1-antytripsyn deficiency, and connective tissue disorders, such as Ehlers-Danlos syndrome and Marfan’s syndrome and polycystic kidney disease. Otherwise, the differential diagnosis of a cerebral aneurysm on radiologic imaging includes an infundibulum (usually manifests as a triangular dilatation with the vessel arising from the apex that measures less than 2 mm), pseudoaneurysm, and mycotic aneurysm (Fig. 1.7).

Secondary polycythemia due to chronic smoking is a risk factor developing cerebral venous thrombosis. Refer to the L-asparaginase and oral contraceptives chapters (Chaps. 21 and 47) for examples of venous thrombosis on imaging.

Tobacco smoking, along with alcohol, is well established as the dominant risk factor for head and neck squamous cell carcinoma (HNSCC). This risk is correlated with the intensity and duration of tobacco use and is synergistic with concomitant alcohol consumption. There are more than sixty recognized compounds in tobacco that have a specific carcinogenic potential. In particular, nitrosamines and polycyclic hydrocarbons can alter the molecular profile of an individual and causes mutations. Nicotine, originally thought only to be responsible for tobacco addiction, is also involved in tumor promotion and progression with antiapoptotic and indirect mitogenic properties. Other factors that can increase the risk of HNSCC include HPV infection and certain occupational exposures. Imaging with contrast-enhanced CT and MRI allows depiction of the anatomy of the larynx and submucosal tumor extension.

Dual-energy CT improves the diagnostic performance and interobserver reproducibility of evaluations of laryngeal cartilage invasion by squamous cell carcinoma. CT, MRI, and PET-CT also provide information regarding cervical nodal disease, systemic metastases, and synchronous malignancies.

On CT or MRI, head and neck squamous cell carcinomas often manifest as ill-defined enhancing masses. Aggressive features of HNSCC include tissue invasion and necrosis (Fig. 1.8). The most common sites of head and neck squamous cell cancer are the floor of the mouth, tongue, soft palate, anterior tonsillar pillar, and retromolar trigone. In addition to locoregional spread, HNSCC can metastasize to distant organs hematogenously, most commonly to the lungs and bones. Metastasis to the brain is an infrequent, but carries a poor prognostic outcome (Fig. 1.9). Besides smoking, alcohol (refer to Chap. 2), betel nuts (refer to Chap. 8), and HPV are the other major risk factors for head and neck squamous cell carcinoma. Interestingly, HPV-positive squamous cell carcinomas generally have a more favorable prognosis and tend to have tumors that are relatively well-defined and large cystic nodal metastases (Fig. 1.10). Otherwise, the differential for other malignant cancers in the head and neck include thyroid cancer, lymphoma, salivary gland cancer, and sarcoma. Furthermore, head and neck abscesses can sometimes resemble necrotic or ulcerated head and neck squamous cell carcinomas and nodal metastases (Fig. 1.11).