Management of Ground-Glass Opacity Lesions
Hisao Asamura
Recently, smaller and fainter nodules are being found on computed tomography (CT) imaging.1,2 This is partly a result of the markedly improved quality of CT images and the increased likelihood of CT examinations in screening programs. On CT images, all noncalcified nodules should be carefully checked because of the possibility of lung cancer. A nodule might manifest as a focal nonlinear opacity regardless of its characteristics (i.e., solid or subsolid, parenchymal or e ndobronchial). The term ground-glass opacity (GGO) is used to describe noncalcified, subsolid nodules. The pathobiological nature, natural history, and proper m anagement of GGOs have become of greater concern in the thoracic community.
According to recent studies on the relationship between appearance on CT and the histopathology of GGOs, a considerable portion of these lesions, although not all, correspond to preinvasive, noninvasive, or early forms of neoplastic growth, especially those of adenocarcinoma lineage.3,4,5,6,7,8,9,10,11 The clinicopathological entity of these tumors has been established only recently, and has never been the subject of clinical studies. Interestingly, some of these tumors show obvious progression to more advanced, invasive tumors, and some show a constant shape for more than 10 years. The rate of growth, if any, is generally slow. A diagnostic workup for these tumors has not yet been developed. Therefore, these tumors are outside the scope of the standard management of lung cancer. Surgical intervention is difficult with regard to the indication and proper mode of surgical resection. The present surgical management of lung cancer, in which at least lobectomy is performed in conjunction with systematic lymph node dissection/sampling, cannot be applied to these GGOs.12 A standard care for these lesions is currently being established. Clear-cut indications and the rationale for limited resection have not been demonstrated. Some of the treatment strategies for GGO lesions will require future clinical trials.
DEFINITION OF GROUND-GLASS OPACITY
The term GGO is currently being used more often to d escribe the CT appearance of a focal, noncalcified lesion with a slight/moderate increase in CT density. Routine CT images with 1-cm thick slices are not suitable for the diagnosis of GGO, and usually the GGO is characterized on high-resolution CT scan images with a slice thickness of 1 to 3 mm. The CT appearance of GGO is characterized as a “focal, transparent” lesion. GGO refers to a localized or focal lesion regardless of multicentricity, and the diffuse ground-glass appearance seen for interstitial pneumonitis should be excluded from this category. GGO lesions are well characterized by a slight/mild increase in CT density, which does not obscure preexisting lung structures such as blood vessels and bronchi. This appearance refers to CT transparency (Fig. 33.1). When the shape of the pulmonary vessels in the nodules is not recognized in the nodule, the lesion is no longer considered GGO, and instead is called a “solid” lesion. GGO lesions, therefore, can be either homogeneous or heterogeneous.
GGO lesions are classified according to the absence or presence of a solid part. If GGO lesions are homogeneous and do not contain a solid part, they are called nonsolid GGO or pure GGO (Fig. 33.2). If GGO lesions contain a solid, cystic, or linear part inside the nodule, they are called nonsolid GGO or complex GGO (Fig. 33.3). The solid part is more likely to be located in the center of the nodule and surrounded by the GGO part, which shows a so-called fried egg appearance. The solid part might be scant or prominent, with various proportions of solid to GGO parts. In the classic solid tumor, the GGO part no longer exists within the nodule (Fig. 33.4). The relationships between the subtype of CT appearance and histopathologic findings are discussed later.
HISTOPATHOLOGIC FEATURES OF GROUND-GLASS OPACITY LESIONS
With regard to histopathology (see Chapter 22), GGO lesions are either neoplastic or inflammatory. A focal inflammation of the lung parenchyma sometimes presents with a GGO on
the CT image, and pathologically this pattern is described as organizing pneumonia. These changes are more likely to be temporary. In contrast, persistent GGOs are more likely to be neoplastic. According to the World Health Organization (WHO) histological classification of lung and pleural tumors, GGO lesions are associated with three pathological entities.5 Atypical adenomatous hyperplasia (AAH) is described as apreinvasive lesion, in which slightly atypical tumor cells line the involved alveoli and respiratory bronchioles. Nonmucinous bronchioloalveolar carcinoma (BAC) is an adenocarcinoma with Clara cells and/or type II pneumocytes growing along alveolar walls, and without stromal invasion. The important feature of BAC is “noninvasive” growth of the tumor, and therefore, this lesion could be considered in situ carcinoma. The third category is adenocarcinoma with mixed subtypes, which shows a mixture of histologic subtypes as well as obvious invasive growth.
the CT image, and pathologically this pattern is described as organizing pneumonia. These changes are more likely to be temporary. In contrast, persistent GGOs are more likely to be neoplastic. According to the World Health Organization (WHO) histological classification of lung and pleural tumors, GGO lesions are associated with three pathological entities.5 Atypical adenomatous hyperplasia (AAH) is described as apreinvasive lesion, in which slightly atypical tumor cells line the involved alveoli and respiratory bronchioles. Nonmucinous bronchioloalveolar carcinoma (BAC) is an adenocarcinoma with Clara cells and/or type II pneumocytes growing along alveolar walls, and without stromal invasion. The important feature of BAC is “noninvasive” growth of the tumor, and therefore, this lesion could be considered in situ carcinoma. The third category is adenocarcinoma with mixed subtypes, which shows a mixture of histologic subtypes as well as obvious invasive growth.
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
