E2334. Utility of 18F-FDG PET/CT in Evaluation for Occult Malignancy in the Setting of Mucoid Impaction
  1. Eric Dietsche; Brigham and Women's Hospital/ Harvard Medical School
  2. Jason Halpern; Rhode Island Hospital/ Alpert Medical School of Brown University
Mucoid impaction is a relatively common finding on chest imaging and can be seen with both benign and malignant underlying etiologies. Despite some suggestive features on a contrast-enhanced chest CT, these signs are not 100% specific, and malignancy often remains within the differential. Various approaches exist to evaluate mucoid impaction, often involving cytologic evaluation from bronchial lavage to assess for underlying malignancy. We describe several features on 18F-FDG PET/CT that can be suggestive of malignancy or help guide referring clinicians in further management.

Educational Goals / Teaching Points
Discuss the current management of mucoid impaction. Review CT findings of mucoid impaction, benign and malignant. Demonstrate the utility of FDG PET/CT. Assess for focal uptake and whether there is endobronchial extension of activity. Assessment of nodal metastatic adenopathy. Search for other potential sources of malignancy and/or distant metastatic disease. Provide recommendations for clinical practice in the setting of mucoid impaction incidentally discovered on chest CT.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
Pathophysiology and current clinical management techniques for mucoid impaction will be reviewed, followed by an algorithm for the imaging workup depending on available patient information. For example, FDG PET/CT should be considered for further evaluation in patients in whom bronchial lavage has not already been performed, if mucoid impaction fails to resolve on serial conventional chest CT, or if the extent of the impaction is increasing. Imaging findings on FDG PET/CT will then be reviewed in a step-wise manner to aid in the interpretation and subsequent recommendations.

If there is no focal FDG uptake in the region of mucoid impaction, malignancy is less likely, though well-differentiated neuroendocrine tumor/ carcinoid could remain a differential diagnosis. If focal uptake is present, malignancy is suspected and the extent can help define the degree of endobronchial spread. If there is suspected malignancy, any FDG avid hilar or mediastinal lymphadenopathy should be reported for staging purposes. FDG PET/CT will also help to determine if there is evidence of distant metastatic disease.