Solitary pulmonary nodules: comparison of classification with standard, thin-section, and reference phantom CT

Standard, thin-section, and reference phantom computed tomography (CT) were performed to evaluate 75 consecutive patients with solitary pulmonary nodules. Follow-up was available for 62 nodules in 59 patients; 53 of the nodules were benign and nine were malignant. Twenty-one of the 62 nodules were assessed as benign with thin-section CT, while 33 of the 62 nodules were assessed as benign with reference phantom CT. Two of the nodules classified as benign with both thin-section and reference phantom CT proved to be malignant (a peripheral, ossified carcinoid and a 3.5-cm-diameter calcified carcinoma). The sensitivity of reference phantom CT (58%) for classification of benign nodules was higher than the sensitivity of thin-section CT (36%). The sensitivity of standard CT was lowest (12%). The presence of fat at thin-section CT was a reliable criterion for benignancy in six hamartomas. While both thin-section and reference phantom CT were useful in the identification of benign pulmonary nodules, reference phantom CT increased sensitivity by 22% compared with thin-section CT.     

CT evaluation of solitary pulmonary nodules: value of 185-H reference phantom

The pulmonary nodule CT reference phantom is widely used in the evaluation of nodules 2 cm or less in diameter. It is used to detect benign patterns of calcification that are not visible on thin-section CT scans. Since 1986, the reference nodules have been manufactured with a nominal composition of 185 H. The multicenter study published in 1986 used nodules with a nominal composition of 264 H, 100 H more than the threshold value reported by Siegelman et al. in 1980. In the multicenter study, one of 37 nodules diagnosed as benign with the phantom proved to be malignant. The purpose of this study was to determine the misdiagnosis rate with the 185-H phantom and to ascertain whether the malignant tumors predicted to be benign actually contained calcification. We retrospectively reviewed 296 cases in which examinations had been performed with the 185-H nodules since 1986. Eighty-five nodules were diagnosed as benign by comparison to the reference phantom. These 85 contained no visible calcification on thin-section CT scans. Ten of the 85 cases were shown to be malignant tumors. Eight were diagnosed as having a high probability of benignity. Two were diagnosed as having a moderate probability of benignity. Calcium was present in the tissue of all six nodules available for review. Fifty-nine of the 85 nodules were still clinically indeterminate at the time of this review. Even if all of the clinically indeterminate nodules are benign, the misdiagnosis rate would be significantly higher than in most previous studies. Although analysis by using the reference phantom with 185-H nodules may indicate a high probability of benignity, close radiologic follow-up is necessary.     

Pulmonary nodules studied by computed tomography

The authors analyzed 177 pulmonary nodules using thin-section computed tomography (CT), calculating the representative CT number (RCT#) from a computer printout. None of the 96 malignant nodules had an RCT# greater than 151 H. Of the 81 benign nodules, 14 were shown to be calcified by conventional radiography and had an RCT# ranging from 763 and 1,023 H. Thirty had an RCT# greater than 200 H; this included 24 which showed no calcification on conventional tomograms. The remaining 37 benign nodules had an RCT# less than 200 H; 6 of them were hamartomas, including 2 which were diagnosed as such due to their fat content.     

Computed tomography of the solitary pulmonary nodule

The value of computed tomography (CT) using thin-slice technique in the differentiation between benign and malignant pulmonary nodules was evaluated both experimentally and clinically. Experiments using a standard reference phantom and simulation nodules showed that CT number varies according to the size of the nodule and the difference of CT unit. A standard CT number above which a nodule should be considered as calcified and benign was first calculated for various sizes of nodules and then was applied to clinical cases. Motion artifact which can give falsely high CT numbers was also created and its characteristic appearance was identified. Clinically 101 cases of solitary pulmonary nodules whose diagnoses were confirmed either histologically or on follow-up were studied. There were 40 benign nodules, 53 primary lung cancers, and 8 metastatic lung tumors. There was no case of malignancy in which calcification was diagnosed to be present on CT. On the other hand, 14 of 40 benign nodules (35.0%) was diagnosed to contain calcium and therefore benign on CT. As for the margin of the nodule described on CT, a moderate to marked irregularity was predominantly seen in primary lung cancers, while most benign nodules and metastatic lung tumors had smooth margins. If CT criteria for benignancy are limited to the nodule both with calcification and smooth margin, 13 of 40 cases (32.5%) would be correctly diagnosed. CT is considered to be useful in distinguishing between benign and malignant solitary pulmonary nodules as far as herein described technique is observed.     

Solitary pulmonary nodules: Part I. Morphologic evaluation for differentiation of benign and malignant lesions.

The solitary pulmonary nodule is a common radiologic abnormality that is often detected incidentally. Although most solitary pulmonary nodules have benign causes, many represent stage I lung cancers and must be distinguished from benign nodules in an expeditious and cost-effective manner. Evaluation of specific morphologic features of a solitary pulmonary nodule with conventional imaging techniques can help differentiate benign from malignant nodules and obviate further costly assessment. Small size and smooth, well-defined margins are suggestive of but not diagnostic for benignity. Lobulated contour as well as an irregular or spiculated margin with distortion of adjacent vessels are typically associated with malignancy. There is considerable overlap in the internal characteristics (eg, attenuation, cavitation, wall thickness) of benign and malignant nodules. The presence of intranodular fat is a reliable indicator of a hamartoma. The presence and pattern of calcification can also help differentiate benign from malignant nodules. Computed tomography (CT) (particularly thin-section CT) is 10-20 times more sensitive than standard radiography and allows objective, quantitative assessment of calcification. Initial evaluation often results in nonspecific findings, in which case nodules are classified as indeterminate and require further evaluation to exclude malignancy. Growth rate assessment, Bayesian analysis, contrast material-enhanced CT, positron emission tomography, and transthoracic needle aspiration biopsy can be useful in this regard.     

Incidence of pulmonary nodules detected by computed tomography in patients with bronchial carcinoma

Computed tomography (CT) is more sensitive in detecting pulmonary nodules than conventional chest radiography. The incidence of pulmonary nodules on thoracic CT scans, not visible on chest radiographs, in patients with small-cell carcinoma of the bronchus (SCCB) was 27%, and in patients with non-small-cell carcinoma (non-SCCB) the incidence was 28%. Some of these nodules may be malignant. This has implications for the surgical staging of patients with lung cancer in the United Kingdom, where there is a lower incidence of benign granulomatous nodules than in the USA.     

Wegener's granulomatosis: findings from computed tomography of the chest in 10 patients.

Radiographs and computed tomography (CT) scans of the chest were reviewed for 10 patients with pathologically proven Wegener's granulomatosis. The CT scans revealed multiple pulmonary nodules in seven patients and a single nodule in one. The nodules ranged in diameter from 2 mm to 7 cm, and most had irregular margins. All of the nodules larger than 2 cm in diameter showed evidence of cavitation in the CT scans. Additional CT findings included associated areas of consolidation (in two patients), pleural thickening (in two) and pleural effusion (in two). Chest radiographs were available for eight patients, and the CT scans contributed information additional to that available from the radiographs for seven of these. In one patient lung nodules were visible in the CT scans but could not be distinguished from surrounding areas of consolidation in the chest radiographs. CT revealed additional nodules in five of the six patients in whom multiple nodules were seen in chest radiographs and in one of these also revealed cavitation tht was not visible in plain radiographs. CT excluded the possibility of a nodule that was suspected from the chest radiographs in a patient who had been treated previously for Wegener's granulomatosis. The authors conclude that Wegener's granulomatosis is characterized in CT scans by multiple nodules with irregular margins and by cavitation in nodules larger than 2 cm in diameter. CT may also demonstrate nodules and cavitation not apparent in radiographs.     

Solitary pulmonary nodule: CT evaluation of enhancement with iodinated contrast material--a preliminary report.

The authors hypothesized that the degree of contrast material enhancement of a pulmonary nodule, measured with computed tomography (CT), may indicate the likelihood of malignancy. Fifty-two patients with uncalcified solitary pulmonary nodules (diameter, 6-30 mm) were studied. Five single serial thin-section CT scans were obtained at 1-minute intervals after injection of 100 mL of nonionic contrast material. Twenty-two patients were excluded because the diagnosis was not clearly established: The observation period was less than 2 years, or the examination was technically inadequate. Malignant nodules were identified in 23 of the 30 remaining patients, and benign nodules were identified in seven. Within the first 2 minutes after the injection, all the malignant nodules had enhanced by 20 HU or greater (only one benign nodule had that degree of enhancement). The authors conclude that the degree of contrast material enhancement of pulmonary nodules as measured with CT may indicate the likelihood of malignancy.     

Distinguishing benign from malignant pulmonary nodules with helical chest CT in children with malignant solid tumors

PURPOSE: To retrospectively assess whether computed tomographic (CT) findings can indicate the benign or malignant nature of pulmonary nodules in pediatric patients with malignant solid primary tumors. MATERIALS AND METHODS: With institutional review board approval, waived parental and patient consent, and HIPAA compliance, the authors determined the incidence of malignancy among 81 pulmonary nodules that were sampled at biopsy within 3 weeks after chest CT (January 1999 to September 2003) in 41 young patients with malignant solid tumors. Three radiologists independently and retrospectively reviewed these scans and the available previously obtained scans, classifying nodules as benign, malignant, or indeterminate on the basis of their number, unilateral versus bilateral distribution, size, margins (indistinct vs distinct), calcification, growth, and associated adenopathy. These classifications were compared with nodule histologic type, and interreviewer agreement was assessed. RESULTS: The median patient age was 14.8 years (mean, 13.7 years; range, 5-21 years). Twenty-four of the 41 patients (58%) had at least one biopsy-proved malignant nodule. Four (10%) patients had both benign and malignant nodules; 17 (42%) had only benign nodules. Reviewer 1 classified 65% (39 of 60) of nodules correctly; reviewer 2, 57% (37 of 65); and reviewer 3, 67% (43 of 64). Interreviewer agreement was slight to moderate (kappa /= .32). CONCLUSION: The frequency of benign nodules and the inconsistency of predictions based on CT features suggest the need for better predictors of pulmonary nodules being malignant or benign, so as to reduce unnecessary thoracotomy in pediatric patients with solid malignancy. .     

Pulmonary lymphangioleiomyomatosis: correlation of ventilation-perfusion scintigraphy, chest radiography, and CT with pulmonary function tests

PURPOSE: To determine the findings on ventilation-perfusion (V-P) scintigrams, computed tomographic (CT) scans, and chest radiographs and correlate them with pulmonary function test results in patients with lymphangioleiomyomatosis. MATERIALS AND METHODS: V-P scintigraphy, chest radiography, conventional and thin-section CT, and pulmonary function tests were performed in 39 patients. The images were graded on a scale of 0 (normal) to 3 (severely abnormal). RESULTS: Imaging abnormalities were found on 92% of ventilation scintigrams, 92% of perfusion scintigrams, 79% of chest radiographs, 100% of CT scans, and 100% of thin-section CT scans. On ventilation scintigrams, 28 (72%) patients demonstrated a speckling pattern. On CT scans, all patients had pulmonary cysts. Univariate analysis showed that extent of disease on chest radiographs and CT scans, cyst size, V-P abnormalities, and degree of speckling were inversely correlated with forced expiratory volume in one second (FEV(1)), diffusing capacity of lung for carbon monoxide, and the ratio of FEV(1) to forced vital capacity (FVC) (P <.01) but not with FVC and total lung capacity. Larger cyst size correlated with extent of disease at CT, but not significantly (P =.056). CONCLUSION: Scintigraphic and radiologic abnormalities are seen in a majority of patients with lymphangioleiomyomatosis. On ventilation scintigrams, a frequently seen speckling pattern may be related to accumulation of radionuclide in pulmonary cysts-a hallmark of the disease at CT. Findings with each imaging modality correlate with certain pulmonary functions.     

Coronal multiplanar reconstruction view from whole lung thin-section CT by multidetector-row CT: determination of malignant or benign lesions and differential diagnosis in 68 cases of solitary pulmonary nodule

PURPOSE: The purpose of this study was to evaluate the usefulness of the coronal multiplanar reconstruction (MPR) view in comparison with transverse helical thin-section CT for both the determination of malignant or benign lesions and the differential diagnosis of solitary pulmonary nodules. MATERIALS AND METHODS: Sixty-eight cases of pathologically proved solitary pulmonary nodule less than 3 cm in diameter were enrolled in this study. For the routine study, transverse helical thin-section CT (1.25 mm collimation, FOV 20 cm) covering the areas with solitary pulmonary nodules as well as whole lung helical thin-section CT (2.5 mm collimation, 1.25 mm reconstruction interval, FOV 34.5 cm, pitch 6:1, high-spatial frequency algorithm) were scanned with a multidetector-row CT (MDCT) scanner. From the whole lung thin-section CT data, coronal MPR views (2.5 mm slice thickness) were reconstructed on a workstation. ROC analysis was used for an observer performance study, in which three observers indicated their confidence level for the determination of malignant or benign lesion for the nodules by means of transverse thin-section CT and coronal MPR. In addition, the observers recorded appropriate disease entities as the final diagnosis of each case. Accuracies of the final diagnosis based on the two sets of images were compared with McNemer' s test. RESULTS: In terms of the determination of malignant or benign lesion, there was no significant difference between the two sets of images (coronal MPR and transverse thin-section CT; mean Az=0.853 and 0.854, respectively). In addition, accuracy of the final diagnosis based on coronal MPR views (74%) was almost equal to that based on transverse thin-section CT (71%) (p=0.3). CONCLUSIONS: The diagnostic efficacy of the coronal MPR view is comparable to that of transverse thin-section CT for the evaluation of solitary pulmonary nodules.     

探讨肺结节内钙化密度与钙化征象的临床意义

目的：研究肺结节内钙化密度与钙化征象对肺结节良恶性预判的性能。方法经病理或随访证实的肺结节240例（良性70例,恶性170例）。利用最大方差和阈值生长法提取肺结节内具有钙化点和钙化密度的像素,并计算每个钙化点的面积（AreaCa）及面积比（Ar）、同一层面内钙化点的总面积（S）及钙化总面积比（Sr）、同一层面内具有钙化密度的总面积（Cs）及钙化密度面积比（Csr）。结果含有钙化密度的结节明显多于含钙化点的结节（49vs26,χ2＝8．360,P＝0．004）,这一现象在恶性结节中尤为突出（良性23vs16;恶性26vs10）;良性肺结节钙化点和钙化密度的面积均大于恶性（P＝0．000）;以钙化点（AreaCa、S、Ar、Sr）对肺结节良恶性预判的诊断性能优秀（Az＝0．906）,以钙化密度（Cs、Csr）对肺结节性质预判的诊断性能中等（Az＝0．727,0．742）。结论在计算机辅助诊断研究中,借鉴医师经验,对肺结节的CT征象直接进行提取、挖掘,或有助于肺结节影像诊断的确立。     

Quantitative computed tomography evaluation of benign solitary pulmonary nodules

A retrospective evaluation of stable solitary pulmonary nodules was completed in 14 patients using a GE 8800 CT scanner and the Computerized Imaging Reference Systems, Inc., computed tomography chest phantom. Patients with a stable nodule for at least 24 months and no evidence of calcification within the nodule by plain radiography were selected for the study. Using the phantom, a quantitative assessment of nodule density was done in each patient. Of 14 nodules, five were categorized as benign. Linear conventional tomography was performed on these five patients, and only one had evidence of benign calcifications. All patients lived in an area endemic for Coccidioides immitis and six of 14 had culture, serologic, or skin test evidence of previous infection with C. immitis. Two of these six patients had nodules that were characterized as benign using the computed tomography chest phantom. This study indicates that the computed tomography chest phantom is useful in identifying benign nodules in patients living in an area endemic for C. immitis pulmonary infections.     

Spiral CT findings in septic pulmonary emboli

OBJECTIVES: The aim of the study was to determine the characteristics of septic pulmonary emboli and their prevalence on spiral computed tomographic (CT) scans. METHODS AND MATERIALS: We evaluated 65 lesions on spiral CT scans in ten patients with septic pulmonary emboli. Spiral CT scans (10-mm collimation) were obtained at 10-mm intervals from the lung apex to the diaphragm and were compared with posteroanterior chest radiographs obtained within 24 h after CT scanning. RESULTS: Only 21 (32%) of the 65 lesions detected on CT scans were also detected on chest radiographs. Peripheral nodules (39 lesions (60%)) were seen in all ten patients, wedge-shaped peripheral lesions (15 lesions (23%)) in nine patients, and infiltrates (11 lesions (17%)) in four patients. Subpleural lesions (45 lesions (69%)) and feeding vessels (35 (54%)) were found in all patients, and cavitary lesions (seven lesions (11%)) were seen in four patients. Subpleural peripheral nodules and wedge-shaped peripheral lesions were seen in nine patients. Thirty-two lesions (49%) ranged in diameter from 10 to 19 mm, and 59 lesions (91%) were less than 30 mm. CONCLUSIONS: Spiral CT is useful in detecting septic pulmonary emboli. On spiral CT subpleural peripheral nodules and wedge-shaped peripheral lesions less than 30 mm in diameter are often found in patients with septic pulmonary emboli.     

Lung nodule enhancement at CT: multicenter study

PURPOSE: To test the hypothesis that absence of statistically significant lung nodule enhancement (< or =15 HU) at computed tomography (CT) is strongly predictive of benignity. MATERIALS AND METHODS: Five hundred fifty lung nodules were studied. Of these, 356 met all entrance criteria and had a diagnosis. On nonenhanced, thin-section CT scans, the nodules were solid, 5-40 mm in diameter, relatively spherical, homogeneous, and without calcification or fat. All patients were examined with 3-mm-collimation CT before and after intravenous injection of contrast material. CT scans through the nodule were obtained at 1, 2, 3, and 4 minutes after the onset of injection. Peak net nodule enhancement and time-attenuation curves were analyzed. Seven centers participated. RESULTS: The prevalence of malignancy was 48% (171 of 356 nodules). Malignant neoplasms enhanced (median, 38.1 HU; range, 14.0-165.3 HU) significantly more than granulomas and benign neoplasms (median, 10.0 HU; range, -20.0 to 96.0 HU; P < .001). With 15 HU as the threshold, the sensitivity was 98% (167 of 171 malignant nodules), the specificity was 58% (107 of 185 benign nodules), and the accuracy was 77% (274 of 356 nodules). CONCLUSION: Absence of significant lung nodule enhancement (< or = 15 HU) at CT is strongly predictive of benignity.     

Pulmonary manifestations of Hodgkin's disease: radiographic and CT findings

The aim of this study was to assess the radiological and CT findings in patients with pulmonary Hodgkin's disease and to analyse to what extent CT provides more diagnostic information. In 37 patients with 41 episodes of pulmonary manifestation of Hodgkin's disease (histological diagnosis: 11, clinical diagnosis: 30) 39 radiographs and 33 CT scans were analysed by two readers in consensus. Pulmonary nodules were recorded in 77% of radiographs (CXR) and 88% of CT scans. Nodules were multiple in 67% (CXR) and 86% (CT) and bilateral in 43% (CXR) and 66% (CT) of cases, respectively. Nodule size ranged from 2 to 100 mm. Of the nodules, 83% at radiography and CT, respectively, were < or =30 mm, and again 83% at radiography and CT, respectively, were irregularly marginated. Diffuse infiltration with and without nodules was less common. With pulmonary manifestations at initial diagnosis of Hodgkin's disease there was always hilar or mediastinal lymphadenopathy. Of 20 episodes, in which radiograph and CT had been obtained within 8 days, CT demonstrated pulmonary involvement when chest radiography was normal in 3 cases and demonstrated more lesions in 12 cases. The typical appearance of pulmonary HD consisted of multiple, irregularly marginated pulmonary nodules. Diffuse infiltration was less common. Computed tomography was superior to radiography not only in characterization of lesions but could also demonstrate pulmonary involvement when the radiograph was normal and should, therefore, be used liberally in addition to radiography.     

Pulmonary nodules on multi-detector row CT scans: performance comparison of radiologists and computer-aided detection

PURPOSE: To compare the performance of radiologists and of a computer-aided detection (CAD) algorithm for pulmonary nodule detection on thin-section thoracic computed tomographic (CT) scans. MATERIALS AND METHODS: The study was approved by the institutional review board. The requirement of informed consent was waived. Twenty outpatients (age range, 15-91 years; mean, 64 years) were examined with chest CT (multi-detector row scanner, four detector rows, 1.25-mm section thickness, and 0.6-mm interval) for pulmonary nodules. Three radiologists independently analyzed CT scans, recorded the locus of each nodule candidate, and assigned each a confidence score. A CAD algorithm with parameters chosen by using cross validation was applied to the 20 scans. The reference standard was established by two experienced thoracic radiologists in consensus, with blind review of all nodule candidates and free search for additional nodules at a dedicated workstation for three-dimensional image analysis. True-positive (TP) and false-positive (FP) results and confidence levels were used to generate free-response receiver operating characteristic (ROC) plots. Double-reading performance was determined on the basis of TP detections by either reader. RESULTS: The 20 scans showed 195 noncalcified nodules with a diameter of 3 mm or more (reference reading). Area under the alternative free-response ROC curve was 0.54, 0.48, 0.55, and 0.36 for CAD and readers 1-3, respectively. Differences between reader 3 and CAD and between readers 2 and 3 were significant (P < .05); those between CAD and readers 1 and 2 were not significant. Mean sensitivity for individual readings was 50% (range, 41%-60%); double reading resulted in increase to 63% (range, 56%-67%). With CAD used at a threshold allowing only three FP detections per CT scan, mean sensitivity was increased to 76% (range, 73%-78%). CAD complemented individual readers by detecting additional nodules more effectively than did a second reader; CAD-reader weighted kappa values were significantly lower than reader-reader weighted kappa values (Wilcoxon rank sum test, P < .05). CONCLUSION: With CAD used at a level allowing only three FP detections per CT scan, sensitivity was substantially higher than with conventional double reading.     

Persistent pulmonary nodular ground-glass opacity at thin-section CT: histopathologic comparisons

PURPOSE: To retrospectively compare pure pulmonary ground-glass opacity (GGO) nodules observed on thin-section computed tomography (CT) images with histopathologic findings. MATERIALS AND METHODS: The institutional review board approved this study and waived informed consent. Histopathologic specimens were obtained from 53 GGO nodules in 49 patients. CT scans were assessed in terms of nodule size, shape, contour, internal characteristics, and the presence of a pleural tag. The findings obtained were compared with histopathologic results. Differences in thin-section CT findings according to histopathologic diagnoses were analyzed by using the Kruskal-Wallis test or Fisher exact test. RESULTS: Of 53 nodules in 49 patients (20 men, 29 women; mean age, 54 years; range, 29-78 years), 40 (75%) proved to be broncholoalveolar cell carcinoma (BAC) (n=36) or adenocarcinoma with predominant BAC component (n=4), three (6%) atypical adenomatous hyperplasia, and 10 (19%) nonspecific fibrosis or organizing pneumonia. No significant differences in morphologic findings on thin-section CT scans were found among the three diseases (all P>0.05). A polygonal shape (25%, 10 of 40 nodules) and a lobulated or spiculated margin (45%, 18 of 40) in BAC or adenocarcinoma with predominant BAC component were caused by interstitial fibrosis or infiltrative tumor growth. A polygonal shape and a lobulated or spiculated margin were observed in two (20%) and three (30%) of 10 nodules, respectively, in organizing pneumonia/fibrosis were caused by granulation tissue aligned in a linear manner in perilobular regions with or without interlobular septal thickening. CONCLUSION: About 75% of persistent pulmonary GGO nodules are attributed to BAC or adenocarcinoma with predominant BAC component, and at thin-section CT, these nodules do not manifest morphologic features that distinguish them from other GGO nodules with different histopathologic diagnoses.     

The significance of pulmonary nodules detected by CT but not by chest radiography in tumour staging

Computed tomography (CT) is more sensitive than the chest radiograph in the detection of pulmonary metastases, but specificity is lower because CT detects more small benign nodules. This study assessed the significance of pulmonary nodules demonstrated on CT when the chest radiograph was normal. Staging CT scans of 146 patients with extrathoracic primary tumours were reviewed. Thirteen per cent of CT scans showed pulmonary nodules despite a normal chest radiograph. In over 80% of these cases the nodules were benign. This has implications for accurate staging. When such nodules are demonstrated on CT, comparison with a repeat scan at a suitable interval will increase diagnostic confidence.     

Solitary pulmonary nodules: CT assessment

Computed tomography (CT) was used to examine 634 solitary pulmonary nodules (SPNs). Each lesion was assessed as benign or indeterminate on the basis of CT criteria. Benign nodules made up 44% of all SPNs and 58% of the 431 that were 2 cm or less in diameter. All malignant SPNs were assessed as indeterminate, and adenocarcinoma (42%) was the most common primary malignancy. A total of 176 (63% of benign SPNs) were correctly assessed as benign by CT. Ninety SPNs assessed as diffusely calcified were not so identified by conventional tomography at outside institutions. An SPN can be reliably assessed by CT as benign if it exhibits high attenuation values, exceeding a critical level and distributed diffusely throughout a CT section through the center of the lesion and a well-defined edge. Although 38 of 283 (13.4%) primary lung cancers contained localized calcification, there was no significant overlap with the diffuse calcification of benign lesions. Central carcinoid tumors may contain focal ossification, but such lesions may be recognized by noting the proximity of larger bronchi. Assessment of SPNs by CT is most effective for lesions 2.0 cm or less in diameter. For larger lesions, the frequency of benign disease was decreased (14.3% of 203), as was the percentage of benign SPNs correctly assessed as benign by CT (37.9%).