Case of the Month—November 2005

FDG-PET Detects Unknown Primary Head and Neck Cancer

History
The patient is a 36-year-old male who initially presented with a mass on the right side of his neck. He was treated with antibiotics for two months and showed no improvement. The patient then underwent right neck mass resection. Cytology analysis revealed squamous cell carcinoma. Further work-up with clinical exam and CT of the neck failed to detect the primary lesion. A PET scan was ordered.

Finding
An FDG-PET whole-body scan demonstrated asymmetric uptake in the tonsils, with more uptake on the right side. Suspicion was raised that the primary lesion was located in the right tonsil.

Follow-up
Based on the FDG-PET finding, the patient underwent a tonsill-ectomy. The primary lesion was identified in the right tonsil (see arrow).

An FDG-PET study shows a primary lesion in the right tonsil.

How Did PET Help?
FDG-PET helped to identify the primary head and neck tumor that was not detected by clinical exam or CT scan. Additionally, the PET findings were incorpo-rated into the radiation therapy plan, helping to reduce radiation treatment volume as well as to spare normal tissues from radiotherapy sequelae.

Discussion
The management of patients with metastases of unknown primary origin is often a clinical challenge. In a study of patients with Cancer of Unknown Primary (CUP), Bohuslavizki et al found FDG-PET to be a valuable diagnostic tool, detecting the unknown primary tumor in about one-third of all patients investigated. The authors also found that FDG-PET assisted in guiding biopsies for histologic evaluation and in selecting appropriate treatment protocols for these patents1.

(1) Bohuslavizki, Karl H. et al, “FDG-PET Detection of Unknown Primary Tumors,” The Journal of Nuclear Medicine, May 2000, 41 (5): 816-822.

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