False + and - PET Scans

Q: Give at least three rationales for false-negative and false-positive positron emission tomography (PET) scans.

Answer: PET scans have become an integral imaging modality in present-day oncology. These are used to locate occult distant metastases, unknown primary lesions, and synchronous second primary tumors. Lately, they have also been increasingly utilized to alter radiation fields and doses for patients not undergoing neck dissection. 

Although biopsy is usually performed in most oncology cases, a false negative (and positive) PET scan requires it for certainty. Some of the rationales for false negative  PET scans are

• Lymph nodes less than 5 mm
• Necrotic or cystic lymph nodes
• Tumors of low metabolic activity, 
• Tumors located at lymphoid tissues with high background physiologic activity, like pharyngeal lymphoid tissues 

A few rationales for False-Positive PET scans are

• Inflammation
• Infection (particularly tuberculosis)
• Medications (like insulin and sedatives)
• Granulomatous processes
• Fibrotic lesions
• Bowel issues
• Metallic implants

#radiology

#oncology

References:

1. Chang JM, Lee HJ, Goo JM, Lee HY, Lee JJ, Chung JK, Im JG. False positive and false negative FDG-PET scans in various thoracic diseases. Korean J Radiol. 2006 Jan-Mar;7(1):57-69. doi: 10.3348/kjr.2006.7.1.57. PMID: 16549957; PMCID: PMC2667579.

2. Long NM, Smith CS. Causes and imaging features of false positives and false negatives on F-PET/CT in oncologic imaging. Insights Imaging. 2011 Dec;2(6):679-698. doi: 10.1007/s13244-010-0062-3. Epub 2011 Sep 9. PMID: 22347986; PMCID: PMC3259390.

3. Betancourt Cuellar SL, Palacio D, Benveniste MF, Carter BW, Gladish G. Pitfalls and Misinterpretations of Cardiac Findings on PET/CT Imaging: A Careful Look at the Heart in Oncology Patients. Curr Probl Diagn Radiol. 2019 Mar-Apr;48(2):172-183. doi: 10.1067/j.cpradiol.2018.02.002. Epub 2018 Feb 6. PMID: 29549978.