a pulmonary nodule is a single , nearly spherical , well - circumscribed pulmonary opacity up to 30 mm indiameter and surrounded by aerated lung tissue ( 2 ) . pulmonary nodules may appear as solid , completely obscuring the lung parenchyma , or as subsolid , not completely obscuring adjacent tissues . a subsolid pulmonary nodule may be further subclassified as a pggn or a part solid nodule , a mixture of ground glass components and focal opacity obscuring the adjacent tissues ( fig . eighty percent of pulmonary nodules are solid , and 20% are subsolid ( 3 ) . subsolid nodules may be benign [ such as inflammatory , hamartoma , focal hemorrhage , or focal interstitial fibrosis ( 4 ) ] , or they may be malignant or premalignant . of subsolid nodules , 4070% resolve spontaneously in 3 months and upon resolution are presumed to have been benign ( 5 ) . subsolid nodules that persist for more than 3 months are considered potentially malignant , with a crude malignancy rate for part solid nodules and pggn of 63% ( 10/16 ) , and 18% ( 5/28 ) , respectively , compared with the rate of 7% ( 14/189 ) for solid nodules ( 3 ) . one study found that 75% of 53 non - resolving pggns were either bronchoalveolar carcinomas ( bac ) or adenocarcinoma with a predominant bac component ; 6% were atypical adenomatous hyperplasia ( aah ) , and 19% were benign ( 6 ) . aah is a less common pathologic finding in surgically resected pggns and is a premalignant precursor of adenocarcinoma that is characterized by proliferation of epithelial cells without invasion into the adjacent tissues ( 7 ) . bac has been described in the 1999 and 2004 world health organization classifications of lung adenocarcinoma as a type of adenocarcinoma with lepidic growth pattern ( along intact alveolar septa ) with minimal , if any , pet - fdg uptake and occurring in relatively low - risk ( such as non - smoking ) patients . patients with bac have varied prognosis , with some having excellent survival and others progressing from early stage to more advanced stage during the 24 years before attempted surgical resection ( 3 , 8) . with the development of better correlation between radiographic appearance of subsolid nodules and the invasiveness of the tumor , in 2011 the international association for the study of lung cancer / american thoracic society / european respiratory society ( iaslc / ats / ers ) has reclassified bac into the subtypes adenocarcinoma in situ ( ais ) , minimally invasive adenocarcinoma ( mia ) , and lepidic predominant adenocarcinoma ( lpa ) ( 9 ) . the new pathology terminology has been adopted to better identify bac on the continuum of premalignant precursor ( aah ) , adenocarcinoma in situ ( ais and mia ) , and invasive lung adenocarcinoma ( 10 ) . patients with aah , ais , or mia have a good prognosis , with near 100% 5-year disease - free survival after complete resection . patients with lpa have 8690% 5-year disease - free survival after surgical resection ( 10 ) , whereas patients with invasive adenocarcinoma have 67% 5-year disease - free survival after surgical resection ( 11 ) . the classification system of early - stage pulmonary adenocarcinoma may improve future clinical trials designed to stratify patients to expectant observation , surgical resection , and/or adjuvant chemotherapy . in 2013 , gould et al . described a management algorithm for individuals with both solid and subsolid pulmonary nodules that takes into account size , radiologic appearance , and independent risk factors for malignancy ( older age , current or past smoking history , and extrathoracic cancer ) ( 1 ) . generally , the likelihood of invasiveness correlates with the initial size of the pulmonary nodule [ e.g. , the prevalence of malignancy is less than 1% for nodules less than 5 mm in diameter , 628% for nodules between 5 and 10 mm in diameter , and 6482% for nodules over 20 mm in diameter ( 12 ) ] , observed growth , or the development of a solid component within the nodule . certain pathologic types of pulmonary nodules may correlate with radiographic appearance . for example , ais typically presents as a pggn and mia is more likely to present as a part solid nodule , whereas invasive adenocarcinomas may present as a solid nodule , a part solid nodule , or occasionally a pggn ( 9 ) . a study showed that 59% of 320 subsolid malignant nodules occur in never - smokers , whereas 25% of solid malignant nodules occurred in never - smokers , a statistically significant difference ( 13 ) . a recent study of 46 resected pggns using the new classification system found that 41% were aiss , 20% were mias , and 39% were invasive adenocarcinomas ( 14 ) . although pet scan has relatively good sensitivity and specificity ( 87 and 83% , respectively ) for distinguishing cancer from non - cancer in solid pulmonary nodules ( 1 ) , the sensitivity of pet scan in subsolid nodules is lower ( 50% ) ( 15 , 16 ) . also , the accuracy of transthoracic biopsy is lower in patients with pggns , with accuracy rates of ( 67 , 85 , and 95% for pggns , subsolid nodules , and solid nodules , respectively ) ( 17 ) . the current case highlights the importance of early consideration of surgical resection for subsolid pulmonary nodules consistent with the 2013 management guidelines ( 1 ) ( table 1 ) . guidelines for evaluation of pulmonary nodulesa 
  table summarizes diagnosis and management of pulmonary nodules as described by gould et al . however , further studies are needed to weigh the benefits and risks of immediate surgical resection versus serial low - dose ct scan follow - up and to determine the optimal duration of ct scan follow - up for those patients not undergoing immediate resection . based on our current understanding of the radiographic , pathologic , and clinical correlates of subsolid nodules , clinicians should consider an individualized diagnostic strategy accounting for the nodule s radiographic characteristics and the patient s comorbidities and personal preferences . the author has not received any funding or benefits from industry or elsewhere to conduct this study .
a pulmonary nodule is a single , nearly spherical , well - circumscribed pulmonary opacity up to 30 mm in diameter and surrounded by aerated lung tissue . in radiographs , pulmonary nodules may appear as solid , completely obscuring the lung parenchyma , or as subsolid , not completely obscuring adjacent tissues . 
 a subsolid pulmonary nodule may be further subclassified as a pure ground glass nodule ( pggn ) or a part solid nodule , a mixture of ground glass components and focal opacity obscuring the adjacent tissues . 
 guidelines for evaluation of solid pulmonary nodules are based on nodule size , recommending vigilance and non - operative management for small nodules ( less than 8 mm in diameter ) and diagnostic biopsy for nodules with a diameter of 8 mm or more . however , subsolid ground glass pulmonary nodules are an exception to this rule . 
 although small in size , persistent subsolid nodules are potentially premalignant or malignant . 
 we present the case of a non - smoker who was found to have an incidental pulmonary pggn . 
 we then discuss the radiologic appearance , histology , clinical outcomes , and evaluation and management strategy of subsolid pulmonary nodules compared with solid nodules .