Objective(s): ¹⁸F-FDG PET/CT has been used to characterize the primary lesion and staging in head and neck cancers (HNC). However, prior studies for detecting distant metastasis and  synchronous tumors are sparse, especially in Indian context. To investigate the frequency and distribution of head and neck carcinomas, distant metastases and synchronous malignancies detected in HNC in a north Indian population.
Methods: Medical records and whole body ¹⁸F-FDG PET/CT examinations performed for initial staging on a total of 281 newly diagnosed HNC patients between 01/2019 to 31/6/2023 in North India were retrospectively analyzed and reviewed to look for distant metastasis and synchronous tumors.
Results: On whole body ¹⁸F-FDG PET/CT, distant metastases were detected in 33 (11.7%) patients, all with locally advanced primary tumors corresponding to T category 3 and 4. Lung (6%) and bone (~6.7%) were the most common sites of distant metastasis. In nine patients metastases were detected below the diaphragm. Synchronous malignancies were discovered and histopathologically proven in 22 (7%) patients. Lung carcinoma was the most common synchronous tumor, detected in 9 patients.  In seven patients synchronous tumour was detected outside the aerodigestive tract, of which four were below the diaphragm.
Conclusions: Of the distant metastasis diagnosed in 11.7% of HNC patients with TNM  tumor category T3 and T4, 3% of metastasis lesions were detected below the diaphragm.  Synchronous malignancy was diagnosed in 7% patients irrespective of primary HNC stage.  These findings demonstrate the advantage of using whole body ¹⁸F-FDG PET/CT as an ideal and preferred modality for initial staging and screening of HNC patients since detection of distant metastasis or a synchronous malignancy changes the management approach in these patients.