Evaluation of precision of guidance techniques in image guided fine needle aspiration cytology of thoracic mass lesions.

BACKGROUND: Transthoracic fine needle aspiration cytology (FNAC) is an established and safe technique for diagnosis of thoracic mass lesions. Computed tomography (CT) scan depicts clear anatomical details and provides access to any area of the body. It is, however, expensive and the needle is not passed in real time. Ultrasound is cheaper, radiation free, and allows real time monitoring. Its limitations are obscurement of lesions by aerated lung, smaller, deep seated, and cavitary lesions. AIMS: This study aims to compare sensitivity and specificity of CT scan and ultrasonography (USG) in thoracic FNAC.
MATERIALS AND METHODS: The study was conducted on patients who presented with thoracic mass lesions in lungs, mediastinum, hilar lymph nodes, thoracic vertebrae, paraspinal soft tissue, and pleura. One hundred and twenty patients were studied. Only those cases in which sonographic guidance was not possible were taken up for CT guided FNAC. The lesions were assigned to benign and malignant categories and into specific diagnoses where possible. Biopsy correlation was available in 113 cases. Patients were lost to follow-up in five lung and two mediastinal masses. STATISTICAL ANALYSIS: Statistical tests applied included diagnostic tests for sensitivity and specificity.
RESULTS: An accuracy of 70.8% was found for image guided FNACs with a sensitivity and specificity of 92.2% and 100%, respectively. CT had a sensitivity of 93.2% and specificity of 100%. For USG guidance, the same was 91.3% and 100%, respectively.
CONCLUSIONS: Precision of USG and CT scan is comparable for guidance in FNAC from thoracic mass lesions.

Introduction

Transthoracic fine needle aspiration cytology (FNAC) is an established and safe technique for diagnosis of thoracic mass lesions.[1] The imaging techniques used for percutaneous transthoracic FNAC include fluoroscopy,[23] ultrasonography,[4] and computed tomography (CT).[35-7] Sonography is used for guidance in pulmonary, pleural or mediastinal lesions in contact with the chest wall and CT for those not approachable by sonography. CT has, among its advantages, clear depiction of anatomical details and access to any area of the body. It, however, is expensive, takes longer to perform and involves radiation exposure. Also, the needle is not passed in real time. Ultrasound, on the other hand, is cheaper, radiation free, and allows sample collection under real time monitoring. The limitations of this modality are obscurement of lesions overlaid by aerated lung, smaller, deep seated, and cavitary lesions.

Materials and Methods

The study was conducted on 120 patients who presented with thoracic mass lesions located in lungs (98 cases), mediastinum (14 cases), hilar lymph nodes (4 cases), thoracic vertebrae (2 cases), paraspinal soft tissue and pleura (1 case each). Complete clinical history, examination and details of relevant investigations were obtained. The patient was evaluated for the suitable imaging technique for guided FNAC with initial evaluation for sonography guided FNAC. Only those cases in which sonographic guidance was not possible were taken up for CT guided FNAC.

The USG machine used was Siemens Sonoline Prima. The transducer (probe) used was convex 3.5 Mhz probe (for superficially placed structures, a linear 7.5 Mhz transducer was used). Hilar masses were evaluated by a 3.5 Mhz probe through the intercostal space ( the “window”).

CT was done on GE hi speed spiral CT scanner CTi. FNAC was carried out using the standard procedure with 23 gauge lumbar puncture needle.

Both air-dried and alcohol-fixed smears were prepared and stained by Leishman–Giemsa and Papanicolaou (PAP) stains, respectively. The lesions were broadly assigned to benign and malignant categories and further categorized into specific diagnoses where ever possible. Tissue was available for biopsy correlation in 113 patients. Patients were lost to follow-up in five lung and two mediastinal masses.

Statistical tests applied included diagnostic tests for sensitivity and specificity. Sensitivity and specificity were worked out with respect to the imaging technique used.

Results

The study included 98 cases of lung masses, 14 mediastinal masses, 4 hilar lymph nodes, 2 from thoracic vertebral lesions and one each from pleura and paraspinal mass. Biopsy correlation was not available in 7 lesions and 6 cases of TB lung. The former were excluded from the study. Response to treatment after 12 weeks was taken as confirmation of diagnosis in the latter.

There were 61 males and 52 females in the study group after exclusion of the seven patients in which follow-up was not available. The mean age of presentation with thoracic mass lesions was 52 (±15) years for males and 48 (±15) years for females. Malignant lesions predominated in both the sexes (females n=37, 71.2%; males n=49, 80.3%). Frequency and distribution of the lesions is depicted in [Table 1]. Most of the lesions were malignant (n=86, 76.1%; including two cases reported as suspicious on cytology which proved to be adenocarcinoma and small cell lung carcinoma (SCLC), respectively).

Table 1

Distribution of cases

Majority of the lesions were >5 cm in size (n=81; 71.7%).

Accuracy was worked out for all thoracic and lung lesions based on the ability of cytology to match the histological diagnosis. Only those cases were considered a match where the cytological diagnosis agreed with the histological typing. For calculation of sensitivity and specificity, the ability to distinguish benign from malignant was considered a match. An overall accuracy of 70.8% was found for all the image guided thoracic FNACs with a sensitivity of 92.2% and a specificity of 100%. For lung lesions, accuracy of diagnosis was 69.6% with a sensitivity and specificity of 92.2% and 100%, respectively. The same for CT guidance and USG guidance is as per [Table 2]. The accuracy for lung tumors was 68.8% with a sensitivity and specificity of 92.2% and 100%, respectively. The figures for non small cell lung carcinoma (NSCLC), SCLC and miscellaneous tumors of the lung (encompassing metastatic deposits, non Hodgkin's lymphoma (NHL), pulmonary blastoma, hamartoma, lung carcinoid and plasmacytoma) are as in [Table 2].

Table 2

Comparison of sensitivity and specificity of imaging techniques

Among the lung lesions, we had 25% (n=23) cases of adenocarcinoma followed by 20.7% (n=19) of squamous cell carcinoma. There were 10.9% (n=10) cases of poorly differentiated carcinoma, 7.6% (n=07) of non small cell carcinoma, 5.4% (n=05) of small cell carcinoma and 3.3% (n=03) metastatic deposits. We also had one case (1.1%) each of pulmonary blastoma [Figure 1], large cell anaplastic carcinoma, plasmacytoma, and malignant round cell tumor. In the benign group, we had 08 (8.7%) granulomatous lesions reported as tuberculosis, 05 (5.4%) reported as inflammatory lesions, and 02 (2.2%) hydatid cysts. Four (4.3%) cases were reported as inconclusive/necrotic material only. Two (2.2%) cases were reported as suspicious.

Figure 1

Pulmonary blastoma. Blastemal cells forming tubular structures (Leishman, ×400)

Out of 13 mediastinal lesions, malignant round cell tumor was the predominant diagnosis (03 cases). There were two cases of seminoma and non Hodgkin's lymphoma. One case each of immature teratoma, malignant thymoma, benign spindle cell lesion, thymoma [Figure 2], ganglioneuroma [Figure 3], and tuberculosis were recorded.

Figure 2

Thymoma. Bland, oval cells with admixed lymphoid cells (Leishman, ×400)

Figure 3

Ganglioneuroma. Ganglion cells with abundant cytoplasm and eccentric nuclei admixed with bland spindle shaped nuclei (Leishman, ×400)

There were four patients with hilar lymphadenopathy. On aspiration, we had one case each of malignant round cell tumor, NHL, microfilaria, and tuberculous lymphadenitis.

The two thoracic vertebral masses aspirated proved to be metastatic deposit from carcinoma prostate and plasmacytoma, respectively.

We had one paraspinal soft tissue lesion, proven to be tuberculous on cytology and one pleural mass which yielded no diagnostic material on aspiration.

Histo-cytopathological correlation of lung lesions revealed a concordant diagnosis in 63 cases (68.5%). Out of the four inconclusive cytological diagnoses, one each turned out to be a hamartoma, carcinoid, aspergillosis, and small cell carcinoma. The five inflammatory diagnoses proved to be tuberculosis (02 cases), aspergillosis and small cell carcinoma (01 case). Most of the seven non small cell carcinomas were adenocarcinomas on histology (n=06; 85.7%) and one (14.3%) was squamous cell carcinoma. Similarly, out of 10 cases of poorly differentiated carcinoma, 5 (50%) were adenocarcinomas; three (30%) small cell carcinomas; and one (10%) squamous cell carcinoma. The single malignant round cell tumor reported was a non Hodgkin's lymphoma on histology. Out of the two suspicious cases, one was an adenocarcinoma and one a small cell lung carcinoma.

Among the mediastinal masses, three (23.1%) cases were reported as malignant round cell tumors, two out of which turned out to be non Hodgkin's lymphomas and one was a neuroblastoma.

There was a 75% concordance in diagnosis on histo-cytological correlation in aspiration cytology from hilar lymph nodes. Single case was reported as malignant round cell tumor. It was proved to be a NHL.

Hundred percent concordances in cyto-histological correlation in the two thoracic vertebral and single paraspinal lesions were found. The aspiration cytology from pleural mass which was inconclusive was proven to be malignant mesothelioma on histopathology.

Discussion

Majority of the cases in this study were from lung (n=92; 81.4%) with a male predominance. The mean age of presentation was 52 (±15) years. Preponderance of lung lesions has been seen in thoracic masses in other studies on guided FNACs ranging from 64.7% to 94.7%.[8-10] Male predominance has been seen in other studies ranging from 52% to 79% with the mean age of presentation between 56 to 57 years.[89]

The incidence of malignancy in our study was 76.1% with most lesions being >5 cm in size. Malignancies have been found to range from 69.5% to 96.5% in the published literature.[8-10]

An accuracy of 70.8% was found for the entire image guided thoracic FNACs with a sensitivity of 92.2% and a specificity of 100%. CT guided lesions had a diagnostic sensitivity of 93.2% and specificity of 100%. For USG guidance, the same was 91.3% and 100%, respectively. Among CT guided lesions, accuracy of diagnosis in other studies ranges from 82% to 85.3%.[911] Sensitivity has been found to be in the range of 88% to 97.71% and specificity from 84 to 100%[91112] for the same. Sensitivity and specificity for malignant lesions has been found to be 91.2% and 100%, respectively, and for benign ones to be 68% and 100%, respectively by Nahar Begum et al.[13]

Accuracy of diagnosis of lung lesions was 69.6% for both the techniques put together with a combined sensitivity and specificity of 92.2 and 100%, respectively. Accuracy for diagnosis of non small cell lung cancers was 86.2% and for small cell carcinoma was 45.5%, respectively, with diagnostic sensitivity being 98.3% and 72.7%, respectively, for the two. This was probably due to occurrence of tumor necrosis more frequently in small cell lung cancers than non small cell ones. Literature reveals accuracy of guided FNACs being influenced by their size and length of the path traversed by needle.[9] Diagnostic accuracy for CT guided FNACs in literature ranges from 77.2% to 95%[14-17] with the sensitivity ranging from 83% to 88%[1516] and specificity approaching 100%.[16]

Among the lung lesions, we had 25% (n=23) cases of adenocarcinoma, followed by 20.7% (n=19) of squamous cell carcinoma. Preponderance of adenocarcinoma over other lesions has been seen in some studies[1317] and that of squamous cell carcinoma in others.[1618]

Out of thirteen mediastinal lesions, malignant round cell tumor was the predominant diagnosis (n=03; 23.1%) followed by two cases (15.4%) each of seminoma and non Hodgkin's lymphoma. Two of the cases reported as malignant round cell tumor were also found to be malignant lymphoma on histopathological examination. In literature, malignant lymphoma has been found to be the most common mass lesion in mediastinum.[19]

Of the four patients with hilar lymphadenopathy, there was one case each of malignant round cell tumor (proved to be NHL on histopathology subsequently), NHL, microfilaria, and tuberculous lymphadenitis.

There were two thoracic vertebral masses aspirated which proved to be metastatic deposit from carcinoma prostate and plasmacytoma, respectively, and one paraspinal soft tissue lesion, which was found to be to be tuberculous on cytology. Caries spine has been reported to be the most common lesion in vertebral masses.[20]

Conclusions

Precision of USG and CT scan is comparable for guidance in FNAC from thoracic mass lesions. USG can, therefore, be used as first line modality in far flung areas where CT scan is not available and when cost constraints are present. Limitations of USG include lesions in contact with chest wall with no aerated lung in between. The advantages of USG include real time monitoring and low cost.