CT and PET for lung nodules – pro

PET scans are universally agreed to be useful to evaluate pulmonary nodules. How is should be used otherwise for lung cancer is mired in controversy.

A solitary pulmonary nodule is defined as a discrete, well-marginated, rounded opacity less than or equal to 3 cm in diameter that is completely surrounded by lung parenchyma, does not touch the hilum or mediastinum, and is without associated atelectasis or pleural effusion. PET is a non-invasive imaging technique used frequently to detect cancer and assess the effects of cancer treatment. However, PET is more costly than other traditional types of imaging. The role of PET or PET/CT scans in oncology is rapidly evolving, with well-defined roles in the common malignancies of breast, lung, colorectal cancer, and lymphoma.

PET scanning using FDG has proven to be an excellent modality for evaluating solitary pulmonary nodules. In a recently published meta-analysis of the available data on FDG-PET scanning, the average sensitivity and specificity of FDG-PET scanning for detecting a malignancy were reported to be 0.97 and 0.78, respectively. Like any test, PET scanning has some limitations. The current generation of PET scanners can miss lesions that are < 1 cm in size, and False Negative results can occur when dealing with carcinoid tumors or bronchoalveolar carcinomas. False-positive results may be seen with certain inflammatory or infectious lesions such as tuberculomas, histoplasmomas, and rheumatoid nodules. Moat nodules smaller than 2 cm are benign. There is general consensus in the various guidelines that pulmonary nodules is one setting where PET plays a definite role.

PET is often used to follow an incidentally discovered lung nodule. But size matters. Around 95% of patients with a malignant nodule will have an abnormal  PET, however, if the nodule has a diameter below 1 centimeter, PET scans are often avoided because there is an increased risk of falsely normal results.
Regarding CT scanning, there are a number of divergent guidelines: One guideline cited below says:

the recommendations apply only to adult patients with nodules that are “incidental” in the sense that they are unrelated to known underlying disease. The following examples describe patients to whom the above guidelines would not apply.

Patients known to have or suspected of having malignant disease.—Patients with a cancer that may be a cause of lung metastases should be cared for according to the relevant protocol or specific clinical situation. Pertinent factors will include the site, cell type, and stage of the primary tumor and whether early detection of lung metastases will affect care. In this setting, frequent follow-up CT may be indicated.

Young patients.—Primary lung cancer is rare in persons under 35 years of age (<1% of all cases), and the risks from radiation exposure are greater than in the older population. Therefore, unless there is a known primary cancer, multiple follow-up CT studies for small incidentally detected nodules should be avoided in young patients. In such cases, a single low-dose follow-up CT scan in 6–12 months should be considered.

Patients with unexplained fever.—In certain clinical settings, such as a patient presenting with neutropenic fever, the presence of a nodule may indicate active infection, and short-term imaging follow-up or intervention may be appropriate.

Previous CT scans, chest radiographs, and other pertinent imaging studies should be obtained for comparison whenever possible, as they may serve to demonstrate either stability or interval growth of the nodule in question.

A low-dose, thin-section, unenhanced technique should be used, with limited longitudinal coverage, when follow-up of a lung nodule is the only indication for the CT examination.

Gould MK, Fletcher J, Iannettoni MD, et al. Evaluation of patients with pulmonary nodules: when is it lung cancer?: ACCP evidence-based clinical practice guidelines (2nd edition). Chest. Sep 2007;132(3 Suppl):108S-130S. Cardinale L, Ardissone F, Novello S, et al. The pulmonary nodule: clinical and radiological characteristics affecting a diagnosis of malignancy. Radiol Med. May 29 2009

nccn.org, nsclc 2011

A . Khan ACR Appropriateness Criteria® on Solitary Pulmonary Nodule . Journal of the American College of Radiology , Volume 4 , Issue 3 , Pages 152 – 155 2007

MacMahon H, Austin JH, Gamsu G, et al. (November 2005). “Guidelines for management of small pulmonary nodules detected on CT scans: a statement from the Fleischner Society”Radiology 237 (2): 395–400.

Patricia Rivera, MD, FCCP; Frank Detterbeck, MD, FCCP and Atul C. Mehta, MD, FCCP
Diagnosis of Lung Cancer: The Guidelines Chest. 2003;123:129S-136S.)

Gould, MK, Maclean, CC, Kuschner, WG, et al Accuracy of positron emission tomography for diagnosis of pulmonary nodules and mass lesions: a meta-analysis. JAMA 2001;285,914-924

MacMahon H, Austin JH, Gamsu G, et al. (November 2005). “Guidelines for management of small pulmonary nodules detected on CT scans: a statement from the Fleischner Society”. Radiology 237 (2)

 Yee Ting Sim et al, Imaging of solitary pulmonary nodule—a clinical review. Quant Imaging Med Surg. 2013 Dec; 3(6): 316–326.

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