PATHOLOGY OF THE THYMUS 391 



As a general principle, malignant thymomata of the thymus grow 

 slowly. This, however, is not always the case. Ambrosini saw five cases 

 which were fatal in from two to nine months. I saw one case fatal in 

 ten months and another in two years. 



On account of the location of these thymomata, pressure takes place 

 not only upon the trachea, but also upon the esophagus, the base of the 

 heart, the arteries and veins of the mediastinal space, upon the vagus, the 

 recurrent pharyngeal, and the phrenic nerves. In a later stage, however, 

 the tumors involve the pleural cavity and the lungs, 



Metastases in the thymus of malignant tumors of other organs seldom 

 take place. 



Sarcomatous Thymomata. These tumors are generally soft, al- 

 though some are found showing general fibrosis of the tumor. The sur- 

 face is usually smooth; in rare cases it is found to be nodular. Local 

 softening of the tumor due to necrosis is not frequently observed. Usu- 

 ally, although at first strictly encapsulated, these tumors in a later stage be- 

 come adherent to the neighboring tissues, invade the organs and spread 

 throughout the entire mediastinal space and the neck. The lymphnodes 

 first involved are the peribronchial. Metastases are very frequent in the 

 axillary and cervical lymphnodes and occasional metastases are observed in 

 the distant organs, as the spleen, pancreas, kidney, liver and adrenals, as 

 reported by Zininiewicz, and finally in the bones and muscles. That sar- 

 comatous thymomata should finally corrode and perforate the sternum 

 is not a characteristic property of theirs. Any malignant tumoT of the 

 chest and any large aneurysm of the aorta can do so. 



The microscopical picture of the thymic lymphosarcoma does not 

 in many instances differ very much from the one of granuloma malignum. 

 Sometimes, the only difference between the two conditions is the presence 

 of Hassall's corpuscles. 



On close examination, the round cell tumors of the thymus, accord- 

 ing to Ewing, are found to differ little in structure from the round cell 

 tumors of the lymphnodes. The lymphocytes are few. The chief cells 

 showing mitoses are rather polyhedral in shape, with acidophile cytoplasm, 

 vesicular nuclei, and well developed nuclecli. They often cling to 

 the walls of the numerous small capillaries where they assume a cubical or 

 even cylindrical form. They frequently produce abortive Hassall's 

 corpuscles. Still, according to Ewing (a), the giant cells are of two main 

 types : 



1st, the poor-staining reticular cells with their irregular contour 

 and containing vacuoles and red-cell detritus. 



2nd, the myeloid giant cells with opaque acidophile cytoplasm and 

 many vesicular nuclei. These giant cells do not look like the smaller 

 giant cells of Hodgkin's disease. Increased connective tissue formation 

 is usually present. 



