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The diagnostic accuracy of a solitary pulmonary nodule, using thin-section high resolution CT: A solitary pulmonary nodule by HRCT
Lung Cancer 13 (1995) 105-112
ELSEVIER
The diagnostic accuracy of a solitary pulmonary nodule, using thin-section high resolution CT: A solitary pulmonary nodule by HRCT Nobuko Takanashia, Yasufumi Nobeb, Hiroshi Asoha, Tokujiro Yanoa, Yukito Ichinose*” aDepartment bDepartment
of Chest Surgery, of Radiology,
National Kyushu Cancer Center, 3-I-1, Notame. Minami-ku, Fukuoka 815, Japan National Kyushu Cancer Center, 3-I-I. Notame. Minami-ku, Fukuoka 81s. Japan
Received 27 February 1995; revision received 30 May 1995; accepted 14 June 1995
Abstract
A solitary pulmonarynodule(SPN) lessthan 2 cm in diameterof 60 patientswasevaluated with thin-section,high-resolutioncomputedtomography(HRCT). The presenceof an irregular margin,spiculation,convergenceof the surroundingstructure, an air bronchogramand the involvementof more than 3 vesselswasobservedmore frequently in malignantnodules than in benignnodules.When one point wasgiven for eachfinding, the meantotal scoresof each histologictype were as follows; adenocarcinoma;2.7, squamouscell carcinoma;2.5, benigntumor; 0.3, tuberculosis;1.3, pneumonia;2.0. When SPNswereclassifiedby the total scores,the SPNswith higherscores(z 3) included18of 33(56%)malignantlesionsandonly 2 of 28 (7%) benignlesions.This meansthat sensitivity and specificity in the diagnosisof malignancyin the SPNswith high scoreswere56%and 93%,respectively.Theseobservations suggest that SPNswith a scorehigherthan 3 pointswould behighly suspicious for malignancy but the numberof suchSPNsis rather limited. Therefore, more sophisticatedmethodsmay be necessary to better differentiate
between malignant
and benign SPNs.
Keywords:High resolutionCT, Lung cancer;Solitary pulmonarynodule;Diagnosis;Adenocarcinoma;Benigntumor
* Corresponding author, Tel.: +81 92 5413231; Fax: +81 92 5514585.
0169-5002/95/$09.50 0 1995 ElsevierScience IrelandLtd. All rightsreserved SSDI
0169-5002(95)00488-M
106
N. Takanashi et al. /Lung Cancer 13 (1995) 105-112
1. Introduction
As a result of the improvement of radiologic equipment, small nodular lesions in the lung are now being detected more frequently. Since the radiographic features of such small pulmonary nodules are usually non-specific, a transbronchial biopsy guided under fluoroscope is usually performed to make a diagnosis [6,11]. The diagnostic accuracy in this technique, however, is reported to be less than 75% [l&8]. Therefore, a solitary pulmonary nodule (SPN) measuring less than 2 cm in diameter is expected to be difficult to diagnose regardless of the technique used to analyze it. In fact, a surgical resection in the majority of patients with SPNs of this size is normally needed to rule out the possibility of malignancy. Recently, several investigators have reported the availability of thin-section high resolution CT (HRCT) to evaluate SPN and the radiographic features suggesting malignancy have been well documented [2,7,12]. However, the frequency of malignant signs in benign SPNs as well as in malignant SPNs is still not well known. Based on our clinical experience, we have noticed that malignant lesions do not necessarily have malignant signs while some benign lesions have malignant signs on HRCT. Therefore, in the present study, we attempted to examine what percentage of malignant SPNs measuring less than 2 cm in diameter can be distinguished from benign SPNs of the same size, using HRCT. 2. Subjects and methods
The subjects consisted of 60 patients with an SPN measuring less than 2 cm in greatest diameter who were treated at the National Kyushu Cancer Center from April 1991 to August 1993. The patient characteristics are shown in Table 1. A pathologic diagnosis was obtained in all patients either by a fluoroscopic guided
Table I Patient characteristics
No. of patients Male/female Age Size: mm (range) Diagnosis Adenoca. Squamous cell ca. Small cell ca. Tuberculosis Benign tumor Pneumonia Others
Cancer
Non-cancer
32 2418 62.0 ZIZ10.4 17.1 f 3.0 (8-20)
28 14114 55.4 f 9.1 13.6 f 4.8 (6-20)
27 4 I -
12 6 5 5
-
N. Takanashi et al. /Lung Cancer I3 (1995) 105-112
107
transbronchial procedure or by a surgical resection. There were 32 patients with lung cancer and 28 with benign lesions. No cases of metastatic lung cancer were observed. The histology of the 60 SPNs was as follows; adenocarcinoma in 27 patients, squamous cell carcinoma in 4, small cell carcinoma in 1, hamartoma in 4, sclerosing hemangioma in 1, a bronchial cyst in 1, tuberculosis in 12, pneumonia or organizing pneumonia in 5, a scar in 3, amyloidosis in 1, and an intrapulmonary lymph node in 1. The CT examinations were performed with a Hitachi W-1000 device (120 kV, 100 mA, 512 x 512 matrix). After scans of the whole thorax with a 10 mm-thick slice were obtained, a scanning of 2 mm-thick sections was done throughout the lesion. No contrast medium was used. The window level and its width were set at -50 and 2000 HU in the mediastinal condition and at -700 and 1500 HU in the lung field condition, respectively. The CT scans were reviewed by a radiologist and six chest physicians. The radiographic features recorded were as follows; an irregular margin, spiculation, a convergence of the surrounding structures, pleural retraction, an air bronchogram, and the involvement of either the arteries or veins. These features have all been reported to be strongly related to malignancy [2,7,12,13]. Since the number of SPNs with a calcified shadow indicating benign lesion, was only 4 cases, this finding was not included in the present study. If the nodular edge was hazy or corrugated, then the nodule was considered to have an irregular margin. Since notching or lobulation was difficult to distinguish from an irregular margin, they were included in this finding. Spiculation was defined as the presence of tine linear strands less than 5 mm in length extending from the nodular margin into the lung parenchyma. Pleural retraction was defined as linear strands extending from the lesion to the pleura. Convergence was recorded if the lung parenchyma surrounding the nodule was closely packed in comparison with the area distant from the lesion, either with or without several lines of more than 5 mm in length radiating from the lesion. Zwirewich et al. [13] reported that the appearance of small cavitations within the nodular shadow were due to small, patent air-containing bronchi. Since we also confirmed this finding by a microscopic examination, the small cavitations within the nodule were considered to be an air bronchogram. The differences in the incidence of each finding between benign and malignant lesions were compared by the x*-test. When the P value did not exceed 0.05, the difference was considered to be significant.
3.Results 3.1. Ot~ferencesin the characteristics between benign and malignant SPNs
The radiographic features by HRCT are summarized in Fig. 1. An irregular margin (94% of cancer vs. 71% of non-cancer), spiculation (53% vs. 18%), the convergence of the surrounding structures (44% vs. 11%) and an air bronchogram (38% vs. Ilo/) were considered to be radiographic features that are significantly more often observed in malignant SPNs than in benign SPNs. Pleural retraction was observed in 39% of benign SPNs and 56% of malignant SPNs (P = 0.292).
108
N. Takaaeshi et al. /Lung Cheer 13 (1995) 105-112
Cancer
Non-cancer Irregular
margin
Spiculation Pleural retraction Convergence Air bronchogram
Involvement of artery Involvement
of vein
involvement of L 3 vessels
I 100%
0
.%
Fii. 1. The frequency of each finding suggesting malignancy. The P value between cancer and non-cancer is
Well-mod.
diff. adenoca.
Well-mod.
diff. adenoca.
Fig. 2. The frequency of each finding according to the histologic type. There were 19 well or moderately differentiated adenocarcinomas, 8 poorly differentiated adenocarcinomas, 4 squamous cell carcinomas, 12 tuberculoses, 5 pneumonias and 6 benign tumors.
N. Takanashi
el al. /Lung
Cancer
13 (1995)
105-112
109
There was no statistical difference in the frequency of the involvement of the artery and vein between malignant and benign lesions. However, malignant lesions tended to involve multiple vessels. When the SPNs were divided based on the involvement of more than 3 vessels, 38% of malignant SPNs possessed this finding. On the other hand, only 2 benign SPNs involved more than 3 vessels (P
Fig. 3. The radiographic features included (A) an irregular margin, spiculation, a pleural retraction, convergence, an air bronchogram and the involvement of vessels in one patient with moderately differentiated adenocarcinoma, (B) an irregular margin, pleural retraction, an air bronchogram and the involvement of vessels in one patient with scar tissue accompanying organized pneumonia, and an irregular margin, spiculation, a pleural retraction and the involvement of vessels in one patient with tuberculosis. Each pair of images belong to the same patient but are some distance apart.
II0
N. Takanashi
et al. /Lung
Cancer
13 (1995)
105-112
Table 2 Scores by histologic types Histologic types Cancer Adenocarcinoma (n = 27) Well-Moderately diff. (n = 19) Poorly diff. (n = 8) Squamous cell ca. (n = 4) Small cell ca. (n = I) Non-cancer Benign tumor (n = 6) Tuberculosis (n = 12) Pneumonia (n = 5) Others (n = 5)
Score 2.74 f 3.05 + 2.00 * 2.50 f 1.00
1.20 1.08 1.20 1.29
0.33 f 0.52 1.33 f 0.89 2.00 f 1.22 1.00 l 0.71
An air bronchogram was frequently found in either well or moderately differentiated adenocarcinoma (53%) and in pneumonia (40%) as compared to the other lesions. The involvement of more than three vessels was detected in 37% of well or moderately differentiated adenocarcinoma, in 38% of poorly differentiated adenocarcinoma and in 50% of squamous cell carcinoma, while no benign lesions and only one case of tuberculoma had this finding. Fig. 3 shows a representative radiogram of HRCT in cases of adenocarcinoma (A), pneumonia (B) and tuberculosis (C). Each lesion showed more than three findings.
3.3. Scoring
One point was given for each finding except pleural retraction whose frequency was not significantly different between the benign and malignant SPNs and the total scores of each histological type are summarized in Table 2. Malignant lesions showed the score of 2.66 while benign lesions had a score of 1.17. In malignant lesions, well or moderately differentiated adenocarcinoma (3.05) and squamous cell carcinoma (2.50) had a high score. In benign lesions, benign tumors and tuberculosis had a low score. However, pneumonia or organizing pneumonia showed a relatively high score (2.00) which is equal to the score of poorly differentiated adenocarcinoma. Fig. 4 shows the distribution of the scores for cancer and non-cancer patients. Eighteen of 32 (56%) malignant SPNs had a score of more than 3 points while only two of 28 benign SPNs (7%) showed such a score. Seven benign SPNs and one malignant SPN, which was poorly differentiated adenocarcinoma measuring 8 mm in the diameter demonstrated a score of 0. However, 19 benign and 13 malignant lesions overlapped with l-2 points. When the SPNs with a score of more than 3 points were regarded as malignant, the sensitivity and specificity in the diagnosis of malignancy were 53.1% and 92.6%, respectively.
N. Takanashi et al. /Lung Cancer 13 (1995) 105-112
Cancer
Non-cancer
(2.66k1.21)
(1.1720.98)
0 l ooooooo l ooooooeo
111
5 4 0 3 0 2 0000000
l ooooooe l eeee
1 000000000000 l
0 0000000
Fig. 4. The distribution of scores for each lesion. The numbers in parentheses are the mean f SD. of the total scores.
4. Discussion When an SPN is found, the most important point is whether or not the SPN possesses the possibility of malignancy. However, it is very diffkult to evaluate the radiographic features of SPN measuring less than 2 cm in greatest diameter by using either a conventional chest roentgenogram or CT. HRCT has been reported to reveal the detailed features of small lesions and the surrounding area 17,131. Therefore, HRCT is thought to be able to satisfactorily detect the radiographic features indicating malignancy, even in small sized SPNs. In the present study, we examined whether the incidence of six malignant radiographic features detected by HRCT differ between malignant and benign SPNs. These six radiographic features, which included an irregular margin, spiculation, convergence, a pleural retraction, an air bronchogram and the involvement of vessels, have been reported to be related to malignancy. According to the studies using HRCT on the malignant lesions, the incidence of an irregular margin is 73-lOtY?h [10,12,13], spiculation 78-100% [2,10,13], convergence 83% [2], pleural retraction 50-100% [2,10,13], an air bronchogram 31-67% [2,13] and the involvement of vessels 93-100% [4,9]. The incidences in the present study may thus seem to be low compared to the previous studies. This may be due to the fact that our subjects were limited to patients with an SPN measuring less than 2 cm in greatest diameter. Although we did not find any specific malignant features, the incidence of all the above features, except for pleural retraction in malignant SPNs, was observed significantly more often than that in benign SPNs. Especially, irregular margin, spiculation, convergence and an air bronchogram were most frequently found in either well or moderately differentiated adenocarcinoma. In our series, benign SPNs included various diseases. As shown in Fig. 2 and Table 2, the radiographic features of inflammatory lesions are closer to malignancy than
112
N. Takanashi et al. /Lung Cancer 13 (1995) 105-112
non-inflammatory lesions such as benign tumors. As expected, most inflammatory lesions had an irregular margin. Although the presence of an air bronchogram has been reported to be a relatively specific feature of adenocarcinoma [3,13], 44% of adenocarcinoma and 40% of pneumonia possessed this feature in the present study. However, we found that the number of air bronchograms within SPN differed between adenocarcinoma and inflammatory lesions. The majority of malignant SPNs had more than three air bronchograms within the SPN while most inflammatory lesions possessed only one or two air bronchograms (data not shown in the results). In order to compare malignant SPN with benign SPN, one point was given to each radiographic feature, except for pleural retraction, whose incidence was not significantly different between malignant and benign SPNs. Except for a case of poorly differentiated adenocarcinoma which lacked any features because of its small size, a score of 0 is considered to be benign lesion. When an SPN was classified by a score of three or less, the sensitivity and specificity in the diagnosis of malignancy was 56% and 93%, respectively. However, this sensitivity was still not satisfactory. Therefore, more sophisticated methods such as giving different points for each finding may be necessary to better differentiate between malignant and benign SPNs. Acknowkdgments
We would like to express our gratitude to Brian Quinn for his critical review, and Yumiko Oshima and Yuko Ishibashi for their help in the preparation of the manuscript. References [I] Cortese DA, McDougall JC. Biopsy and brushing of peripheral lung cancer with fluoroscopic guidance. Chest 1975; 75: 141-145. [2] Kuriyama K, Tateishi R, Doi 0, et al. CT-pathologic correlation in small peripheral lung cancers. AJR 1987; 149: 1139-1143. [3] Kuriyama K, Tateishi R, Doi 0, et al. Prevalence of air bronchogram in small peripheral carcinomas of the lung on thin-section CT: Comparison with benign tumors. AJR 1990, 156: 921-924. [4] Mori K, Saitou Y, Tominaga K, et al. Small nodular lesions in the lung periphery: new approach to diagnosis with CT. Radiology 1990; 177: 843-849. [S] Radke JR, Conway WA, Eyler WR, et al. Diagnostic accuracy in peripheral lung lesions. Chest 1979; 76: 176-179. (61 Shiner RJ, Rosemnan I, Katz I, et al. Bronchoscopic evaluation of peripheral lung tumors. Thorax 1988; 43: 887-889. [7] Siegelman SS, Khouri NF, Leo FP, et al. Solitary pulmonary nodules: CT assessment. Radiology 1986; 160: 307-312. [S] Stringtield JT, Markowitz DJ, Benz RR, et al. The effect of tumor size and location on diagnosis by tiberoptic bronchoscopy. Chest 1977; 72: 474-476. [9] Yamada K, Nomura I, Matsumura M, Noda K. A thin-sliced CT analysis of the relationship between solitary pulmonary lesions and the surrounding vessels.Lung Cancer 1992; 32: 845-850 [in Japanese]. [IO] Yamada K, Nomura I, Matsumura M, Noda K. Three-dimensional computed tomography for evaluation of peripheral small lung cancers. Jap J Thoracic Dis 1993; 31: 959-970. [ll] Zavala DC. Diagnostic fiberoptic bronchoscopy. Chest 1975; 68: 12-19. (121 Zerhouni EA, Stitik FP, Siegelman SS, et al. CT of the pulmonary nodule: a cooperative study. Radiology 1986; 160: 319-327. [13] Zwimwich CV, Vedal S, Miller RR, et al. Solitary pulmonary nodule: high resolution CT and radiologic-pathologic correlation. Radiology 1991; 179: 469-476.
ELSEVIER
The diagnostic accuracy of a solitary pulmonary nodule, using thin-section high resolution CT: A solitary pulmonary nodule by HRCT Nobuko Takanashia, Yasufumi Nobeb, Hiroshi Asoha, Tokujiro Yanoa, Yukito Ichinose*” aDepartment bDepartment
of Chest Surgery, of Radiology,
National Kyushu Cancer Center, 3-I-1, Notame. Minami-ku, Fukuoka 815, Japan National Kyushu Cancer Center, 3-I-I. Notame. Minami-ku, Fukuoka 81s. Japan
Received 27 February 1995; revision received 30 May 1995; accepted 14 June 1995
Abstract
A solitary pulmonarynodule(SPN) lessthan 2 cm in diameterof 60 patientswasevaluated with thin-section,high-resolutioncomputedtomography(HRCT). The presenceof an irregular margin,spiculation,convergenceof the surroundingstructure, an air bronchogramand the involvementof more than 3 vesselswasobservedmore frequently in malignantnodules than in benignnodules.When one point wasgiven for eachfinding, the meantotal scoresof each histologictype were as follows; adenocarcinoma;2.7, squamouscell carcinoma;2.5, benigntumor; 0.3, tuberculosis;1.3, pneumonia;2.0. When SPNswereclassifiedby the total scores,the SPNswith higherscores(z 3) included18of 33(56%)malignantlesionsandonly 2 of 28 (7%) benignlesions.This meansthat sensitivity and specificity in the diagnosisof malignancyin the SPNswith high scoreswere56%and 93%,respectively.Theseobservations suggest that SPNswith a scorehigherthan 3 pointswould behighly suspicious for malignancy but the numberof suchSPNsis rather limited. Therefore, more sophisticatedmethodsmay be necessary to better differentiate
between malignant
and benign SPNs.
Keywords:High resolutionCT, Lung cancer;Solitary pulmonarynodule;Diagnosis;Adenocarcinoma;Benigntumor
* Corresponding author, Tel.: +81 92 5413231; Fax: +81 92 5514585.
0169-5002/95/$09.50 0 1995 ElsevierScience IrelandLtd. All rightsreserved SSDI
0169-5002(95)00488-M
106
N. Takanashi et al. /Lung Cancer 13 (1995) 105-112
1. Introduction
As a result of the improvement of radiologic equipment, small nodular lesions in the lung are now being detected more frequently. Since the radiographic features of such small pulmonary nodules are usually non-specific, a transbronchial biopsy guided under fluoroscope is usually performed to make a diagnosis [6,11]. The diagnostic accuracy in this technique, however, is reported to be less than 75% [l&8]. Therefore, a solitary pulmonary nodule (SPN) measuring less than 2 cm in diameter is expected to be difficult to diagnose regardless of the technique used to analyze it. In fact, a surgical resection in the majority of patients with SPNs of this size is normally needed to rule out the possibility of malignancy. Recently, several investigators have reported the availability of thin-section high resolution CT (HRCT) to evaluate SPN and the radiographic features suggesting malignancy have been well documented [2,7,12]. However, the frequency of malignant signs in benign SPNs as well as in malignant SPNs is still not well known. Based on our clinical experience, we have noticed that malignant lesions do not necessarily have malignant signs while some benign lesions have malignant signs on HRCT. Therefore, in the present study, we attempted to examine what percentage of malignant SPNs measuring less than 2 cm in diameter can be distinguished from benign SPNs of the same size, using HRCT. 2. Subjects and methods
The subjects consisted of 60 patients with an SPN measuring less than 2 cm in greatest diameter who were treated at the National Kyushu Cancer Center from April 1991 to August 1993. The patient characteristics are shown in Table 1. A pathologic diagnosis was obtained in all patients either by a fluoroscopic guided
Table I Patient characteristics
No. of patients Male/female Age Size: mm (range) Diagnosis Adenoca. Squamous cell ca. Small cell ca. Tuberculosis Benign tumor Pneumonia Others
Cancer
Non-cancer
32 2418 62.0 ZIZ10.4 17.1 f 3.0 (8-20)
28 14114 55.4 f 9.1 13.6 f 4.8 (6-20)
27 4 I -
12 6 5 5
-
N. Takanashi et al. /Lung Cancer I3 (1995) 105-112
107
transbronchial procedure or by a surgical resection. There were 32 patients with lung cancer and 28 with benign lesions. No cases of metastatic lung cancer were observed. The histology of the 60 SPNs was as follows; adenocarcinoma in 27 patients, squamous cell carcinoma in 4, small cell carcinoma in 1, hamartoma in 4, sclerosing hemangioma in 1, a bronchial cyst in 1, tuberculosis in 12, pneumonia or organizing pneumonia in 5, a scar in 3, amyloidosis in 1, and an intrapulmonary lymph node in 1. The CT examinations were performed with a Hitachi W-1000 device (120 kV, 100 mA, 512 x 512 matrix). After scans of the whole thorax with a 10 mm-thick slice were obtained, a scanning of 2 mm-thick sections was done throughout the lesion. No contrast medium was used. The window level and its width were set at -50 and 2000 HU in the mediastinal condition and at -700 and 1500 HU in the lung field condition, respectively. The CT scans were reviewed by a radiologist and six chest physicians. The radiographic features recorded were as follows; an irregular margin, spiculation, a convergence of the surrounding structures, pleural retraction, an air bronchogram, and the involvement of either the arteries or veins. These features have all been reported to be strongly related to malignancy [2,7,12,13]. Since the number of SPNs with a calcified shadow indicating benign lesion, was only 4 cases, this finding was not included in the present study. If the nodular edge was hazy or corrugated, then the nodule was considered to have an irregular margin. Since notching or lobulation was difficult to distinguish from an irregular margin, they were included in this finding. Spiculation was defined as the presence of tine linear strands less than 5 mm in length extending from the nodular margin into the lung parenchyma. Pleural retraction was defined as linear strands extending from the lesion to the pleura. Convergence was recorded if the lung parenchyma surrounding the nodule was closely packed in comparison with the area distant from the lesion, either with or without several lines of more than 5 mm in length radiating from the lesion. Zwirewich et al. [13] reported that the appearance of small cavitations within the nodular shadow were due to small, patent air-containing bronchi. Since we also confirmed this finding by a microscopic examination, the small cavitations within the nodule were considered to be an air bronchogram. The differences in the incidence of each finding between benign and malignant lesions were compared by the x*-test. When the P value did not exceed 0.05, the difference was considered to be significant.
3.Results 3.1. Ot~ferencesin the characteristics between benign and malignant SPNs
The radiographic features by HRCT are summarized in Fig. 1. An irregular margin (94% of cancer vs. 71% of non-cancer), spiculation (53% vs. 18%), the convergence of the surrounding structures (44% vs. 11%) and an air bronchogram (38% vs. Ilo/) were considered to be radiographic features that are significantly more often observed in malignant SPNs than in benign SPNs. Pleural retraction was observed in 39% of benign SPNs and 56% of malignant SPNs (P = 0.292).
108
N. Takaaeshi et al. /Lung Cheer 13 (1995) 105-112
Cancer
Non-cancer Irregular
margin
Spiculation Pleural retraction Convergence Air bronchogram
Involvement of artery Involvement
of vein
involvement of L 3 vessels
I 100%
0
.%
Fii. 1. The frequency of each finding suggesting malignancy. The P value between cancer and non-cancer is
Well-mod.
diff. adenoca.
Well-mod.
diff. adenoca.
Fig. 2. The frequency of each finding according to the histologic type. There were 19 well or moderately differentiated adenocarcinomas, 8 poorly differentiated adenocarcinomas, 4 squamous cell carcinomas, 12 tuberculoses, 5 pneumonias and 6 benign tumors.
N. Takanashi
el al. /Lung
Cancer
13 (1995)
105-112
109
There was no statistical difference in the frequency of the involvement of the artery and vein between malignant and benign lesions. However, malignant lesions tended to involve multiple vessels. When the SPNs were divided based on the involvement of more than 3 vessels, 38% of malignant SPNs possessed this finding. On the other hand, only 2 benign SPNs involved more than 3 vessels (P
Fig. 3. The radiographic features included (A) an irregular margin, spiculation, a pleural retraction, convergence, an air bronchogram and the involvement of vessels in one patient with moderately differentiated adenocarcinoma, (B) an irregular margin, pleural retraction, an air bronchogram and the involvement of vessels in one patient with scar tissue accompanying organized pneumonia, and an irregular margin, spiculation, a pleural retraction and the involvement of vessels in one patient with tuberculosis. Each pair of images belong to the same patient but are some distance apart.
II0
N. Takanashi
et al. /Lung
Cancer
13 (1995)
105-112
Table 2 Scores by histologic types Histologic types Cancer Adenocarcinoma (n = 27) Well-Moderately diff. (n = 19) Poorly diff. (n = 8) Squamous cell ca. (n = 4) Small cell ca. (n = I) Non-cancer Benign tumor (n = 6) Tuberculosis (n = 12) Pneumonia (n = 5) Others (n = 5)
Score 2.74 f 3.05 + 2.00 * 2.50 f 1.00
1.20 1.08 1.20 1.29
0.33 f 0.52 1.33 f 0.89 2.00 f 1.22 1.00 l 0.71
An air bronchogram was frequently found in either well or moderately differentiated adenocarcinoma (53%) and in pneumonia (40%) as compared to the other lesions. The involvement of more than three vessels was detected in 37% of well or moderately differentiated adenocarcinoma, in 38% of poorly differentiated adenocarcinoma and in 50% of squamous cell carcinoma, while no benign lesions and only one case of tuberculoma had this finding. Fig. 3 shows a representative radiogram of HRCT in cases of adenocarcinoma (A), pneumonia (B) and tuberculosis (C). Each lesion showed more than three findings.
3.3. Scoring
One point was given for each finding except pleural retraction whose frequency was not significantly different between the benign and malignant SPNs and the total scores of each histological type are summarized in Table 2. Malignant lesions showed the score of 2.66 while benign lesions had a score of 1.17. In malignant lesions, well or moderately differentiated adenocarcinoma (3.05) and squamous cell carcinoma (2.50) had a high score. In benign lesions, benign tumors and tuberculosis had a low score. However, pneumonia or organizing pneumonia showed a relatively high score (2.00) which is equal to the score of poorly differentiated adenocarcinoma. Fig. 4 shows the distribution of the scores for cancer and non-cancer patients. Eighteen of 32 (56%) malignant SPNs had a score of more than 3 points while only two of 28 benign SPNs (7%) showed such a score. Seven benign SPNs and one malignant SPN, which was poorly differentiated adenocarcinoma measuring 8 mm in the diameter demonstrated a score of 0. However, 19 benign and 13 malignant lesions overlapped with l-2 points. When the SPNs with a score of more than 3 points were regarded as malignant, the sensitivity and specificity in the diagnosis of malignancy were 53.1% and 92.6%, respectively.
N. Takanashi et al. /Lung Cancer 13 (1995) 105-112
Cancer
Non-cancer
(2.66k1.21)
(1.1720.98)
0 l ooooooo l ooooooeo
111
5 4 0 3 0 2 0000000
l ooooooe l eeee
1 000000000000 l
0 0000000
Fig. 4. The distribution of scores for each lesion. The numbers in parentheses are the mean f SD. of the total scores.
4. Discussion When an SPN is found, the most important point is whether or not the SPN possesses the possibility of malignancy. However, it is very diffkult to evaluate the radiographic features of SPN measuring less than 2 cm in greatest diameter by using either a conventional chest roentgenogram or CT. HRCT has been reported to reveal the detailed features of small lesions and the surrounding area 17,131. Therefore, HRCT is thought to be able to satisfactorily detect the radiographic features indicating malignancy, even in small sized SPNs. In the present study, we examined whether the incidence of six malignant radiographic features detected by HRCT differ between malignant and benign SPNs. These six radiographic features, which included an irregular margin, spiculation, convergence, a pleural retraction, an air bronchogram and the involvement of vessels, have been reported to be related to malignancy. According to the studies using HRCT on the malignant lesions, the incidence of an irregular margin is 73-lOtY?h [10,12,13], spiculation 78-100% [2,10,13], convergence 83% [2], pleural retraction 50-100% [2,10,13], an air bronchogram 31-67% [2,13] and the involvement of vessels 93-100% [4,9]. The incidences in the present study may thus seem to be low compared to the previous studies. This may be due to the fact that our subjects were limited to patients with an SPN measuring less than 2 cm in greatest diameter. Although we did not find any specific malignant features, the incidence of all the above features, except for pleural retraction in malignant SPNs, was observed significantly more often than that in benign SPNs. Especially, irregular margin, spiculation, convergence and an air bronchogram were most frequently found in either well or moderately differentiated adenocarcinoma. In our series, benign SPNs included various diseases. As shown in Fig. 2 and Table 2, the radiographic features of inflammatory lesions are closer to malignancy than
112
N. Takanashi et al. /Lung Cancer 13 (1995) 105-112
non-inflammatory lesions such as benign tumors. As expected, most inflammatory lesions had an irregular margin. Although the presence of an air bronchogram has been reported to be a relatively specific feature of adenocarcinoma [3,13], 44% of adenocarcinoma and 40% of pneumonia possessed this feature in the present study. However, we found that the number of air bronchograms within SPN differed between adenocarcinoma and inflammatory lesions. The majority of malignant SPNs had more than three air bronchograms within the SPN while most inflammatory lesions possessed only one or two air bronchograms (data not shown in the results). In order to compare malignant SPN with benign SPN, one point was given to each radiographic feature, except for pleural retraction, whose incidence was not significantly different between malignant and benign SPNs. Except for a case of poorly differentiated adenocarcinoma which lacked any features because of its small size, a score of 0 is considered to be benign lesion. When an SPN was classified by a score of three or less, the sensitivity and specificity in the diagnosis of malignancy was 56% and 93%, respectively. However, this sensitivity was still not satisfactory. Therefore, more sophisticated methods such as giving different points for each finding may be necessary to better differentiate between malignant and benign SPNs. Acknowkdgments
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