Head and Neck Cancer

FDG-PET, is considered to be a useful technique in the evaluation of primary head and neck small cell carcinoma (HNSCC). The imaging technique can be performed either 50 minutes after the injection of FDG injection or up to 90 minutes after, because of the continuing improved target-to-background ratios. Normal variants of uptake in adenoidal, palatine, and lingual tonsils, in laryngeal and neck musculature (scalene, vocalis, cricoarytenoid), or in glands (salivary and parotids) need to be kept in mind.

Staging of the primary tumor was tried by some investi-gators,2 but CT and physical examination remain the mainstay in tumor staging. FDG-PET has a role in only 5% of patients, but it can identify the unknown primary in about 20% to 50% of these cases.3-6

Routine panendoscopy can identify the small lesions that may not be seen by PET;7 however, FDG-PET seems to predict tumor curability with radiotherapy.8

Adams et al.9 reported that FDG-PET has a sensitivity of 90% and a specificity of 94%, which are better than MRI (80% and 79%, respectively) and CT (82% and 85%, respectively).

Kau et al.10 studied 70 patients suspicious for lymph node metastases and found that the sensitivity and specificity of FDG-PET for detecting lymph nodes were 87% and 94%, respectively, compared with those of CT (65% and 47%) and MRI (88% and 41%) (Figure 33.1).

Several studies have compared the sensitivity and the specificity of all imaging modalities (FDG-PET and conventional imaging).11-14 False-negative PET studies are found because of small tumor burden in nodes, cystic degenerations of metastatic nodes that are only surrounded by a small rim of viable tumor, low tracer uptake in a metastatic node, imaging artifacts, and proximity to the primary tumor. Additionally, in distant metastases or in synchronous second primary tumors, which are present in 8% of the cases,15 the rate of PET detection is very high16 (Table 33.1).

figure 33.1. A transverse 18F-fluoro-2-deoxy-d-glucose (FDG)-positron emission tomography (PET) scan in a middle-aged patient who had a history of an enlarged right neck lymph node at level 7 that had been excused and demonstrated squamous cell carcinoma. PET/computed tomography (CT) images were obtained with FDG to determine if there was evidence of a primary squamous cell carcinoma. Transverse PET images (with (C) and without (D) attenuation correction) and CT (A), and fused PET/CT (B) images, are displayed. Focal increased FDG is seen in the right palatine tonsil region; this is greater than the normal FDG uptake expected in the lymphocyte-rich tonsils. Biopsy of the right tonsil demonstrated a primary squa-mous cell carcinoma. PET has been reported to detect between 15% and 35% of unknown primary squamous cell carcinomas in the head and neck.

figure 33.1. A transverse 18F-fluoro-2-deoxy-d-glucose (FDG)-positron emission tomography (PET) scan in a middle-aged patient who had a history of an enlarged right neck lymph node at level 7 that had been excused and demonstrated squamous cell carcinoma. PET/computed tomography (CT) images were obtained with FDG to determine if there was evidence of a primary squamous cell carcinoma. Transverse PET images (with (C) and without (D) attenuation correction) and CT (A), and fused PET/CT (B) images, are displayed. Focal increased FDG is seen in the right palatine tonsil region; this is greater than the normal FDG uptake expected in the lymphocyte-rich tonsils. Biopsy of the right tonsil demonstrated a primary squa-mous cell carcinoma. PET has been reported to detect between 15% and 35% of unknown primary squamous cell carcinomas in the head and neck.

FDG-PET in Evaluation of Recurrent Head and Neck Cancer

Most recurrences occur in the first 24 months after therapy for HNSCC. Distant recurrences are more common in patients with locally recurrent disease than distant metastases at initial staging, with the lungs the most common site of distant recurrence.17

Early detection of recurrent head and neck cancer has a crucial role in predicting the clinical outcome, because patients with early-stage HNSCC who undergo salvage surgery have a 70% 2-year relapse-free survival (RFS), whereas those with recurrent advanced-stage disease undergoing salvage surgery have a 22% 2-year RFS.18

FDG-PET is more sensitive, specific, and accurate in the detection of local recurrent head and neck cancer19-21 and in the detection of recurrent HNSCC, regardless of the primary treatment modality (surgery versus radiation therapy)21-25 than CT or MRI (Table 33.2).

The negative predictive value of FDG-PET is very high, but the positive predictive value is somewhat lower for local recurrence in the region of the primary tumor because of false-positive findings (i.e., laryngeal muscle uptake, adipose tissue uptake, or radioactive saliva in the floor of the mouth, throat, or vallecula).

TABLE 33.1. Studies comparing CT, MRI, US, and PET for nodal staging in head and neck cancer.

Author

Year

No. of patients

CT/MRI/US

Sens

Spec

PET Sens

Spec

Hannah et al.12

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