Aspiration biopsy of intrathoracic lesions

Aspiration biopsy of intrathoracic lesions

;URREN DIAGNOSTIC PATHOLOGY Mini-symposium: fine needle aspiration biopsy Aspiration biopsy of intrathoracic lesions W. Olszewski INTRODUCTION How...

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;URREN DIAGNOSTIC PATHOLOGY Mini-symposium: fine needle aspiration biopsy

Aspiration biopsy of intrathoracic lesions

W. Olszewski

INTRODUCTION

However, in the thorax and especially with mediastinal masses, the procedure requires an experienced aspirator and special imaging modalities for guidance. The majority of tumours, particularly peripherally located lung lesions, regardless of their size and location, can be aspirated successfully under biplane fluoroscopy. The advantages of FNA biopsy under fluoroscopy guidance, which is widely available, are that it is easier, faster and less expensive than using computed tomography (CT). Mediastinal lesions, hilar masses and small peripheral lung tumours, especially in paravertebral locations can be safely and adequately aspirated with CT-guidance. Ultrasonography (US) can also be used for monitoring FNA biopsy mainly for the suprasternal and parasternal approach to the anterior and superior mediastinum. 2 This technique also allows aspiration of subpleural lung tumours. Transbronchial FNA biopsy is done mostly for hilar tumours in cases with central lesions and negative bronchoscopy or for hilar or peribronchial lymph nodes for staging of lung carcinoma.

Of all the anatomical locations, intrathoracic tumours are probably lesions in which fine needle aspiration (FNA) biopsy combined with modern imaging modalities has the greatest impact on patient management. The main indication for FNA biopsy of intrathoracic lesions is to investigate the nature of a mass, or masses, of unknown origin or to confirm suspected malignancy. From a practical point of view this procedure allows: 1. Separation of non-surgical from surgical cases. 2. Separation of neoplastic from non-neoplastic lesions. 3. Classification of tumours (evaluation of histologic type of turnout). 4. Staging of primary lung carcinoma and assessment of resectability. 5. Identification of residual or recurrent tumours, or relapse following therapy. There are several contraindications for FNA biopsy of intrathoracic tumours, but most are relative. The following contraindications should be considered and the risk of biopsy must be weighed against the diagnostic benefits: haemorrhagic diathesis, anticoagulant therapy, severe pulmonary hypertension, uncontrolled cough and advanced emphysema. However, some authors suggest the only absolute contraindications for FNA biopsy are an uncooperative patient and a suspected hydatid cyst. 1

Complications The most common complication following transthoracic FNA biopsy is pneumothorax, with a reported frequency in the literature from a few to over 50% but with only a small fraction of cases requiring insertion of a drain. Minor haemoptysis is also reported in most studies. Air embolism is a very rare complication. Only a few well documented cases of neoplastic seeding of the needle tract have been reported with fine needle technique. For review see Weisbrod, 2 Koss et al3 and Young. 4 The percentages of these complications, especially pneumothorax, is lower for transbronchial than for transthoracic aspiration biopsy.

THE TECHNIQUE OF FINE NEEDLE ASPIRATION BIOPSY Generally the technique of FNA biopsy is similar to that used for tumours or masses in other anatomical locations.

Professor W. Olszewski, D e p a r t m e n t o f Pathology, Institute of O n c o l o g y , W a r s z a w a , Poland Current Diagnostic Pathology (1995) 2, 146-152

9 1995 Pearson ProfessionalLtd

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LUNG The recognition of the benign or malignant nature of a lesion and establishing the histologic type of malignancy are essential steps in planning further management of the patient with a lung tumour. Besides tissue biopsy, done at the time of bronchoscopy, several different types of cytology specimens may be useful in the microscopic evaluation of lung pathology: these are sputum cytology, and bronchial brushings and washings. In advanced malignant tumour, evaluation of pleural effusion should also be considered as a proper initial step in an evaluation of a case. It is worth stressing, that the diagnostic efficiency and sensitivity of these methods differ significantly depending on the location and nature of the tumour. Evaluation of these types of cytologic specimen allows the correct microscopic diagnosis to be established in most centrally located primary lung carcinoma (e.g. arising from main bronchus) and numerous intermediately located lesions. However, with peripherally located primary carcinomas and metastatic lesions these techniques for collecting material for cytologic evaluation fail in the majority of patients. Thus, for peripherally located primary tumours and for metastatic lesions of the lung, transthoracic FNA biopsy is the method of choice; it allows for a fast, safe, and reliable cytologic evaluation which may reveal not only the malignant or benign character of a turnout, but often also allows accurate histologic typing of the neoplasm befk)re thoracotomy.

Lung carcinoma Aspirates of hmg carcinomas, are usually cellular yielding sufficient numbers of turnout cells for a definite microscopic diagnosis of malignancy. Tunlour cells with varieties of morphological features appear in sheets, clusters, groups or singly. The cellularity of smears, proportion of cells in aggregates versus isolated cells and the morphology of tumour cells are determined by the histological type of lung carcinoma. Smears usually contain some macrophages and a variable number of inflammatory cells. According to the World Health Organisation, (WHO) classification, lung carcinomas can be classified into four main categories: adenocarcinoma, epidermoid carcinoma, large cell anaplastic and small cell carcinoma. There are several subtypes and what is very important for the precise typing of lung carcinomas is that some turnouts are heterogeneous and present difficulty as far as the histologic type is concern. Cytopathology of the main histologic types of lung carcinoma will be b r i e f y presented. For details concerning cytopathology of lung carcinomas see Koss et al, 3 Young 4 and Tao. 5

Adenocarcinoma Tumour cells appear mostly in sheets and clusters. Cohesive papillary or monolayer aggregates are present. The tumour cells are cuboidal or columnar with eccentric, pale, often vesicular nuclei. Nucleoli are prominent and

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frequently multiple. This histologic type of lung carcinoma often presents as a peripheral tumour; it clearly needs to be differentiated from metastatic adenocarcinoma, especially gastrointestinal carcinoma, on cytological (and radiological) examination.

Epidermoid carcinoma The microscopic features of aspirates of this histologic type of lung carcinoma depend largely on the stage of differentiation of the tumour cells. Microscopic presentation of well differentiated (keratinizing) epidermoid carcinoma is similar to that seen in sputum or bronchial brushings, isolated tumour cells of various shapes, often elongated with dense, eosinophilic cytoplasm, are characteristic of this tumour. However, it should be pointed out that small groups or clusters of tumour cells with vesicular nuclei and conspicuous nucleoli are also frequently present. Less well differentiated epidermoid carcinomas often contain numerous such groups of cells in aspirates, a finding which should not lead to the conclusion that the malignant cells represent an adenocarcinoma. The cytologic features of poorly differentiated adenocarcinoma and epidermoid carcinoma may overlap making impossible correct histologic typing of tumours on FNA. Large cell carcinoma Aspirates are usually highly cellular and contain large cancer cells appearing singly or in small groups. Necrotic cells are common. This histologic type is recognized, as in tissue sections, mostly by the absence of characteristic features for adenocarcinoma or epidermoid carcinoma, and by the large size and pleomorphism of its inalignant cells. Small cell carcinoma The Inost characteristic features seen in FNA of this histologic type of lung cancer are the marked cellularity of the smears and diffuse dispersion of tumour cells. The cytoplasm of tumour cells is very scanty, ill-defined and numerous nuclei are completely stripped of cytoplasm. As a rule, smears contain two types of nuclei: larger and

Fig. 1--FNA of small cell carcinoma of lung. The smear is cellular and shows either numerous almost totally dispersed tumour cells with scanty cytoplasm or cells appearing as naked nuclei. Note also the presence of t w o types of nuclei: large nuclei with coarsely granular chromatin and smaller pyknotic nuclei. H&E.

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well-preserved nuclei with coarsely granular evenly distributed chromatin and smaller, darker pyknotic nuclei (Fig. 1). Due to the fragility of tumour cells, crushed nuclei in the form of haematoxylin-stained streaks are often seen. This microscopic feature is characteristic for the oat cell subtype of small cell carcinoma. Aspirates of the intermediate cell subtype of this tumour contain cells with larger nuclei, not uncommonly with small nucleoli and more abundant cytoplasm. Subtyping of small cell carcinoma on fine needle aspirates is difficult. At present, in considering the protocol for staging and treatment of lung cancer, the most important task for the pathologist is to recognize carcinoma of the lung and to separate small cell carcinoma from non-small cell tumours (adenocarcinoma, epidermoid carcinoma and large cell carcinoma). My experience as well as some other published results 6 indicate that in most cases already established cytologic diagnostic criteria allow confident separation of small cell carcinoma from other histologic types of lung carcinoma. Of course, as with small surgical pre-operative biopsies, there may be tumour heterogeneity and therefore a mixed histologic type cannot be excluded.

Metastatic tumours Peripheral, well-defined lung mmours, especially when multiple, are clinically and/or radiologically suspicious of metastatic disease. The task of recognising the metastatic/secondary nature of the lung lesions is not so difficult when dealing with a patient with a known history of malignancy. It is also made easier if the cytologic features of the FNA specimen can be compared and correlated with the histology or cytology of the primary tumour. Some metastatic turnouts have more or less characteristic microscopic features like breast carcinoma, malignant melanoma or spindle cell sarcomas, all of which can be differentiated from primary lung lesions. However, in dealing with metastatic epidermoid carcinoma in a patient with a history of, for example, uterine, cervical or laryngeal carcinoma, it is often impossible to tell if it is primary or secondary lung tumour of that histologic type. In such circumstances the clinical setting should be taken into consideration before the final cytologic diagnosis is made.

Benign lesions The absence of malignant cells in desquamative cytology specimens (sputum, bronchial washings) does not exclude malignancy; nor does it allow a specific diagnosis of a benign tumour to be made. FNA biopsy on the other hand makes it possible in some cases to establish the firm microscopic diagnosis of a benign lesion and even to recognise the histologic type of benign tumour. These are most commonly hamartomas or tuberculomas. Hamartoma

This is the most common primary, benign tumour of the

lung which may radiologically mimic carcinoma and should be diagnosed microscopically. The FNA cytologic features are characterized by the presence of an admixture of epithelial and mesenchymal tissue. In addition to sheets of regularly arranged, benign epithelial cells, fragments of fibromyxoid tissue and cartilage are seen. The background of the smears is usually clean without evidence of necrosis or inflammation. The importance of cytologic diagnosis of hamartoma is not only the confirmation that the enucleation of the tumour will be an adequate surgical procedure but also that in some cases thoracotomy may be obviated. Tuberculoma

Tuberculous lesions that must be differentiated from carcinoma are tuberculomas which appear as a round, circumscribed peripheral lung nodule. Aspirates are characterized by the presence of necrotic debris and inflammatory cells: lymphocytes, epithelioid cells and multinucleated giant cells. In most cases smears contain only necrotic material and carrot-shaped epithelioid cells. The microscopic, morphologic features of necrosis in tuberculosis are different from that seen in turnout necrosis which, even in the absence of viable cells, usually allows the distinction to be made between tuberculosis and cancer. Since not only tuberculosis, but other granulomatous infections may be a source of similar cytologic features in FNA, bacteriological study of aspirates should be a routine part of the diagnostic protocol.

Management As mentioned above, the management of the patients with lung tumours has changed significantly since the introduction of FNA biopsy as the routine method for diagnosis of lung and hilar lesions. The guidelines for the management of the patients with lung tumours are presented in Figure 2. The suggested indications for further diagnosis or treatment based on the results of FNA biopsy are as follows: 1. Established cytodiagnostic criteria for evaluation of fine needle aspirates avoid false positive diagnoses in most cases. 2. Separation of small cell carcinoma from non-small cell carcinomas. 3. Some benign lesions like hamartoma or tuberculoma can be correctly diagnosed on fine needle aspirates. 4. FNA technique (transthoracic or transbronchial FNA) allows for the staging of some tumours; for example, hilar and mediastinal masses. A cytologic diagnosis of small cell carcinoma is the basis for chemo- and radiotherapy. Recognition of nonsmall cell tumour requires further investigation for staging and assessment of resectability of the turnout. When the firm diagnosis of a benign tumour is made, thoracotomy and surgical resection may be avoided. Mostly due to the sampling errors, false negative diagnoses cannot be avoided. Negative cytologic diagnosis

ASPIRATION BIOPSY OF INTRATHORACICLESIONS

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TUMOUR OF THE LUNG MANAGEMENT

//

Malignant

/

Benign Negative

cytology

Radiochemotherapy

/

Surgical biopsy

Surgery

Surgery Radiochemotherapy

Fig. 2--The management guideline for the patient with lung tumour considering cytologic diagnoses done on FNA biopsy (see text).

when in disagreement with clinical and/or radiological data should prompt thoracotomy and histologic diagnosis. SPACE OCCUPYING LESIONS OF THE

MEDIASTINUM A knowledge of anatomy, radiologic data and pathology are essential in the evaluation of mediastinal aspirates since there is a predilection of certain turnouts to localize in a particular mediastinal compartntent: for example, thymomas are localized primarily in the superior and anterior mediastinum, while neurogenic tumours occur almost exclusively in the posterior mediastinum. It should be pointed out that among malignant tumours, metastatic carcinomas are much more common than primary malignant tumours of mediastinum. The Table presents details concerning the usual localization of space-occupying lesions of the mediastinum.

Table--Space-occupying lesions of the mediastinum Anterior

Middle

Thymoma Thymic lymphomas Germ cell tumours

Tuberculosis Neurogenic turnouts Sarcoidosis Meningioma Hyperplastic lymph nodes Lymphomas Metastatic carcinomas Congenitalcysts

Malignant teratoma Benign teratoma Rare thymic tumours cclrc inomas can'inoid

Metastatic carcinomas Substernal thyroid Congenital cysts Modified from Koss et al 1992.

Posterior

Anterior mediastinum Inflammation

Acute or subacute inflammatory conditions of the mediastinum, due to their rather characteristic clinical features, are practically never targets of FNA biopsy. On the other hand, chronic mediastinitis may radiologically simulate neoplastic growth. While the value of FNA is limited due to extensive fibrosis and consequently scanty cellular aspirates, occasionally, when dealing with more cellular samples, the inflammatory nature of a mass may be confirmed. Cysts

Different types of mediastinal cysts may be aspirated successfully. Most of these cysts are of bronchial, pericardial or enteric origin. Aspirates usually contain clear fluid and scanty numbers of cells, or are acellular. However, the combination of the cytologic findings together with radiological data allows confirmation of the benign nature of the lesion. Congenital cysts should be differentiated from numerous pathologic conditions seen in the mediastinum which may appear as cystic lesions; for example, thymomas or teratomas. Repeated F N A biopsy from the periphery of the mass may allow adequate material to be obtained to establish microscopic diagnosis. Thymomas

These tumours, which arise from the epithelial component of thymus, consist of epithelial and lymphocytic components. Depending on the proportion of these two cell types, thymomas are classified as predominantly epithelial, mixed or lymphocytic types. This classification does not predict clinical behaviour of the tumour. A

150 CURRENTDIAGNOSTICPATHOLOGY new classification, based on immunophenotyping of cells, has been recently proposed. The epithelial cells present a rather monotonous appearance with occasional differences in size and shape of cells and nuclei. However, there is no correlation between these microscopic features and clinical behaviour. The only reliable criteria of malignancy is infiltration of surrounding structures by neoplastic cells or rarely the existence of distant metastases, criteria which cannot be assessed by FNA. Cytopathology

In keeping with the histologic pattern of these tumours, the aspirates of thymomas are composed of a mixture of epithelial and lymphoid cells. Depending on the histologic subtype of the tumour, the epithelial cells or the lymphocytes may dominate the cytologic picture. The most characteristic cytologic feature of thymoma in FNA is the presence of epithelial cells intermingled with lymphocytes (Fig. 3). The epithelial cells have uniform, regular nuclei with a fine granular, evenly distributed chromatin pattern and smooth, regular outline. Small, inconspicuous nucleoli are present. The cytoplasm is usually scanty and ill-defined. However, it should be stressed that the epithelial cells in aspirates of thymomas, not uncommonly present irregularity in size and shape of cells and nuclei. Occasionally coarsely granular chromatin with clumping may be seen. Epithelial cells often appear in small or large tightly knit clusters but small, loosely arranged groups of epithelial cells are also present (Fig. 3). The groups or clusters of epithelial cells in the background of numerous lymphoid cells can be misleading and result in the false positive diagnosis of metastatic carcinoma. In addition, Hassall's corpuscles of the thymus trapped within the neoplasm may, because of their characteristic tightly cohesive whorls of keratinized cells, be misdiagnosed as metastatic keratinizing epidermold carcinoma. In such circumstances, even immunocytochemistry may be misleading, since both epithelial cells of thymomas and Hassall's corpuscles are keratin positive. For the correct diagnosis of the thymoma, the full knowledge of clinical and/or radiological data can

Fig. 3 I F N A of thyrnoma localized in anterior mediastinum. The smear consists of loosely arranged sheets of benign epithelial cell and lymphocytes. Notice the close relation between these two types of cells. H&E.

not be overestimated. It should also be stressed that besides metastatic carcinoma or very rarely primary carcinoma, lymphomas, especially of the non-Hodgkin types, also need to be considered in the differential diagnosis when dealing with aspirates of the anterior mediastinum. This latter consideration is especially true of FNA of the lymphocytic predominant type of thymoma, which may contain almost exclusively lymphoid cells. However, a non-monotonous cytologic picture of lymphoid cells is against the diagnosis of lymphoma and a few groups of epithelial cells are nearly always found. As mentioned above, lymphocytes are always present in aspirates of thymomas and their proportion is in inverse ratio to the epithelial cells. The lymphoid cells are dispersed in the background or in intimate relation with epithelial cells in groups or clusters (Fig. 3). Germ cell turnouts

Various types of primary germ cell tumours can be found in the mediastinum, especially in the anterior mediastinal compartment. It should, however, be remembered that germ cell tumours can be metastatic to mediastinal lymph nodes. The most common primary germ cell tumours are teratoma (benign or malignant), seminoma and embryonal carcinoma. Their FNA cytologic features have been fully documented in FNA biopsy of mediastinal masses. 7 Teratomas. The cytologic features of teratoma vary from case to case and from aspirate to aspirate due to the heterogeneity of tumours. Therefore~ sampling error must always be taken into consideration especially in making the diagnosis of a benign teratoma. Aspirates differ greatly in cellular yield, but generally numerous types of the epithelial cells are present. While benign squamous cells may be seen as well as viable cells with vesicular nuclei, more frequently epithelial cells are present either as pyknotic nuclei or as keratinizing anucleated squames. Epithelial cells of glandular types of bronchial or intestinal type are also often present (Fig. 4). Fragments of mesenchymal tissue are seen

Fig. 4~FNA of a mediastinal mature teratoma. In this example there are large sheets of benign glandular cells of intestinal origin. H&E.

ASPIRATIONBIOPSYOF INTRATHORACICLESIONS 151 lesion in the mediastinum, especially in the superior compartment. Any benign o~ malignant pathologic conditions can arise from the thyroid tissue in that location. The abnormality most often encountered is nodular goitre which is usually a retrosternal extension of a lesion of the neck. The cytologic feature of such a lesion is identical to that seen in cervical goitre. 3 Cytologically different tumours arising from an ectopic mediastinal thyroid have been described] Middle mediastinum

Fig. 5--FNA of a malignant mediastinal teratoma, consisting of necrotic tumour cells which are characteristic of a poorly differentiated epidermoid carcinoma. H&E.

but not as frequently as would be expected from the histological pattern of most benign teratomas. Malignant teratoma can also be diagnosed cytologically. The most common type of malignant tumour arising in a teratoma is an epidermoid carcinoma (Fig. 5). Since only a part of the tumour may be composed of malignant growth the possibility of a false negative diagnoses due to sampling error should always be kept in mind.

Seminoma. The cytologic features of seminoma are identical to that seen in aspirates of tcsticular seminomas) Smears contain dispersed rather monotonous populations of tumour cells. The tumour cells have round or oval nuclei with finely granular chromatin and conspicuous nucleoli. Cytoplasm is usually scanty but the identificalion of glycogen helps to differentiate the seminomas from lymphoma cells. It is worth emphasizing that when aspirates of mediastinal masses contain granulomatous tissue elements consisting of lymphocytes, epithelioid cells and multinucleated giant cells, the possibility of seminoma should always be considered in the differential diagnosis in addition to inflammatory diseases of lymph nodes such as tuberculosis. Embryonal carcinoma. Since these tumours are often part of mixed germ cell tumour, the aspirates may show features of carcinoma, most commonly of adenocarcinoma type. The characteristic turnout cells have vesicular, irregular nuclei and often prominent nucleoli and either form groups or clusters or appear singly. The presence of such cells in a young person, usually male, without clinical evidence or a history of adenocarcinoma elsewhere, should always raise the possibility of embryonal carcinoma or mixed germ cell tumour. In such circumstances evaluation of tumour markers in serum or in aspirates, especially alpha fetoprotein (AFP) and human chorionic gonadotrophin (HCG), may be of great diagnostic value. 8 Substernal thyroid Ectopic thyroid may be the origin of a space-occupying

L ymt) homas Both Hodgkin's and non-Hodgkin's lymphomas may present in the mediastinum either as the primary location or as part of a generalized disease involving thymus and/or lymph nodes. While the microscopic features of lymphomas in FNA are similar to those seen in FNA obtained from peripheral lymph nodes, 3 certain types or subtypes of lymphoma occur more frequently in the mediastinum. For example, the most frequent subtype of Hodgkin's disease involving the mediastinum is nodular sclerosis. It should be stressed that the FNA cytological diagnosis of Hodgkin's disease is very difficult; indeed it is the most frequent source of false negative diagnoses due to the sampling errors. FNA smears of non-Hodgkin lymphoma are less challenging; they are characterized by a monotonous population of totally dispersed lymphoid cells in different stages of maturation. The most common types of nonHodgkin's lymphoma presenting in the mediastinum are the T-lymphoblastic lymphomas consisting usually of convoluted cells and the centroblastic lymphomas of B-cell origin. h!flammato~ T conditions q/'mediasti,al lynq)/z nodex Enlarged mediastinal lymph nodes are not uncommonly targets of FNA biopsy, either for confirmation of their granulomatous nature (tuberculosis, sarcoidosis) or as a staging procedure in patients with lung tumours. The cytologic features of these conditions are well described by Koss et al. 3 Metastatic tumours Metastatic carcinomas are by far the most common malignant neoplasms of the mediastinum, mainly in the middle compartment. However, all other anatomical areas of the mediastinum may be involved in advanced stages of malignancy. The most frequent metastatic mediastinal turnouts are of lung origin and any histologic type of lung cancer can spread to the mediastinum. Small cell carcinoma of the lung is the histologic type which most often, clinically and radiologically, needs to be differentiated from a primary turnout of the mediastinum. Not uncommonly the primary tumour is not seen on the chest X-ray and the patient with such a lesion presents with a mediastinal tumour of unknown origin. Aspirates from such lesions, like those primary small cell carcinomas of the lung (see above), are highly cellular and yield numerous small diffusely dispersed

152 CURRENT DIAGNOSTIC PATHOLOGY tumour cells with scanty cytoplasm. Such microscopic features must be differentiated from primary non-Hodgkin l y m p h o m a of the mediastinum. The presence of small, tight groups or clusters of tumour cells - some with pyknotic nuclei - favours a diagnosis of small cell anaplastic carcinoma. While immunohistochemistry may be very helpful in the differential diagnosis, since antibody panels can confirm the epithelial nature of a tumour (keratin-positive, leucocyte common antigen-negative), immunostaining will not distinguish between epithelial metastatic carcinoma and a primary carcinoma of that histological type arising from the thymus. Mediastinal metastases of non-small cell lung carcinomas do not create such diagnostic problems. Aspirates of secondary large cell anaplastic carcinoma - as with aspirates o f a primary focus in lung - are usually characterized by the presence of large numbers of necrotic cells. With prior knowledge of a primary tumour of the lung, confirmation of mediastinal metastases is usually an easy task. However, suspected metastatic epidermoid carcinoma must be differentiated from a primary thymic carcinoma of that histologic type. Likewise, metastatic adenocarcinoma must be differentiated from some primary mediastinal germ cell tumours. The second common source of mediastinal metastases is breast cancer. As a rule the primary focus is known at the time of mediastinal F N A biopsy; recognition of the nature of the metastatic lesion is not difficult providing there is an awareness of the characteristic features of primary and/or metastatic breast cancer. Tumour cells appear mostly in small groups with rather well defined and preserved cytoplasm and often have characteristic intracytoplasmic vacuoles.

Posterior mediastinal Neurogenic tumours These tumours occur almost exclusively in the posterior mediastinum and are the most c o m m o n tumours in that location. There are two main groups: tumours of the sympathetic nervous system such as neuroblastoma and ganglioneuroblastoma in children, and tumours of the peripheral nerve sheathe like neurofibroma, neuri lemmom a or malignant schwannoma which occur in adults. Neurilemmoma is the most c o m m o n of these and on F N A are rather scantily cellular, yielding tightly packed clusters of elongated cells with spindled nuclei. This feature allows the diagnosis of a benign tumour o f mesen-

chymal tissue. The presence of large groups of cells with nuclear palisading enables classification of such lesions as of neurogenic origin.

CONCLUSION M y e x p e r i e n c e ] as well as that of others 3-5'7 indicates that intrathoracic F N A biopsy is a valuable method in the evaluation of intrathoracic masses. If proper use is made of modern imaging modalities such as CT and US in the performance of guided F N A biopsy, the material for cytologic evaluation can be safely aspirated anywhere in the lung or the mediastinum. Due to already established progress in clinical cytology, cytodiagnostic criteria for F N A allows not only accurate diagnosis of the malignant nature of the lesion but also, in the vast majority of cases, the ability to accurately evaluate the histologic type of the turnout, and false positive diagnoses can be avoided? ,6 Prior knowledge of the clinical and radiological data is very important and will prevent false negative diagnoses as a result of sampling errors. It follows, that the proper use of F N A requires very close cooperation between clinicians, radiologists and pathologists. Furthermore, F N A biopsy allows improved management of patients with intrathoracic masses and as such should be considered as a fast, cost effective, safe, reliable method for the diagnosis of the patients with intrathoracic lesions.

References 1. Weisbrod G L. Transthoracic needle biopsy. World J Surg 1993; 17:705-711. 2. Werneke K. Percutaneous biopsy of mediastinal turnouts under sonographic guidance. Thorax 1991; 6: 157-159. 3. Koss L G, Woyke S, Olszewski W. Aspiration biopsy: cytologic interpretation and histologic basses. New York: Igaku Shoin, 1992. 4. Young J A. Lung, pleura and chest wall in fine needle aspiration cytopathology Young J A, ed. London: Blackwell Scientific Publication, 1993: 97-121. 5. Tao L C. Lung, pleura and mediastinum. New York: Igaku Shoin, 1988. 6. Di Binito K, Colautti I, Patriarca S, Falconieri G, Barbazza R, Vielh P. Cytologic typing of primary lung cancer: study of 100 cases with autopsy confirmation. Diagn Cytopathol 199l; 7: 7-10. 7, Olszewski W. Mediastinum in fine needle aspiration cytopathology. Young J A, ed. London: Blackwell Scientific Publication, 1993; 122-133. 8. Sangalio G, Livirghi T, Grordano F, Ravani E, Schaffino E. Primary mediastinal embryonal carcinoma and chorion carcinoma. Acta Cytol 1986; 30: 543-546.