Incidental, subsolid pulmonary nodules at CT: etiology and management

Abstract

Pulmonary nodules, both solid and subsolid, are common incidental findings on computed tomography (CT) studies. Subsolid nodules (SSNs) may be further classified as either pure ground-glass nodules or part-solid nodules. The differential diagnosis for an SSN is broad, including infection, organizing pneumonia, inflammation, hemorrhage, focal fibrosis, and neoplasm. Adenocarcinomas of the lung are currently the most common type of lung cancer, representing 30-35% of all primary lung tumors, and the subtype of bronchioloalveolar cell carcinoma (BAC) commonly presents as an SSN. In 2011, a new classification system for lung adenocarcinomas was proposed by the International Association for the Study of Lung Cancer, the American Thoracic Society, and the European Respiratory Society. An important feature of the new system is the relinquishment of the term BAC in favor of more specific histologic subtypes. It has been reported that these subtypes are associated with characteristic CT findings. This article reviews the new classification system of lung adenocarcinomas, discusses and illustrates the associated CT findings, and outlines the current recommendations for further diagnosis, treatment, and follow-up of SSNs based on computed tomography findings.

Figure 1

A pure GGN (arrow) demonstrates a focal hazy opacity through which the normal pulmonary parenchymal architecture is visualized.

Figure 2

A part-solid nodule (arrow) shows both ground-glass and solid components.

Figure 3

A low-dose chest CT scan shows a part-solid nodule with bubble-like lucencies (arrow).

Figure 4

1.25-mm thick sections through the left upper lobe obtained over a 4-year interval (a, baseline; b, 4 years) show change from a pure GGN to a part-solid nodule, which subsequently proved to be poorly differentiated invasive adenocarcinoma.

Figure 5

Pathology-CT correlation.

Figure 6

1.25-mm thick section through the left upper lobe shows a small (<5 mm diameter) rounded GGN (arrow) with smooth margins and adjacent normal parenchyma, consistent with a focus of AAH.

Figure 7

1.25-mm thick sections through the right upper lobe obtained over a 3-year interval (a, baseline; b, 3 years) show growth of a pure GGN (arrow). The lesion was resected, and a high magnification photomicrograph (C) shows a well-differentiated non-mucinous AIS (hematoxylin and eosin stain; original magnification 200×). Enlarged neoplastic cells are distributed along intact alveolar septa with no associated invasion.

Figure 8

1.25-mm thick sections through the right middle lobe obtained over a 3-year interval (a, baseline; b, 3 years) show growth of a part-solid nodule (arrow) with increase in size of the central solid component. The lesion was resected, and a low magnification photomicrograph (c) shows a well-differentiated microinvasive non-mucinous adenocarcinoma (hematoxylin and eosin stain; original magnification 20×). The bulk of the tumor shows a lepidic (bronchioloalveolar) growth pattern in which neoplastic cells are distributed along intact interstitial structures. In the upper right portion of the photomicrograph, neoplastic cells are arranged in a more complex acinar growth pattern with stromal invasion measuring less than 6 mm in greatest dimension. The area of invasion has a more solid appearance at low magnification.

Figure 9

CT through the lower lungs demonstrates bilateral ground-glass opacities. Histologic examination of a biopsy specimen revealed multifocal invasive mucinous adenocarcinoma.

Figure 10

1.25-mm thick sections through the right upper lobe obtained over a 3-year interval in a man with a previous left pneumonectomy for squamous cell lung cancer (a, baseline; b, 2 years; c, 3 years) show growth of a part-solid nodule (arrow). FDG-PET/CT (d) obtained at the 2-year time point reveals minimal activity within the nodule (arrow). Because the patient was already under treatment for biopsy proven squamous cell cancer recurrence elsewhere in the body, and due to the danger of a lung biopsy in a patient with a single lung, no tissue proof was obtained for this presumed indolent, primary lung adenocarcinoma.

Figure 11

1.25-mm thick section through the right upper lobe shows a GGN (arrow). FDG-PET/CT demonstrates no significant activity within the nodule (arrow). The nodule was subsequently resected and histopathologic examination revealed mucinous AIS.