Incremental Value of FDG PET/CT in the Evaluation of Ascites of Malignant Origin with an Unknown Primary

Objectives The study aims at assessing the incremental value of FDG PET/CT in patients with ascites of malignant origin, with an unknown primary.

Methods The data at our department was analyzed retrospectively from 2010 to 2014. PET/CT scans were performed in 28 patients diagnosed with cytologically proven ascites of malignant origin where the primary tumor was yet to be identified. Each PET/CT scan was interpreted and reported by two experienced nuclear medicine physicians. Lesions with non-physiological uptake of FDG more than the surrounding background were considered abnormal; the nature of the lesions was assessed based on the CT images used for co-registration and also based on any additional investigations when available.

Results Twenty-eight patients (16 males) with a mean age of 49.2 years (95%CI: 42.8 to 55.5 years) and mean duration of ascites=4 months (95%CI: 3.1 to 5 months) underwent FDG PET/CT. The grade of ascites did not correlate with the duration (r = 0.09, p = 0.69). On the PET/CT images, a primary could be identified in 21 patients (detection rate=75%). In exception to 1 patient with primary in lung, all patients had malignancies in the abdomino-pelvic region. The most common kind to be found was in the female genital tract (n=6) followed by the gastro-intestinal tract (n = 5). Eight patients (28.6%) had omental, serosal and/or mesenteric deposits. Sixteen patients (57%) had abdomino-pelvic lymphadenopathy while 7 patients (25%) had distant lymph nodal metastases. Liver metastases were found in 6 patients. It was also observed that FDG PET/CT offered a site for percutaneous and endoscopy-guided histopathological confirmation in 7 and 9 patients respectively.

Conclusions In the context of ascites of malignant origin, our study shows that FDG PET/CT not only provides valuable insight regarding the possible primary tumor site, but also provides crucial information regarding the choice of modality for approaching a confirmation of the diagnosis.