P1.03-076 Nodal Staging of Patients with Pulmonary Malignancies - The Predictive Value of Different Patterns of Mediastinal 18FDG-PET Activity

Abstract

In patients with pulmonary malignancies, 18FDG uptake in mediastinal nodes is a sensitive but non-specific indicator of metastatic disease. The pattern of tracer uptake may improve the predictability of such findings. To retrospectively i) compare 18FDG-PET scans and EBUS findings in patients with documented pulmonary malignancies; and, ii) compare the pattern of 18FDG uptake in mediastinal nodes in patients with / without documented mediastinal node metastases. 62 patients with documented pulmonary malignancies underwent 18FDG-PET scintigraphy followed by EBUS within the ensuing 3 weeks. One-two nodes were assessed in each patient, determined by 18FDG-PET findings and accessibility of the FDG-positive nodes. The mediastinal nodal status from each procedure was compared. EBUS resulted in mediastinal nodal status downgrading in 25 (40%) patients. No upgrading was noted. Downgrading most likely occurred when there several non-enlarged lymph nodes of similar 18FDG-avidity distributed randomly and bilaterally in the mediastinum, often with bilateral hilar uptake (17 of 25 patients). Further, only 2 of 19 patients exhibiting such a pattern of mediastinal tracer distribution were found to have lymph node metastases (10%), and both had metastatic disease elsewhere on the PET scan. 21 of 23 patients with positive EBUS findings demonstrated discrete 18FDG-avid lymph nodes ipsilaterally, with minimal-to-no 18FDG-avid nodes contralaterally. EBUS findings in 14 (23%) patients were inconclusive, despite multiple sampling. Enlarged, rounded lymph nodes with avid FDG uptake (SUV>4) were also more likely to harbor metastatic disease. Conversely, a Hounsfield unit of >55 was associated with benign disease. The pattern of mediastinal 18FDG uptake was highly predictive of metastatic disease, and may circumvent the need for EBUS evaluation. Prospective analysis of these parameters will be undertaken.