Anatomy

Artifacts

Imaging of the head–neck area is frequently affected by artifacts, which are caused by

1. the specific anatomical conditions of the head–neck area
   
2. dental treatments
   
3. specific clinical impacts of the disease of the patient on physiological functions.

Anatomical conditions of the head–neck may have an impact on field homogeneity in magnetic resonance imaging (MRI). Field homogeneity is frequently impaired by the irregular nonrounded shape of the head and neck area, the pronounced changes of body shape along the long axis of the body, and large proportions of air and bone in the examination field. As a consequence, fat saturation techniques as well as diffusion weighted imaging (DWI) may be impaired.

Dental metal artifacts including amalgam fillings, implants, and other nonremovable dentures also may affect the field homogeneity in MRI resulting in signal extinction, distortion of anatomical geometry, and impairment of fat saturation technique as well as DWI with possible involvement of an area much larger than the dental metal itself (Figure 7.5). Computed tomography (CT) imaging may also be impaired by superimposing dental metal artifacts (Figure 7.6). In contrast to MRI, metal artifacts in CT are limited to the axial scan plane level of the metal. Patient positioning with pronounced reclination of the head may allow the relevant anatomical area to be moved and avoid superimposing metal artifacts (Figure 7.7). In patients with extensive dental metal applications, positron emission tomography (PET) may provide accurate tumor staging and volume measurement compared to CT or MRI, leading to improved preoperative planning [1] (Figure 7.6). However, dental metal may also affect attenuation‐corrected PET images and may also affect measurements of standardized uptake values (SUVs) [2]. In conclusion, a combined interpretation of PET‐CT and MRI helps to avoid false‐negative readings [3] (Figure 7.8).

Disease‐related artifacts typically include swallowing artifacts (Figure 7.9), as tumors of the neck as well as treatment effects frequently induce an increased urge to swallow, especially when salivation is reduced or increased due to the disease or the therapy. Swallowing artifacts mainly affects the accuracy of anatomical evaluation of imaging diagnosis. Patient positioning in supine position may also be challenging for the patient due to disease‐related or cervical spine pathologies with reduced ability of cooperation and may result in motion artifacts of the entire head–neck (Figure 7.10).

However, the effect of any of these conditions on diagnostic image quality is very individual and cannot be predicted on theoretical considerations. In any case, a diagnostic procedure should be attempted once the correct indication for the specific diagnostic procedure is validated.

Dental Metal Artifacts in MRI: Tumor Evaluation Not Affected

Dental Metal Artifacts in PET‐CT: Tumor Evaluation Not Affected

Dental Artifacts Effect Depends on Degree of Head Reclination

Complementary Information by PET‐CT and MRI

Swallowing Artifacts

Cervical Spine Kyphosis

Impact of Dental Metal on Different MRI Techniques

MRI techniques deliver very robust image quality and show clearly the primary tumor (arrow) as well as cervical lymph node metastases (arrowhead) (Figure 7.11). TSE T1 wi (a) looks unaffected, but (a) shows the “fat” not the “water” image, so Dixon imaging characteristics swapped completely due to dental metal material. In DWI (b, c) a complete signal loss is observed in the oral cavity and oropharynx due to dental metal effects. As a consequence, the primary tumor is not visible, and also lymph node evaluation is limited on the ADC maps (arrowheads).

Pre‐Therapeutic Findings

Most diseases of the head and neck show clinical evidence in a relatively early stage of disease due to the early impairment of physiological function, including breathing, chewing, swallowing, smelling, or tasting. Most pathologies are located superficially and can easily be assessed by clinical examination. As a consequence, diagnostic imaging modalities should focus on the evaluation of the extent of pathologies into deep spaces and on the detection of pathologies that are confined to deep spaces that are not accessible to clinical examination, or when clinical examination fails to explain clinical symptoms of a patient. As an example, small tumors at a T1 stage that are located at the level of the mucosa can easily be diagnosed by clinical examination, but can be missed by CT, MRI, or PET imaging. In contrast, these imaging modalities are superior to clinical examination in the evaluation of the extent of large tumors, the potential infiltration of a tumor into adjacent organs as bone, cartilage, vessels, or nerves, or the detection of lymph node metastasis in deep areas.

In conclusion, clinical examination and imaging modalities provide complementary information in the diagnosis of head and neck diseases.

Most malignant tumors of the head and neck are squamous cell carcinoma (SCC). In contrast, adenoid cystic carcinoma (ACC) is a relatively rare tumor, mostly arising from the salivary glands or the adenoid tissue of the Waldeyer’s ring. Despite the relatively low incidence, ACC has a special clinical significance: ACC frequently shows perineural tumor spread. As a consequence, complete surgical removal of the tumor is challenging and loco regional tumor recurrence is frequent [4].

Nasal Cavity and Paranasal Sinuses

Malignant diseases of the nasal cavity and paranasal sinuses account for 3–5% of all malignant head and neck tumors. SCC is the most frequent tumor entity (Figure 7.12). A minor part of about 10% is constituted by melanoma, lymphoma, esthesioblastoma, and other less frequent tumors (Figure 7.13).

Men are twice as likely to be affected as women. Main age of tumor manifestation is the sixth and seventh decades. Main causes of malignant diseases of the paranasal sinuses include nicotine and alcohol abuse, like most head and neck carcinomas, but also chronic exposition of toxic dust containing nickel, tannine, or chrome pigments in the context of occupational diseases.

As malignant disease of the nasal cavity and paranasal sinuses is frequently accompanied by chronic inflammatory or allergic disease, and different malignant diseases show very similar characteristics, differential diagnosis is a challenge for clinical examination as well as for imaging modalities. However, complementary functional and anatomical diagnostic information facilitates the final diagnosis, especially in this area.

SCC of the Paranasal Sinuses

Sinonasal Melanoma

Salivary Glands

The majority (over 80%) of salivary gland tumors occur in the parotid gland. Most parotid tumors are benign, including pleomorphic adenoma, which is the most important benign tumor. In contrast, about 50% of minor salivary gland tumors are malignant.

SCC is the most frequent malignant tumor found within the parotid gland (Figure 7.14). In the majority of cases it is a metastasis of a primary skin or head and neck malignancy [5].

Histopathology of primary salivary gland malignancies is very complex and diverse, including adenoid cystic, mucoepidermoid, and anaplastic carcinoma.

The SUVs of FDG are significantly higher in most malignant tumors than in benign tumors. However, few benign tumors, such as Whartin tumors, may show high SUVs, whereas some malignant salivary gland tumors, including adenoid cystic carcinomas, low‐grade mucoepidermoid carcinoma, or necrotic SCC, may not have significant FDG avidity [3]. FDG PET‐CT is not able to improve the differentiation of benign from malignant salivary gland lesions when compared to MRI. However, PET‐CT is advantageous in primary staging and in detection of distant metastases and synchronous cancers [6].

Parotid Malignancy (SCC)

Nasopharynx

The incidence of nasopharynx malignancies is much lower compared to oropharynx or hypopharynx tumors in most western societies, but a higher incidence is reported in South‐East Asia and northern Africa. The most frequent histologic entity of nasopharynx malignancies is SCC (Figure 7.15), less frequent are ACC (Figure 7.16) and lymphoepithelial carcinoma (Schmincke–Regaud tumor). The latter has a frequent association with Epstein–Barr virus (EBV) and is highly sensitive for radiation therapy.

At the time of diagnosis, nasopharynx malignancies have frequently reached an advanced stage because early tumor stages are often nonsymptomatic. In advanced tumor stages, tumor infiltration of the base of the skull may cause headache or cranial nerve malfunctions. Lymph node metastases of nasopharyngeal tumors frequently involve the retropharyngeal and bilateral cervical space.

Perineural tumor extension into intracranial spaces is a typical complication of advanced tumor stages (Figures 7.16 and 7.17). Imaging diagnosis is of highest importance because perineural tumor spread is difficult to diagnose by clinical examination, but has a high clinical relevance. This includes decreased survival as well as higher risk of local recurrence and metastatic disease. The trigeminal and facial nerves are the most frequently affected nerves by perineural tumor spread [7, 8]. MRI is the established gold standard in assessment of perineural tumor spread [8], whereas the role of FDG PET‐CT remains to be evaluated [7, 8].

Nasopharyngeal Carcinoma

Adenoid‐cystic Carcinoma without FDG Accumulation

Perineural Tumor Extension of Nasopharyngeal SCC

Oropharynx

The incidence of oropharyngeal carcinoma amounts to up to 2/100,000 population. Men are affected three to four times more often than women. Histology is mostly SCC, less frequent adenocarcinoma or others. Due to different patterns of tumor spread and lymphatic drainage, tonsillar carcinomas (Figure 7.18) are differentiated from tumors of the anterior or posterior palate arch, the soft palate, and the tongue base. Exogenous noxes, including alcohol abuse, smoking, and chewing tobacco, play an important role in tumor genesis, as in all tumors of the upper aerodigestive tract. However, in the past decade the most common cause of oropharyngeal SCC has shifted to the human papillomavirus (HPV). HPV p16‐related oropharyngeal SCC have a significantly better response to treatment and improved prognosis compared to tobacco‐related SCC [9]. This circumstance has led to major adjustments in the 8th edition of the Staging Manual of the UICC [10].

Clinical symptoms depend on tumor site and size. Tumors of tonsils and tongue ground may remain without clinical symptoms up to advanced tumor stages, and lymph node metastases may be the initial finding in those cases.

Tonsillar SCC