Diagnostic pitfalls in fine needle aspiration of solitary pulmonary nodules: two cases with radio-cyto-histological correlation

Fine needle aspiration is an important tool used in the preoperative evaluation of solitary nodules of the lung. It provides a definitive diagnosis in most patients at low cost with minimal trauma. Modern imaging techniques with experienced personnel, often results in a fine needle aspirate of the solitary pulmonary nodule under investigation. False positive errors in this situation are therefore uncommon. However, procedural related contamination, the presentation of the cells in a more distorted and incomplete tissue structure than histological slide and interpretative errors by the cytopathologist, all can lead to false positive results. Prior detailed clinical knowledge about the patient, procedures and methods of radiology in obtaining the aspirate specimen is extremely useful in the accurate interpretation of fine needle cytological specimens.

Solitary pulmonary nodules are characterized as opacities of the lung surrounded by parenchyma without atelectasis and adenopathy most of which are discovered on routine chest x-rays in an asymptomatic individuals. 50% of solitary lung nodules are malignant. Only less than 5% of all primary lung neoplasms are benign, most of which are hamartomas. So when a clinician suspects a neoplastic lesion it is highly probable to be malignant. [1] Since prompt management of malignant solitary pulmonary nodules presenting at stage 1 (T1, N0, M0) could have 5 year survival rate up to 80%, [2] early diagnosis is extremely important.

Percutaneous transthoracic needle biopsy is a well-established method of obtaining cytologic samples from a pulmonary nodule. Properly performed, this fine needle biopsy is a simple and safe procedure. Needle biopsy has a high sensitivity and specificity for malignancy. Modern imaging techniques using CT scan guided aspiration increases the chance of accurate aspiration. However, some authors do challenge this concept by accusing this method to be less sensitive in terms of providing too peripheral or too little tissue for evaluation. [3] Still others advocate this only in inoperable individuals. [3, 4]

In our first patient that turned out to have a pulmonary hamartoma, was misdiagnosed as a malignancy on fine needle biopsy simply because of inadequate study of all the available materials compounded by lack of complete clinical details of the patient. Fine needle aspirations of hamartomas have been misdiagnosed as fibroma, chemoductoma, and poorly differentiated anaplastic carcinoma.[5] Aspiration of a solitary pulmonary nodule indicates that clinical or radiological suspicion of malignancy was the foremost diagnosis. When studying fine needle aspiration we tend to look for malignant features. Needle diameter has also been considered important in terms of obtaining enough cartilage and fibromyxoid elements to enable one to make the correct diagnosis. It is likely that needles larger than 22-gauge obtain true cartilage more often. [6] However increased risk of pneumothorax, hemorrhage and needle track spread seems to discourage the usage of larger bore needles. Scant cellularity and absence of cartilaginous tissue in the smear could be quite misleading and raise the possibility of malignancy [7] as seen in our case. Nevertheless it is more likely to encounter false negatives rather than false positives due to inadequate aspirate sample. [8] It is also important to review cellblocks or all aspirated material, as diagnostic material may be available. Retrospective review of the CT images and the Chest Xrays showed no identification of calcification, cartilage or fat and was therefore, not suggestive of hamartoma. (Fig. 1)

Our second diagnosis was compromised by aspiration contamination by hepatocytes and lack of insight of the past medical history. This case eventually turned out to be a middle lobe syndrome. The aspirate contamination by hepatocytes resulting in the presence of "odd" cells in a lung aspirate was confirmed by review of the CT images that shows the tip artifact of the biopsy needle adjacent to the liver parenchyma. (Fig. 5). In the presence of fine needle aspiration biopsy being conducted under image guidance by experienced radiologists such contaminated tissue aspirates remain extremely rare and to our knowledge not reported. Thus, the lesson we learned in this case is to be aware of the diagnostic pitfalls of liver tissue contaminants in the cytological analysis of right lung aspirates leading to a false positive diagnosis of malignancy in benign lesions.

Clinical history together with radiological and laboratory results markedly reduces the number of all possible diagnoses into a small subset of probable ones. Clinical information can be the single most important factor in the reliability of a test. On retrospective review we found that the patient with pulmonary hamartoma, happened to have a pulmonary nodule 4 years back in a routine chest roentgenogram. Apparently no further investigations were done at that time. The nodule had recently doubled in size and remained suspicious for malignancy. Patient also was essentially asymptomatic and the only risk factor was her smoking habit for 40 years. Such information if available at the time could have averted the cytopathologists final report of the aspiration cytology as malignant. In retrospective review of our second case with liver aspirate contamination, we found the patient to be completely asymptomatic with no history of smoking at all. The patient only had shown an irregular pleural-based right middle lobe lesion that seemed to be parenchymal, in her routine chest x-ray. In this case the finding of the odd looking nuclei of liver origin in a supposed lung aspirate was a complete surprise.

Besides the importance of clinical presentation and past history of the patient, with experienced cytopathologist, the percentage of false positive diagnoses has been shown to be low [9] while false negative diagnoses usually are attributed to sampling errors not interpretive ones. [8]

Artifacts, inadequate specimen or inaccurate localization of aspiration are the factors that need to be kept in mind as diagnostic pitfalls in the interpretation of fine needle aspiration biopsies of solitary pulmonary nodules. In this context, we were not able to find many related articles in our search on all the medical literature listed in Pubmed. It could be partly because of rarity of such an error or failure of reporting these errors. We strongly believe that reporting these types of errors will raise the awareness of both the clinician and pathologist in the interpretation of fine needle aspiration biopsies. Tissue contamination can occur with CT-scan guided aspiration techniques leading to interpretative errors for the unwary cytopathologist. Complete study of the entire specimen, including the cell blocks is also recommended since different cell components may be represented in different cell preparations. Last but not the least, detailed clinical history of the patient is an invaluable tool to assist in the accurate diagnosis of fine needle aspiration biopsies.