Pulmonary microvascular cytology. A new diagnostic application of the pulmonary artery catheter.

When pulmonary disorders involve primarily the microvasculature, definitive diagnosis is difficult and, in some cases, is not possible until autopsy. In patients with amniotic fluid embolism, fat embolism, and lymphangitic carcinomatosis, terminal pulmonary arterioles and capillaries contain abundant diagnostic material. We hypothesized that withdrawal of blood from a pulmonary artery catheter, particularly in the wedge position, should recover diagnostic cells and debris in patients with these disorders. We describe the technique of pulmonary microvascular cytology and show examples of the recovery of fetal squames in amniotic fluid embolism, fat globules in fat embolism, and malignant cells in lymphangitic carcinomatosis. Megakaryocytes, normal inhabitants of the pulmonary capillary bed, are readily seen in wedged blood and confirm the microvascular origin of a blood sample.

Amniotic fluid embolism.

Amniotic fluid embolism is the most unpredictable and catastrophic complication of pregnancy, accounting for 10% to 20% of maternal deaths. The pulmonary edema commonly seen in this syndrome is probably due primarily to alveolar capillary leakage and may be potentiated by high maternal extracellular volume, low colloid osmotic pressure, and, in some patients, by depressed myocardial function. In patients in whom resuscitation is successful, diuresis leads to rapid resolution of pulmonary edema. Amniotic fluid does not ordinarily enter the maternal circulation, and the identification of large numbers of fetal squames in the postpartum pulmonary microvasculature is probably of clinical significance.

Pulmonary microvascular cytology in the diagnosis of lymphangitic carcinomatosis.

The diagnosis of lymphangitic spread of carcinoma in the lungs is sometimes difficult. We studied the cytologic characteristics of blood drawn through a wedged pulmonary-artery catheter from eight patients in whom lymphangitic carcinomatosis was confirmed by subsequent autopsy, lung biopsy, or clinical evaluation. The sites of the primary tumors were the prostate, breast, esophagus, and lung. Malignant cells were found in seven of the eight patients. Cytologic findings were normal in 16 of 17 patients with cancer but without pulmonary metastases and in 22 of 23 patients with nonmalignant pulmonary disorders. In a patient with cancer with tumor embolism to the lungs, the findings were positive, probably because of extensive intravascular tumor in large hepatic veins. One false positive finding occurred in a patient with extensive pulmonary infarction. Megakaryocytes, which are present in large numbers in the pulmonary capillary bed, are the hallmark of a satisfactory pulmonary vascular blood sample for pulmonary microvascular cytologic study. Familiarity with the cytologic characteristics of these cells in Papanicolaou preparations is essential to avoid mistakenly identifying them as malignant. Although transbronchial lung biopsy remains the diagnostic procedure of choice in this disorder, our findings suggest that the presence of malignant cells in pulmonary microvascular-cytology preparations in patients with cancer and unexplained dyspnea constitutes presumptive evidence of lymphangitic carcinomatosis. Pulmonary microvascular cytology may be particularly valuable when lung biopsy is refused or is thought to be too hazardous.