Transbronchial forceps biopsy is a well accepted and established retrieval tool for the histologic analysis of parenchymal lung disease [1
]. The requirement of histologically proven diagnosis in suspected lung cancer is evident. However, on the background of tumor heterogeneity, forceps biopsies are always hampered by small sample sizes and thus uncertain representation for the tumor. In addition, larger samples will likely become even more important regarding the steadily increasing amount of information that is expected to be gathered from tissue samples in pinhead size. Particularly surface and receptor analyses, prognostic or predictive genetic markers and/or upcoming epigenetic changes will become more important.
In non-neoplastic diseases a number of entities like sarcoidosis or bronchiolitis obliterans may be diagnosed on material obtained by transbronchial forceps biopsy. Thus far, the efficacy of TBB in non-neoplastic lung diseases has only been addressed in a few studies [1
Small size is the major factor limiting the usefulness of TBB in clinical practice. Therefore the adequacy of samples has always been a matter of debate. In needle biopsies of solid organs such as kidney or liver with histologically distinct and thus countable structures (e.g., number of glomeruli), specimen adequacy can be determined easily. In contrast, specimen adequacy in lung biopsy has not yet been clearly defined and depends on clinical context. However no such approach has been implemented, because alveoli vary largely in size, shape and quality and cannot be easily rated. Moreover, two separate histologic structures - bronchioli and alveoli - should be present in a biopsy. Additionally there are several artifacts, which are typical for a forceps biopsy such as atelectasis, intraalveolar hemorrhage and so called bubble artifacts [4
]. The frequent presence of artificial atelectasis may obscure diagnostic features and also be misinterpreted as interstitial fibrosis [10
]. Several studies have rated the adequacy of the transbronchial biopsy based on alveolar content and specimen size. In a multivariate analysis, the number of alveolar spaces necessary for an adequate biopsy was defined as 20 [6
]. Morphometry has been shown to be an efficient method to evaluate sample size [6
A promising approach to obtain more representative samples in bronchial biopsy seems to be the introduction of modern cryoprobes. With this technique, the sample is collected while still being frozen, with the tissue attached on the frozen probe's tip. The value of the biopsy under diagnostic aspects is influenced not only by the size itself but by the absolute as well as relative content of alveolar structures, bronchial wall and neoplastic or reactive changes of the tissue samples [1
In our series the size of the biopsy specimens differed significantly between cryoprobes and TBB specimens. However it has to be emphasized that in each TBB only one of the up to 4 biopsies was included in the analysis. Usually we decided to include the largest piece. In cases lacking alveolar tissue, present in other biopsies of the case, we included the largest alveoli-bearing biopsy specimen. The rationale behind this was the fact that for the diagnostic value of a biopsy only continuous tissue areas can be included in the diagnostic process, as topographic information is essential in histopathology, especially in diagnoses predominantly driven by pattern information. Strictly speaking every specimen in TBB has to be interpreted for its own, as the exact topographic relation between specimens of different biopsy site remains unclear, at least for the histopathologist.
Our results show an important difference between forceps biopsy and cryobiopsy. The latter samples are larger, and a trend to superiority with respect to the alveolar tissue fraction is observable. In the group of cryobiopsies we found alveolar tissue in a higher proportion of cases as compared to the group of forceps biopsies (73 vs 56%). The absolute value as well as the relative amount of alveoli is undoubtedly superior in the cryoprobe. In addition, artifacts in the alveolar part were not observed in the cryogroup but in each sample obtained by forceps biopsy.
The increased amount of tissue available for histological and molecular access may significantly improve the diagnostic value of bronchoscopical lung biopsies which has to be investigated in further studies.