Original articleFDG-PET in the Pretherapeutic Evaluation of Primary Squamous Cell Carcinoma of the Oral Cavity and the Involvement of Cervical Lymph Nodes
Introduction
With an incidence of one in 10,000, squamous cell carcinoma of the oral cavity is one of the most common tumors of the head and neck region, showing an increase in incidence over the last years.1, 2, 3, 4, 5
In order to plan individual treatments and prognostic evaluations, knowledge of the tumor size and the lymph node status are mandatory for this tumor entity, as demonstrated in several recent studies.6, 7, 8
In addition to clinical evaluation, tumor staging is based on magnetic resonance imaging (MRI) and computed tomography (CT). Using CT, morphologic tumor representation is often degraded by scattering radiation due to metallic inlays or prosthetic restorations, especially in the dental area. In MRI, motion artifacts can limit the diagnostic validity concerning tumor localization and extension.
To establish the presence or absence of metastases in the head and neck area, imaging modalities like ultrasound (US), CT, and especially MRI with its excellent soft tissue visualization and a mean accuracy of 60–70%,9, 10 gained wide acceptance in conjunction with clinical inspection and palpation. Although specific criteria that indicate malignancy (dimension, contour, and structure) have been defined for these imaging procedures,11, 12 a very difficult limitation remains. Morphologically inconspicuous or invisible lymph nodes can also contain tumor cells. However, 40% of all lymph node metastases are smaller than 1 cm in diameter10 and in numerous cases only micrometastases are present.
In contrast to morphologic information, positron emission tomography (PET) with 2-deoxy-2[18F]fluoro-D-glucose (FDG) is indicative for metabolic changes as increased anaerobic glycolysis.13 Such a change of glucose metabolism is typical for primary tumors as well as tumor spread in lymph nodes and distant metastases.
A relationship between the intensity of FDG uptake and the grade of malignancy has been described for several tumor entities.9, 14, 15
The aims of this prospective study were to determine: (1) Whether the primary tumor can be better delineated by metabolic characteristics with FDG-PET rather than with CT and MRI. (2) Whether lymph node metastases are detected more frequently and with higher accuracy using FDG-PET than using US, CT, or MRI.
Additionally, a possible correlation between the standard uptake value (SUV) of the primary tumor and the histopathological grading as well as the DNA-image cytometry was assessed.
Section snippets
Patients
From November 1997 until May 1999, 77 patients with histologically proven primary squamous cell carcinoma of the oral mucosa were treated in the Clinic and Policlinic of Oro-Facial-Maxilla-Surgery of the University of Technology, Dresden. This prospective study is based on 38 patients studied prior to treatment. The patient group consisted of 28 males, at the age of 41 to 79 years (mean 59 ± 11 years) and 10 females, 42 to 89 years old (mean 66 ± 14 years). In these patients, the preoperative
Primary Tumor
The postoperative examination of the operative specimen, performed by a pathologist, confirmed the presence of a squamous cell carcinoma of the oral mucosa in all patients.
Using CT, the visualization of the primary tumor was positive in only 22 out of 31 cases. CT was negative for seven T1 and two T2 tumors, yielding the lowest sensitivity of 80% of all applied imaging modalities for the oral cavity (Table 2). The undetected tumors were located in the dental area of the processus alveolaris,
Discussion
The suspicion of a malignancy of the oral mucosa is apparent after clinical inspection and palpation in most cases, since the oral cavity is easily accessible. The diagnosis is confirmed by biopsy, even before diagnostic imaging is applied. The rational for the application of MRI and CT in the diagnostic work-up of a patient with squamous cell carcinoma of the oral cavity is to obtain additional information concerning the extent of tumor and its relationship to neighboring structures such as
Conclusion
This study showed that FDG-PET can identify tumor-related increases in glucose metabolism of tumors of the oral cavity with high sensitivity. When compared to other imaging modalities, especially the MRI, no diagnostic gain was established when evaluating primary tumors. This is true particularly since one cannot do without conventional radiological techniques for further planning of treatment anyway. PET seems to be indicated if CT and MRI are limited by artifacts. An increase of sensitivity
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