Evaluation of the role of electron microscopy in the diagnosis of lung tumours with an alveolar pattern

ABSTRACT

The lung is a common site for both primary and metastatic tumours which are sometimes impossible to differentiate. Both the special stains and electron microscopy were used in an attempt to solve such a difficulty. The present work comprised five cases that presented as lung masses all having an alveolar pattern. All cases were stained with PAS, and Macson trichrome. All Cases were also studied by electron microscopy. Other special stains and immunohistochemical stains were used whenever needed. The PAS stain was of value in diagnosing the alveolar soft part sarcoma by the presence of the characteristic PAS positive crystals which were further identified by the electron microscope. Both the PAS and the trichrome stains were of value in diagnosing the alveolar rhabdomyosarcoma which was also confirmed by electron micoroscopy in the form of thin and thick filaments arranged in a hexagonal array with cross striations. On the other hand, electron microscopy was of great value in differentiating the remaining three cases. It showed electron dense membrane bound granules within tumour cells suggestive of melanosomes in one case. This was confirmed later to be a melanoma by the Masson Fontana which demonstrated black pigments within the cytoplasmic as well as S100 positivity. The other two cases showed electron microscopic features of adenocarcinoma. One of them also demonstrated intranuclear inclusions and cytopiasmic myelinoid bodies, characteristic of granular pneumocytes, thus diagnosed as bronchoalveolar carcinoma. The last case also showed confluent irregular pools of glycogen suggestive of a renal cell carcinoma, confirmed later by the presence of an occult renal mass which was proved histologically to be a renal cell carcinoma. From the present work it can be concluded that both special stains and electron microscopy can be of value in differentiating primary and metastatic lung tumours presenting histologically with an alveolar pattern