Detection of fetal keratin with high molecular weight cytokeratin immunostaining in lung biopsy material from a patient with amniotic fluid embolism

Amniotic fluid embolism (AFE) is a rare and fatal disorder in which the diagnosis can be challenging for clinicians and pathologists. A healthy 36-year-old woman (gravida 4, para 2) was admitted for delivery in the 40th week of gestation. At the fifth minute following birth, during expulsion of the placenta, the patient suddenly collapsed with bradycardia, shallow respiration, and loss of consciousness. After evaluation, an emergent pulmonary embolectomy for acute thrombo-embolism was performed, however the patient could not be weaned from cardiopulmonary bypass, and died of severe right ventricular dysfunction following the operation. Microscopic examination of the biopsy material detected clearly visible fetal epithelial squames inside pulmonary vessels, both with routine hematoxylin-eosin (HE) staining and immunostaining for high molecular weight cytokeratin (HMW-CK). The diagnosis of amniotic fluid embolism (AFE) was made, which was confirmed as the cause of death. We show that HMW-CK staining can be a useful means of detecting amniotic fluid-derived fetal keratin within alveolar tissue. We suggest that this technique, used in addition to HE staining and in combination with sudden-onset clinical findings, may increase the accuracy of diagnosis in AFE.