938 Fig. 4. Smear of pleural effusion sediment showing several early granulocytes with morphologic features similar to the cells in the bone marrow (Wright-Giemsa stain, ×1,000). 51%, lymphocyte 19%, histiocyte 9%, band form 6%, pro- myelocyte 3%, myelocyte 5%, metamyelocyte 5%, normo- blast 3/100 WBC, blast 2%) (Fig. 4). Hematologic findings of the peripheral blood were Hb 8.7 g/dL, WBC 150×109/L (neutrophil 62%, lymphocyte 7%, monocyte 5%, promye- locyte 2%, myelocyte 18%, metamyelocyte 5%, blast 0%, normoblast 1/100 WBC), platelet 109×109/L. The ratio of erythrocytes to nucleated cells in the effusion was 8 as com- pared to a ratio of 18 in the blood, suggesting that the nucle- ated cells in the effusion were not solely due to bleeding into the pleural cavity. The pleural fluid was negative for Gram stain and acid fast bacilli. The patient was diagnosed with CML complicated with pleural effusion. Bilateral chest drainage catheters were inserted to control the pleural effusion. The patient was retreated with hydroxyurea and allopurinol, and the amount of pleural fluid decreased in accord with the de- crease in the WBC count of peripheral blood. Due to loculat- ed pleural effusion, however, the effusion did not completely resolve. At this point, a right chest tube was substituted for the right chest drainage catheter. Pleurodesis was performed for the right pleural effusion, thus relieving dyspnea of the patient. Two months after the appearance of the pleural invol- vement, the patient died due to hypercarbic respiratory fail- ure. Until that time, however, no peripheral blood blast cri- sis was detected. DISCUSSION Development of extramedullary disease in the pleura of H.W. Kim, S.S. Lee, M.-H. Ryu, et al. patients with CML is frequently accompanied by increased blasts in the pleural fluid. Analysis of pleural fluid, however, does not always show excess blasts, and in some cases, all stages of granulocytes and a few blasts are found in the pleural fluid or ascites (9, 11). Categorization of the cytomorphologic fea- tures of extramedullary diseases in 18 patients with CML showed that extramedullary disease could be sorted into 3 types, depending on the proportion of blasts to more mature differentiated granulocytic cells (6). These 3 categories were blastic, showing a predominance of blasts (5 patients, 28%); immature, showing a predominance of blasts and other non- blastic myeloid precursors (8 patients, 54%); and mature, with a full spectrum of granulocytic maturation from blasts to granulocytes (5 patients, 28%). The patient described here had serous pleural effusion after 3 months of treatment with hydroxyurea and gemcitabine. Because he had multiple malignancies and the pleural fluid was an exudate, we hypothesized that the pleural effusion of the patient was caused by his malignancies. Pleural fluid cyto- logy, however, showed no evidence of gastric, lung or pancre- atic cancer cells but revealed premature and mature leuko- cytes, and variable numbers of blasts. We therefore regarded the pleural effusion of the patient as related to CML. There are several possible mechanisms of exudative pleural effusion in CML patients. The first mechanism is leukemic infiltration into the pleura, which usually occurs at the time of or just prior to bone marrow evolution to blast crisis phase (2, 3). The most common sites are the lymph nodes, bone and nervous system, while infiltration of the brain, testis, skin, breast, soft tissues, synovia, gastrointestinal tract, ovaries, kid- neys and pleura occur less frequently (4). Involvement of the pleura has been rarely documented, and isolated pleural blast crisis in the absence of medullary transformation is extremely rare (2). In these cases, pleural fluid analysis revealed vari- able stages of granulocytes and leukemic blasts. The second mechanism is pleural reaction secondary to bleeding into the pleural cavities that may cause pleural effu- sion in the patient with CML (5). Predisposing factor such as leukostasis and platelet dysfunction may have a role in hem- orrhagic effusion. Thus, the cytologic findings in the effusion are due to leukemic cell contamination and pleural reaction as a result of bleeding into the pleural cavity. If this is true, the ratio of red blood cells to nucleated cells in the blood and effusion should be similar. In our patient, however, the ratio of red blood cells to nucleated cells was higher in the blood than in the pleural effusion, and thus it is more likely that the large numbers of nucleated cells in the pleural fluid orig- inated from the pleural cavities. A third possible mechanism underlying effusion is pleural extramedullary hematopoiesis. It can present as a discrete mass in almost any organ, including the liver, spleen, breasts, lymph nodes, kidneys, thyroid, pancreas, endometrium, and medi- astinum, or in the serous effusion. But, unlike pleural leuke- mic infiltration, extramedullary hematopoiesis includes hema-